Author Topic: Rear diff knock posi rear  (Read 277 times)

sixpack_sid

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Rear diff knock posi rear
« on: September 29, 2019, 08:12:36 AM »
I have a 79 ta with the 8.5 rear diff. When I drove it yesterday, it started making a clanking noise while turning. Then, it started clanking on the highway when going straight. I noticed it more at low speeds. I took the diff cover off and used marking paint. The wear marks are not centered. The yoke is tight. The axles have a bit of play when moving in and out. Can I recenter them with shims, or do I need to rebuild the diff? I am not familiar with working on rear ends. 

sixpack_sid

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Re: Rear diff knock posi rear
« Reply #1 on: September 29, 2019, 08:18:26 AM »
updated Pic:

https://imgur.com/a/2gjIBUD














WoiUnV4p1I9QgbtBLKS3TebBd7alQzEmM_yHNokbHx0Td7h0MI6jT0yTbDSGORp_Sfy8zQs2Yemd8uheMpIhL15zbcNInOpnK0
« Last Edit: September 29, 2019, 09:44:57 AM by sixpack_sid »

Ryoko

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Re: Rear diff knock posi rear
« Reply #2 on: September 29, 2019, 09:23:08 AM »
It's time to pull the carrier and pinion for inspection.

sixpack_sid

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Re: Rear diff knock posi rear
« Reply #3 on: September 29, 2019, 09:25:16 AM »
It's time to pull the carrier and pinion for inspection.
How do I do that and what am I looking for? Do you know of any instructional videos that go in depth on this type of diff?

Fbird

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Re: Rear diff knock posi rear
« Reply #4 on: September 29, 2019, 10:01:35 AM »
lets hold up on the rebuild there..... can you get a pic to actually POST. (yes its a PITA on this website as you must have an online picture account somewhere)
axles are going to have some play in them thats how it is
wear marks "off center" depends how you are turning it and what you are using to mark it with.
Pinion is tight....compared to what? Just the pinion installed with OLD bearings should take around 20 INCH lbs to rotate...so by the time you turn EVERYTHING....yeah its not going to be very easy.

So needing to describe "clanking" a whole lot better to get where you need to be...
67 Firebird
1980 Turbo TA (injected 400 now :) )

Re: Rear diff knock posi rear
« Reply #4 on: September 29, 2019, 10:01:35 AM »

sixpack_sid

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Re: Rear diff knock posi rear
« Reply #5 on: September 29, 2019, 10:19:44 AM »
lets hold up on the rebuild there..... can you get a pic to actually POST. (yes its a PITA on this website as you must have an online picture account somewhere)
axles are going to have some play in them thats how it is
wear marks "off center" depends how you are turning it and what you are using to mark it with.
Pinion is tight....compared to what? Just the pinion installed with OLD bearings should take around 20 INCH lbs to rotate...so by the time you turn EVERYTHING....yeah its not going to be very easy.

So needing to describe "clanking" a whole lot better to get where you need to be...


I used Prussian Blue to mark the pinion gear and turned the axle forward. You can see the wear mark on my updated pic. I will need to buy a dial indicator to measure the play and post results. Thanks.

sixpack_sid

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Re: Rear diff knock posi rear
« Reply #6 on: September 29, 2019, 12:25:12 PM »
The backlash is .018 on my dial indicator. The axle end play is .029.Does that mean the bearings are shot? What's my next step?
« Last Edit: September 29, 2019, 12:37:02 PM by sixpack_sid »

Ryoko

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Re: Rear diff knock posi rear
« Reply #7 on: September 29, 2019, 12:34:13 PM »
Just a thought: Are you sure it's not a U-Joint going bad?

sixpack_sid

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Re: Rear diff knock posi rear
« Reply #8 on: September 29, 2019, 12:38:44 PM »
Just a thought: Are you sure it's not a U-Joint going bad?
I'm not sure. I'll check. Thanks.

sixpack_sid

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Re: Rear diff knock posi rear
« Reply #9 on: September 29, 2019, 12:52:56 PM »
The u joint closest to the diff is bad. Will changing it solve my problem?

pancho400cid

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Re: Rear diff knock posi rear
« Reply #10 on: September 29, 2019, 03:53:08 PM »
It can't hurt.  Probably should do both U-joints.

Some in-and-out play on the axles is normal, so not a sign bearings are bad necessarily.  No guarantee they are good either.

Was the car running fine for a good length of time and then the noise started or has some recent repair work been done on the rear end?
« Last Edit: September 29, 2019, 03:57:02 PM by pancho400cid »
1978 Trans Am - Chesterfield Brown - current project
1978 Trans Am - Silver - SOLD!

