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MG MGA - Differential thrust washers

Does anyone know the original thickness of the differential wheel washers (ATB7072) or, failing this, the thickness of the currently available fibre replacements.

I've removed mine (bronze) and they measure 0.034 to 0.036 ". The cupped differential pinion washers appear to be a similar thickness.

Finally does anyone know a supplier of the original type bronze washers?......................Mike
m.j. moore

Copper washers from Moss US P/N 267-130 0.034" - 0.035"
Fibre washer from Moss US P/N 267-140 0.035"
Are your washers copper or bronze?
Mike
Mike Ellsmore

Another one of my pet peeves. Newer is not always better. Just because the factory tried a cost reduction with the MGB (that didn't work out very well), does not mean we should all switch to using the crappy fiber thrust washers in MGA.

I think Moss got it the wrong way around. Instead or changing MGA thrust washers from bronze to fiber for cost reduction, they should have changed MGB thrust washers from fiber to bronze for improvement in longevity of this problem part. BTDT, and helped a lot of people replace the fiber washers. I have never seen the bronze thrust washers wear out. See here: http://chicagolandmgclub.com/photos/b_clunk_11

Does anyone know of a current source for the flat bronze thrust washers? There is no way I would ever put the fiber pieces in my MGA.
Barney Gaylord

Another one of my pet peeves. Newer is not always better. Just because the factory tried a cost reduction with the MGB (that didn't work out very well), does not mean we should all switch to using the crappy fiber thrust washers in MGA.

I think Moss got it the wrong way around. Instead or changing MGA thrust washers from bronze to fiber for cost reduction, they should have changed MGB thrust washers from fiber to bronze for improvement in longevity of this problem part. BTDT, and helped a lot of people replace the fiber washers. I have never seen the bronze thrust washers wear out. See here: http://chicagolandmgclub.com/photos/b_clunk_11
Barney Gaylord

Thanks Mike,Barney. I was impatient this morning and popped along to Moss to get a set of washers. I thought that while the axle was out it would be a good time to try and get rid of the 4 degree backlash at the front end.
The fibre washers I bought were a similar thickness to yours Mike and only a couple of thou, at most, thicker than the metal ones I took out.

After cleaning up the gears and replacing the original washers there appears to be quite a bit of axial play in the splined gears sufficient to get in easily a 30 thou feeler gauge.

I would have thought then that the replacement flat washers need to be close to 50 thou thick to remove the backlash? I think I'll look around for some thicker metal and make up a couple................Mike

PS The original flat washers looked like bronze but may be 50 year old copper.
m.j. moore

Bronzes are a very complex subject, and I've been looking at this for years.

I suspect that they are made of a rolled phosphor tin bronze, possibly low leaded.
See: http://www.copper.org/resources/properties/microstructure/phos_bronze.html
It would be wonderful if somebody with access to a metallurgical lab could get the actual parts analyzed for composition!

Further, these washers have odd loading characteristics, which makes it more difficult. There is both a lot of hammering, and as a result of the intermittent motion, no opportunity to form a hydrodynamic oil film for lubrication or cushioning. Many of the bearing bronzes are clearly not suitable, as they are cast or sintered, and would fall apart under the loads involved.

They are certainly NOT copper, as copper would simply hammer out into a foil. Most brasses would be subject to dezincification, which is the much discussed corrosion resulting from EP gear oils.

Regarding backlash: this is the result of wear on all 4 thrust surfaces, and needs to be addressed as such. Spacing only two of the 4 makes the gear engagement incorrect, leading to evil tooth loading. In fact, my experience usually shows maximum wear on the spherical pockets for the planet thrust washers, which makes sense as both the loading and speeds are greatest there. (this is why they changed the side washer material but not the planet washers) Just figures that these are the most difficult to make! I've heard of guys doubling up the spherical washers in extreme cases. Note that the geometry of the gears means that the thickness of the planet washers does not translate directly to clearance reduction at the side gears; rather, the planet washer change will be substantially greater than the clearance change at the sides.

FRM
FR Millmore

Apologies - my reference to copper (sic) washers were to the cupped washers not the bronze flat washer that have been replaced by fibre.
Mike
Mike Ellsmore

This thread was discussed between 28/12/2011 and 29/12/2011

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