Esso equivalents are GP90 and GX90, but Mobil specifies GX90 for the gearbox and HD90 for the axle, so you can't rely on the letters to tell you whether they are for gearbox or axle. Additional confirmation of application is that the label includes a drawing of either a gear change or a rear axle respectively. Corrected May The final differentiation between gear and axle oils is one of smell - GL5 oils i.
It's engine oil as used in 4-cylinder gearboxes that does not have this smell. December With Vee's engine and gearbox out as part of work on both I had the opportunity to investigate this aspect in the 'open air' so to speak. It's said that there are at least 16 ways of installing the crossmember components, and maybe 32!
John Twist has an eight minute video where he discusses the differences between the crossmembers and restraint methods over the years. However he's not clear when he is talking about 3 sync and 4-sync, at various points he questions himself 3.
However careful consideration can eliminate most if not all of the incorrect options, and the following relates to 4-synch OD both for 4-cylinder and V8: The first is which way round the crossmember goes. It seems there is always a dip on one face and that faces forwards - 2 ways. However Bee has hers installed the wrong way round , but without a forward-facing restraint rod the only effect is to put the tapped hole for the speedo cable clip on the wrong side.
But both Bee and Vee came to me with the cable above the crossmember, which to me reduces the risk of damage from objects on the ground. The first change in crossmember shown in the Parts catalogue is with the change to Mk2 and 4-synch. It's clear Mk1 only had one hole in the crossmember bracket for the rubber mount stud, but Mk2 cars have two, which changes the fore and aft position of the crossmember relative to the gearbox. On 4-sync cars the correct position is the front-most hole - so now we have 4 ways.
John Twist says at 3. But that can't be right as the 4-synch gearbox casing is the same both with and without OD, and to move the crossmember relative to the rubber mount and the gearbox would affect how it lined up with the chassis rail holes. Next, crossmembers on other than Mk1 roadsters have a vertical restraint pin. The upper yoke that holds the pin and is bolted to the gearbox with the rubber mounts can go either way round. Several drawings show this part for the Mk1 GT i.
On 4-sync OD boxes the correct way has the 'flat' side of the yoke facing forwards - 4 ways. John Twist says it goes this way round for OD as it gives more space to get the rear mount-to-gearbox bolts in past the OD, and that I can see. But although it fits either way round I can't see any reason why it needs to be the other way round for non-OD boxes as John Twist says, as the space at the front is the same for both OD and non-OD. Finally the yoke under the pin can rotate on the pin to be either way round.
Again the Mk1 GT is symmetric so can go either way round, but the Mk2 has the welded nuts off-set which changes their position relative to the holes in the crossmember.
With the upper part orientated for OD boxes the correct way is with the welded nuts behind the pin - 16 ways. Which ever way round the upper part goes, the lower part is turned to line up the nuts with the holes in the bottom of the crossmember. Did I say 'finally'? Another 'twist' is that some replacement rubber mounts instead of being rectangular are 'Z'-shaped , and depending on which way up they are fitted they can be in either shear bad or compression good.
But that is obvious from Testing the various options for 2, 3 and 4 showed that the only way that everything lined up was when things were assembled as described, and the upshot is that the mounts end up centrally on the crossmember , with the nuts on the lower yoke lining up with the holes in the crossmember, and the crossmember lining up with the holes in the chassis rails.
That still leaves two sets of tapped holes in the chassis rails to mount the crossmember. Clausager shows a i. This is a non-OD, and prior to the auto, are they for the 3-synch OD gearbox? Or maybe an option for the unused V4 engine and gearbox? Which to use is determined once the gearbox and engine are joined together and the engine has been fitted to its mounts. However if the gearbox and the engine are installed separately then for 3-synch non-OD and 4-synch gearboxes at least use the rear-most mounting position.
It's further complicated on the V8 by the mounting plates for the engine mounts being handed but capable of being installed on either side. When the V8 came to me it was like that and I found the crossmember had been fitted in one pair of holes one side and another pair on the other side!
