1977 differential clutch pack change?
Thread Starter
Advanced
Joined: Oct 2015
Posts: 99
Likes: 1
From: Morristown/ Knoxville area Tennessee
1977 differential clutch pack change?
I have a 3.08 differential that is operationally fine, no noise or whining a good diff. I am changing the ring and pinion to a 3.55 gear ratio. Is there any reason I need to change out the clutch's and spider gears in the posi unit that is operating fine? The pre load on the posi is tight and no back lash in the spider gears. Just wondering if it worth and extra 175.00 to replace the clutches, they look fine, no marks or scoring.
Melting Slicks
Joined: May 2012
Posts: 2,192
Likes: 343
From: Allenton Wisconsin
A couple of questions to ask yourself.
How many miles on the diff? The clutches do wear.
Is this the time I should go on the cheap and have regrets later?
My .02 cents worth is do all you can the first time, it saves you from the second time. T
How many miles on the diff? The clutches do wear.
Is this the time I should go on the cheap and have regrets later?
My .02 cents worth is do all you can the first time, it saves you from the second time. T
Thread Starter
Advanced
Joined: Oct 2015
Posts: 99
Likes: 1
From: Morristown/ Knoxville area Tennessee
I understand your point. The diff has 89k miles on it. The fluid was clean, gears are good, there was no problems. How can I tell if the clutches need replacing or if they have wear, without tearing the posi unit apart. Can you check this by visual inspection of what you can see of the clutches, and springs and spider gears. The posi load is appears to be very firm when you turn it? You can't turn it with your hands, I need to use a bar when I have it on the vice with one of the axle yokes in it.
Last edited by flyguy767; Dec 10, 2015 at 10:18 AM.
Melting Slicks
Joined: May 2012
Posts: 2,192
Likes: 343
From: Allenton Wisconsin
When I acquired my 69 it had 88K on the odometer. Purchased it from an older couple who only put 2K on it in the 10 years they owned it. Every tight corner the rear banged. Changed out the oil [old lube very dark] and added the posi additive but still had to do some figure 8s to get the discs to release. Now have 105K on it and no problem. If I ever have to go into the diff itself I will replace the disc kit. To answer your question of measuring the disc themselves without removal I don't think so and it sounds like everything in your diff is in good order, but changing them isn't very difficult. T
Safety Car
Joined: Jan 2009
Posts: 4,000
Likes: 299
From: New York
If it checks good you have nothing to gain, if it is questionable then go all out and freshen it up maybe even beef it up.
I am not saying anyone is right or wrong. I just learned in life if all is good leave it all alone.
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Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
That logics works fine with the 80-96 Dana posi units since clutch wear has no effect on spider gear backlash. And due to the design of the inner discs as compared to the outer discs, chatter is nearly impossible to happen.
But the eaton design is opposite. 9 discs per side, identical stamp patterns on both the inner and outer discs, and coil springs pushing the side gears apart versus the belville spring of the Dana always forcing the side gears together keeping the spider gears in constant mesh. Not to mention GM changed the inner discs to the slotted design in '71.
With an average wear of .001 per disc surface, that equals .017 wear per clutchpack. That gives you .013 spider gear backlash assuming they were originally set at .001 minimum setting. Spider gear operating range is .001-.005.
And if money is an issue, it doesn't cost anything to take it apart, clean out all the metal shavings between the slots, and shim them back to .001-.002 backlash.
Only special tools needed are a large flat blade screw driver and a dial caliper.
Mike
But the eaton design is opposite. 9 discs per side, identical stamp patterns on both the inner and outer discs, and coil springs pushing the side gears apart versus the belville spring of the Dana always forcing the side gears together keeping the spider gears in constant mesh. Not to mention GM changed the inner discs to the slotted design in '71.
With an average wear of .001 per disc surface, that equals .017 wear per clutchpack. That gives you .013 spider gear backlash assuming they were originally set at .001 minimum setting. Spider gear operating range is .001-.005.
And if money is an issue, it doesn't cost anything to take it apart, clean out all the metal shavings between the slots, and shim them back to .001-.002 backlash.
Only special tools needed are a large flat blade screw driver and a dial caliper.
Mike