Help selecting gear oil weight

[Soma07]

Hi all,

The car is a 93 Pontiac Trans Am, 7.5" 10 bolt rear, 3.42 gears, Auburn posi. The manual calls for 80w90 GL5 with a bottle of GM Limited Slip additive.

Normally I've been running Valvoline 80w90 with the GM additive. However I've been having constant problems with leaking from the pinion seal and gear whine. Now I sure the gears are not setup properly which would explain the whine but I've replaced the pinion seal 3 times in the 2 years o've owned it and the repairs never last more than a few weeks before the leaking starts again. The mileage (160,000 and counting) probably isnt helping either.

This weekend I'll be picking up an entire new rear end (im sick of messing with this one) and I plan on changing the oil in it before it goes on the car. Any suggestions on what brand/weight oil to run that might help with the problems I've been having? Perhaps a heavier oil (say 75w140) would help? Otherwise I'll just stick with the 80W90 and the additive and hope for the best.

Thanks!

BTW in case you think I'm crazy its actually cheaper for me to buy a used rear end ($200) than it would be to buy a rebuild kit and pay someone to redo the current one. Not to mention it will have less than 1/2 as many miles.

 

[sprintman]

Redline 75W90 and a bottle of their additive to 'tune' the LSD. Check their web site for full explanation.

 

[Soma07]

Thanks for the suggestion, I always hear Redline gear oil is good stuff. However could anyone recommend an off the shelf oil? I'm afraid I dont have time to order any Redline and have it here by Monday

Thanks!

BTW I already have an extra bottle of the GM Limited Slip addative so I dont nessecary need an oil that has its own LSD additive.

 

[BOBISTHEOILGUY]

There is a lot of differences between otc gear oils and specialized gear oils. If you want just an otc gear oil just pick your favorite brand and use it as most of those are pretty generic and give pretty much the same results.

IMO though, I like a gear oil that will climb as soon as you start to move. Most will not do that. The rear end requires oil to be splashed to lubricate and this isn't the best system. Many truckers have problems with gears in the rearend mostly due to that problem.

Here is a picture on how the schaeffers 80w90 climbs in comparision to others.

gearoil climbing

On this page, you can see how most will also create bubbles and mix with water, not that means much in your rearend but shows the difference in how this oil resists these problems in comparision. gear oil test

and one last thing... We have a local site supporter rep with schaeffers in your backyard..
Ron McCready
(321) 228-3641
call him and he can answer your questions about this. He is very knowledgable about rearends as he had a mechanic shop for the last 15+? years turning wrenches so he knows his stuff on this and also can give you any advise if you need any on that as well.

BTW, This oil is already equip't for LSD and you don't need the additive.

 

[widman]

I'd Put Delo Gear Lube 80w90 in it and leave out the GM additive. You can see my other posts as to why.

 

[MolaKule]

I had an older GMC truck that had pinion bearing and seal leakage for years.

We found the drive pinion race was slipping and yawing in the housing. The pinion drive bearing race is press fit into the case; if the case is slightly too large, the race will slip, yaw, and maybe even rotate.

If this is the case, you can either have another diffy put in, or have the race pinned or "peened" into the diff housing.

 

[MolaKule]

BTW, for the GM 10 bolts, I run nothing but 75W140 in diffys with locking mechanisms, especially the Auburn types.

No other lube will stand-up to the shear created by these locking differentials.

 

[Soma07]

Thanks for the advice guys! Sorry I forgot I posted this or I would have checked back sooner.

Anyways the new (well new to me) rear end is in! The fluid was changed recently so I didnt tempt fate by changing anything just yet. I put about 400miles on it this weekend inluding a few laps on a mini-road course and it was flawless. After all this time its nice to walk into the garage without seeing a puddle of gear oil on the floor

In a few months I'll change the fluid out and inspect it for any abnormal wear.

MolaKule: Are you talking about a locker style differential? The Auburn I have is just a normal limited slip/posi/whatever you call it. Its the OEM diff in these cars.

Jason
93 Trans Am

 

[TooSlick]

Soma07,

The Mobil 1, 75w-90 is an excellent PAO based, synthetic gear lube. You may find that you need to "tune" it with some of the GM friction modifier. It should lower your axle temps noticably over the stuff you are currently using ....

Many OTR trucks have switched from 85w-140 petro gear lubes to 75w-90 synthetics in the axles. They run much cooler and fuel efficiency is improved by a few percent ....

Mike Sparks has the Amsoil stuff available, if you decide to go that route. They make three different synthetic gear lubes you could run in this application, including an 80w-90 grade.

TooSlick

 

[Soma07]

quote:

---

Originally posted by TooSlick:
Soma07,

The Mobil 1, 75w-90 is an excellent PAO based, synthetic gear lube. You may find that you need to "tune" it with some of the GM friction modifier. It should lower your axle temps noticably over the stuff you are currently using ....

Many OTR trucks have switched from 85w-140 petro gear lubes to 75w-90 synthetics in the axles. They run much cooler and fuel efficiency is improved by a few percent ....