Swapping those plates over with everything in-situ was a real challenge. The first time I refitted the crossmember was with the mounts on the gearbox, the gearbox back in the car, and the car on a full-height ramp, so getting the crossmember back on the mount studs was the next challenge.
Some have slotted the crossmember holes but mine aren't. Slackening the mount to gearbox bolts made it easier, but then retightening the mount to gearbox bolts with the crossmember on was not possible for a reason I can't recall. In the end I found that with one side hooked over its stud, the other side popped in when given a hearty upwards shove of the crossmember. Of course it went in the wrong hole, but a firm pull downwards got it off again, and another shove got the stud in the right hole.
The next challenge was to get the lock-washers and nuts on the mount studs, for which some have drilled holes in the bottom of the crossmember to take a socket extension at the appropriate angle, fitting the socket to the end afterwards.
But I found that with the original rubbers it's not difficult to twist the crossmember first one way then the other, and use an offset ring-spanner which allowed me to tighten them half a flat at a time. Of course getting old nuts off may be more challenging, in which case as a last resort I'd chisel the rubbers off. I was warned not to replace the rubber mounts unless I needed to, as new ones are much harder than old, and presumably it's much harder to get the stud in the crossmember, as well as tighten the nuts.
Having said that one would expect the 'Z' mounts to be more compliant than rectangular. This was all for the V8 of course, other gearboxes may vary. Restraint Rods: See also Engine Mounts and the section on restraint brackets there. Mk 1 roadsters had a crossmember with welded nuts at the rear for a restraint rod bracket. A short rod passed through the crossmember and brackets and was retained by a nut.
The front of the rod has a 'U'-bracket that goes around a protrusion on the bottom of the gearbox casting close below the speedo cable, and a special pin goes through the bracket and protrusion with rubber bushes between them. Mk 1 GTs and initially all Mk2 cars don't appear to have the restraint rod, until In Feb 74 still chrome bumper a new restraint rod was added to North American cars. This used a welded bracket on the front face of the crossmember, and a longer rod going all the way to a bracket that attaches to the two bottom bolts that secure the bell-housing to the engine.
Other markets got this arrangement at the start of rubber bumpers. The V8 never had a restraint rod. And in case you wondered what the crossmember bolted up to - a tapped plate in a cage, so it can move around to accommodate some dimensional differences. Oil Change For what oil to use see Lubrication. Take the car for a run of 10 miles or so to warm things up and allow the old oil to run out a little easier, especially the gear oil in the V8.
You can live with not changing the oil for a bit while you ponder how to shift it, but not if you have already drained the oil and can't refill it. I had the front of the car up on ramps and the rear on axle stands so I could do both gearbox and rear axle together, and the car was relatively level making refilling with the correct quantity easier.
The drain plug on both the roadster and V8 are hollowed-out and although at first it didn't look like there were any bits in the hollow, when I stuck a screwdriver in there I did get some bits out.
The largest was about 1mm in size, the rest much less than that, I suppose it is inevitable in a manual gearbox but I'd rather not have seen it. Free the sump with at least two of the bolts on opposite sides or ends still loosely fitted so it doesn't fall away all at once. I had to use a bit of gentle leverage to get the sump parted from the OD body, there is a handy tab on the sump adjacent to the large hex plug for the relief valve expressly for this purpose, it seems. Be ready for more oil to drain out once you have broken the sump seal, quite a bit more comes out here, I left that to drain rather than try getting the sump completely off at that point and fill my sleeves with oil.
The old one took quite a bit of scraping to get off the sump, in hindsight it would probably have been OK to put back as the outer ring was fine. The filter and sump were as clean as a whistle, but got a wash in petrol anyway.
The roadster sump came off without any tearing of the gasket, and I decided to leave it stuck to the sump and not clean underneath as any bits should have been on top of the screen. The little specks in this photo are globules of oil or petrol, not bits as I first thought. Touching the screen made some vanish and other appear.
I did pour some petrol into the sump through the screen, gave it a good swill and poured it out again, hopefully that should have washed out any fine sludge, it looked clean enough in there from peering through the screen. The hex plug for the relief valves also came free easily, a little more oil draining out. Be careful not to lose the little O-ring between it and the valve or any of the other bits inside.
