[kingbuzzo]

I have a 74 TA with a 10 bolt 3.08 with likely an aftermarket posi (eaton) but have never cracked it open.

It has been fine for the last three years I have owned the car however she has developed a clunk noise emanating from the rear passenger side - usually when I go over a pothole.

I looked underneath and the exhaust, sway bar and shock usual suspects seem to be in order however when i move the rear wheels on either side in either direction there is mild a clunk noise.

Does this mean the axle shaft is coming apart, or a c clip issue or is the posi going?

Understood that not much can be diagnosed without taking it apart but just wondering what I could be facing.

Thanks!

[67drake]

Did you check the U-joints too?
I’ve had rear ends with so much ring and pinion gear lash they would clunk if I shifted from park to reverse, or whatever, and they’ve lasted for years that way.
Having said that, you could jack the back up and see how much slop is actually in there, but opinions will vary how much slop you can have before a well broke in set is “out of spec”

[steve25]

You may have one or two cracked leaf springs on that side, did you look at those?

You may also have worn spider gears and cross shaft in the rear.

Jack one side off the ground with the trans in neutral and chock the front wheels so it can’t roll.

Grab that rear jacked up tire and see how much rotational play there is .

I just went thru this with my own Jeep liberty.

New kit of spider gears and crosshaft are about 130 bucks .

[b-man]

I would check the axle, which of course requires removing the differential cover to access the C-clips. Not so bad as this gives you a chance to identify your posi unit and put some fresh gear lube in there, don’t forget the little bottle of friction modifier additive.

The bearing design unfortunately uses the axle itself as the inner bearing race. Once the hardened surface on the axle becomes worn you need to replace the axle and bearing.

However if the axle isn’t too worn so as to be unsafe, you can buy an ‘axle saver’ bearing that is essentially an offset bearing (towards the outside) that allows the bearing to ride on an unworn portion of the axle.

I once owned a 1976 T/A and had to use one of those special axle saver bearings and it worked out fine. I was transplanting a set of 1979 rear discs and axles onto it and finding another disc brake axle would have been difficult.

[kingbuzzo]

Leafs look ok...unless you are in Toronto,,,u joints look ok to me

It clunks if I move the wheel back in forth on the stands - i'll try to make a video of what I mean

Bearings sound daunting to me but I'll keep that in mind too.

[b-man]

Pretty straight forward job to fix the axle bearings, really not that difficult

You’re not pressing the bearings off the axle, might need a slide hammer with a hook attachment to yank the old bearing out of the end of the axle housing. Been a while since I did the job but it’s fairly easy.

[AG]

Sounds like the spider gears cross shaft hole could be worn.

[kingbuzzo]

Except I'm a computer guy lol

Is the spider gear complicated to replace vs the bearing?

[b-man]

If something’s wonky with the differential you’re best off taking your car to a shop that specializes in rear end repair. There’s a chance that you’ll be needing to replace your posi unit so be ready for that.

Use your computer skills to generate the coin for repairs would be my advice.

[steve25]

A new crossshaft can be carefully centered with brass shim stick and tack welded in place if need be, then the shim stock is removed .

that could get you another 15K miles out of the carrier if you don’t beat on the car too hard, but it will still need to be taken out of the rear end to do that.

[mrennie]

If I understand correctly, the clunking is when pulling/pushing on the end of the axle? So in and out make the noise rather than up and down?

An up/down motion making a clunk could be axle bearings and shaft wear.

An in/out motion making a clunk is likely excessive end play, with the play being between the end of the axle and the cross shaft (axle pushed in) versus the C-clip and the recess in the side gear (axle pulled out).

On an Eaton clutch posi, shims are inserted between the case and clutch stack behind the side gears, to adjust clutch action. When the clutch plates wear, or if there are insufficient shims, the side gears sit further in the case (further from the cross shaft), which results in more end play which could cause a clunking noise when the car is turning or rocking side to side.

[b-man]

Buy a new rear end cover gasket.

Pull the cover, which will of course drain out the gear oil and look at what’s going on inside while moving the wheels back and forth like you did previously.

