The Stovebolt Site Forums The Shop Area Engine Shop No Rear Tranny Mount?

Greetings - I sure enjoy reading the posts about our old trucks. I have a 53 1/2 ton. The PO installed a '54 235 engine, transmission, open drive shaft & axle. I noticed a bad vibration when decelerating and after a little investigation found (among other things) that there is no rear mount for the tranny! I don't know much about this stuff, but this looks like a problem to me!! Anybody ever see this before? The crossmember is there and the ears on the tranny case appear to have approx. the same centerline holes as those on the crossmember but are forward about 3 or 4" and maybe 2 or 3" above. Anybody have a 54 or maybe 55 1st that they could take a photo or two so I can see what the mount is supposed to look like? I can order mounts from Chevy Duty, LMC, etc.. but would like to have some idea of what they are supposed to look like before doing that. Any other advice would be much appreciated.

There is no transmission mount on a 54/55st 1/2 ton with manual transmission. Prior to '54, a transmission mount was used (and there was a frame cross member for it - there is no transmission-mount cross-member on the '54/55st frame)

Where are the rear motor mounts on your engine? In 54/55st (and later) they are below the clutch (bell) housing. The engine sat on the rear motor mounts. The 54/55st rear motor mounts are different from pre-54 rear motor mounts.

In prior years (on trucks) I think the rear motor mounts were to the sides of the clutch housing (producing a lot a shear stresses?).

In 54/55st, the frame cross-member rail for the rear motor mounts are, I think, different from earlier frames (maybe someone else has info on this). I think this was discussed in a recent posting on 53/54 frames.

Tim

Thanks for the info on the trany mount - as you suspect, the motor mounts are on the sides of the motor - does seem like the shear load on the motor mounts would be increased by hanging the tranny on the back of the bell housing. So far though, no problems with that. The vibration is another thing, however. It looks like the rear axle is rotated with the u-joint pointing up too high. I have heard that this can cause vibration, so I'll see if I can get a measurement on it. The axle mounting looks kinda goofy to me, as well - apparently the brackets were cut off and re-welded on the top of the axle - then the u-bolts were set in from the bottom.

You'll definitely get vibration if you have excessive pinion angle. Please post your findings.
Ed

Ed
Thanks for your reply-
The transmission output shaft is about 2 degrees downward from level and the driveshaft is about 4 degrees down. The rear axle input (pinion?) is 10 or 12 degrees (the front is higher than the back). I'm thinking that the pinion angle should be about the same as the tranny shaft, right? If my calculations are correct it is about 8-10 degrees off.

Ed
Thanks for your reply-
The transmission output shaft is about 2 degrees downward from level and the driveshaft is about 4 degrees down. The rear axle input (pinion?) is 10 or 12 degrees (the front is higher than the back). I'm thinking that the pinion angle should be about the same as the tranny shaft, right? If my calculations are correct it is about 8-10 degrees off.

The axle and transmission should be equal but opposite. That way it will not vibrate. You can get new spring perches at any hot rod/ speed shop etc. and weld them in at proper angle.
Ed

If you have an open driveshaft he didn't use the same one from the truck the engine came from. 54 still had closed driveshafts. Who knows what kinda rear axle you got.

I don't know much about the Chevy side, but my '54 GMC 1-ton Panel has an open driveshaft. From what I have heard, at least some of the '54 models did away with the torque tube.

You are right, I didn't think of that.

Really good info guys - thanks. Sorry for the delay - I've had trouble posting until today. As for the axle, it has a casting number 2 018 188. And it looks like it was used on a vehicle with coil springs judging by the extra brackets and pads still hanging on it. After considering all of the advice you guys came up with, I was thinking that I would have to at least grind the brackets off & reweld new ones or maybe even replace the whole thing. So I soaked the U-bolt threads w/ liquid wrench & WD40, used a wire wheel on them,etc... and prepared to do battle, assuming that at least one would break since they were solid rust. I blocked the frame on both sides & supported the axle with jacks. Wonder of wonders, all eight nuts came loose, although not without a lot of effort and the use of a BFW (3/4" drive breaker bar borrowed from a neighbor)! Then it ocurred to my feeble brain that if I loosened the rear nuts and tightened the front ones the axle might rotate forward!! After a lot more liquid wrench and sweat (it was 92 deg and humid - no shade) I started to see results! Now the nuts appear to be evenly spaced on the U-bolts where before the front ones were not quite all the way on and the rear ones were almost out of thread they were on so far. After I had the axle almost rotated perfectly, just in time I noticed my new emer. brake cables were VERY tight - Yeah I went almost 15 degrees rotation. Thanks again - I would never have figured this out without your help!! Once I get the engine fixed I'll let you know if the vibration is gone. Darwin

Darwin,

As far as the shop manual goes, all 1/2 tons had torque-tube though 1954 model year.
1955 first series (same body as '54) went to open driveshaft.

1954 3/4 & 1 ton with 3-speed tranny had open drive shaft, whereas '53 & prior had that short "torque-tube" back to the carrier bearing, then open drive to the rear end.

If you still have that vibration after you've corrected all your drive-line angles, check the tailshaft bushing in the rear end of the tranny (where the slipjoint & and universal yoke are): I had a similar vibration in my '54 3/4 ton, and it turned out to be a very worn bushing.

Hope you get it licked!

Frank & All:
I just now got back from a test drive! NO MORE vibration when I decelerate!! One more small victory. It really feels good to get another bug worked out - I think it's better when a person has to work at it for a while. If it's too easy, we just don't appreciate it (apparently that goes for other things in life, as well). Now on to the scariest part of all for me - the dreaded "new wiring harness" nightmare. Thanks for all your help on this stuff. See you on the electrical forum!!
Darwin