Author Topic: Limited Slip problem  (Read 279 times)

Pontiac_SE

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Limited Slip problem
« on: September 07, 2019, 05:41:41 AM »
I have just put together a rear end, the parts I have used is old but good GM parts.
Original GM limited slip and a 2:41 gear, axles are nice original.. all new bearings and preload and backlash is spot on.

When I drive it is quiet in the rear but after a while it will make a cracking noise when I drive slow.
I guess it is the limited slip that is making the noise, I have 80w90 that already has LS additive then I have added two 4oz with Kendall LS additive and it is still making noise not much but still.

The limited slip comes from another T/A -77 low mileage and didn’t have this problem, but it have laying in a box for 2 years if that matters.
What should I do?
Firebird -93 (sold)
Firebird -94 (sold)
Firebird Esprit -71 (sold)
Trans Am -79 Y84 (sold)
Trans Am -77 Y82 (finally got one)

hakitup

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Re: Limited Slip problem
« Reply #1 on: September 07, 2019, 09:49:17 AM »
Noise happens driving straight or turning? If it is the LS clutches, it will only happen during a turn. My pops when I first get off the freeway after a long drive I added friction modifier and it helped but didn’t stop it completely. I have new clutch plates that have an aggressive hex pattern not like the swirly originals.

Tom H
"I don't know what you call it, I only know the sound it makes when it lies!!"

Pontiac_SE

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Re: Limited Slip problem
« Reply #2 on: September 07, 2019, 10:26:58 AM »
Only when I turn but it doesn’t need much turning before it makes noise.
The clutch plates is original from 1977 in this one.
Firebird -93 (sold)
Firebird -94 (sold)
Firebird Esprit -71 (sold)
Trans Am -79 Y84 (sold)
Trans Am -77 Y82 (finally got one)

highway star

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Re: Limited Slip problem
« Reply #3 on: September 07, 2019, 06:28:39 PM »
Only 4 oz. of additive is required. And don't use Valvoline, it's recycled oil & smells terrible like old oil.
I just ordered Castrol gear oil, it has a "sweet" smell.

hakitup

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Re: Limited Slip problem
« Reply #4 on: September 07, 2019, 08:59:58 PM »
The 74 Pontiac bulletins dealer book I bought at the Nats addresses the posi. It said to add the friction modifier the drive the car in a figure eight to work in the oil. I thought it was kind of funny because I was having an issue with it. Before I added the modifier it sounded terrible, kind of like it was coming apart.

Tom H
"I don't know what you call it, I only know the sound it makes when it lies!!"

Re: Limited Slip problem
« Reply #4 on: September 07, 2019, 08:59:58 PM »

Pontiac_SE

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Re: Limited Slip problem
« Reply #5 on: September 08, 2019, 09:40:32 AM »
I started with GULF 80W90 LS and it sounded terrible then I added 4oz Kendall additive, after that it got little better.
After a few days I added one 4oz more and it got a lot better but still I can hear it from time to time and it is really annoying.
Firebird -93 (sold)
Firebird -94 (sold)
Firebird Esprit -71 (sold)
Trans Am -79 Y84 (sold)
Trans Am -77 Y82 (finally got one)

Fbird

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Re: Limited Slip problem
« Reply #6 on: September 11, 2019, 06:39:56 AM »
after adding the friction modifier did you do a few "figure eights" to work it in the clutches? Normal driving will take weeks to "work in". a few tight figure eights and you should be good.
67 Firebird
1980 Turbo TA (injected 400 now :) )

Pontiac_SE

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Re: Limited Slip problem
« Reply #7 on: September 11, 2019, 09:25:26 AM »
Yes I tried the figure eight, didn’t help.
Firebird -93 (sold)
Firebird -94 (sold)
Firebird Esprit -71 (sold)
Trans Am -79 Y84 (sold)
Trans Am -77 Y82 (finally got one)

Fbird

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Re: Limited Slip problem
« Reply #8 on: September 11, 2019, 11:25:52 AM »
going to need to determine the "break-away" torque of your clutch pack assembly. you may need to disassemble and clean EVERYTHING....but that sux.

http://www.premierwestgears.com/RebuildLimitedSlipDifferentials.html

good read.
67 Firebird
1980 Turbo TA (injected 400 now :) )