If it’s looking bad inside there put the rear cover back on with the new gasket and refill the rear end with the old lube you drained out. Drive it or flatbed it to a shop and pay the man.

Perhaps source the new posi unit yourself so you end up with the unit of your preference and maybe a ring and pinion set if your old gear set is either questionable or you just want to change ratios.

[kingbuzzo]

Originally Posted by b-man

If something’s wonky with the differential you’re best off taking your car to a shop that specializes in rear end repair. There’s a chance that you’ll be needing to replace your posi unit so be ready for that.

Use your computer skills to generate the coin for repairs would be my advice.

Yer prolly rite b-man...except they laid off our entire team last week and i just started two months ago...it never ends

😒

[kingbuzzo]

Originally Posted by steve25

A new crossshaft can be carefully centered with brass shim stick and tack welded in place if need be, then the shim stock is removed .

that could get you another 15K miles out of the carrier if you don’t beat on the car too hard, but it will still need to be taken out of the rear end to do that.

I finally got the cheby carb replaced with a proper pontiac qjet with Cliff's help and this car is a rocketship now - this is going to be difficult - night and day difference however it was clunking before the carb swap...just my luck

[kingbuzzo]

My car makes tons of annoying noises but this is definitely in/out. Does that mean that the eaton posi can be salvaged if I get the rear end guy to put in some shims?

Originally Posted by mrennie

If I understand correctly, the clunking is when pulling/pushing on the end of the axle? So in and out make the noise rather than up and down?

An up/down motion making a clunk could be axle bearings and shaft wear.

An in/out motion making a clunk is likely excessive end play, with the play being between the end of the axle and the cross shaft (axle pushed in) versus the C-clip and the recess in the side gear (axle pulled out).

On an Eaton clutch posi, shims are inserted between the case and clutch stack behind the side gears, to adjust clutch action. When the clutch plates wear, or if there are insufficient shims, the side gears sit further in the case (further from the cross shaft), which results in more end play which could cause a clunking noise when the car is turning or rocking side to side.

[kingbuzzo]

hopefully this works...

https://1drv.ms/v/c/25a158799a95b9ef...ry3Lg?e=JkJv7s

note: its the same on either side of car...but definitely pronounced when I go over a bump on the passenger side for some reason...

Thanks all

[mrennie]

Yes, the Eaton posi can be rebuilt. Clutch plates, shims etc. are available.

Typically, it would be disassembled and inspected, plates replaced if required, then shimmed to provide the required clearance. You can shim too tight, which makes it difficult to insert the cross shaft and might require thinner c-clips.

This video (part 1 of 2) will show some of the details of reassembling an Eaton unit along with some additional tuning steps.

https://m.youtube.com/watch?v=CGq15JBBUQw

[400 Lemans]

You need to tighten the leaf spring u-bolts. You can see the leafs shifting a bit.

[kingbuzzo]

Good video.

Ok, so it's likely salvageable but at a cost.

I remember upgrading my gears from 2.x to 3.42's fifteen years ago and it was like 1500$ at the rear end shop.

Given my current financial situation, am I better off finding a junk rear end for now, rebuilding this unit, or hoping for the best until I can afford a mosier or something better?

Based on the stack of bills that came with the car it appears he replaced the posi around mid 2000s.

Thanks!

[Sirrotica]

Originally Posted by 400 Lemans

You need to tighten the leaf spring u-bolts. You can see the leafs shifting a bit.

To add to this, the 2nd gen F bodies have a habit of breaking the main leaf through the center bolt hole as they age, and rust accumulates between the leaves. The design of the rubber insulator and U, and T bolts will hide the broken spring leaf, but the car will likely be squirrely on a full throttle blast as the rear axle will be able to steer the car.

I used to own a 76 T/A with a 455 that had both rear spring main leaves broken. During a burn out I almost put the car in the ditch on both sides of the road as the rear axle was allowing the rear of the car to steer side to side. Upon examination both main leaves had broken but the rear axle had to be taken off of the springs to see the broken main leaves. Just beware that this is fairly common in these 50 year old cars that have seen salt during their lifetime, and could be the clunk you're hearing when striking a bump. The weakened spring may also allow the axle to hit the bump stop making a clunk.