The Stovebolt Site Forums The Shop Area Driveline am i supposed to have a transmission crossmember?

hi guys

quick question, does stock 3100 have a transmission cross-member?

i have a cross-member under the bell housing but nothing further back.

ive read reports of people having to move or install modified members when fitting power brake master cylinders - but when i looked under my truck theres no member in the way and heaps of space....whats the skinny?


(my truck has a 235 engine stock manual 4 speed)
cheers
mike

no cross member under a standard trans, it just hangs off the bellhousing

Bill

What year is your truck?
Up to 1953 there was a transmission cross member.
Starting in 1954 with the new angled bellhousing mounts the trans crossmember was dropped.

Hi guys,
mine is supposed to be a 49. when i look here -

http://www.gmheritagecenter.com/doc...hevrolet-Trucks/1949-Chevrolet-Truck.pdf

(frame 70) it doesnt show a transmission cross member...so im not sure whats going on lol

hmm, maybe its a terminology thing...


ive looked through the gmheritage center docs and the frames from 1947 right through to after 54 look the same (regarding transmission crossmember)

the frames all have what gm calls an `engine rear support` cross member (see frame 70)

http://gmheritagecenter.com/docs/gm...hevrolet-Trucks/1949-Chevrolet-Truck.pdf


the design of this crossmember was changed a little in 1954 to solve some member cracking issues but otherwise the member apears to have always been there.... or am i missing something??

but theres many a post here talking about removing it or not having it so i assume this is to accomodate different engines/transmissions fron stock?

..im just getting more and more confused lol!

Here is that page with the 1949 frame.

I think is is showing structural parts of the frame (parts that are riveted/welded).

The transmission support is referred-to in the Shop Manual: Removal step 1-C and installation step 5-D (used through 1953).

That support is no longer referred-to in 1954, when cross-member under the engine rear (under clutch housing) was strengthened by way of of new design. 1954 Engineering Features manual.

ah, interesting - you make a good point!

thanks, that explains a lot.

so my truck is missing this member (have to say it doesnt surprise me the PO owner from what i see was a real joker)
- so when i upgrade to power brakes i may as well buy the matching member

thanks for your help!

cheers
mike

Mike,

Many people report that cross member being missing from pre-54 trucks. The best guess as to "why" is that the cross member was removed to more easily remove/install a transmission, and then the cross-member was simply not put back into place?

hi yes thats possibly why its missing but truth be told ive discovered so many horrors on this truck done by PO that nothing would surprise me.

case in point, i just discovered he had taken an angle grinder to the brake drums to grind away the worn lip of the drums and in doing so destroying a lot of the drum surface. ....nothing would surprise me now lol

Seems like it would be rather obvious if the crossmember had
been removed, that is quite a large section and they're riveted
into the frame at many points.
You say it's titled as a 3100 but are you sure you don't have a
3600 frame???

Denny G

Denny,

Is there no need for the 3600 and larger trucks having a transmission mount because the engine-mount frame cross-member being shorter and stronger than the one on the pre-1954 3100?

The transmission crossmember which the torque tube ball collar support bracket,mount bolts to, is bolted to the frame (not riveted), on a 3100. I am guessing that is why it isn't included in the factory pictures of the frame. If you are running a torque tube rear axle, you need to find a crossmember and the torque tube ball bracket/mount.
Carl

Thanks, Carl.

I thought they were bolted onto the frame, but I've only worked on 1954 enclosed drive-shafts in the last 30 or so years (no manual-transmission cross-member).

The 1954 Hydra-Matic cross-members are also bolted on (both the rear-engine cross-member and the rear-transmission cross-member).

My 1950 3100 has a crossmember

...pic...

Bolted to the frame

..in the back ground in this pic...

If I had gone with a booster brake kit I would of had to remove that crossmember.

I think this is the member you are talking about. I have a 52, 216 4 speed, this is what I have.

http://m.ebay.com/itm/121278080166?nav=SEARCH

Hi guys,


aaahhh i think i worked it out....


the transmission mount attaches/sits under the torque tube flange

my truck has no torque tube it has an open drive

so im guessing thats why the crossmember is missing


so my question now is.....would it be best to fit a crossmember and mod up a support to the tranny casing....i think i should


a really nice pic on this excellent gallery.

http://www.cardomain.com/ride/1969206/1950-chevrolet-3100/

(click `photos`, `load more` then 3rd line of pics down)

Hey, my bad guys, I've got two 3600's here but no 3100. Been
helpin' a friend out with his 3100 and thought the
transmission crossmember was riveted, Just call him
to check it out, bolted in just as ya'll say. Should
have kept me yap shut since I couldn't head out to
the garage and check it out in person.

DG

I have seen so many of these trucks without the crossmember with no ill affect that I believe it is not necessary.

Once the rubber pad in the torque ball support bracket gets mushy from gear oil, this crossmember serves no purpose, except for a little extra lateral support to the frame. I believe that support bracket was designed to take out some of the wiggle out of the torque tube. If you go to an open drive shaft, I wouldn't attach the transmission to the crossmember, as it will likely fight with the front engine mount and the two mounts at the bell housing.
Carl

What about the 1954 1/2 ton trucks' torque-tube "wiggle"? Management of weight, not wiggle was what was being dealt with.

GM stated for 1954 trucks that the change in design of the frame and rear-motor-mount cross-member allowed for removal of the transmission mount (and cross member). The new rear-motor-mount cross-member was stronger in 1954 and later, allowing it to bear the weight of those parts of the drive train.

Think that larger crossmember in '54 might have just been
because the HM was now being offered as an option? Even though
the rear of the HM was supported there was still more weight on
the rear engine mounts with the HM than with the other options.

As far as I know there never was a problem previously,
cantilevering the 150lb SM420 from the bell housing. The whole
works, engine and trans being mainly supported by the rear
engine mounts, kind of like a teeter tauter favoring the front
or engine side.

DG

We can speculate and make assumptions based on the information in the 1954 Truck Engineering Features manual (linked-to above).

The 1954 3100 H-M has a significantly different frame set-up compared to standard transmission 3100 trucks. The H-M-equipped 3100s had a set of two bolt-on frame cross-members: one under the rear engine (where the standard cross-member was) and an additional cross-member under the rear of the H-M transmission.

The extra cross-member was needed for the very heavy H-M transmission; and, the two cross-members were bolt-in to allow the transmission to be easily removed from below (with or without the engine).