MDchanic

This is a followup to this post from about ten days ago.

1973 Delta convertible, probably 113,000 miles (could it be 213,000...?), originally a 350, with a 260 motor (from a '78, and, no, I didn't do it), TH375 (seems original), original-type driveshaft with U-joint at trans and "CV" joint at differential, no perceptible play or clunk in the driveshaft, original-appearing open rear, seems to count out to 3.08:1, original wheels, new 235/75x15 tires, drum brakes that look original (no, not the shoes) and in good condition, new Bilstein shocks all around, "new" rear springs from a '73 98 sedan.

The car has had this problem since I got it last fall, but with very worn shocks, sagging rear springs, broken front springs, and bald LAREDO tires, I figured it would go away as I fixed things.

It's got a distinct, harsh, speed-related (not RPM-related) vibration with peaks around 30mph and 65mph, that can't be localized to any one part of the car while driving. No clear steering wheel shake, but there is some gas pedal vibration.

I thought it was probably the driveshaft, and it may be, but I just put it up on stands and had my kid work the pedals while I walked around and looked at it.
The vibration is the same with the rear wheels off the ground as it is when driving, and about the same with the wheels off or on (drums on - didn't want to risk the "driver" stepping on the brake and blowing the pistons out of the cylinders). Looking at it, neither of the wheels, nor the driveshaft, seems to be jumping or vibrating, but with the wheels off, the whole rear end is vibrating, with no clear place where it's vibrating more, and that vibration is clearly the vibration in question.

So, does anybody have experience with this?
Does it seem like the driveshaft?
Could it be the axle?
Could a bad drum do this, even with heavy steel wheels and tires on?

I'd rather not just replace parts blindly, if I can avoid it.

Thanks,

- Eric

Oldsmaniac

My guesses would be rear/ bent axle or bearing problem, bad wheel(s), maybe motor mounts.

MDchanic

Thanks, Joe.

I don't like to hear "bent axle," and I can't imagine how it could have gotten bent by an 8:1 350, but it shouldn't be motor mounts, since the motor and trans aren't vibrating, and it shouldn't be wheels, since it does it with the wheels off. It's not singing or rumbling, so I don't think it's a bearing, but that may be possible as well.

- Eric

greenslade

would a bent axle show as a wheel wobble?could it be related to drive line angles?just guessing.

MDchanic

Driveline is 100% stock, wheels show no visible wobble, vibration is the same with wheels on or off, so I don't think so - that's why I'm stumped.

I'd hate to get the driveshaft rebalanced, put it back on, and have the same problem.

- Eric

TripDeuces

Could one of the caps on the u-joints have shifted. Not sure what kind of retainers yours uses but a missing c-clip or cap not set in the saddle correctly would do that. Have you tried putting it in gear with the rearend off the ground so you can watch everything underneath?

If when installing new u-joints a roller bearing or two fell out you can get that also. Sometimes they just knurl themselves into the shaft from poor maintenance. Maybe just replacing them is a good idea anyway. I think if a balance weight fell off you would be able to see it or at least where it had been.

Homestar

I am going through the same problem.
Mine vibrates at around 30- 45 MPH.
Its not a wobble or a shake, its a fine vibration. Seems mechanical.
I had my drive shaft off while I restored the car.
I am told my shaft may be mounted 180 degrees off.
I will try that next.
Unmount from the rear end and rotate 180 and reattach.
I already replaced both u-joints. The car was fine before the restoration.

Did you try rotating your tires?

You should jack up the rear end and chalk your wheels.
Let the drive line free wheel in gear, I found a bent rim and bad tire that way.
. They were causing a bad wobble.
Also I noticed the front of the rear end was moving up and down as shaft turned. So I replaced the u-joint (Again) and it got much better, but I've got my eye on that up and down movement that could still cause vibration.

