Technical 1950 Chevrolet 2 dr. styleline vibration

I have a 1950 Chevrolet, restored, 350 small block. Went from a manual 3 speed to a rebuilt 350 turbo automatic and developed a vibration. After checking pinion/transmission angle with a angle finder there's a 7 degrees difference, figured that's it. I have the 1950 original rear end housing/axles with 1973 chevelle station wagon 3.5 gearing, After taking ubolts off and lifting rear end to shim perches I see the perch is mounted to front of axle by a bolt and bracket and pivots, so my question is would shims work or any other fix, would I be better to look at new leaf spring kit install and weld new perches.

 

well, first of all you do not have the original housing and axles if you have the gears from a 73 Chevelle.

 

Same housing and axle that's in the 1949 to 54 manual with the pivoting perches I noted. Just bought the car 3 weeks ago, was told it had a 73 chevelle rear end. Wondering if he changed the internal gearing and keep original housing

 

Have you only gone from a 350 with manual, to auto?? If so, theoretically the drive shaft angles are approximately the same..
I wouldn't start chasing diff angles if it was ok before the mods you have done..
A couple of questions ....
Did you use the original drive shaft, or have another one made?
Is the vibration there while engine is running and not moving, or while you are driving??
Engine running, could be a wrong (external balance) flexiplate, or bent..
Driving, could be a bent driveshaft, worn universal joints..

 

Look more into it and there are some great driveline angle threads on here. Of all the things I've assembled through the years, zero pinion angle related vibration. 1973 Chevelle rear end guts don't fit a 1950 housing, so that's out. Agree with looking at the u-joints, check the drive shaft for dents, a sure sign its been mishandled and possibly bent.

 

By your description it sounds like the builder used the rear end mount system that the '50 had originally and adapted a newer style rear to it. If so, what keeps the housing from tipping fore and aft randomly? there must be some sort of traction bar system.
Pictures would help.

 

New drive shaft/u joints built and balanced but shop, engine is smooth idling, not moving, The vibration fades out above 40 mph. The person I bought it from said when he did the automatic install ,also put in new flex plate. He bought and started restoring in 1990, only reason for selling was cancer, and couldn't work on it anymore.

 

The rear end from my research (1950 manual)seems to be original, has the pivoting perches connected in front of axle, and 2 braces connected to the top of the rear end angling out and connecting to the frame each side. I was told that he install a 1973 chevelle rear end, after see the setup thought he changed internal guts.

 

I'm going to double check but all the information he had in writing done to the car showed 1973 chevelle rear end. All the mounts ,springs etc look original to the car

 

That's why from research I've done so far I think the pinion angle is the problem. With a angle finder the transmission is at 88 degrees(2 degrees down) and the pinion 81 degrees(9 degrees down) the ujoint out of the transmission is almost straight on, no angle with all of the angle in the pinion ujoint. You can probably tell this is all new territory for me. I'm fairly mechanically inclined but this is new to me.

 

That simply won't work, and is your vibration.

With engine/trans at 2 degrees down, the pinion needs to match. So to keep it easy to visualize, the front of motor is "up" 2, and the front of the pinion shaft also needs to be "up" 2.

When you rotate the rear end to move the pinion from 9 down, upwards to 2 up, that will raise the driveshaft at the back quite a bit. That should get you a normal "working angle" at the front U-joint, I would think. A cross style joint needs 2 or 3 degrees to keep the grease travelling under the needle bearings. At your zero now, it is not greasing properly, and I'd want to inspect that joint to see if it's worn out now.

So raise up the pinion to 2, then measure the u-joint working angles to see if you can at least be at 2 or the preferred 3 degrees. Note: when you do measure angles, the weight has to be on the rear springs just like driving. You can't have the frame on jack stands, and have the rear end hanging down.

 

One of the things I'm trying to find out is with the 1950 rear assembly is the perches are mounted in front of the axle bolted to a bracket welded to axle that lets them pivot, if I shim them will that change the pinion angle, because of the pivoting factor. I have ordered shims and have the axle ubolts off but seen the way the perches pivot made me wonder if shims would work

 

I've never worked on, or looked at that Chevy system. I am sure plenty of people here can help with that.

