38 60 Special - rear end clunk LOUD

[joeceretti]

Ok so here's the story. Everything was great! I put all new springs on my brakes and rebled and the brakes were nice and solid. I took it for a trip around the block to make sure and put it in neutral and pressed the clutch and hit the brake, they worked better than I expected and the wheels locked up. Upon restarting it seemed fine until I went to make a left turn and there was a LOUD clunk/bang/clang from what seemed to be the rear left. So, I pulled the drum back off and the brakes still seemed fine. So then I assumed it crushed the bearing. Pulled the backing plate off and pulled the half shaft out and the bearing looks as good as ever, nice and smooth. If I drive straight no abnormal noise whatsoever, if I turn the clunk is back... this happens even at very slow speed.

I've carefully checked everything in the suspension and the drive shaft and it seems fine. I can't get it to clunk when I manually turn the back wheels. Maybe I should pull the front left drum off?

Could it be something in the differential? Could locking the wheels up cause this?

EDIT: A little more info. Left turns clunk loud and right turns thud more quietly.

[Bill Ingler #7799]

Just a thought but did you torqued the rear axle nuts to 285-315?   Bill

[joeceretti]

The torque wrench I found only goes to 250. I torqued to that and then a touch more. I had the axle out this morning and it looks fine.

[joeceretti]

I am 99% certain now it's something in the differential. Took the rear drums off and pulled all the brake components out. Put the drums and wheels back on for leverage and I can in fact make it clunk in the rear end without any drag from the brakes. I can actually turn the wheels back and forth at least 6 - 8 inches before it hits the gearing on either side. Next will be to pull the axles out and remove the carrier assembly I guess. Good news though, my axle seals haven't been leaking.

[Steve Passmore]

Thats not unusual Joe to have 6" of play on a wheel, remember it's turning all the planetary gears and the normal backlash before it bites on the pinion. The one wheel will show up all the lash which is shared by two in use.

Back in the 80s my 37 Buick convertible I had a nasty clunking noise when turning sharp right that I was convinced came from the rear, it was so pronounced. I even had someone hanging out the rumbler seat and confirmed the rear end. I had the complete diff apart and checked all tolerance, same with all the brakes, even had all the springs and shackles converted to silent block instead of the 'U' hangers, nope, noise still there. This went on for 3 months until one day I turned sharp right towards a garage door in the quite of night and the noise rebounded off the door in front of me. Front wheel bearing braking up on the outer race and grinding but only when the pressure of a right turn was put on it.   I think I've said before these under car noises are notorious for confusing us.

[joeceretti]

That makes more sense. I did replace the front bearings last year and this year cleaned and regreased... but that's where all the force goes when the wheels lock up. I am going to pull the front drum off before I go crazy on the rear end.

FYI, for anyone wondering how to get the rear axles out. Once I had the backing plate off I removed the key, slid the drum on loosely, put the nut on about half way and gave the drum a solid yank outwards and the axle came loose with ease.

[joeceretti]

Pulled both front drums off. Bearings are as perfect as they were last month when I cleaned and regreased them. Another observation... I backed it slowly out of my driveway and upon getting to the edge of the curb while turning left the clunk is sharp and loud and actually shakes the rear end of the car.

[joeceretti]

If I slowly turn the wheels bit by bit and move them back and forth I eventually hit a spot in the gears were there are obviously one or more missing teeth. That has to be why at first I couldn't get it to clunk by hand. Eventually when I hit the bad spot I can clunk it quite loudly by hand. Pulling the carrier off tomorrow morning. For now some rum.

[joeceretti]

I've found two differentials locally to me. One from a 38-50 and the other from a 39-50. I am going to drain the oil and look for pieces of metal and then, either way if I find some or not, pull the carrier off tomorrow morning.

I am surprised that there isn't much response on here to this. I have been responding to myself quite a bit though. Not much trouble with these rear ends I suppose? A usual, Bill and Steve are very helpful, thank you both. I really appreciate it. I've learned quite a bit about this car but the differential is foreign to me. Not for long though. Typically I am forced into figuring out a repair. As far as I know, and I have searched, nobody around here has a clue about these cars. Either I fix it, park it in a field and let it rot, or modify it. I choose to fix.