One thing I learned is it is best to figure it our yourself.
I was led in the direction of a bent axle for the wobble. It was only the rim.
I found it free rolling it in gear on a lift.
Look at it really good. Be inovative and you will find it.
Rotate you tires.
Or
You can also rent a car for $40 and swap the tires and rims to your car.
Feel the ride.
Its cheaper than bringing it to a mechanic and you learn it for yourself.

~ good luck Charlie Brown!

MDchanic

Well, everything LOOKS straight and properly installed, but I'll take a look at the joints to be sure nothing is out of place.

For the love of all that is holy, people, it does it with the wheels on or off the car. It CAN'T be a wheel bent or out of balance if it does it when the wheels are stacked against my Chevelle.


Interesting thought - something else to take a look at.
It'll be a major pain though, as the rear joint has TWO U-joints in it.

I would think it would be visible as well.

Interesting thought. I had thought the shaft was balanced independently of the transmission and the rear end, but I suppose it's worth a shot.

Ain't that the truth...

- Eric

walkerolds

As others have suggested, remove the driveline and check the u-joints for missing clips or a stiff feeling joint. If you can support it in some makeshift saddles at either end and turn the shaft, you should be able to detect a possible "bent" drive shaft.

Mark the driveline position at the differential yoke when you remove it and re-install 180 degrees from removed position. Speed related vibrations typically indicate a balance problem due to harmonics.

If the rear joint has "2 u-joints" they are usually coupled together to keep them from wobbling. Maybe something is amiss there. You might ask around for a local driveline shop who can check it out for you to see if they see any problems. It isn't as expensive as you might think, and they are good at what they do.

My 2 cents, Good Luck.
Gary W.

rustyroger

An unbalanced driveshaft won't necessarily be obviously bent, going through vibration at two different rotation speeds tells me that is the first place too look, check to see if any weights have come off (look for broken spot welds).
Is it a two piece shaft?, could be it has been seperated and reassembled incorrectly.
Having read some of your posts I know you are not a dummy mechanic, but I know I have sometimes been stumped for an answer and a fresh opinion has come up the right diagnosis.
Let us know what you find.
Good luck!.
Roger.

TripDeuces

I wasn't referring to the axles or wheels when I said get underneath it. I meant look at the driveshaft as it rotates to see if it wobbles. Bent axles and wheels hum, it's a rotational sound if that makes sense. They don't do what you're describing.

MDchanic

Yeah, I did that - no obvious driveshaft movement.

I agree that it doesnt sound or feel like I would expect an axle to, and I would think a bent axle would give me at least a little wheel wobble, which I didn't see.

I'll pull the shaft and look it over...

- Eric

BlackGold

Balancing a driveshaft is dirt cheap, at least in my neck of the woods, so I'd start there.

But my vote is for the bushing in the tailshaft of the transmission. A little extra clearance there will cause a speed-sensitive vibration.

HurstOlds1775

My first thought was 180 out with the drive shaft. Sometimes they do have a small scribe mark after the ujoint on the shaft to line up with the rear end scribe mark. But then I was thinking that I have to agree with the tail shaft bushing getting worn. That would transfer the vibration to the last part rotating. My 2-cents! And thanx for your advice with my no compression in #1 cylinder 455!!

dhoff

If it has the double u-joint on the one end don't they usually have a ball and seat in between them, like on an older 4 wheel drive it could be worn or need greased?

MDchanic

Oh yeah, it sure does. And it looks nobody's ever touched it.

If all goes well, I'll know what's inside it tomorrow.

- Eric

Yellowstatue

My '81 Regency had a speed vibration and when I found a 2:41 limited slip axle and installed it, my good vibrations had 'discapeared' the carrier bearings were bad!

MDchanic

I know you've all been on the edges of your seats waiting to hear more about this problem, so here it is:

I got the driveshaft off and apart today - no big deal, the shaft comes off the driveshaft with four beefy bolts through the flange (no U-bolts like the A-bodies), and a few good swats with the sledgehammer, and the universals come apart just like usual - remove the clips inside the cage, then drive the caps out and remove the crosses. The locating ball in the middle of the "CV joint" at the rear end pops out with a bit of help from a screwdriver.

