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Topic: REBUILDING 75 DIFFERENTIAL

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REBUILDING 75 DIFFERENTIAL (1/13)
 5/19/04 7:09pm
skid63
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Joined: 5/5/2004
Posts: 13

My rear differential has a little leak and I am planning on buying a rebuild kit to fix it. Are there any special tools I should have before starting this task or recomendations for removing bearings and or seals?

skid63 |saluteflag|

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REBUILDING 75 DIFFERENTIAL (2/13)
 5/19/04 8:14pm
kstyerLifetime Member
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CUYAHOGA FALLS, OH - USA

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1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!


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Please don't take this the wrong way. As much as I hate to say it, if you don't have those answers, you should not attempt to rebuild the rear end. They do require special tools, and they are VERY precise in their set up. It's very easy to make a huge costly mistake.

Having said that, if someone does know what they are doing, it can be set up quickly and easily. I would recommend you find someone who knows to assist, or assist them. It will be a good education.

As much advice as I give, there is no way I can teach someone to do this unless it's face to face, and hands on. I wish I could. If you want to do some limited repairs, I may be able to walk you through that.
Find a pro to help. Good Luck.
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REBUILDING 75 DIFFERENTIAL (3/13)
 5/19/04 9:05pm
skid63
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I am a helicopter mechanic by trade, and by no means a GM master mechanic, but I have replaced bearings/sleeves/seals on helicopters a few times in the 20+ years I have been in my trade. So I do have little trade off there in the knowledge base between the two. I just never did it on a car before and puting the question out to those who have. Yes, you are probley right, and should look for (hands on) assistance with this problem. It's just that I am a little stuburn and usually don't shy away from things I haven't done before. I am willing to try any thing (once), no matter if I screw it up or not. At least I can say I tried. That's the best way to learn. I think... I'm just looking to suck up as much information and knowledtge as I can...If you don't want to give it, move on to something you want to anwer. |thumb|

skid63

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REBUILDING 75 DIFFERENTIAL (4/13)
 5/19/04 9:10pm
cthulhuLifetime Member
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Hot Springs, AR - USA

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69 Conv #'s match 427, TKO-600/.64, 3.36HD-Posi, HT, T/T, PS, PB, PW, SP, Leather, Comp XE264HR & Roller Rockers & Lifters, Air-Gap RPM intake, Holley St Av 770 VS, MSD 6AL+Dist+Blaster SS, K&N, Jet-Hot Hooker Side-Pipes, Steeroids, Al Rad, Spal Fans


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i had a haynes and found a howto on the internet to rebuild my diff..

it was a pain... but doable if you can follow instructions..
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REBUILDING 75 DIFFERENTIAL (5/13)
 5/19/04 10:24pm
kstyerLifetime Member
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CUYAHOGA FALLS, OH - USA

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1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!


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Skid63. That's a horse of a different color. You have some good background and know gears, bearing, races, shims and preloads. I feel better.
For everyone less informed, this is brief and allows for existing mechanical skill and knowledge to know what I am talking about.

You will need to secure the carrier in a stout vice or holding fixture.

The carrier that holds the ring gear is spaced with shims on either side of the carrier. Once the bearing caps are removed, us a pry bar to persuade the carrier out of the housing. It has a preload and won't come out easily. Keep the shims in the same location for a good starting point. Once the carrier is out remove the yoke and drive the pinion gear to the interior of the case to remove it from the front/outer bearing. There is also a shim under the inner bearing on the pinion gear. Be careful not to damage or lose it when removing the bearing. If you are using the same ring and pinion use the same shims in the same locations as a starting point.

If you are using new ring an pinion gears, look for marking on the pinion for a + or - and a number. This is the difference from the base setting to the pinion gear installed. This means if the pinion has a -2 it is .002 less the base spec. The shim would be .002 different than the 0 point. 0 point of pinion depth is found with special tools. But if you track the shim from the old one, you can get by. Compare you new pinion to the old pinion and adjust the shim thickness based on the numbers. If there are no numbers assume 0. I said assume because sometimes the original number was painted instead of stamped, and is gone. If old and new are both 0, or both the same, use the original shim.
When removing the old bearings from the pinion gear, you will see a sleeve between the two bearing inner races. This a preload crush sleeve, and must be replace with a new one. When installing the pinion gear nut, you will set rotational preload in inch pounds. Check the specs. This will require a holding bar or fixture to hold the yoke/pinion gear still while tightening the pinion gear nut. If you overshoot replace the crush sleeve. Backing off won't do it.

The side shims on the carrier need to be redone when replacing the ring and pinion also. Set the carrier in place without the shims. Move the carrier so the ring gear sets at 0 tolerance to the pinion gear. Add shims to the left side (ring gear side) to maintain 0 tol. Now measure the clearance on the right side. Add shims to maintain 0 with not play in the carrier side to side. Now add .008 to the right side. This sets the carrier preload and move the ring away from the pinion to create some backlash. Check the spec for total backlash. Measure it by rotating the carrier with a dial indiator on ring gear tooth.
There is a spreader that can be used to spread the housing so you can drop the shims in place. There is also a curved driver to tap them in if the spreader is not available. You can use a soft punch. Just done mushroom the shim and mess up the parallel surface or the bearing will whine and wipe out.