 

The pivoting perches are only used with a torque-tube drive-line setup. If the car has been updated to an open drive-line, then the spring pads should be welded directly to the rear-end housing. Redo your perches or find a way to "lock" the pivots. Post some pics if you can, that will tell us what rear-end is in the car, and if it's mounted correctly.
I am Butch/56sedandelivery.

 

As F&J said, when you measured the pinion angle, you did it with the car at ride height with the weight of the car on the rear suspension. Correct? The measurement would be incorrect if the car was jacked up, with stands on the frame to allow you to get under it.

 

Yes car was setting with weight on suspension

 

Working on pictures. Just talked to previous owner. the rear end, brake hubs, etc are all from a 1973 chevelle station wagon. He had all the mounts, perches, etc removed from the 1950 original rear end and welded to the 1973 and also used the 1950 springs.

 

Should off added the rear end, brake hubs,etc, is all from a 1973 chevelle station wagon rear end with all the mounts welded on, from the original 1950 and 1950 springs used

 

Here are a few pictures of the car

 

Before you go tearing things apart, some answers to this post are in order.

If you used the original driveshaft (for the Chevelle rear) there should be no change.
It is important to know conditions of vibration, moving, not moving, standing still but revving the engine..

Also, does the flexplate & damper on the front match the engine?? i.e., do you have an engine (older) with a 2 piece oil seal or an engine (late '80's & up) with a one piece seal??

 

The driveshaft was fabricated new at a shop also balanced, different drive shaft was used when it had the manual trany. The vibration is very pronounced up to 40 and fades out, standing still idle or revved up no vibration. The flex plate and transmission was install new by previous owner after being rebuilt by transmission shop. The 350 motor was rebuilt before installing and is out of a 1971 Impala as was the 350 turbo automatic. I ask the previous owner( I bought car from) about transmission install and flex plate , all of which he said was correct. He had a 3 speed manual in the car at first and decided to change to automatic because it was geared to high starting out in low because of 73 chevelle rear end ratio. He did say when the manual was in the car, there was no vibration

 

Ok, I never looked at that type of Chevy rear suspension for the original torque tube drive...but what is keeping the new rear end from rotating? I see something that might be part of the Chevelle rear trailing arm suspension?

What is this that I circled in white? Where does it attach to the frame?, or where, if not the frame?

I think they used the two upper Chevelle arms to keep the rear end from rotating, but it has to be in a bind, or at the least, be poor geometry. IMO

Something looks way wrong, and I agree with Butch on mounting the rear end solid with perches welded to the rear with Ubolts, which does away with the pivots....and an upper arm would not be used, if that is what is marked X

 

You are correct in thinking the shims will not work.

The shims will only change the angle of that rotating pivot bracket.

The shims are only used between a normal leaf spring and a normal solid perch pad on the axle.


Don't put much into what the owner said about the vibration was not there. You need to fix his mess, and while doing so, you get your angles matching on the joints. Then go for a ride to test

 

'49-'54 Chevies have a torque tube. If it is open driveline it is later, it is not likely that a torque tube is mated to a turbo 350.

First things first, get your motor angle sorted out. You should be close to 3 degrees not 7. Then once you have that working for you worry about your pinion angle.

 

Chassis engineering's rear end kit will save your Rear end. Pun intended. that set up you have is not the best engineered system and most likely the cause of many issues. the chevelle rear end should work very well if set up properly. I have one in my car and I am mounting it with the C.E. kit which works really well. The perches will need to be welded to your current housing and the rest bolts to stockish holes in the frame. It also uses more common 2.5 inch wide leaf springs. You will no longer need or want the upper control arms connected to your frame from the original chevelle. you have a really cool car and I am looking forward to seeing the progress.

 

There's 2 mounted to top of rear end angling out and connecting to the inside of frame both sides

 

The only thing really different is the drive shaft.

Clamp a couple of ounces of wheel weights to the drive shaft with a hose clamp & see if that changes anything.

 

The transmission angle is 2 degrees down not 7, the pinion is 9 degrees down , difference of 7