[Bill Ingler #7799]

Joe: Looks like you are in for a lot of work and before I would tear into the differential I would make 100% sure that the differential is the culprit. Have you checked all your spring eyes, spring bolts, rubber bushings or spring shackles to make sure one is not broken or missing bushings. You said the brakes locked up on you which would throw some strain on the rear suspension. I would especially check the eye bolt which holds the front spring eye to the frame. If your differential is original to the car then the ratio should be 3.77 to 1. This should be stamped on the front bottom of the differential. If you do end up using another differential, then check to see if that differential carries the same ratio as your original. As long as you have the axles pulled check your axle bearings. Have you changed the bearings since you have owned the car? Original bearings used in 38 were New Departure. These are sealed bearings so if they are original to the car, then any grease left in the bearing is from 1938. I have seen 2 cars almost lost on tours when the original bearings became so hot they caused a fire.  Bill

[joeceretti]

I was told the rear bearings were recently changed. It is clear now that they have been. They are MRC88128 bearings and the seals behind them look new. There have been no leaks on either side that I could see.

Wasn't the gear ratio on the 38-60S supplied as 3.92:1? My mpb shows that and it lists the 38-50 and 39-50 as the same part number and same ratio.

I recently rebuilt the springs and was confident that they were not the culprit. I did carefully inspect everything external, the spring mounts included.

I don't think it's that much work but maybe I am missing something. I have been researching but what I think is basically this...

1) Drain old oil.
2) Pull axle half shafts.
3) Remove old diff.
4) Clean up the seal seat area.
5) Replace with the "new" diff. Including a new seal and some sealing compound.
6) Replace axle half shafts.
7) Fill with oil.
Drive.

I will be placing a rare earth magnet in the bottom of the axle housing.

I suppose the lots of work or not much work is all relative. In a shop this would be expensive. For me I like it, as long as I have a clue. I hate, and refuse, to do anything without knowing as close to 100% what is going on. Hence, the time I am spending figuring things out. Taking things apart. Putting things back together. Learning the parts and the relationship to them all. Then I will be confident that the repair is as good as I can do it and hopefully as good as anyone else can or better.

The real thing is, what am I missing. AND this all depends on the condition of the replacement differential I get.

EDIT: The 39-50 diff is from a hearse. I have to imagine that a hearse would typically be driven more easily and better maintained  than a regular passenger car but I suppose that this many years later anything is possible.

[Bill Ingler #7799]

Joe: I do not see in my Master Parts Book where 3.92 was ever a ratio used as you can see below. Your 38-60S as well as the 38-50 and 39-50 all used a 3.77 rear according to my book.   Bill

[joeceretti]

Yours has the Cadillac logo so I assume it is correct. This is a capture from my book.

Another of those strange oxymorons.

[joeceretti]

The cover of my book looks like this...

[joeceretti]

Whichever is right, I will find out. I am 100% positive that the diff I am buying is from a 39-50. I will count the teeth and report back.

[Steve Passmore]

Mmm all very confusing. Both my 37 and 38 manuals confirm Joes 3.92 but just to muddy the waters a little more look what mine states the ratio is for the 60 series.

Can you clarify Joe whether you have driven this car before? I was assuming it was a new symptom your dealing with when I gave my reply and that you had not had this when using the car before but axle problems couldn't have happened while it was sat in your workshop, so is this a first test? if so then one never knows what has happened to these cars in the past and why they were taken off the road years ago.

[joeceretti]

I've put about 3,000 miles on it since last year. I have been driving it to work through every little noise. Up until this happened I had worked out 95% of the squeaks and rattles. When I first got the car there were two distinct clunks in the drive train. First was u-joints and second was a loose bolt on the transmission stabilizer. It has been driving smoothly and nearly vibration free even at highway speeds. This happened when I locked the brakes up two days ago. Definitely something new. As for the ratio, I took a snip of my 38 Shop Manual Supplement that was issued by Cadillac especially to include specs for the 38 60S. It also shows 3.92. (Attached)

I'm going to pull the differential off this morning to check for damage and will count the teeth just to be 100% sure.

[Philippe M. Ruel]

Joe, sorry for what seems to happen to your car.
You can't expect a bunch of answers in a 12-hour lapse. I just dicovered this thread.

What I would do (and maybe you did it) is put the rear end of the car on safe jack stands under the axle, start the engine and engage 1st gear so that rear wheels turn above the floor. Then try to stop one wheel at a time by hand (it can be done if the differential works properly) and listen to where the noise comes from.

And yes, these rear axles are usually the last part to fail on our cars.

[joeceretti]

I will do that Phillipe. I wasn't being impatient. Just posting what I discovered as I went along to give anyone interested in helping as much information as possible.

[joeceretti]

Merci Phillipe! I did just what you recommended. I set the idle as low as I could without stalling and then tried to stop the wheel from turning. I couldn't do it. So, I put a bar on the ebrake cable and pulled one side and then the other. CLANG CLANG CLANG... from the rear. Loudest from the left side but still there on the right.