leaking differential

[Alex McDaniel]

My 1970 differential is leaking a good amount of fluid from the front end. Ive read that replacing the fluid with ATF, driving in tight circles, and then draining and replacing with fresh/correct fluid can fix that problem in some cases. Anyone had any experience with this remedy?

If this does not fix the problem and I end up having to change out the pinion seal (never done this before), how many approx lbs. does the pinion nut have to be torqued? My wrench only goes to 100 lbs. Ive also read the doing this incorrectly can cause premature bearing failure.

Ive pulled off the wheel assemblies for bearing rebuilds and will be changing the bushings, ujoints all around too. Is it worth while to go the extra number of paces and remove the entire differential if it does need seal replacements, or can the job be done just as effectively while its still in the car?

Thanks a bunch.
Alex

[Duke W.]

Re: leaking differential

Boy, you've heard some tall tales! ATF will probably wipe out the diff in no time at all. "Driving in circles" is to distribute the Positraction additive added to 80W-90 GL-5 gear oil to the clutch pack to prevent chatter.

The procedure for changing the pinion seal is in your Chassis Service Manual. The pinion nut does not have a torque spec. The spec for setting up the diff is bearing drag torque. To change the pinion seal you mark the nut orientation to the pinion and bump it back to the same position or just a smidge more.

As long as you are disassembling the entire rear suspension, I would recommend you remove the diff to replace the seal, check the yoke end play and open the cover for an inspection.

Do you get The Corvette Restorer? The last two issues have article on the diff, which provide insight beyond the service manual overhaul procedure.

Duke

[Joe L.]

Re: leaking differential

Alex-----

I don't think that the ATF scheme you describe will do you any good, at all. In fact, it might do more harm than good. If the pinion seal is worn and needs replacement, there's no "shortcut trick" like this that's going to change that. The theory behind this ATF trick is that the ATF will "rejuvinate" a dried out seal. However, the types of seals used for these Corvette applications don't "dry out" that way and can't be "rejuvinated".

The pinion nut may require a great deal of torque to remove. However, upon re-installation it is not torqued to a specific torque value. It is torqued until the torque required to rotate the assmbly reaches a specified value. So, no torque wrench is necessary FOR THE NUT. A torque wrench is necessary to measure the ROTATIONAL force required to turn the assembly and reach the specified value. This requires a LOW RANGE torque wrench, NOT a high range torque wrench.

In any event, you shouldn't even CONSIDER performing this operation unless you have the experience and skill to do it AND you have in your possession and read the Chevrolet or Corvette Service Mnaual appropriate to your year. The procedure for replacing the pinion seal is well described in that tome.

[Alex McDaniel]

Re: leaking differential

Thanks Duke and Joe for your expertise and insights. I read the 'ATF theory' in Chevrolet Corvette Restoration Guide by Lindsay Porter.

Im using the Hanes Repair Manual along with the 1970 Assembly Manual for most of the work Im performing. Will get the 1971 Chevrolet Chassis Service Manual asap (1970 edition covers the 1969 Corvette).

Do you think too much posi additive could cause the seal to leak? Shortly after I added the additive the leaking began. Just the front though, not the sides. Most likely not Im thinking.

Joe, I think Im following you regarding the torquing process. Essentially break the pinion nut loose, then measure the resistance when turning the assembly/nut?

Alex

[Duke W.]

Re: leaking differential

Most automotive shaft seals are made from a family of elastomeric materials that are usually referred to as "nitrile". Their aging characteristics - hardening, cracking, and loss of elasticity are primarily a temperature-time function, and above 250F nitriles rapidly age. "Viton" will provide equivalent life to about 400F, so they can provide additional life in elevated temperature applications.

Pinion seal leaks are a common Corvette malady. Certain oils have "conditioners" that can soften and swell seals, but they are little more than a stop gap measures and are rarely 100 percent effective.

Hypoid gears require special EP additives in the oil, which is denoted by the symbol "GL-5". ATFs are only rated GL-4, so using ATF in a diff for any length of time has a good chance of scoring the ring and pinion, which is a much bigger problem than a leaking pinion seal.

Duke

[Tom S.]

Re: leaking differential

Alex
You said that the leak started after you added more adative.Are you sure that you did not over fill it? That will cause seals to go rather quickly, and also are you sure that it is not coming out of the vent? I would check it out real good to make sure its not the vent, as the oil gets warm it expands and this could be your problem. The front of the rear end below the pinion is the lowest point and sometimes it looks as though that is the leak when it is not.
Tom

[John H.]

Re: leaking differential

Alex -

The measurement of pinion bearing drag with a low-range torque wrench is only done with the differential disassembled, with only the pinion gear installed, as part of the pinion setup procedure; it cannot be done on an assembled differential unit. The only procedure you can use on an assembled diff is as outlined earlier, by marking the pinion nut position prior to removal and returning it to that position on re-assembly after replacing the pinion seal. The end of the spline cavities under the big washer also require application of a non-hardening sealer, or it will leak through the splines instead of through the shaft seal.

[Alex McDaniel]

Re: leaking differential

Thanks Tom for the info.
Let say I did over fill it when adding the additive(added until just under the pour hole). Are the seals now ruined and need replacement? Added approx 2 years ago. Not a lot of miles since then.

Also, where is the vent located on the differential casing?
Alex

[Alex McDaniel]

Re: leaking differential

Thanks John. What type of sealer would you recommend for the splines? Ive also read that an application of lithium lube to the seal is needed. Your thoughts?
Alex

[Alex McDaniel]

Re: leaking differential

Thanks for the heads up Duke. Adding the ATF was my next step on the list. Sure glad I checked in here first.

[Clem Z.]

just wipe the ID of the seal with rear gear oil

so it does not have a dry startup till some rear gear oil gets to the seal.

[John H.]

Re: leaking differential

Alex -

A non-hardening sealer like Permatex #2 works fine on the end of the splines under the washer, and the lip of the seal should be lubed as Clem mentioned. Also, pay particular attention to the Service Manual illustration when installing the new seal - it does NOT bottom out in the recess in the housing - it should have a 1/16"-1/8" gap between the flange on the seal and the nose of the housing. If you drive it in flush, the seal lip will be damaged.

[Tom S.]

Re: leaking differential

Alex
The vent is on the top of the rear end, on the left hand side or drivers side of the car.I have seen seals leak with a plugged up vent also so make sure it is clean.Good luck.

Tom