Now use gear marking paint or paste and rotate the ring and pinion several turns. Rotate it in the direction of forward vehicle motion. You want the pattern to be centered on the face of the tooth. Valley to top, and toe to heel.

If the pattern is off you will need to adjust the shims. The pinion shim to adjusts depth. Thicker will run it to the Valley. OR you may need to change carrier side shims to change heel toe position. Be sure to add on one side and subtract the other side to maintain equal preload. There is some influence from any shim is multiple pattern direction, so it may not be simple, but not that bad either. Don't worry about coast side pattern until the drive side is correct. Then the coast side will be good or something is misaligned or bend.

With your knowledge I would recomment a tape from Richmond Gear. It shows ring and pinion install and set up. They used to and may still supply it with new gear sets. Good but not for rookies. It's too brief. There are also some decent books from Summit and Jegs.

I'm fairly sure you have or can get you hands on micrometers, feeler gauges, beam type inch pound torque wrench, foot pound torque wrench, gear mark compound, prybars, and holders to hang on to the pinion. With out the pinion depth measurement tools you may go through a few crush sleeves, but hopefully not more than one or two. You will need to know where you can locate the shims, if needed. It's not likely you will find a pinion depth gauge or case spreader, but you can still do the job.
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REBUILDING 75 DIFFERENTIAL (6/13)
 5/20/04 4:53am
SundayMoney
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Corydon, IN - USA

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1969 Black Coupe,355ci,SRT Heads,Crower Cam,Edlebrock, Holley,Bowtie 1.6 rollers,Headman Hedders,4spd,3.55 rear.


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I have to agree with Ken. When I rebuilt my rear suspension in '02, I did all the work myself. Except for the diff. It's not that expensive to have the pros do it. Good Luck |cheers|

Dave

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REBUILDING 75 DIFFERENTIAL (7/13)
 5/20/04 4:57am
SundayMoney
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Corydon, IN - USA

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1969 Black Coupe,355ci,SRT Heads,Crower Cam,Edlebrock, Holley,Bowtie 1.6 rollers,Headman Hedders,4spd,3.55 rear.


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Sorry! guess I didn't read the whole thread! |headscratch| It's early |wavey|

Dave

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REBUILDING 75 DIFFERENTIAL (8/13)
 5/20/04 5:40am
Hoover
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If it's just an oil leak problem - maybe just the side pinion seals and carrier to case gasket may do it. I just replaced those on my '81 as part of a rear suspension/bushing overhaul. I had the carrier and diff out anyway so it was no big deal. I know the front pinion seal would be a big deal (for me anyway) so I left it alone. Don't forget to replace those bushings!
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REBUILDING 75 DIFFERENTIAL (9/13)
 5/20/04 10:32am
After Shark
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I found a local racer that builds race cars to do mine. Provided that parts and $150 bucks for labor and I was good to go.

also if you are replacing the pinion bearing there are companies that offer a crush sleeve that is preset so you don't need to worry about the pinion depth. Saves a lot of work and hassle.

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REBUILDING 75 DIFFERENTIAL (10/13)
 5/20/04 11:17am
kstyerLifetime Member
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CUYAHOGA FALLS, OH - USA

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Actually pinion depth is a function of the shim, not the crush sleeve. The preset crush sleeves do work, but they are for situations where the rear may be redone frequently. Such as Racing. In this case they are not as concerned with noise and long life. It may work out fine, but I would prefer the one use adjustable.
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REBUILDING 75 DIFFERENTIAL (11/13)
 5/20/04 11:58am
hank51Lifetime Member
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Ken, that's exactly the way the guy I paid did it. |thumb|
Hank
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REBUILDING 75 DIFFERENTIAL (12/13)
 5/21/04 4:29pm
skid63
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Thanks,
Alot of GREAT info/post over the last couple of days. Now I know were I stand on the subject. Knee deep in a aligator pond! If I decide to do it on my own, I will let you all know how it goes

skid63 |hammer|

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REBUILDING 75 DIFFERENTIAL (13/13)
 5/21/04 5:50pm
kstyerLifetime Member
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CUYAHOGA FALLS, OH - USA

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1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!


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Pat, you can see why I was hesitant. But with your background you may be able to pull it off. If you decide to do so, keep in touch. I will help with any procedure or info that I can. I have done a lot of rear ends. But it's not for a rookie without the background. Just be sure you have a shop manual and can get the shims, etc. before you start. A good job will last for years. A fair job will work but make noise. A bad job can not only destroy the rear, but the housing as well.

Just what you need, more food for thought.
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