All of the universal joint parts were in at least reasonably good condition -

• The front U-joint had been recently replaced (non-greasable ),
• The locating ball looked to be in good shape, popped in and out of its little hole smartly, and moved smoothly,
• The rear U-joints were tight and smooth, but upon disassembly, two races of one cross were slightly galled.

The two rear crosses were different from one another, indicating that at least one had been replaced along the way. One of them was a bit of a loose fit in the yoke (just needed a gentle tap for the cups to come out), but I haven't tried swapping cups and yokes to see if the problem was the cups or the yoke. They weren't loose enough to show any play.

Both crosses and the ball at the rear joint were well lubricated with reasonably fresh grease.

SO, it doesn't look like the universals were to blame.

On the other hand, the driveshaft had a big, long dent in it, like someone had hung the car up on a rock or something, and one balance weight looked amateurishly welded on. It looked straight when sighting down it, but I know that's no way to tell.

The differential flange looked good, was solid, and had the usual rotational play before "taking up," but no radial play or endplay.

The transmission was another story.
When I grabbed hold of the output shaft, I found I could move it 3/16" (I measured it) in any direction, up, down, or sideways.
I don't remember wiggling very many output shafts (did I just type that?), but I'm pretty sure that those I've felt in the past had no play at all, so I guess that at this point, the prize goes to BlackGold for his prediction:
So, where am I now?

• Good universals (I'll buy a couple for the rear joint tomorrow)
• Good rear (as far as I can tell)
• Questionable driveshaft
• Bad tranny

I'll bring the driveshaft to the truck place in Scarborough for balancing and possible straightening, as I have no way of knowing if it's good or bad.
I've got a spare TH400 (Code OB, 1968 98, 455 high-comp., 66,000 miles), but it's in my father's shed 350 miles away. I could go get it, but if I were to drive the car there, I could put it in on a lift, which would obviously make my life a lot easier than bench-pressing it in the driveway.

So, unless someone nearby has a good TH400 that they want to sell me cheap, I'll probably get the driveshaft balanced, put it back together, wait for the right time, and take a nice, slow drive to the old man's house to put the transmission in.
Meanwhile, there's about a thousand other things I've got to work on as well.

Thank you all for your advice so far, and if anyone has had any experience with loose TH400 output shafts (especially how long they last before they quit, and whether there's a fix that doesn't involve total disassembly of the transmission), by all means do let me know.

I'll keep you posted.

- Eric

MDchanic

Having reviewed the manual, it appears as though the tailshaft housing is fairly easy to remove, possibly without having to remove the transmission from the car.
Once the housing is off, can the tailshaft bushing be removed and replaced without an "excessive" amount of labor (it isn't clearly shown in the manual)?
Has anyone actually done this?

The transmission in all other respects operates very well, so if I can solve this problem without pulling the trans., I will be a happier person, especially since I'd rather save my "good" OB trans for the "right" car .

- Eric

ps: in case it's important, the trans. in the car is actually a TH375, and not a full-out TH400

z11375ss

My money is on the driveshaft being out of balance. I have had this problem with several cars I have hopped up in the past. I had one where I bought the driveshaft from a reputable company like SLP and it turned out to be out of balance although it was sold to me as being "balanced". After balancing by Surge Friction in Chicago the car had no wobble whatsoever. It is a cheap and easy check. Question, does the mirror vibrate at the wobble speed? I could always tell if it was the driveshaft if the mirror was throbbing. Good luck!

Homestar

I know you've all been on the edges of your seats waiting to hear more about this problem, so here it is:

HeckYeah!

Thanks for update !!!

MDchanic

Nope, no particular mirror vibration - more a seat-of-the-pants sort of vibration.

- Eric

oldcutlass

Without the yoke inserted, I believe your going to have that play in the tailshaft. I'd replace the u-joints first, and then if needed get the drive shaft balanced.

