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MG MGA - Gearbox washers

I am rebuilding my 1957 MGA gearbox. I ordered new laygear thrust washers. The new front washer is 0.0025" thicker than the old front which seems right. But the new rear thrust washer is 0.002" THINNER than the old one.
OLD FRONT: 0.1515"
NEW FRONT: 0.154"
OLD REAR: 0.156"
NEW REAR: 0.154"

Since both new washers have the same dimension (0.154")it would seem that this is correct?

Does anyone know what the factory specs were on these parts. Is there enough tolerence that it does not matter?

The total dimension on the combined old washers is 0.3075.

The total on the new is 0.308. This is only a difference of 0.0015".

Probably not worth worring about. However, it would be useful information to know how close the suppliers new parts are to the factoy specs.
H Speer

The new rear thrust washers are available in several different sizes from Moss, 0.155" being the smallest. It is very possible that a thicker thrust washer was needed on original assembly from the factory, or the gearbox has been rebuilt before and someone added the thicker washer to take up the endfloat. Either way, the laygear endfloat tolerance is listed in the workshop manual (actually I'm using the Haynes manual). I can't remember the spec offhand.

I'm doing mine right now. I know how much endfloat I need to take up, so I can order the appropriate size washer to make up the difference or use a combination of new and old washers, whatever gets me the closest.
Mark J Michalak

Thanks Mark. Actually, my official MG Workshop Manual does not give the laygear end thrust spec. For $80 this manual has several errors and is very short on factory specs.
H Speer

I rebuilt my MGA gearbox three decades ago, and didn't remember anything about endplay in the factory manual. I started wondering if I had missed something when I got into my TR6 gearbox a few years ago and discovered a range of thrust washers for it. I'm glad to hear you say there is no spec in the MGA factory manual. Now that I have a Haynes manual, too, I guess I'll have to check it if I have the 'box out again sometime. Though with an 1800 in her now, I might be inclined to go for a 5-speed if my old 'box gives up the ghost.

Ken
k v morton

The full workshop manual is available here online for free - in sections as a PDF file, so you can just download the section you need.

The 1600 and 1500 service parts lists are also there in full.

http://www.clancy.ch/Owners_Pack.html
dominic clancy

I'm going back to the garage right now to assess what parts I need to order for my winter projects. I will look in the Haynes manual and get you the endfloat tolerance.

It's funny: the Haynes manual gives the laygear endfloat, but then it tells you to check the 3rd gear endfloat and it doesn't give you that spec. Apparently the workshop manual does. C'est la vie.
Mark J Michalak

Laygear endfloat according to Haynes manual: 0.002" to 0.003"
Mark J Michalak

Thanks Mark in Chicago. I used the thickest combination of thrust washers and ended up with 0.002" end thrust.

That laygear is a BEAR to fit. Once the first motion shaft and main shaft are in place the laygear has to be lifted in place and the new lay shaft inserted. Sounds easy but everything has to be aligned perfectly, especially the thrust washers, nearly impossible to do.

After struggling for over an hour with aligning drifts and screwdrivers with no success I concluded that what I needed was a rod the same diameter as the layshaft but with a tapered end that would pick up and align everything.

Where was I going to get such a rod. Then the light went on. You have the perfect rod, it's called the old, worn layshaft. I ground a taper on it and it went in perfectly picking up washers and laygear in a jiffy. Then with it shoved home, I just inserted the new shaft and pushed the old one out. This is probably obvious to everyone but it takes me awhile these days.
H Speer

After the same struggle, my solution was to assemble the gear and washers on a rod that was just as long as the combination of parts. I used something easy to cut to length; I think a piece of copper pipe or a wood dowel. I laid the assembly in the case and then inserted the shaft from the end like you did.

Ken
k v morton

Put laygear and thrust washers in the box first, and slip a thin metal rod (welding rod) through it to hold the thrust washers. Once the input gear and mainshaft assembly are in place, stand the box on end, push the laygear into position, orbit the metal rod to align the thrust washers, and drop the layshaft in. Takes only a minute and works every time.
Barney Gaylord

My technique is similar to Barney's except that I use two thin scewdrivers, and leave the box on its side. I then line up one end and remove the screwdriver carefully, slide in the end of the layshaft and tap gently home with a rubber mallet. Once I reach the other end, I just use the screwdriver to align the washer and then tap the layshaft all the way in.

Works in seconds if you have a second pair of hands, and in minutes with one pair.
dominic clancy

On the topic of washers, dooes anyone know what the new bronze interlocking washers measures- either from SF or Moss? The thickness is not listed in either of their catalogues. I need to know so I can determine if I can take up enough endfloat.
Mark J Michalak

This thread was discussed between 14/02/2009 and 17/02/2009

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This thread is from the archive. The Live MG MGA BBS is active now.