The Stovebolt Site Forums The Shop Area Driveline Clutch 9" vs 10 3/4" applications AD truck

I have a '48 GMC 1/2 ton. It has a 4 SPD trans but the smaller 9" clutch assembly. I understand that someone may have swapped in the 4 spd at some point. Was the smaller clutch just used on 3 spds or some 4 spds as well? Will the smaller clutch be ok? I won't be towing with it.

If the 9" is working it should be fine if everything is stock. I think the larger clutch requires a different flywheel, the bolt pattern is different and the wear surface is also different.

The truck wasn't running when I bought it and hasn't yet. I pulled the trans to check the clutch which I am replacing. I was just curious if anyone had any solid information on the subject.

If the trans, pressure plate and clutch are out, measure the machined face of the flywheel and the size of the pressure plate. Its probably larger than 9. 55-57 used a 9.5 but the flywheel was actually machined enough to be able to use a 10.00. GM apparently gave us 6 guys the short shrift and used a smaller clutch but a 10 inch clutch and pressure plate will fit. You might find the same with yours. Four speed truck commonly came with 10.00, some with 11 so take a look and see what the flywheel will accommodate.

My truck is a '48. The machined surface of the flywheel is 9" which matches the clutch and pressure plate.

Bigger is not always better. A smaller disc makes shifting easier & is better for the syncros in the trans. As long as it can handle the torque of the engine & the driver knows how to use a clutch.
The syncros have to slow down or stop the disc & gears in the trans.

George

1/2 ton trucks standard size with 4sp is 9", heavy duty available with 10-3/4". Heavy duty requires flywheel with 9 mounting bolts for the pressure plate, instead of 6 for the standard duty. Believe 3/4 and up trucks got the bigger clutch

Thanks to all!

Hi GTOKID, Just my 2 cents, but don't put a 10 3/4 clutch in as they're way expensive $$$$$$$$$. Carters and 40's carry them and all you have to do is look at the prices for each piece as they have to be rebuilt. I have a 1.5 1946 and have changed the clutch twice, once after buying and once because the disk rusted to the flywheel. Since your truck is a 1/2 ton, I'd put a 10" or 11" in where you can buy clutch kits all day long provided your flywheel will take the bigger pressure plates, but even then its no biggie to replace that. Just a suggestion, Good luck.