MDchanic

Yeah, OldCutlass, you're right.

I've been doing some "research" (using Google, in other words), and I now understand that the tailshaft bushing bears on the outer polished surface of the yoke, and that some radial play (but not endplay) is normal with the yoke out.

It looks like the spec. is about 0.009" of play, so now I've got to drag myself under there with the driveshaft and see how much play I can feel with the yoke in. I haven't decided yet whether I'll try to put a dial indicator on it (probably more trouble than it's worth).

The other thing I've noticed is that two cups on one cross (the one between the driveshaft and the front of the "CV" joint, on the axis that goes through the joint coupler) are a tight slip fit through the holes. Actually, almost all eight of the cups can be gently tapped through these two holes. I haven't encountered this before, but it would seem to me that this means I need to replace the joint coupler, unless the new cups fit a whole lot tighter. NAPA lists it for about $60, but I'm really trying to avoid spending more than I have to on this beast... Grrrrrrrrr .

- Eric

edit: New U-joint cups pretty much just drop in to "CV" joint coupler holes, so I'll be picking up another coupler at NAPA when it comes in tomorrow morning...

MDchanic

Ran into PO - He told me he was the one who changed the front U-joint, so at least I know it's new.

He also told me he had JB-welded up a hole where a plug had fallen out on the road while the owner before him had had it. The hole was in the front of the yoke, in the axis of rotation, leading from the space between the end of the output shaft and the yoke to the outside world, and apparently trans. fluid had been pouring out of it, which is why he had gotten the car cheap.

I wonder... Is there anything I should know about this plug (can't see anything under the JB-weld now )? Is it, by chance, some sort of pressure relief that shouldn't be blocked? Or is it just one of those manufacturing oddities that can be safely eliminated?

Thanks,

- Eric

MDchanic

I was definitely mistaken about the tailshaft bushing.

With the yoke in place a bit farther in than it would usually ride, there is NO perceptible play.
With the yoke in place a bit farther out than it would usually ride , there is a TINY bit of play, probably less than the specified 0.009".

So, that's not the problem.

The PO SWORE it NEVER had any sort of a vibration while he owned it.
Right.

I'll bring the driveshaft to be balanced in a few days (Damned holidays!).

- Eric

MDchanic

Chapter XVIII

I took the driveshaft to a good "driveline specialist" place (Williams Brothers in Portland). Big shop, busy, driveshafts all over the place.

The guy took one look at it, and actually looked shocked.

He noticed the same things I did: The big dent in the middle of the shaft and the amateurish welding on one of the weights and on the trans. end, but he was much more concerned about them than I had been.

He also noticed two things I didn't:
1. The yokes don't line up. When looking at the shaft sideways, the yokes on both ends should be aligned. In other words, if it's rotated correctly, you should be able to see through both sets of U-joint holes. He said these were "eighty to ninety degrees off," and he was right.

2. The "slip-yoke" (the front yoke thats slides in and out of the trans. tailshaft) has been running too far out of the trans. In other words, the driveshaft is probably about an inch shorter than it should be.

He said he could fix it by installing a whole new shaft tube, but I'd have to go home and put the yoke in the right position in the tailshaft and measure how long it's supposed to be.

Then he told me something I really didn't want to hear:
It'd cost anywhere from $200 to $250 to fix, depending on whether it needed a new slipyoke after they pulled it apart.

That ain't no $80.

And after spending $110 on a a pair of U-joints and a new coupler sleeve .

So I took it back and told him I'd try to source a used one first.

Anyone got a used '73 Delta 88 driveshaft? Can be just the shaft with no joints.

From what I can tell, all models had a 124" wheelbase, and should be the same
(98s and wagons had a 127" wheelbase, and should not be the same).
The length on my bad one is 54", center to center of the U-joints, so the right length is probably about 55".

Waiting for your flurry of replies...

- Eric

ps: yes, I posted it in the Wanted section.

Yellowstatue

Unfortunately there won't be any flurries in this heat