C4 rear gear synthetic oil, 75-90 or 75-140?
Thread Starter
Drifting
Joined: Nov 1999
Posts: 1,324
Likes: 18
From: St. Peters MO
C4 rear gear synthetic oil, 75-90 or 75-140?
I run a C4 with DANA 44 in heavy autocross use, I have broken 3 gearsets over the last 10 years or so, and just rebuilt another and installed it. I filled it with Mobil 1 syn. 75w-90 for break in. All new gears, bearings, races, clutch pack, etc...,
My question is: would I benefit with running a heavier synthetic oil like 75w-140 to help with the shock loading encountered in hard autocross use?
Not trying to compare brands or trash any one brand, but compare the difference between 75w-90 and 75w-140 of similar fluids.
C4 Vette, DANA 44, no cooler, very minimal "track" use, but heavy autocross use, and minimal street use.
My question is: would I benefit with running a heavier synthetic oil like 75w-140 to help with the shock loading encountered in hard autocross use?
Not trying to compare brands or trash any one brand, but compare the difference between 75w-90 and 75w-140 of similar fluids.
C4 Vette, DANA 44, no cooler, very minimal "track" use, but heavy autocross use, and minimal street use.
Race Director
Joined: Oct 2000
Posts: 14,059
Likes: 1,165
From: N. Alabama
The Dana 44 is pretty dang tough. There are a couple of vendors that do some magic to the chunk, though, or so they claim. But, I wonder if the gears had too much tolerance and were slamming engagement?
LT4 here and have been running over 350RWHP for several years (lately 372) on a 140K mile drivetrain - all original.
LT4 here and have been running over 350RWHP for several years (lately 372) on a 140K mile drivetrain - all original.
Last edited by SouthernSon; Mar 13, 2014 at 07:50 AM.
Drifting
Joined: Oct 2006
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From: Romeoville IL
It's been a few years since I change the fluid on my old C4; but I thought the 75-140 was the recommended fluid to put in? I'm almost positive that's what I put in when I changed mine (friction modifier in of course).
Le Mans Master
Joined: Oct 2007
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From: Akron Ohio
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I'm curious to know what broke specifically as well. Once we know that then determining if a heavier oil will fix it or not will be easier.
If it is the teeth of gear as pictured above, then a heavier oil might handle the heat better. Keep in mind heavier oil also increases the resistance.
I have used AMSOIL Severe Gear 75W-90 for years in both autocross and heavy track use without ever changing anything internal to the diff.
http://www.amsoil.com/shop/by-produc...-EA?zo=1934716
If it is the teeth of gear as pictured above, then a heavier oil might handle the heat better. Keep in mind heavier oil also increases the resistance.
I have used AMSOIL Severe Gear 75W-90 for years in both autocross and heavy track use without ever changing anything internal to the diff.
http://www.amsoil.com/shop/by-produc...-EA?zo=1934716
Race Director
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From: Color my life with the chaos of trouble.
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Thread Starter
Drifting
Joined: Nov 1999
Posts: 1,324
Likes: 18
From: St. Peters MO
Bearings and races all looked good when dis-asembled, good wear pattern on teeth.
Previous 2 failures were both ring gear with 2-3 teeth sheared off in a row. Pinion gear looked good in both of those as did bearings and races.
I'm not an engineer, but it looks like shock loading to me.
Corvette is stock LT1 putting out a whopping 268 h.p. and 294 lb./ft of torque at the rear wheels at last dyno session. Automatic transmission, which has been destroyed and rebuilt only once.....so far.
This car has the **** beatin' out of it by two competitive drivers running race tires (Hoosier A6's or Continental scrubs) 18" dia. front and back 315 Hoosiers or 305 Continentals.
ALL rear end failures happened on concrete surfaces (great traction) on low speed autocrosses.
Fluids changed annually in rear end.
Burning Brakes
Joined: Nov 2011
Posts: 1,201
Likes: 16
From: SoCal
Never blew up a Dana 44, but plenty of GM 12 bolts in RR applications. Anyway, you need to make sure it's setup right. ...minimum R&P backlash, pinion depth for maximum tooth contact and carrier pre-load at the tight side of the spec. heavier oil is better but it won't prevent the shock loading damage that is trashing pinion. Something else to consider, a different ratio may give you better pinion tooth contact.
