The Stovebolt Site Forums The Shop Area Driveline rear crossmember

so i'm working on a 1951 3100 panel, 235 6, sm 420.
i'm installing the drive train and i have a couple questions that i hope someone can help with.

first let me say i did not remove the drive train so i don't know what was there before and second, this is a first time doing anything this major.

ok so, i'm missing the lower dust cover for the bell housing/flywheel. is it ok to install the motor and put that on after i locate one? if not and it needs to be in place, how do you get the tranny bolts through the bell housing?

next, should there be a rear crossmember supporting the tranny? i don't have one but it seems odd that the tranny just hangs off the housing unless i'm missing something.

thanks.

this forum is a very helpful tool.

" . . . i'm missing the lower dust cover for the bell housing/flywheel. is it ok to install the motor and put that on after i locate one? if not and it needs to be in place, "
Yes, it is OK to install without - and/or put one on later (GM thought it was needed).

" . . . how do you get the tranny bolts through the bell housing?"
Install two upper transmission bolts from the outside; and, two lower transmission bolts from inside the bottom of the clutch housing.

" . . . should there be a rear crossmember supporting the tranny?"
Yes - there should be a rear-transmission crossmember on 47-53 1/2 ton trucks.
Many were removed when a transmission was removed (and, the "mechanic" failed to put it back on). Some people (including GM) think it is needed.
There is a rear-transmission support/mount assembly that mounted on that crossmember. Several suppliers sell that mount/assembly.

ok thanks for all the answers to my questions.

so it sounds like i need a crossmember and a mount assembly. is that correct?

One post disappeared.
Your choice, it seems, on both items.

I'd like to have the dust shield on any 47-55st truck.
And, I'd want the transmission mount on any pre-1954 Stovebolt 1/2 ton truck.

Are you using the original torque tube rear end? If so, you definitely need the crossmember and the mount assembly. That mount assembly supports the transmission torque ball assembly.
The torque tube is heavy and the leaf springs put a lot of additional downward force at the torque ball area.
Carl

An interesting observation.
1954 trucks did not come from the factory with a rear trans mount or crossmember.
The frame is drilled for the crossmember if one wants to install one though.
The parts book only lists the set-up up to 1953.
I know the bellhousing mounts made a change in 54, but I think Chev may have just decided the trans mount and crossmember were not needed.
????????????

Dave,

Might those holes in the 1954 frame be available for the necessary removable-crossmember for the Hydra-Matic option?

I'll check my Hydra-Matic and non Hydra-Hatic frames tomorrow (If I remember).

Yes, Chevrolet decided in 1954 that the mount was no longer needed (for non-H-M trucks) - the new rear engine frame crossmember was much stronger in 1954.
pages 49-50 for frame changes - for greater strength

Recent........Lengthy post on the transmission cross member topic:

https://www.stovebolt.com/ubbthread...9/6/rear-transmission-support-sm420.html

Yes for a'53 3100 series and if using the stock torque tube with sm420 gearbox, you need that cross member and support plate. Check your local craigslist.

Boy Tim, you are quick on documentation!

I guess my point is, in 1954 the bellhousing mounts changed to improve on engine rotational force, not vertical force.
The same manual transmissions were used as in 53 and earlier, but now with no crossmember or trans mount.
I believe Chev decided the up and down force from the torque tube was not enough to continue with the crossmember and mount.

Once I realized this many years ago I stopped worrying about a bad trans mount and would leave a bad mount off completely on customers trucks.

When I take a look at the flimsy design of the mount in question, I don't see where it did much in the first place. In fact, it reeks of the smell of something added after all of the designing was done and production had begun. Kind of, "Well crap. Now we have a vibration issue to take care of." "Hey Bill, come up with something to make that vibration go away that does't cost an arm and a leg and is easy to bolt on."
Carl