Whereas on the roadster it was in a groove in the end of the hex plug and didn't come free in washing, on the V8 as I recall it was loose on top of the hex plug i. Careful teasing with a pair of long-nosed pliers got the cylindrical filter out together with the valve assembly. Quite a few bits involved here 13 on the roadster! Whereas the V8 was similar to the drawing in the Workshop Manual the roadster seemed a bit different having a very coarse screen round the upper part of the valve which isn't shown in the drawing, and a large spring above the valve plunger which is shown much smaller in the drawing.
I didn't find any of the 'valve ball, valve spring or low pressure valve plug' on either car. The larger O-ring should be in the groove in the relief valve body so shouldn't come free. The roadster had three shims between the valve plunger and the spring not shown in the manuals which sets the hydraulic pressure - more shims sharpens engagement, less shims softens it, I didn't find any on the V8.
While you are away from the car put a clean empty container under the OD to catch any bits e. If you don't they might roll away or not be noticed on a driveway until too late. Again the filter and valve components were as clean as a whistle, but got rinsed in petrol before replacement in the correct order.
On the V8 the new OD sump gasket got a smear of Hermetite Red non-setting on both sides, I tightened the sump bolts bit by bit in a logical sequence to avoid warping.
Filler access There have been two questions recently about where to find the chrome bumper dipstick and filler, so here they are. Note the access hole and rubber bung were still fitted to rubber bumper cars, and I found that the easiest way to refill the V8 with the side-fill gearbox was with the tubing down through the access hole and into the side-fill hole. However it appears that 77 and later cars had a different console that may have to be pulled towards you i.
March Two people have stated on the MGOC forum that theirs do not have the bung, but three others have confirmed that theirs do including a reshell. Whilst side-fill is easy to clean around the filler hole and get the end of the tubing into it without picking up any dirt, top-fill needs a bit more care. I loosely inserted the dip-stick to stop any dirt falling in, then from underneath wiped round the dipstick and the top of the casing.
I'd seen recommendations to use a long length of plastic tubing up from the filler hole top or side into the engine compartment so one can refill in relative comfort, but opted to do the V8 from the right-hand footwell instead. The gear oil for the V8 gearbox comes in 1 litre squeezy bottles and the nozzle of these fitted neatly into the end of the plastic tubing, and I had enough room to empty each bottle in turn even with the steering column on that side of RHD cars.
The 4-cylinder uses engine oil in the gearbox and OD, the 1-litre bottles of this don't have the nozzle like the gear and diff oil bottle do, so you will need a funnel in the end of the tubing for either 1-litre bottle or 5-litre can. I also did the roadster from the footwell and rather than try to wield a 5-litre can in the limited space decanted 1 litre at a time into an empty diff oil bottle so I could use the same method as for the V8.
Squeeze for a few moments then release and wait a couple of seconds, and the oil in the tube will drain down and air come back up to replace it and expand the bottle again. Much easier than trying to squeeze a litre in all in one go.
It will take time for the oil to flow everywhere so don't pour in the whole of the recommended amount in one go or it will probably overflow. Even though a dry-fill with OD takes 3.
Testing with the dip-stick showed it was just above the MIN mark even through there wasn't much more than half the quantity in yet. With the V8 I was able to get about 2. At this point I ran the engine on both cars in 3rd and 4th I had the rear of the car raised to do the rear axles as well, remember switching OD in and out to distribute the oil.
While the V8 was fine OD on the roadster wouldn't engage, which concerned me a bit. However when I removed the tube and checked again with the dipstick it was now off the bottom. I put another litre in making 3 litres so far and tried again, this time it was OK - phew! MAKE SURE it is supported safely, don't be underneath the car with the engine running, and make sure there is some run-off room in front of the car.
After the next decent run check the level and the plugs again to give you confidence there are no leaks, then you should be fine to leave it the normal service intervals. Thus the LH type has closer to a '3rd and a half' ratio than the D type, but both offer a useful mid-way point between 3rd and 4th for spirited twisty bits or a long steepish climb.