Melting Slicks
Joined: Aug 2004
Posts: 3,003
Likes: 89
From: Indy IN
Geez... I've never seen a 44 get destroyed in autocross.. You've either got to be dropping a big very sudden amount of torque on it or something isn't set up right..
In autocross (unless it is Pro Solo kind of use) you aren't looking a drag strip starts for the most part. If you don't bang it with just dropping the clutch I don't see how you could do that much damage..
If you are dropping the clutch with slicks there's a simple solution for that... Don't.. You really can't gain that much from a dropped clutch start at an autocross anyway.. Have a bit of sympathy for the machinery and you should be fine...
In autocross (unless it is Pro Solo kind of use) you aren't looking a drag strip starts for the most part. If you don't bang it with just dropping the clutch I don't see how you could do that much damage..
If you are dropping the clutch with slicks there's a simple solution for that... Don't.. You really can't gain that much from a dropped clutch start at an autocross anyway.. Have a bit of sympathy for the machinery and you should be fine...
Thread Starter
Drifting
Joined: Nov 1999
Posts: 1,324
Likes: 18
From: St. Peters MO
first pic is the veiw from the back side of the pinion gear, shows the tooth that is missing, along with the next 4 cracking.
Yes, this is a DANA 44 used for autocrossing, perhaps 15 - 20 passes per year of drag racing, with a stock automatic transmission. I do run sticky racing tires only for autocross, and street tires for drag racing.
Second pic is from the front showing cleanly sheared off tooth
This was the one that broke in 2013. this was a stock, un-opened DANA 44 unit with 3.45 :1 gear ratio out of a 94 Corvette that was wrecked and I bought it and stuck it in "as-is" at the time, actually lasted about 3 full years with nothing but fluid change. The ring gear was not damaged visually, but the tooth off the pinion gear got caught under the ring gear and busted out a hole in the case.
Newly rebuilt one just installed is set-up tight, very tight, with outstanding pattern in the paint on the gears. Backlash on ring gear right at low end (0.006") all new bearings. I am hopeful for many years of use.
Yes, this is a DANA 44 used for autocrossing, perhaps 15 - 20 passes per year of drag racing, with a stock automatic transmission. I do run sticky racing tires only for autocross, and street tires for drag racing.
Second pic is from the front showing cleanly sheared off tooth
This was the one that broke in 2013. this was a stock, un-opened DANA 44 unit with 3.45 :1 gear ratio out of a 94 Corvette that was wrecked and I bought it and stuck it in "as-is" at the time, actually lasted about 3 full years with nothing but fluid change. The ring gear was not damaged visually, but the tooth off the pinion gear got caught under the ring gear and busted out a hole in the case.
Newly rebuilt one just installed is set-up tight, very tight, with outstanding pattern in the paint on the gears. Backlash on ring gear right at low end (0.006") all new bearings. I am hopeful for many years of use.
Max G’s
Joined: Nov 2008
Posts: 2,751
Likes: 78
From: Monroe OH
NCM Sinkhole Donor
My suggestion would be stay with 75-90. Also, I would make sure to add friction fortifier. I have been running a d36 for 7yrs and have been putting down 392rwtrq for 3yrs and run a6's. I use Royal Purple gear oil and add 2 bottles of the GM friction multiplier.
Safety Car
Joined: Sep 2010
Posts: 3,752
Likes: 190
From: Indiana PA
Redline Heavyweight Shock Proof Gear Oil for the diff. I've personally never heard of anything going wrong in the D44 other than the clutch packs needing rebuilt from time to time.
I run their Smurf Blue Lightweight in the ZF6 and have no issues.
I run their Smurf Blue Lightweight in the ZF6 and have no issues.
Le Mans Master
Joined: Oct 2007
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From: Akron Ohio
2025 Corvette of the Year Finalist - Modified
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St. Jude Donor '09-'10-'11
I would double and triple check your tooth engagement/alignment and run a good quality oil. The AMSOIL linked above comes with enough fiction modifier in it for a C4 differential, so no need to add more. It is also designed to handle high shock loading.
Where are you buying your gears from? It may also be a bad batch of gears or cheap manufacturing.
Where are you buying your gears from? It may also be a bad batch of gears or cheap manufacturing.