M4A2 Sherman clutch shim question

[Malcolm Towrie]

We’ve got the two 6-71 Detroit’s out of the Sherman for resealing due to oil leaks.
Both clutches have shims between the housing and flywheel. Hopefully the sketch shows the location and the other photo shows a shim.

One clutch had one shim per bolt, the other clutch had two. The shims are 0.032” thick.

Cleaning up the heat checking involved removing a total of 0.020” from the flywheel and pressure plates, ie 0.012” from one and 0.008” from the other.

The only manual I can find that mentions these shims is for the M36, which uses the hull of the late M4 A2 HVSS. All it says is when friction disk gets down to 0.370” thick, remove the shims. Our friction disks are 0.455” and 0.425” thick so well above this minimum spec.
Trouble is I lost track of which clutch is which when we got then surfaced. Anyone have any info of how the OEM determined these shim thickness?

Thanks,
Malcolm

83CDD2F0-8FEA-4DA2-8926-554B1795EA6E.jpg

0F74D19B-6140-4D03-ADDD-AE621F544435.jpg

[Colin Alford]

Malcolm,

My read is that both engines should have had 2 x 1/32” shims per bolt (for a total thickness of 1/16”)

All references seem to agree with two shims when total thickness of clutch driven plate(disk) is greater than .370”, and no shims when thickness is less than .370”.

[Colin Alford]

Information from post-war civilian manuals

[Colin Alford]

There is some discrepancy regarding minimum thickness of clutch driven plate (disk) which would indicate that it should be replaced.

In my prior post I included images from TM 9-1750G (Power plant maintenance) which indicate the plate should be replaced if it is less than .303”

TM 9-745 (M36B2 vehicle maintenance) agrees with the .303” thickness.

TM 9-731B (M4A2 vehicle maintenance) shows .340” as the minimum thickness.

[Malcolm Towrie]

Fantastic info, Colin! Thank you very much.

You’re right, all the info you gave me clearly states that, with the thickness of frictions I have, there should be two 1/32” shims per bolt. That’s what I’ll install. Mind you, I’ll have to make 12 new shims, which will be a pain. Wonder how much laser or water jet cutting costs??

And the Detroit manual gave some interesting info. The shims aren’t to control the diaphragm spring pressure on the pressure plate, as I had assumed, but to keep the release bearing in its working range. I assume that allows the bearing to release enough to allow the spring to apply full pressure and to pull spring back enough to let friction plate spin freely.

Thanks again. I love MLU.
Malcolm

[rob love]

When I google the shim number listed in Colin's part manual, it does come up as a shim for detroit diesel. Might be worth a try asking the local detroit dealer. The number seems to be expanded a little to D81260-755429 SHIM.

[rob love]

Originally Posted by Malcolm Towrie

We’ve got the two 6-71 Detroit’s out of the Sherman for resealing due to oil leaks.

The rule about Detroits is if they are not leaking, they are out of oil. This applies to Harley Davidsons as well, and most of the older Chev engines.

[Perry Kitson]

The old timers always said, "the only thing keeping the oil in was the paint".

[Jesse Browning]

Are there match marks on the parts? Supposed to be, but my clutch didnt have any either.

[Malcolm Towrie]

Originally Posted by Jesse Browning

Are there match marks on the parts? Supposed to be, but my clutch didnt have any either.

You mean match marks to identify which parts come from which engine? Didn’t know that so I haven’t been looking for them.
Malcolm

[Jesse Browning]

The match marks are usually for keeping everything balanced, but if marked differently could give a clue to origin.

[Lynn Eades]

Malcolm, so based on what you have said, then the purpose of the shims might be to prevent over bending the spring and risking breakage ( as well as the travel)