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MG MGB Technical - Layshaft Thrust Washers

I'm in the process of pulling my 4-synchro tranny, but have questions about the layshaft thrust washers before I start tearing things apart. The Moss catalogue shows round thrust washers, but the Vicky Brit cataloque shows layshaft thrust washers with a forked tab (!?) The Moss catalogue says that there are different 2 layshaft thrust washers, one for the trannys used in the 18GK and earlier engines and another for the 18V engines. Which (round or forked tab) goes with which? Why aren't they interchangable? Or are they?
Neil Glick

For the 4-synch gearboxes my books do show different thrust washers for the 18Gx to the 18V, the latter being the forked type. But they also indicate that the later type can be used on the earlier box. I presume the fork was an improvement which stopped the washers rotating with the laygear, which would wear a groove in the layshaft and enlarge the hole in the washer. If I'm correct (and I'm only guessing) then for forked washers (if that is what you have) all the wear on the washers will be on the face that is against the laygear. That being the case, is it possible to reverse ther washers and hence get a new face towards the laygear? If the size and shape of the two components the washer faces are against is different, then you should be able to. But even if they are the same you might be able to reface the worn side with soft metal and *then* turn them round, and the soft-faced side won't be getting any further wear. I only suggest this as all bar one of the washers seem to be unobtainable.
Paul Hunt 2

Neil-
According to my factory parts catalogue, the circular layshaft thrust washers were also used on all transmissions installed on 18V engines up until the 18V 846, 18V 797, and 18V 801 engines.
Steve S.

I have rebuilt a couple of later full-sycro boxes with the forked thrust washers and if I recall they are faced for wear on one side only and so cannot be reversed. I also recall poor availability of replacement washers. In the case where face wear was not excessive but I needed to take up end-float I was able to put a shim behind the thrust washer to get the corrected gap. Since the forked washers do not rotate this is just a static spacer.

Cliff
Cliff Maddox

Cliff,
So, if I use the later forked thrust washers, what do the forks fork onto? Will I have to modify anything?
Neil Glick

Neil,

At least on the later transmissions the forks fit over bosses or ribs on the inside of the case. I'm not sure but possibly someone else can confirm if all cases have something in this location that will capture the washer fork. I that think possibly they do. As soon as you get your tranny apart you will know, and you can't really pre-buy these things anyway because of the variables.

Cliff
Cliff Maddox

Steve S - are you going by the image? If so I agree that only round ones are shown. But other sources show the earlier round washers *and* the later forked washers. My Leyland Catalogue uses the phrase 'use prior to', which usually means the later parts superceed the earlier ones in the earlier assemblies. If components have changed but are not interchangeable then specific reference numbers, car number etc. are given for each. With the 'use prior to' I'd expect the later forked washers to fit the earlier gearboxes without modification i.e. lock onto something which will stop then rotating with the gear and be an improvement, much like rocker pedestal shims for example. But as Cliff says you aren't going to know what you will need until you dismantle and check clearances.
Paul Hunt 2

Paul-
I'm going according to the parts listing. The illustration shows only the circular thust washers. I checked the references that Neil mentions and they do indeed show different thrust washers. The parts catalogue listing also uses the term "use prior to". However, it uses that term to refer to the floating wristpin pistons prior used to the ones that use press-fitted wrist pins, so interchangability is always questionable whenever the term is used.

Cliff-
My parts catalogue (which ends with the 1974 models) shows two part numbers for the 1800 transmission casing: 22H 1044 and 22H1463, the latter being for use with 18V/846F/101 ON, 18V/847F/101 ON, 18V/797AE/101 ON, 18V/798AE/101 ON, 18V/801AE/101 ON, and 18V/802AE/101 ON engines. The earlier part number is presumably for all transmission prior to those. The 18V/797, 18V/847, and 18V/802 engines were for use in overdrive-equipped verions of the 18V/796, 18V/846 and 18V/801 engined non-overdrive equipped models. This part number change coincides with the change of the thrust washer design, sadly implying that it could be that the later forked thrust washers are noninterchangable with the earlier ones.
Steve S.

They are not available new anyway!

You are stuck reusing the old ones and any excessive end float has to be addressed in other ways, like shimming.
Chris at Octarine Services

Neil,

I have rebuilt a number of early and late model full sync 4 speed, and OD boxes of same, and may be able to provide you some guidance. First, unless you know the history of your 27 year(minimum) old vehicle, or I misunderstood/misread the previous comments, I would NOT relate a car VIN or engine number to the type of transmission that should be/is in your car. Some have put full sync boxes in pre 1968 spec car, with minor work. Hence, a full sync box could be exchanged in any MGB between 1962 and 1980. Therefore, I would suggest you consider the following to identify your gearbox. Assuming you have a full sync box, I believe that the different type of thrust washers can be identified by determining if you have a dip stick (top oil fill) on your box. If you are not familiar with the dip stick it is usually located just behind the radio console on the right side. I have been told that if you have a dip stick, you do not have the tab on the thrust washer and if you have a side oil fill and no dip stick, than you have tabbed thrust washers. As for the thrust washer interchange between boxes, I would have to measure a couple washers to see if they are the same thickness as there are obviously differences in the casting of the cases, such as the boss to locate the thrust washer, hence the boss on the box that contacts the thrust could be a little thicker/thinner depending on your point of reference. I believe ALL other internal parts in both full sync boxes are the same.

Having provided the above comments/information the larger problem that I have encountered is the lack of availability of different, usually thicker, of thrust washers identified in the factory parts manual or service manual. As already previously stated, if you have tabbed thrust washers, it is easy to add static shims behind the washer to get the required float required by the service manual. On the other type of thrust washers, some have indicated that since nothing is available, put back what you took out even though the measured thickness might be close to 10X that which is required. Since I view the spinning lay gear as grinding slap hammer against the aluminum housing, I have elected to have custom thrust washers made by a local machine shop when and where necessary. I would recommend this same process to anyone rebuilding a box and is typically not that costly of an item to have ground to the required thickness. Standard sizes are available through a number of sources but may need to be fine tuned for your specific box.

HTH

Fred
Fred Wright

There are some on eBay US item 260145100419

Peter
Peter Caldwell

This thread was discussed between 24/11/2007 and 04/12/2007

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