Mike Sparks has the Amsoil stuff available, if you decide to go that route. They make three different synthetic gear lubes you could run in this application, including an 80w-90 grade.

TooSlick

---

Thanks for the advice. I was thinking about the M1 gear oil but alot of fellow F-body owners shy away from it saying it caused their differential to chatter. I dont know if they were using any of the GM LSD additive though.

Also upon doing a little research it seems that Auburn does not recommend the use of any syntheic fluid with their differentials. See question #2

http://www.auburngear.com/aftermarket/faq/

Jason
93 Trans Am

 

[Kevin in Texas]

quote:

---

Originally posted by Soma07:

quote:

---

Originally posted by TooSlick:
Soma07,

The Mobil 1, 75w-90 is an excellent PAO based, synthetic gear lube. You may find that you need to "tune" it with some of the GM friction modifier. It should lower your axle temps noticably over the stuff you are currently using ....

Many OTR trucks have switched from 85w-140 petro gear lubes to 75w-90 synthetics in the axles. They run much cooler and fuel efficiency is improved by a few percent ....

Mike Sparks has the Amsoil stuff available, if you decide to go that route. They make three different synthetic gear lubes you could run in this application, including an 80w-90 grade.

TooSlick

---

Thanks for the advice. I was thinking about the M1 gear oil but alot of fellow F-body owners shy away from it saying it caused their differential to chatter. I dont know if they were using any of the GM LSD additive though.

Also upon doing a little research it seems that Auburn does not recommend the use of any syntheic fluid with their differentials. See question #2

http://www.auburngear.com/aftermarket/faq/

Jason
93 Trans Am

---

Niether does Eaton. Eaton recommends a mineral based oil with the FM additive.

http://www.eatonposi.com/prod6.htm

 

[MolaKule]

"MolaKule: Are you talking about a locker style differential? The Auburn I have is just a normal limited slip/posi/whatever you call it. Its the OEM diff in these cars."

I was referring to the posi/limited slip in my '86 Burb.

Originally, it had a regular 3.08 diffy for gas mileage. I could not pull anything with it, so I changed the diffy to a 3.42 gear ring and pinion, with the addition of an Auburn unit.
Approx. the same time, I changed the cam to a CC 260H, so I could pull our pop-up camper and 5X8 wood wagon. So the 3.42 gears, the Auburn unit, and the CC 260H are all third party components.

It sounds like GM wised-up a bit since the mid-80's. Maybe they heard about the 1/4 mile 8 second Burb.

 

[MolaKule]

PS.

I replaced the Rochester "fix-once-a-month" carb with a Holley 4158 Spreadbore
with the super pumper power squirt. It still has the 700R4 slushomatic and can
shift down into passing gear at 75+ mph. It's a screamer. Standard HEI ignition
and factory ignition advance curve weights. EGR and CATS have been relocated.

 

[Kevin in Texas]

quote:

---

Originally posted by MolaKule:
BTW, for the GM 10 bolts, I run nothing but 75W140 in diffys with locking mechanisms, especially the Auburn types.

No other lube will stand-up to the shear created by these locking differentials.

---

Molecule, I have a Eaton G80 Locker in my '01 burb. Do you think that I too should use a 85W140 or is mine a newer or different style that does not shear the oil as bad?

 

[MolaKule]

Golly Kevin, that's a toughy. if the owner's manual shows a chart allowing the use of the
75W140, go with it. Since you live in south Texas, I realy don't think you'll have any problems with the 75W140.

 

[widman]

If you want the full answer, get yourself different viscosities of the same gear oil. Put one in and drive it hard. stop and measure the temperature (a good laser pyrometer is handy). Then change oil and run the test again. The lower temperature is the better option, as heat is the enemy and the symptom of a problem. I have the advantage when I put it in a bus and send it on a 1200 mile dirt road mountain trip. Two days later at the bottom of a 2 hour descent with engine braking, I check the temperature

 

[Dominic]

I currently run 75W90 in my Torsen equipped 3.23 GM 10bolt (2002 Camaro). I flushed the GM stuff out after 2,000 miles (50% full!) and filled with Valvoline SynPower 75W90 when I installed my torsen (www.torsen.com).

Do you think I might could get better biasing, or would be better off, from a high performance point of view, running a 75W140 or maybe the Schaeffers 80W90 instead of OTC 75W90?

 

[carl97ss]

soma07, i have had simular problems as you and found a few things to solve my seal problem on my 125k mile 10 bolt. I put black RTV silicon sealer around the pinion seal where it slips into the housing. I put a polyurathane torque arm bushing in. This reduces rear axle rotatation during hard ,preventing an excessive pinion angle that stresses the bearing and seal. Lastly, i put in BRM LCA with Poly mounts. This also stabilized the rear axle. I found that when i applied all of my 420 lb.ft of torque to my rear wheels, the pinion seal would start to leak. Doing the above stopped the leaks for me.