Pontiac_SE

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Re: Limited Slip problem
« Reply #9 on: September 11, 2019, 12:44:53 PM »
Thank you I will check the break-away torque.
Firebird -93 (sold)
Firebird -94 (sold)
Firebird Esprit -71 (sold)
Trans Am -79 Y84 (sold)
Trans Am -77 Y82 (finally got one)

Pontiac_SE

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Re: Limited Slip problem
« Reply #10 on: September 14, 2019, 03:12:34 AM »
Well, just checked the torque and it is around 60ft-lb which is very low.. I am really beginning to hate this car....
Firebird -93 (sold)
Firebird -94 (sold)
Firebird Esprit -71 (sold)
Trans Am -79 Y84 (sold)
Trans Am -77 Y82 (finally got one)

Fbird

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Re: Limited Slip problem
« Reply #11 on: September 15, 2019, 06:08:16 AM »
at 60 lbs  this is sounding like NOT THE clutches issue.....

don't take this one wrong.....
you check the lug nuts?
67 Firebird
1980 Turbo TA (injected 400 now :) )

Pontiac_SE

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Re: Limited Slip problem
« Reply #12 on: September 15, 2019, 06:29:18 AM »
Don’t worry I won’t take it wrong, I actually checked them and everything else..
The only thing that’s not been changed is the brake drums, it’s the original to the car.

About 5 years ago I had to change the brake shoes because the wheel cylinder leaked, beginning to think that the drums are “contaminated” or something.

I think I will buy all rear brake parts new and replace it..
Firebird -93 (sold)
Firebird -94 (sold)
Firebird Esprit -71 (sold)
Trans Am -79 Y84 (sold)
Trans Am -77 Y82 (finally got one)

firebirdparts

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Re: Limited Slip problem
« Reply #13 on: September 15, 2019, 07:01:19 AM »
60 ft-lb is actually high according to the shop manual.
I want to be like Paul Kenny when I grow up
Joe Bays
1977 Y82 4-speed (red interior)
1978 Skybird 350
1978 Redbird 305
1979 Redbird 301 4-speed
1992 Lincoln Mark VII LSC/SE (red)
1970 Datsun Pickup
1953 Chevy pickup (converted 4x4)
1988 T-bird Turbo Coupe

Pontiac_SE

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Re: Limited Slip problem
« Reply #14 on: September 15, 2019, 07:47:36 AM »
I did take a look in the service manual and I cannot find the break away torque just rotating torque and it says at least 35 ft-lb, I have approx 45 ft-lb.
What torque should the break away be?
« Last Edit: September 15, 2019, 07:50:05 AM by Pontiac_SE »
Firebird -93 (sold)
Firebird -94 (sold)
Firebird Esprit -71 (sold)
Trans Am -79 Y84 (sold)
Trans Am -77 Y82 (finally got one)

Re: Limited Slip problem
« Reply #14 on: September 15, 2019, 07:47:36 AM »

Fbird

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Re: Limited Slip problem
« Reply #15 on: September 16, 2019, 06:39:07 AM »
going from MEMORY here....like 35 yrs ago....best I recall was 70-140 lbs BREAK AWAY.....
The hard part of measuring this is having the proper tools/adapter to do it as it must be measured per the CL of axle rotation. as shown here
https://www.musclecardiy.com/performance/how-to-rebuild-factory-limited-slip-differentials/

obviously different bolt patterns would require different "adapters"...
again IIRC there were 2 "s" springs available from GM one is like 190 lb and the other was like 300 lbs which gave you about a 60 lb INCREASE in breakaway torque.
67 Firebird
1980 Turbo TA (injected 400 now :) )

Pontiac_SE

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Re: Limited Slip problem
« Reply #16 on: September 16, 2019, 08:51:58 AM »
I did use an adapter so it was centered when I checked the the torque.
I have bought all rear brake parts so I will change them and if that doesn’t help I will take the diff apart..
Firebird -93 (sold)
Firebird -94 (sold)
Firebird Esprit -71 (sold)
Trans Am -79 Y84 (sold)
Trans Am -77 Y82 (finally got one)

Fbird

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Re: Limited Slip problem
« Reply #17 on: September 16, 2019, 01:29:09 PM »
some confuse HOW to test this.
Hope the brakes solve the issue otherwise that sux.
67 Firebird
1980 Turbo TA (injected 400 now :) )

Re: Limited Slip problem
« Reply #17 on: September 16, 2019, 01:29:09 PM »
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