The Stovebolt Site Forums The Shop Area Engine Shop No Tranny Crossmember?

I recently purchased a 65 C10 1/2 ton Short Bed. A previous owner replaced the truck tranny with a 65 Muncie 4 speed car tranny.

I was hooking up the Emergency Brake Cables yesterday (previous owner unhooked the cables when they ran the 3" flowmaster exhaust) and noticed there is no transmission crossmember! Holy Crap ! The truck has the standard engine motor mounts, and the bellhousing motor mount, but the trans. is just cantilevered off the bellhousing.

The previous owner says he didn't do the conversion but put thousands of miles on the truck this way!

This has to put tremendous strain on the tranny ears that fasten it to the bellhousing, right?

I am going to build a crossmember... but has anyone else ever heard of someone doing this and not having problems?

Your comments and ideas are sincerely appreciated.

You got it right in one go there John.

No rear support will put alot of undue strain on the box.
The thing to be wary of would be sudden dropping of the clutch pedal from a standstill and high load down shifts.

The truck'll luv ya with a new crossmember under it!

John,

Wait to hear from someone who has a 1965 1/2 ton truck. Do you have any documentation that has a drawing/photo of the frame (usually somewhere in the Restoration Kit items)?

There might not have been a transmission crossmember. For example, during the Advance-Design series of trucks, there was a crossmember from 47-53, but the frame crossmember and motor mounts changed in 1954, and there was no need for a cross member for 3-speed and 4-speed transmissions (the hydra-matic-equipped trucks still used a crossmember).

Tim

Fair advice Tim......

I only know that the gearbox in question was designed for a passenger car and engineered to run a rear mount.

As John stated, the original truck box has been removed,
so could only improve John's worries about strength.

There are (4) holes in the bottom of the frame on each side that correspond to the approximate location of where a tranny crossmember might go?

Stock 64 - 66 owners.... your 1/2 ton has a transmission crossmember, right?

Thanks

There is a 1965 Chevy Truck Shop Manual on ebay right now.

Hoyt

This is what I'm worried about John........
maybe the previous owner had a failure of the original truck gearbox, and found that the muncie car box bolted straight up to the bellhousing and was easier to find/fit......after removing the crossmember!

They did not use a crossmember on those models from the factory. The originnal trans. were cast iron & not very long. If you have a car type trans especially an aluminum case it would be a good idea to put a crossmember in it. You can fab. one or there are universal ones readily available. Be sure to use a soft rubber mount. If there is any deflection in the frame you dont want it deflecting the engine/trans.

Doc,

No Worries. I just ordered a tube type crossmember kit that I will modify to work with the '65 C-10 frame / Muncie trans.

Some have posted here that these trucks did not have a transmission crossmember. Makes me curious why the factory punched holes in the frame in this area? Perhaps 4 wheel drive or 3/4 ton trucks used a tranny crossmember?



Thanks,

John

The rear crossmember was used in the automatic transmission models. I ran an aluminum case Muncie 4-speed in a dirt track race car for many years without a rear crossmember, and we went from closed throttle to full throttle, 2,500 RPM to 6,000 and back to 2,500 RPM in 2nd. gear 4 times a lap for up to 100 laps. I can't remember ever breaking a trans case except once when the car ended up as the meat in the sandwich in a 3-car pileup, one car on top of the other.
Jerry

Jerry & John,

All 1954 1/2 ton frames also came from the factory with the frame drilled for for the hydra-matic crossmember.

John,

The drive trains (in particular, the transmissions) and frames were built in different factories. The extra "unused" holes were drilled out of convenience - they got used if they were needed when an automatic transmission was part of the build.

Tim

I wouldn't add a crossmember. It'll add too much stiffness to the drivetrain making it prone to vibration and potentially breaking. My two cents, drive it until something happens, seems to be working as is,
Scott

Jerry,
Maybe, with a crossmember.....
that box might have survived a three car pile-up.......
..........NOT!

Gentlemen thanks for the input.

I must say I am now in a quandry. Initially it seemed a no brainer to add a crossmember... perhaps not.

As Scott stated adding the third crossmember could result in high loads on the components. From an engineering perspective 2 crossmembers are better than 3.

And Jerry has first hand experience with an unsupported 4-speed Muncie in a dirt track car... I would say that qualifies as severe duty!

It is hard to argue with success. But then again it may just be dumb luck that the tranny ears haven't snapped off!

How about adding a tranny crossmemmber but using studs and locking nuts on the crossmember to tranny mount. That way it could be left loose enough to not bind, but would prevent the tranny from falling out in the event there was a failure?

What do you think?

Did the trucks equipped with the automatic transmissions have the engine, the bellhousing and the transmission crossmember ?