In theory that should mean that the D-type has a higher road speed for a given rpm than the LH, and indeed it does at But it has a fractionally lower road speed in straight 4th at How can that be when they both have the same diff and in 4th the gearbox ratio is ?
Maybe down to the different tyres. The D type is not as strong as the LH and has a vacuum switch and relay to prevent the driver from disengaging OD under certain conditions - high revs and no throttle - which could overstress the unit.
The wiring and a description of this circuit can be found here. Although specific to the D-type OD the above document contains this very clear description of how the Laycock overdrive switches ratios, which also applies to the LH-type: The gear train consists of a sun wheel A , planet wheels B , planet wheel carrier D , and annulus or ring gear C.
The input is via the planet carrier, and when the sun gear is locked to the ring gear the whole unit rotates as a single unit to give direct drive. But if the sun wheel is locked to the casing so it cannot rotate, when the planet carrier is rotated the ring gear is 'overdriven' at a higher speed than the planet carrier to give the overdrive ratio.
Believe it or not this is exactly the principle used by the Sturmey Archer 3-speed hub dating from that many of us will have been familiar with when we were in short trousers. How does that give three gears? The Laycock unit always applies the input to one of them the planet carrier , and either locks the sun wheel to the ring gear or to the casing to give either direct drive or the overdrive ratio.
The Sturmey Archer does basically the same, but can reverse the input and output so that the ratio difference can either be used to gear the output down i. Lots of videos and descriptions online, with varying degrees of complexity and confusion! Also complex is understanding what determines the OD ratio, and comparing the drawing above with endless descriptions of epicyclic gearing is no help. The ratio for the simple system drawn above is determined by the number of teeth in the ring gear, divided the number in the ring gear plus the number in the sun gear.
The number of teeth in the planet gears has no effect. But the Laycock planet gears have two diameters - the larger engaged with the sun wheel and the smaller with the ring gear and now the planet gear tooth count does have an effect Updated December There were three types of LH OD for the MGB - chrome-bumper 4-cylinders cars had one with a black but see below Laycock label, 4-cylinder rubber-bumper cars had one with a blue label with a different speedo drive ratio.
The V8 was different again in that it operates at a higher pressure, although the speedo drive ratio on all V8s is the same as the chrome bumper 4-cylinder. Speedos have the turns per mile tpm stencilled on the dial - 4-cylinder chrome-bumper cars have a tpm speedo and all V8s have a tpm speedo, whereas 4-cylinder rubber-bumper cars have a tpm speedo. On the face of it the V8 should have different speedo gearing to the chrome-bumper 4-cylinder, but they have different axle ratios as well which also has to be taken into account.
Another factor is the wider tyre of the V8 but the same profile, which results in a 2. This seems to be resulting in an overall 2. On and later LHD models it remained on the ignition switch with white wires - oddly via the fuel pump inertia cut-off switch, see Schematics for all variants.
It is strongly recommended that the overdrive circuit be fused - especially the and later version with the manual switch in the gear lever, see Overdrive Fusing. Gearbox switches - accessing the switch: The overdrive gearbox switch is screwed into the top of the gearbox. The 3-synch switch can only be seen or accessed from above by removing the large access panel on top of the tunnel, which needs the tunnel carpet to be pulled back.
For the 4-synch access is much more restricted - it can just about be seen from underneath, but really the only way to access it remains from above.
Updated March There is a small removable plate on top of the tunnel in front of the gear lever, which together with unbolting the rear crossmember and allowing the gearbox to swing down a bit, and levering it across to the right-hand side, gives just about enough access for the medium hand. Prior to for other than North American cars the tunnel carpet again has to be pulled back, but after that with the centre console and arm-rest cubby the gear lever hole in the carpet can be cut round the removable panel, and a section of carpet dropped back on top for refitting.
It can be tapped round with a hammer and drift, but that may not always work, and I'd be wary of doing that putting it back in case it damages it. Also refitting and getting the threads started would be difficult! Some have cut a hole in the side of the tunnel and fitted a cover plate to give better access. Short of tapping round with a hammer and drift original switches can only be removed with an open-ended spanner or grips, which is impossible without cutting a hole in the side of the tunnel with the gearbox installed as their hex is narrower than the terminal end of the switch.
