The Stovebolt Site Forums The Shop Area Engine Shop Engine mount strength

I've been through two sets of rear engine mounts on my '50 since I put the 261 in a few years ago. To be fair, the first ones were killed by an oil leak, and the second ones might have been cheesy repops. I'm wondering if they are just too weak for that engine. Is the reason they went to the angled mounts in '54 for strength reasons? I'm wondering if I should just change out my crossmember and use a later model bellhousing when I put in my 302. I tore out this set driving with a bed full of bark dust, that was fun. I hate having a loose engine. Good thing I run an electric fan.

Do you have the transmission mount on your truck?

The 1954 and later rear mounts and frame cross-member must be a little stronger set-up because they allow the transmission mount to be removed.

Are you drag racing? If not, my guess is that you have a problem not related to the 261.

There are people on the oldGMCtrucks site with experience mounting the 302 in a variety of trucks. They'd have experience and advice on rear mounts.

I would think with the front mount on the 216,s and 235,s when you install a 261 or 302 with this type of mounting and the engine in good cond or with some speed parts installed the twisting force could be more than the mounts can take...doc

Sorry, I am not familiar with that mount. But, if its tearing loose at the metal/rubber bond, thats about normal for todays quality. If possible, fab. a mount plate utilizing a do-nut type thru-bolt mount cushion. Those will never fail, everything being in compression.
Doug

Yeah, it tears loose at the bond. I am running the SM420 with no rear mount. I haven't really been drag racing but I have pulled a few stumps in 1st gear and driven on some pretty rough roads. That can't be too good for the mounts.

I just changed my 54 rubber mounts for urethane mounts...they sandwich the cross member and have nothing to break loose but the grade 8 thru bolt. I would think they would be tougher than the stock 50 mounts and not subject to oil contamination.

One thing I did note....there was no urethane single front mount available that I could find. The urethane mounts are very rigid and don't pull down as easily as the stock rubber mounts. I torqued mine to 65 ft-lbs.

Can't speak to the problems you might encounter with a cross member change but it seems like a viable alternative.

Dave

If you have a 1950 1/2 ton truck, there was a mount at the rear of the 3-speed manual transmissions that attached to a frame cross member. I would suppose that the rear transmission mount served a purpose on pre-1954 trucks. However, Jim Carter does not show a transmission mount for a 4-speed (that weights about 3 times more than a 3-speed).

The Master Parts Catalog says the transmission mount is for 1/2 ton trucks through 1953.

I have the original 4 speed, it has a crossmember with a mount but I removed the mount because the rubber was gone and it leaks at the bell a bit.

However, the rear transmission mount doesn't seem to take any torque off the side mounts anyway.

I'm planning to drop a Jimmy 302 in it later this summer. I have two front mount options, the original style 2-bolt mount, and the saddle mount with a single bolt. I'm leaning toward modifying the front crossmember to accept the GMC mount rather than changing the engine front plate (which doesn't have the tab that the Chevy engine does). I haven't decided what to do with the rear mounts yet. I'm also switching to a Saginaw 4 speed so that may help with the rear situation a bit.