Fbird

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Re: Rear diff knock posi rear
« Reply #11 on: September 30, 2019, 06:36:56 AM »
.018 back lash is way out there!! should be more like .008-.010 maybe .012 on a well used set. This is a very particular measurement with MANY variable so I will disregard the way out number if the rearend is NOT howling under power or decelleration.
 Now per your "I am not familiar with working on rear ends. "...
Prussian blue SUX for gear patterns. (need gear marking compound ...BUT prussian blue will give you enough idea if it is way jacked up ;)) I wouldn't worry too much about the patterns (yes plural as you have drive side and coast side) if it doesn't HOWL or WHINE....clunking is different
 The .029 axle slop has no affect on the bearings as the bearings are NOT pressed on the axles...they are pressed into the housing, but .029 axle slop indicates your Limited Slip Differential is probably worn out (alot on 1 wheel burnouts now?) as you should be around .015-.020 on midlife used posi..

Clunk is usually 1. u-joint , 2. Clutch BITE (feels like getting kicked in the ASS SIDEWAYS ...while slow turn in parking lot) ONLY DURING TURNING!!



67 Firebird
1980 Turbo TA (injected 400 now :) )

DeCaff2007

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Re: Rear diff knock posi rear
« Reply #12 on: October 05, 2019, 06:51:06 AM »
I'm late to the party here, but here's a few things:

1.  Sorry but that pic is horrendous.  It won't tell us much, anyway.

2.  That backlash, as Fbird said, is way off.  I actually agree with most of what he said, except for "wear marks "off center" depends how you are turning it and what you are using to mark it with." 

What do you mean "how you are turning it"?  Forward and backward lol........

It's called a "gear pattern" and it depends on pinion depth and backlash (which are in turn set by shims) and yes, the wear on the gears.

1976 T/A 400, 4-speed swap.... 

Check out my resto thread:  http://transamcountry.com/community/index.php?topic=48626.0

It's all trial and error until something lines up...

Fbird

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Re: Rear diff knock posi rear
« Reply #13 on: October 06, 2019, 07:18:01 AM »
if you are turning the pinion WITHOUT any drag on the ring gear your pattern will be "fuzzy" and not a good representation of the contact patch. A much better LOOKING pattern is achieved by turning the pinion as opposed to trying to push or pull the ring gear around and load the pinion. Yes you must turn it BOTH ways..there are 2 patterns to access. BTW using an IMPACT gun to turn it will look like crap too. You need to make at least 3 FULL revolutions of the RING rear to displace the gear paint and to also ensure ALL the teeth on the pinion gear get to cycle a couple times. It's kind of a "pattern average" of ALL the pinion teeth having input on each paint mark.
67 Firebird
1980 Turbo TA (injected 400 now :) )

Aus78Formula

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Re: Rear diff knock posi rear
« Reply #14 on: October 06, 2019, 06:04:46 PM »
Take it to a workshop that has diff experience and get their opinion first on what the noise is and what it means, not from a bunch of forum guys.

Re: Rear diff knock posi rear
« Reply #14 on: October 06, 2019, 06:04:46 PM »



cyber104

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Re: Rear diff knock posi rear
« Reply #15 on: October 07, 2019, 06:05:23 AM »
Take it to a workshop that has diff experience and get their opinion first on what the noise is and what it means, not from a bunch of forum guys.

That's the best piece of advice thus far lol - inexperience can lead to a toasted diff real quick
1978 TA 4-Speed W72

langss

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Re: Rear diff knock posi rear
« Reply #16 on: October 07, 2019, 12:30:04 PM »
By any chance did you recently change the "Gear Oil" in the rear end. And if you did, did you add the Friction Modifier. The reason I ask, my Wife took her car in for service and they found a Pinion Seal leak, so they changed the seal. According to the dealer, when the car was making similar noises, the friction modifier additive was not required in her car. I had to go buy a bottle and add it myself.... Just a thought before you start spending a ton of money.

Ford5of5

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Re: Rear diff knock posi rear
« Reply #17 on: October 08, 2019, 03:13:47 PM »
I had a "rank", "rank", "click", "click", "rank" sound in my 99 Silverado at slow speeds in forward and reverse, but no sounds when putting it in gear. My first thought was a wheel bearing went bad but when I walked next to the truck as someone drove it slowly, I narrowed the sound down to the middle of the drivetrain. I knew the truck was used to tow so figured it just needed U joints. I pulled the shaft out to install new joints and found a crack in it. The crack easily visible and approximately 30% of the circumference of the shaft. The shaft on that truck was aluminum, I think. Just one more thing to check out.

Re: Rear diff knock posi rear
« Reply #17 on: October 08, 2019, 03:13:47 PM »
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