However modern replacements are to a different design with the hex being the widest part of the switch. There is not much swing, a point socket is not enough, but by turning the socket round on the extension 90 degrees at a time you can get at least 32 points which is just enough. Thus - if your gearbox is out - it may be worth considering replacing an OE switch with one of the new design then, so making future access easier.
Note this isn't needed with the reverse light switch as that faces the side of the tunnel, so not only is getting a socket on it not feasible, but it can be accessed by grips from underneath. The only 'adjustment' on these switches is provided by spacers, and a loose or worn switch can prevent the OD functioning or reverse light coming on or make it erratic.
In the case of wear causing non or erratic operation removing a spacer may be all that is required. OTOH a missing spacer can cause it to be on when it shouldn't be. It's always been said that these spacers are fibre, and there were originally two of them.
However everyone else including the Parts Catalogue shows 3H as being for the right-angle speedometer drive and various hydraulic unions! Incidentally the OD and reverse light switches are the same part number. Vee's OD occasionally drops out on the overrun then back in if I briefly pull the gear lever towards me, so while the engine and gearbox were out in I did experiment taking the spacer out and seeing what happened.
With no spacer I found the OD switch was closed in other gears as well as fourth V8s originally had OD in 3rd and 4th but this was changed to 4th only at some point , and definitely needs some spacing. Comparing it with a 4-cylinder gearbox that was handy, that had two OD switch fibre spacers of different size and thickness. One was the same thickness as the copper spacer at 0.
So back to two spacers, and being different thicknesses allows for two different reductions, but not supported by any of the documentation. What lies inside. UK 4-cylinder cars always had OD on 3rd and 4th.
North American spec cars originally had OD on 3rd and 4th, changing to 4th gear only in Feb , possibly because of unreliability of the additional switch those cars needed to provide it in conjunction with TCSA. V8s originally had OD on 3rd and 4th, changing to 4th gear only to prevent damage to the OD unit. However four cars after the apparent change point claim to have had OD 3rd from new, the last being May The Parts Catalogue states it changed at " G A" i.
The transcript of a talk by Don Hayter in has Geoff Allen who worked in Rectifications during the development of the V8 stating that the modification was done on the press and early cars, but then Geoff agrees with Victor Smith that the mod wasn't done until car number or thereabouts!
In David Knowles's 'MG V8' Geoff Allen writes that "Over the Easter Bank Holiday, and for several days and overtime evenings afterwards, a number of shop rectification fitters worked on the ten press cars and two other cars to remove the overdrive operation on third gear, due to problems with the gearbox in overdrive third.
Most of the cars had a straightforward gearbox change, but on some we dismantled the gearbox and replaced the selector lever with the modified one, which was eventually fitted to all V8s from gearbox number onwards".
Clausager says "early production cars had it operating also on third". But there seems to have been a lot more than that, and for a lot longer than Easter , as Clausager dates car number to Jan 74 and car number to Feb 74 i. Maybe only press cars were modified, customers cars waiting until they broke! However for there to have been a "straightforward gearbox change" there would have to be supplies of already modified gearboxes available.
Vee's gearbox number is higher than her chassis number, which is a lot more than the numbers above imply. May The current issue of Enjoying MG from the MGOC has an article on the Costello V8s, including a reprint of a Motor magazine test dated June 2nd , in which they write "Ken has had to blank off overdrive on 3rd gear since a couple of converted machines were brought back under warranty with broken third gears after the customers had repeatedly changed down from overdrive under full throttle in third gear".
Maybe the factory thought by using a detuned V8 they would avoid that, but clearly not. Switch actuation: There is a round shaft with a cut-out under the switch, but the portion that operates the switch is different on the V8 to the 4-cylinder. On V8s with OD on 4th gear only, the shaft again moves to the left but only as 4th gear is selected, so the switch is only operated in that gear. However if the gear lever is pulled further to the right while in 4th the lever moves still further, and if it is pulled to that position in neutral or 3rd gear the shaft also starts to move, so adjustment is pretty critical, as below.
