Technical Hanging trans off rear of engine? Rear mount/Mid-plate question

On my 61 Olds, the 394 is mounted with a front cradle mount and 2 rear mounts with two rubber cushioned ears that bolt to a removable crossmember, sort of like a 57 Chevy. The trans, a Roto-Hydramatic, has no rear crossmember, and simply "hangs" off the back of the engine.

I've always seen drivetrains mounted with a rear trans crossmember. Obviously the Olds doesn't have a bellhousing attached to the trans and is rather part of the block. But lets say it was for a Chevy or Ford, or even later Olds or Pontiac. In lieu of a rear trans crossmember and transmount, could you hang a trans off the back of an engine with just front or side mounts and then a rear mount or cushioned mid-plate? I feel like that would be a lot of stress on the transmission's bellhousing, but I could be totally wrong. I also vaguely remember my 57 Chevy with a turboglide having only front and rear engine mounts but I don't recall whether it had a rear trans crossemember or not. Has anyone done this?

 

Pretty sure 57 was the final year before Chevy moved the mounts ..as for the rest , I don't know ?

 

The iron hydramatic in a 59 Chevy pickup hung off the back of the motor....as did the iron Powerglide in the Chevy cars from 55-57

 

OK, so it's doable. Is it a worthwhile consideration that both of those transmission are iron as opposed to an aluminum case? On one hand the iron trans would be stronger, but on the other hand also heavier. It's just one of those things that I feel like I shouldn't do. But retrofitting a rear crossmember is also going to a nightmare because of the chassis design.

I was considering a standard side mount with a mount like this in the rear. Seems sketchy but it could be in my head.

 

What are you planning to do?

I can't tell from your post if you're swapping to a different transmission, or you're worried that the 59 year old design is lousy and needs to be modified, or what?

 

Fair point.

I'm swapping a SBC/700R4 into the '61 Olds Super 88. The Olds has a very wide chassis that is narrow in height, so there's not a ton of room for a rear crossmember and exhaust. I'd like to try to utilize the factory crossmember that lands about where the engine meets the trans, but in doing that, I'll be hanging the 700R4 off the back of the Chevy like the Hydro was slung off the back of the 394. The difference being that the hydro had no bell and had like 8 bolts around the perimeter of the mounting surface, whereas the Chevy has 6 and has the bell on the trans. Ultimately the only thing mounting the engine and trans would be the two side mounts and the rear mounts. Just trying to formulate a plan.

 

Ford did it for years too, in their truck line. The bellhousing had two feet and the transmission hung out in mid air! No support at all!






Bones

 

In a late model round track car you use solid side motor mounts , then you install the mid mounts you have pictured then the bell housing . That leaves a gap the thickness of the mid mounts across the

top of the bell housing. Then the trans with no rear mount

 

Volkswagen Beetle -- the engine is hung off the transmission!

 

I bought the LAST two, A-1 Automatic Racing Transmissions, aluminum Powerglide, adapter bell-housings they had for the Tri-Five Chevrolet's. The stock bell-housing is cut off the aluminum Powerglide, and the A-1 bell-housing is bolted to the front pump (like the SFI endorsed race bell-housings). There are mounts on both sides of the A-1 bell-housing to bolt the transmission in like the stock transmissions were (iron Powerglide and manual trans). I will probably add a rear cross-member just to be safe however. Like I said, I have two; anyone need the other one? I am Butch/56sedandelivery.

 

I would add a crossmember at the back of the transmission. The transmissions that are designed to hang off the back of an engine have full circumference bellhousings. The exception...if you get one of the 4x4 transmission cases, with the matching 6 bolt cast aluminum dust cover and brace rods that go to the plates between the engine and motor mounts, then it would be stout enough to hang off and not use a rear mount.

