PaPaPork

Gents, advice for a novice/amateur mechanic needed!

Last Year
So I was driving my 79 last October and as I was pulling into my driveway I noticed a whine. I just parked the car and forgot about it.
The next day I was trying to pull out of the garage and the car would move by a couple inches and stop, and I mean stop hard like hitting a wheel chock! I looked under the car and found no obstacles and no major leaks. I changed it to D, pulled up a couple inches, then back to R and pulled out of the garage and onto the road, about 4 houses down going about 20mph I hear BAM BAM BAM!!! stopped, tried to make a U turn to get back to the garage but car had the "invisible chock" syndrome again, had to do a little forward and a little backward without any throttle and slowly made it back to the garage and parked the car for the winter

This Year
I finally got my daily driver ready for the summer (had a bunch of OBD codes over the winter) so I need to take care of my 79 but I'm no mechanic so I'm not sure what to look for!


Initial Evaluation
I took the spare tire tub off (for access) Diff has fluid, no visible damage in the rear suspension area but again no clue what to look for (not a mechanic), visually the U joints looked OK. I took the driver side rear wheel off, brake was ok. I tried to spin the wheel by hand (car lifted and in Neutral) no luck! so I tried using a crow bar across the wheel lugs with no luck either - the half shafts would move only by a degree or two either direction

car history
Pinion seal was replaced by a local shop 4 or 5 years ago. The PO went over the car in early 2000, polyurethane bushings, shocks, breaks, leaf, edelbrock head/intake/cam package 4.11 rear (or something of similar ratio) and so on, car always had a whine when lifting foot of gas at high rpm (engine breaking sort of speak).


please help
Any ideas/hints are greatly appreciated ! I can take pics or movies of any components in question and post them here if that would help - just let me know...

dugsgms74

I'd suspect a parking brake problem, see if you can pull the rotors off and take a look.

sstopczy

That or disconnect the half shafts at the U-joints if the rotor is still riveted to the hub and try to turn it. If it turns you know your problem is with the differential and not your hub assembly/parking brake.

CA-Legal-Vette

While possible, my first thought was "can't be the parking brake because they never work." . Seems unlikely that a parking brake bind would produce intermittent symptoms and on both rear wheels. Not too hard to check this. Remove the rear calipers and rotors and try to turn the wheel hub again. If they still won't turn, your problem is likely in the differential, which would be my first guess.

If you haven't got much experience working on these cars, I don't think it would be wise starting on a differential removal, diagnosis and rebuild. Best find an appropriate local shop.

JimLentz

Sounds like a bad bearing.

PaPaPork

I only checked the driver side. Will Check the other side and parking brakes tomorrow.

I realize rebuilding diffs is best left to pros (used to be a few on this forum doing diffs for others) however i would like to pin point my problem, you know, do a proper diagnosis even if someone else will do the repair.

Thanks for all the ideas! Keep'em coming!

PaPaPork

Wheel Bearing?

PaPaPork

I like the idea!

Also can my problem be trans related?

JimLentz

Yes, it sounds a lot like what happened when a wheel bearing went out on my brother's 1970 Mustang.

0HoosierPE

Sounds like the cross pin for the spider gears has slipped. There is a retaining pin that holds the cross pin in the carrier and if the retainer pin breaks or falls out the cross pin slips out as the differential rotates and hits the pinion. When you go the other direction the pinion will the push cross pin push back in and it will be quiet until it slips back out.

PaPaPork

So i checked the other side and it does the same thing, the half shaft rotates a couple degrees and thats it. Since i have the same symptom on both sides is it safe to assume that the problem is not wheel bearings nor brakes?

vette1500

PaPaPork

Thanks for the reply. Do we have a concensus that since both wheels only move by a couple degrees (in neutral) it has to be the diff? Or is there a chance its the trans or something else?
I'm getting mentally ready for the task of dropping it... this will be the biggest car related task for me so far, but hey! I ain't going to learn much without trying now will i.... ; )

65GGvert

Narrow it down. Disconnect the ujoint at the drive shaft, that will either eliminate or point to the transmission. Then the half shafts, drop one and check again, if it moves it must be in that wheel, if not, drop the other. If the rear gear still doesn't move with all three shafts removed, there's no doubt it's in the rear axle.

PaPaPork

**********UPDATE************

Since I'm not experienced mechanically this was quite an experience and I am happy that I decided to attack the problem by myself!

I disconnected both halfshafts ujoints at the diff. I was then able to spin them both by hand together with the wheel assembly. So the wheel assembles were eliminated as potential culprits

then I disconnected the driveshaft U joint at the diff and I was able to spin the driveshaft by hand (trans in N) so the diff is the problem!

did I mentioned everything was locked up? it was quite difficult to disconnect Ujoints without being able to spin them:/

anyhow, dropped the spring, then the diff with a friendly neighbor assisting. and it looks totally F***Ed up in there!!

just take a look yourself!

TimAT

The ring gear bolts backed out. Not an uncommon problem. But it does require a decent size pile of new parts to fix. And them parts are not cheap. Not outrageous, but not cheap. Easy fix would be to get a rebuilt unit from one of the vendors, but you'd probably have to eat the core charge.

PaPaPork

Gents, so i've been looking for a core diff hoping that it will turn to be in good working order So i can just drop it in or at least score a core diff on a cheap

1 what are the differences in diffs across the years? I am looking for a 63-79 right now but how about bbc vs sbc? Are the yokes different? Any recomendations on how to narrow my search?

2. what do i pay attention to when inspecting? Leaks, free spin, no loose bolts and chunks inside. What else?

toobroketoretire

The big blocks used different side yokes with forged steel caps and not u-bolts. Other than that the rear ends are the same.

PaPaPork

UPDATE

I found a local gentelman with a small block joke diff and I need some advice!

Should have taken photos but i was so excited i forgot. Anyhow here is the descriprion:

1.Heavy outside rust comming of like fish scale.
2.It had to be tapped with a hammer on the yoke to break loose, after that it would turn by hand.
3. Inside i found some "needle *****" rust on the carrier, no fluid just some gray mud on the bottom (oil plus micro shavings?) I also found some nail clipping size shavings here and there.
4. The ratio appears to be 3.08

The owner claimed that this unit was rebuild and i can bolt it in and go. Is this an option? I think this might be a core and not even a complete one since nobody wants a ratio like that i would have to eat the core on ring an pinion to say the least.

My question to you is how much is such a diff worth? Owner thinks its worth 400... With my divorce and medical bills i dont want to overpay even 10 dollars if i choose to buy it...

What do you guys think about all this? Give it a try, replace my diff with this one and see what happens? Or just a core? In either case whats a realistic selling price for a unit like that?

Cheers!
KC

JimLentz

Seems to be a few issues with that differential and I wouldn't personally put it in the car as it sits. I also think it is overpriced based on your description. It might have been rebuilt, but was it done properly and how long ago? Based on seeing shavings it doesn't sound good.