This difference in operation is primarily controlled by different selector levers, but the plungers that engage with the switches are also different. March Since restoration Vee's OD is dropping out more frequently on the overrun since getting her back on the road, so needs a thinner spacer or so I thought But whilst one online source for the copper washer states it is 1. So no choice but to order one and see what arrives I can't live with the dropping out so the switch will have to be removed and a thinner spacer obtained from somewhere.
Using the above methodology cover plate removed, gearbox dropped and levered across to the right , tapping with a drift did start it moving, and I had enough room to get my hand in and unscrew it the rest of the way, catching the washer with my finger-tips into the bargain, probably less than an hour start to finish.
Testing the switch for continuity - just out of interest - I was surprised to find how little movement of the button was needed, but then pushing it further the connection got erratic, and needed to be pushed fully in quite hard to get a connection again.
So I suspect that behaviour is the cause of why it is operated in a non-OD gear with no spacer, and why with the spacer it gets erratic. New switch arrived next morning, operates early in the travel of the button like the old one, but stays operated with further movement instead of being intermittent.
I decided to try shaving the new fibre washer, so rubbed it between two sheets of glasspaper, and got it down to 40 thou in about 5 minutes! It was a bit of a fiddle getting the switch started in the gearbox as it is at a slight upwards angle and with my hand in there I couldn't see, but eventually it went in. Hand tight I tested it for continuity So back out and refitted quicker this time with the original 50 thou, and it operates as it should with the lever pulled straight back So back out again and a ponder additional shims.
I have a set of front wheel bearing shims which are slightly bigger but should still do the job, and after trying 3 thou and 5 thou with no difference I end up with 15 thou before it stops operating when it shouldn't. It still operates with the lever pulled straight back at the same position without the extra 15 thou which is just before it finally snicks into position, and pushing and pulling the lever around doesn't break continuity. So tightened it as above , fitted the wires, and rechecked continuity from the engine compartment right through to the solenoid earth and all was well, so refitted the crossmember and went for a test drive with the interior as-is.
Engaged and stayed in as it should, although really it needs a longer test decelerating from higher speeds to be sure. Back home refitted the interior stuff - including a piece of carpet on top of the removable panel, time will tell. Subsequently it's still dropping out quite often so take the 10 thou out, and on a 40 miler it probably dropped out twice, and is engaging when I pull the lever towards me in third. I'm not really bothered about that so I'll take the 5 thou out as well so it's as it was before.
Still dropping out when hot, but not engaging in 3rd when pulling the lever across towards me, so I'll have to try the 40 plus a 5 and see what that does both hot and cold! Still dropping-out, so progressively reduced the shims until the switch was closed all the time then added a 5 thou, which leaves it very marginal to being closed when reversing!
So connected a relay to the reverse-light circuit to definitely disconnect OD in reverse, as well as move the PO-fitted overdrive tell-tale light to the output of the gearbox switch so I can see when the solenoid is powered, which will also allow me to confirm that it is the switch opening that is causing the dropping-out. It is, and it still happens as the gear lever eases forward on the overrun, so maybe it's getting worse.
In December the gearbox comes out to deal with the whining that has started since the engine rebuild, so an opportunity to do something internally, which may be nothing more than curing the 'easing forwards' symptom. Having the opportunity to examine the plunger, it seems to me that making the groove deeper under the switch in the 'at rest' position would allow me to screw the switch in further, so it is operated sooner and for a longer distance as 4th gear is engaged.
Also the possibility of changing the selector lever and plunger so the original switch closes in 3rd and 4th, maybe with a third switch operated by the selector rod to give operation in 4th gear as per the TCSA system.
That would be accessible with the gearbox in-situ so has advantages. But really, it's the easing forwards on hot overrun that needs to be resolved. July Note that later versions of the Leyland Workshop Manual and Haynes, when they describe testing the gearbox switch, state WSM, Haynes only marginally different "Using a test lamp connected across the switch terminals, switch on the overdrive, and see that the lamp lights when 4th gear is selected, but no other". Not only is it incorrect in the gears involved as UK cars always had OD on 3rd and 4th, and misses out having to turn on the ignition, but more importantly by connecting a test lamp ACROSS the switch terminals, the lamp would only light when it was in a gear i.