 

Don't know how hard you're gonna beat on your Olds, but the kid that hangs around my shop has a OT 2wd pickup he runs in the sand. Blown SBC hooked to a powerglide. He uses front and mid mounts. Tranny just hangs off the mid plate. I wondered about the stress, but he told he's had the truck 10ft in the air coming off the dunes, and he runs 5:88 gears with paddle tires. In the 4 years he's run it this way he's twisted 2 driveshafts a blew 3 ujoints, and the tranny has stayed in one piece. He's got some whoopie- do rear suspension thing going on that won't let him use a rear tranny mount.

 

Like Jim says,use that back mount,and mount her in rubber..

 

I wouldn't bet on the cast trans being stronger than the aluminum one? hit a cast bell with a big hammer and one good hit will break it. Not so with the aluminum. And believe it or not a mag wheel is stronger than a steel wheel? Three mounting locations might put the assembly in a bind. you need a certain amount of movement to avoid stress. I know a guy used solid engine & trans mounts in a stock car, first race broke the water jacket from the drivers side of the block.

 

You don't have room for a small diameter tube cross member ? Say 1 inch round or square tubing to
clear the exhaust . I swapped a 500 Caddy motor into a 62 Olds 88 for a guy and we made room for a crossmember for the Caddy long tailshaft 400. It had mid mount engine mounts and a tranny crossmember. I used schedule 80 black iron 3 inch pipe for the exhaust go through and then 1 inch round tubing for the crossmember. He has been driving it for 10 years like that.

 

Also look at the rear trans crossmember in an Olds or other full size GM from a few years newer, perhaps 65 or so. Might be long enough and thin enough to be able to adapt it?

 

I seem to recall many cross members being oval , about 1 1/2" - 2" x 3" - 3 1/2" ..

 

I've heard that it's bad to use front mounts {Hurst mount style} with a rear cross member trans mount, something about it being too much unsupported weight, but I've seen it done without any problems. Same thing about what you want to do, front or side mounts and a mid mount, some say yes, some say no. I'm thinking squirrel has the right idea, an aluminum dust cover with support rods back to the block. Had an 88 Chevy 2wd with a 4.3 V6 and Turbo 400 that was that way from the factory, even though it had a rear mount. I don't know why they thought it needed the extra support, but it was factory.

Most, if not all, semi truck transmissions are bolted to a circular bellhousing and don't use a rear mount, the trans just hangs out in the breeze. Think about how much torque goes through that setup! I think that circular bellhousing is the key though, the trans is supported 360* at the front.

 

A little visual help!






Bones

 

I do remember tri 5 chevys with slicks and being lanched hard enough to pull the wheels breaking tail housings on Muncies.

 

Have a 5 speed truck transmission hanging off my Stude trucks bell housing......factory shit's been hanging thru many a clutch's renewal.........and a few burn outs.........

 

I would look at it from a safety point of view. Even if you use some kind of stock mounting points that normally don't employ a rear trans crossmember........a crossmember could be added. Anything that gives some rear support is better than nothing. If the trans is hanging in the air it allows a lot more leverage for forces to act on it. If it fails and the driveshaft drops and digs in, bad things can happen. Personally I would make new side mounts and a trans mount, but it depends on lots of things on your individual build and your preferences.

If you havent swapped an engine before, here is how I recommend doing it.

Get an engine tilter from Harbor Freight and a Cherry Picker if you don't have some other type of hoist or crane.

First I make a temporary junk transmission mount that I can C clamp in place and move around. I put the trans mounting holes in it and a couple/or one loose bolts so you can pivot the engine/trans slightly. Normally you will be centered in the frame.
Then I take the hoist/cherry picker and set the engine and trans in place with the trans on the temporary mount and some wood wedged under the sides of the engine.
Then I move the cherry picker to the side. You may have to put a jack and a jackstand under the frame on the side you are going to use the cherry picker. Probably need to remove the front wheel to allow room for the cherry picker to operate. Measure the front frame horn to the floor BEFORE jacking and removing the wheel......so you can return the car to the correct height after the wheel is removed.