John

You'll need to have a rubber mount at the talishaft housing if you decide to add the X-member, so that will provide enough flexibility. It's really unnecessary, though, and it adds a degree of difficulty to changing a clutch, and/or any sort of exhaust system work.
Jerry

Just thought I would comment. Years ago I had a 55.2 with a very warm 396 in it. It was mounted at the front of the engine and at the bell housing with stock truck mounts. I had a Muncie 4 speed car tranny in it without a rear cross member. The truck had the stock 3.9 gears with 11x31 offroad tires on it. It was driven hard on many occasions. I never had any problems with the trans. I am not saying that it is not possible to break the trans off from the bell housing, just that it will take more torque and horse power than most trucks will be equiped with.

Lonnie's comment prompts me to make one too. Years ago I had a '67 Firebird with a warm Chevy 350 and Muncie 4-speed with all the correct side mount motor mounts and correct rear crossmember and mount.

I never broke the case. Everything inside the case, but never the case. My own experience would suggest the age and maturity of the driver might have as much to do with transmission reliability as crossmembers.

There was one surefire way to split a Muncie case wide open. It would last forever if it was run in 2nd. gear on the dirt track. The 1.88:1 2nd. gear ratio against a 4.56:1 rear end gave us just the right final drive to work on a "short" 1/4 mile dirt track, 8.57:1! That allowed the car to coast through the turns at around 3,000 RPM, and accelerate to 6,500 or so at the end of the short straight. A "long" 1/4 mile, measured around the infield instead of the fence, required a rear end swap to a 4.10:1 ratio. That's where a lot of the Eaton 3/4 ton 4.10's went! If the trans was run in 3rd. gear instead of 2nd. with the 4.56 gear for the long track, the case would split wide open. Putting the driving load that close to the center of the case overstressed it!
Jerry

Don't worry about it. 1955 56 and 57 all trucks and cars were like that from the factory. There is less strain on the tranmisson with out the weight of the engine hanging on it.

If a rear crossmember and mount is added to a to a car or truck that came with a transmission cantilevered off of an engine with a front mount and two rear side mounts, one now has what is called an "indeterminate structure", and it is quite possible that the loads on the transmission to bellhousing ears and bolts will be greater than without the added rear crossmember. (this may be the longest sentence that i've ever written - sorry).

If one is worried about the load on the upper ears due to the weight of the transmission, a quick and dirty calculation will show that that load is less than the load on the lower ears with a forward engine mount and an aft transmission mount (like a pre-1952 Chevy passenger car). I have read that the "best mounting arrangement is center side engine mounts and a rear transmission mounts. This results in low bending moment and loads on the transmission to engine attachment joints.

The 1955-57 Chevrolet passenger cars came with the cantilevered transmissions. Has any one seen the ears break?

Have we ever determined just how the 1965 truck in question was originally built? if it came with the cantilevered transmission, there should be nothing to cause concern. If it came with a rear crossmenber mount, then there may be some changes to be made.

Hoyt

Hoyt,

The '65 C10 manual shift 1/2 ton truck was originally made with engine and bellhousing mounts and no mount on the transmission. It was also built with with a cast iron case manual transmission designed for use without a crossmember.

What makes this different is a Muncie aluminum case transmission is being used that was designed to have a transmission crossmember.

It is my understanding that if the truck came with an automatic transmission the factory installed a transmission crossmember.

Anybody know if the 55-57's Chevrolet manual shift passenger cars used aluminum or cast iron case transmissions?

The 55 - 57 trannys were cantilevered and they were cast iron. I have a 55 hardtop that has run a muncie since the early seventies with no issues. This car has seen a variety of small blocks and big blocks which pushed it anywhere from mid 14's to mid 12's. I broke spider gears, side gears, ring gears, and pinions in the stock rear ends and never had a tranny issue. Upgraded to a dana 60 and haven't broken anything since. The driveline in this car has been abused severely. I would not worry about the lack of a tailshaft crossmember.

John

I think it is safe to say, the reason the Muncie is built for a crossmember mount is because of the engine trans mounting arrangement. That is mid engine and rear of trans for the mounts. I do not think you will find any later model engine trans mounting configuarations that have front, center and rear mounts.

Thanks again to everyone for their opinions, experience and advice.

Actual experience trumps theory, at least IMHO. Contrary to my original plan I will not install a tranny crossmember.

Real world testimony by Hotrod Lincoln, Lonnie Gallaher and John1, in applications nearly identical to the one in question, leads me to the conclusion that it is likely that the tranny will be ok-as-is.

Again thanks to everyone for your input.

John

Guys, I'll finish up by saying that I was under the impression that the engine/gearbox assembly was only mounted by the 2 front engine mounts.

This is the only set-up we have in this country.........a mount either side of the engine block and one at the rear extension housing of the gearbox......no intermediate mounts.

I can see why there is such a difference in the structural strength of this set-up compared to ours if not running a crossmember!

It's been educational.

For what it is worth, my 67' had a three speed, no rear mount, and I switched to a 4 speed and never added one. The only diff was short vs long tail and threaded vs non-theaeded ears between the GMC and Chevy parts. No ear breakage.

Cavebull