It would be extinguished in an OD gear when the switch contacts were closed. Also the wiring would need to be left connected to the switch for the lamp to light, most people seem to removing the wiring from a component when asked to test a circuit, which you should rarely do. In order for the lamp to light as described - even for a late North American spec car - the test-lamp would need to be connected between the solenoid side of the switch and earth for it to light in 4th gear, and would illuminate in 3rd and 4th on a UK car.
But even then it requires access to the switch contacts or solenoid bullet connector which is not easy. Far easier to part the connector in the OD wire where the gearbox harness joins the main harness and insert the test-lamp or ammeter there.
That will test the continuity of the whole circuit from 12v supply, through manual and gearbox switches, and solenoid. Schematics: D type 4-cylinder to 68 LH type without ignition relay 4-cylinder 68 to 76 and V8 LH type with ignition relay - UK 4-cylinder, on LH type with ignition relay - North America 4-cylinder, on As the overdrive solenoid contains moving parts you might be tempted to connect 12v to it and see if you can hear it clicking, like you might a relay, but the D-type differs to the LH-type as described below.
Diagnostics - D-Type: Updated February The earlier D-type unit has a relay and vacuum switch as well as the manual and gearbox switches. In normal use operating the manual switch will operate the relay, and the relay contact supplies power to the solenoid if the gearbox is in an overdrive gear. Prev of 2 2 Next. Packman Original Poster 58 posts months. Hi, I've just had my engine bay re-sprayed Bare Metal and took the opportunity to have a new gearbox and clutch fitted whilst it was all out.
Drove the car home last Friday, Some 30 Miles , all working well apart from the overdrive. The person who undertook the job for me is not an MG specialist and will now need a detailed list of what to check first and what to check last and of course all points in between.
He and I know that the gearbox and overdrive will have to come out of the car again to carry out some of the checks but some help is now required. Nigel - I'm possibly looking for your input here, along with others who have specialist knowledge. The Haynes Manual shows a relay in the circuit and I thought that this might just be wired up incorrectly but i took a trip to my local MG specialist in Bexleyheath today who advised that the Roadster never had a relay in the overdrive circuit.
He also took some time to scare me witless on potential problems. So to re-cap I just want to know what to check first and what to check last. Thanks Packman. Geordie MGmike posts months.
The first thing to try is to make sure 12v is getting to the OD solenoid. If the volts are there the problem is inside the OD, otherwise follow the cable back to where the volts are. That's a good mid point to check also.
Volts here and the problem is likely to be the inhibitor switch on the top of the gearbox, no volts and the problem is back towards the dash switch. If the volts all all okay and the box is suspected, check the resistance of the coil for an open circuit.
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Started by blakey Jul 7, Replies: 5. Started by Momikey Jun 27, Replies: 6. Started by tdskip Jun 12, Replies: 5. Started by Momikey Jun 9, Replies: 3. What is needed for a 'big brake' upgrade; how well does it work? Started by Sarastro Mar 13, Replies: Tie Rod - Engine: What is it and where does it go? Started by blueskies Dec 14, Replies: General Tech Water Wetter, does it work?
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Accept Learn more…. Compression test: What does it tell me. Apr 17, Mar 7, Wednesday at PM. Jul 17, Feb 5, Nov 19, Nov 14, Sep 23, Jul 16, How does the flasher unit work.
Jun 28, Jun 26, Analyzing Problem of Flasher Unit [warning lamp does not work]. Jun 14, May 13, Sep 1, How does overdrive Annulus effect speedometer. Jun 17, Jan 29, Jan 26, The correct tool does make it easier [fill steering rack].
Oct 18, Aug 13, TR6 How does this steering lock come off. Jun 5, TR6 Overdrive does not engage. May 11, Apr 25, Mar 19, Jan 8, Nov 29,
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