Put the cherry picker in from the side of the vehicle and put the engine tilter in place. Raise the engine enough to remove the wood you wedged in to hold the engine off the oil pan.

Center the engine in the frame.



Rotate the engine using the engine leveler and a level on the intake manifold or across the valve covers.


Raise or lower the cherry picker until you have the engine at an angle that is compatible with the rear end.



Make a temp engine support that bolts to accessory holes in the heads and tack weld it to the frame.


Once this is done you can move the cherry picker out of the way and your engine is mounted exactly how you want it. No more wedging things here and there and causing the location in one direction to change while trying to get another location correct. Its hanging in the air exactly where you want it. Now bolt the engine mounts to the block and start making paper patterns for the frame adapters. None of those wooden blocks and crap in the way and nothing changes......its rock solid and you can fab to your hearts content.

This method gives a builder the ability to move the engine in all three planes at the same time.

 

A 57 turboglide had bellhousing mounts and was aluminum.

 

The late 1950's F100 6 cylinder engines all had tranny's hanging off the bell housing with no rear tranny mount at all.
Even the tranny body did not have a mounting point if used in another vehicle.

I also know of guys with front mounted engines who have used a rear tranny mount plus a custom additional mount at the mid point which is roughly where the bell housing is.
One guy used the flat head Ford engine mount cushions for this purpose.

 

I confess that I didn't read every post and I'm not known as the smart, good lookin' guy on the forum....... but it just seems reasonable to me that the engine/trans pumpkin needs more than a single pair of mounts creating a pivot point that will whiplash up and down at will. You need front to back mounting as well as side to side. Four mounts just on the block will do ya. Rubber mounts and/or donuts help greatly with noise and vibration at all attachments. You don't need 0 movement; you just need a degree of control. Two on the block and something on the trans is fine, also.
Apologies to any who have already gone over this. I skimmed and because I'm in a hurry and have to go back to mowing and get finished before dark, I may have missed a lot.

 

And with only FOUR bolts. I am Butch/56sedandelivery.

 

Thanks for so many informative replies everyone. In terms of relative abuse, this car will see very little above some 3/4 throttle pulls to get up to speed. The days of beating my cars to death are largely over.

The main reason I ask is because of simple logistics. The way the frame is under the car, it will basically cause me to build a rear crossmember where the exhaust has to pass through it. Even then, it will be a low point under the vehicle which is concerning given how low the car is. If I could use just a mid-mount and front engine mounts, like a 57 Chevy, it would keep everything contained to places where there is clearance for exhaust.

The main difference between the '57 bell housing mounts and the Howe mount is that the bellhousing mount was cast into the bell, and was also halfway back on the bell, whereas the Howe mount basically sandwiches the bell housing flange in-between the mount and the block. I don't know if the extra 2 inches or so really makes that big of a difference, and I'm leaning towards no based on most of the replies here. Perhaps I'm underestimating how strong the aluminum case is.

 

They are not strong. Those who have gotten away with it are lucky, not skillful.

I once had a 700R4 roll off of the bench. The case was empty, as it was in the process of being rebuilt (for myself, thankfully, not for a customer).

The bell section kicked off three large pieces.

I recently had a TH425 delivered, to be used for internal spare parts (chain, sprockets, etc.). The carrier had sheared off a large chunk of the bell.


My brother, back in the 1980s, failed to seat the converter properly on a TH350, before going full-gorilla on the bolts, and sheared off a large chunk of the bell.

My next-door neighbor, in 2005, was putting a fresh 4L80E in his commercial van, did the same thing my brother did, with the same results.

There is no way I would ever mount any aluminum-case GM automatic without a crossmember under the tail (or t-case, on a 4x4).

 

If you do front engine mounts, you will want to do bell housing/mid engine mounts. That is how the 57 Chevy did them.
If you do front mounts and a rear trans mount you risk cracking the bell housing from torque twist.


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I work for GM. Trust me, if they could have saved the cost of putting in the crossmember, and the rubber mount, they would have.