Pumpkin Lube
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Le Mans Master
Joined: Jul 1999
Posts: 7,072
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From: Maryland
Pumpkin Lube
1970 350/300 TH400 3.08 I drag race it a couple of times a year (I may start doing more of that though!!) regular driving about 5k miles a year. Newly freshened up rearend (new seals, opened, inspected, cleaned) 56k miles on it since new. I'm in the middle of redoing my rear suspension. On the advice of my mechanic who did the rear end overhaul, (Tony's Corvette) I got synthetic gear lube Royal Purple 85 W 140. I also have some of the GM posi additive on the shelf. Someone told me with synthetic I don't need the additive, others have said I still do. Which is it and is there a way to tell by driving the car? Is there any reason I shouldn't put the oil in the rear before I install it? Seems it would be easier to get at now, than later. Thanks, ~Juliet
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Team Owner
Joined: Jul 1999
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From: Huntersville NC
Re: Pumpkin Lube (Juliet)
Seems it would be easier to get at now, than later.
Melting Slicks
Joined: Aug 2001
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Re: Pumpkin Lube (Juliet)
On the advice of my mechanic who did the rear end overhaul, (Tony's Corvette) I got synthetic gear lube Royal Purple 85 W 140. I also have some of the GM posi additive on the shelf. Someone told me with synthetic I don't need the additive, others have said I still do.
Is there any reason I shouldn't put the oil in the rear before I install it? Seems it would be easier to get at now, than later.
Le Mans Master
Joined: Sep 2000
Posts: 5,635
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From: Orlando Floriduh
Re: Pumpkin Lube (Mac)
Juliet... I saw an article awhile back (sorry I can't remember where) that talked about this exact thing. Apparently some synthetics are actually TOO slippery and the posi won't work correctly. Others needed the additve. The jest of the write up was to just use the GM fluid and the GM additive. :confused:
[Modified by silvervetteman, 6:22 AM 6/2/2002]
[Modified by silvervetteman, 6:22 AM 6/2/2002]
Racer
Joined: Mar 2001
Posts: 438
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From: Houston, Texas
Re: Pumpkin Lube (Juliet)
I bought some Pennzoil Gearplus 80W. Says right there on the bottle that adding a friction modifier is not needed nor recommended. Now, I haven't had a chance to street test this lube yet, but I will soon as i finish the front suspension, rebuild the brake, paint the engine, new interior... Well it may be awhile before I can get back to yuo :lol:
Thread Starter
Le Mans Master
Joined: Jul 1999
Posts: 7,072
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From: Maryland
Re: Pumpkin Lube (MNJack)
That is an astute observation!! :lol: You would have to suck out some gear oil to make room for the posi, which would be a bit messy.
Melting Slicks
Joined: Oct 2001
Posts: 2,064
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From: Halifax, Nova Scotia, Canada
Re: Pumpkin Lube (Juliet)
I was wondering about if it would leak on install out the vent tube or if it was difficult to tell when it was 'full' when it's not installed.
Last fall I had the rear out to paint and change the fluid. I suspended it with a rope attached to the side yokes. (attached to the ceiling of garage).
This allowed for tipping the unit on it's nose to remove the cover and also add the fluids.
I used genuine GM fluid and one bottle of additive. I slightly under filled with fluid until the cover was installed and the rear was positioned level again, then filled to the hole. (Drove a few hundred Mi. this year, no chatter)
I used teflon tape on the fill plug as it always tended to seep a bit.
keep the rear level until it is installed and it will not leak out the vent.
I used a floor jack to raise the unit in place. A simple "one person" job.
Hope this helps.
Barry
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Race Director
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Re: Pumpkin Lube (Juliet)
It depends on the product. For example, Redline 75W-90 is supposed to have the additive and is for use in limited slip diffs. Redline 75W-90 NS does not have the additive and is for use in open diffs. I've heard from others that Redline 75W-90 works well in limited slips, as is, without adding the additive. I've used commercially available mineral based gear oils that claimed no additive was required for limited slips, and they chattered.
I now only use the GM axle oil and additive, because I know it works. I don't think 75W-140 is a good idea. The spec is 80W-90 GL-5 (Mil-L-2105). As far as I'm concerned, using anything else is an R and D project! Typical synthetics are 75W at low temp because of their superior viscosity index, but a 140 will be more viscous at high temperatures and just create more heat; 140s are typically used in HD trucks that have slower turning but higher loaded hypoid gearsets. You don't need or want 140 in a typical car axle.
Occassional drag racing with a base engine/automatic is not going to stess your axle. It's the 5000 rev clutch drops and power shifts in manuals that kill it.
Duke
[Modified by SWCDuke, 9:22 AM 6/2/2002]
I now only use the GM axle oil and additive, because I know it works. I don't think 75W-140 is a good idea. The spec is 80W-90 GL-5 (Mil-L-2105). As far as I'm concerned, using anything else is an R and D project! Typical synthetics are 75W at low temp because of their superior viscosity index, but a 140 will be more viscous at high temperatures and just create more heat; 140s are typically used in HD trucks that have slower turning but higher loaded hypoid gearsets. You don't need or want 140 in a typical car axle.
Occassional drag racing with a base engine/automatic is not going to stess your axle. It's the 5000 rev clutch drops and power shifts in manuals that kill it.
Duke
[Modified by SWCDuke, 9:22 AM 6/2/2002]
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Re: Pumpkin Lube (Juliet)
With all due respect to your mechanic, I always wonder why so many people recommend products other than what originally came with the car, based on the theory that 'it's better'. What do they base their claims on? Personal experience? Conclusive field testing? Word of mouth? Marketing hype? What are the credentials of this person? If there's so much data available that proves these lubricants are superior, why is it never available for scrutiny?
The lubricant originally installed by GM allowed our cars to go hundreds of thousands of miles without significant wear. I know that the inner ends of the yokes wear, but do not believe that ANY lubricant would prevent this. What additional benefit could an unproven substitute provide, making it worth the risk?
I work for one the 'big three' aircraft engine manufacturers. We typically deny several million dollars worth of warranty claims per year based on the owner's use of non-approved lubricants or other shade tree modifications. We couldn't do such a thing without undeniable proof that these substitute materials and methods were the primary cause of the failure.
The lubricant originally installed by GM allowed our cars to go hundreds of thousands of miles without significant wear. I know that the inner ends of the yokes wear, but do not believe that ANY lubricant would prevent this. What additional benefit could an unproven substitute provide, making it worth the risk?
I work for one the 'big three' aircraft engine manufacturers. We typically deny several million dollars worth of warranty claims per year based on the owner's use of non-approved lubricants or other shade tree modifications. We couldn't do such a thing without undeniable proof that these substitute materials and methods were the primary cause of the failure.
Melting Slicks
Joined: Aug 2001
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Re: Pumpkin Lube (Mike Ward)
With all due respect to your mechanic, I always wonder why so many people recommend products other than what originally came with the car, based on the theory that 'it's better'. What do they base their claims on? Personal experience? Conclusive field testing? Word of mouth? Marketing hype? What are the credentials of this person? If there's so much data available that proves these lubricants are superior, why is it never available for scrutiny?
I work for one the 'big three' aircraft engine manufacturers. We typically deny several million dollars worth of warranty claims per year based on the owner's use of non-approved lubricants or other shade tree modifications. We couldn't do such a thing without undeniable proof that these substitute materials and methods were the primary cause of the failure.
As a result, people expect the recommended lubricants to be the minimum standard so they seek higher quality products in hopes of extending life expectancy and improving performance. The 'snake oil' vendors will always find a market for their brand of products.
Needless to say, aircraft engine manufacturers want a peerless reputation so they insist on the best compatible lubricants and maintenance to qualify for warranty claims. Plus the dollars and cents (sense?) of aircraft maintenance are completely different, for good reason.
Thread Starter
Le Mans Master
Joined: Jul 1999
Posts: 7,072
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From: Maryland
Re: Pumpkin Lube (Mac)
OK, OK, you all make some very good points. I'll call Tony tomorrow and ask again to make sure I just didn't mis-understand him when I picked up my diff & T-arms at his shop. (I very well might have, since what Duke explained makes a lot of sense). I'm sure Tony would not steer me wrong & fall prey to snake oil claims. :eek: At any rate, there's nothing in the diff now. I just finished painting the frame. It'll be tomorrow before I'm ready to install the pumpkin. It will be a miracle if I get this thing back together & aligned before drag racing Saturday. :jester
Melting Slicks
Joined: May 1999
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From: Moon Township PA
Re: Pumpkin Lube (Juliet)
Juliet, not to beat this dead horse any more, but the man in my area who rebuilds Corvette differentials for a living only puts in either the GM brand of lube or Mobil 1 diff. lube PLUS only the GM brand of posi additive. FWIW, I have been using Mobil 1 + GM posi additive and I like it.
Gary
Gary
