froggy47

Leaving all the other fluids aside, oil, p/s, clutch, brake, coolant, and I know it's easy to change both at the same service,

but,

which one needs more frequent changes (street/autx/hpde use) tranny or diff?

BQuicksilver

good question. also which gets hotter? (hopefully not to hijack)

rustyguns

how many street miles per year and how many road race track days a year?

JimbeauZ06

I changed my trans fluid 3 times this season, but the diff only twice.

I guess I'm more sensitive to the trans since I occaisionally get the "Trans Overtemp" message in the DIC. Cooler going on soon!

Should I be equally worried about the diff though?

0Randy@DRM

Diff fluid. Hotter and should get changed more often.

Froggy you are a auto-x guy, and they are hard on diffs.

Randy

96CollectorSport

Diff fluid definatly works harder!!! The diff works on friction, if the tranny does then you have problems (or an automatic). Even with coolers I change diff fluid after every other track event, tranny fluid I do twice a year.

froggy47

I was thinking that too, my poor diff is almost always in a tight (parking lot) turn on scca courses.

For the other question (Rustyguns) about 5- 6 k miles total, maybe 200 track miles & 200 autox miles the rest street/fwy.

I use redline.

rustyguns

i recommend both twice a year, once in middle of racing season

redline rocks! which ones you use?

davidfarmer

Gm engineers told me the tranny was the one to watch for assuming you aren't running coolers. I think the fact that the gears are constantly changing relative speeds really stresses things. The diff gears all move at the same speed relative to each other.

froggy47

D4atf for tranny

75w/90 (includes the friction modifier already) gear oil for the diff.

Guess I'll do both 2x yr. I do always see "sparkles" when I drain, so I know there is (normal) wear going on in both. Don't have any issues with either. 30k miles.

rustyguns

did you notice the transmission shifting better after putting in the D4atf?

i went to royal purple syncro max and it was like a diff transmission! smooooth shifting but i hear redline is better

ever try redline 75/140 shockproof in the rear end? and is suppose to run cooler

froggy47

A bit smoother than oem fluid, yes.

Have not tried any RP yet. Seems that Redline is used by lots of "real racers" in all the different motorsports series.

No on 75w/140.

I have called Redline tech support many times, they are very good, actually I think it's just one guy. I explain in detail the car/use & go with his reccomend.

ZR1 MK

I say the trans fluid takes a bigger beating.
I change my fluids every 3 years, but I use magnetic drain plugs and additional magnets to prevent particals from floating around. Although they wont collect bronze particals.
My rear case was drilled and tapped at the bottom to help fluid changes, but it also helps in removing all the crud.

95jersey

What is the regular interval? 15k miles? 30k miles? Obviously road racing puts more heat and stress, but an event may only be a couple hundred miles. Are we seriously saying this fluid need be changed every few hundred miles under HPDE conditions? I have a hard time beleiving that oil breaks down that quickly even under higher than normal temps. Isn't the prime reason to change oil the fact that dirt and debris effect it rather than breakdown (especially with synth)? No way your getting that much dirt/debris in a couple hundred miles.

I change mine frequently and only drive 3000 miles per year, but I can't beleive that oil breaks down that fast.

froggy47

Well my thinking is not that the syn fluids break down, but I am thinking that wear & tear particulates from let's say a few less than prefect high rpm shifts (syncro material) and more especially from a hard worked diff (diff clutch material) are building up in the tran & diff, and that it's a good thing to get rid of them with a fluid change.

I know my engine oil life monitor is giving me a change (I don't go to zero) at about 4500 miles (full syn) and that if I was granny driving to the golf course it could likely be double that.

So I think it's just smart preventative maint. if you plan on keeping the car for some time & driving it hard.



Thanks all for the posts.

96CollectorSport

I would change the fluid if it smells burnt or once a year (whichever comes first), weather that takes you one event or 15 events, if you have coolers and they are working then you should be able to go longer between changes. If you are not using coolers then you should be changing your fluid more often. After you change your fluid, just check and see how it's doing. More than likely your going to have the car up in the air to change tires.
From my experiance I notice that the diff fluid will smell burnt before the tranny.
By the way HPDE can be harder on your car than racing, it all depends on how hard you drive the car, but a typical SCCA weekend the cars are only on the track for 60 minutes total. How many 20 minute sessions do you get at a typical HPDE? 7 or 8 for a typical 2 day event? And you don't replace engines every year, or drivelines every 2 years or so. Just saying they can both take a toll on your car, it's just that most people who do HPDE have more time on the track and a fraction of the maintenance of a race car.

meldog21

I just sent in my second set of oil samples for analysis. I'll post up the results when I get them. The report should provide some sort of idea how well the three oils did. I put approximately 7000 miles, including 5 track days, on my oils in the last 10-11 months. 02 Z06 with a total of approx 46000 miles.

I do not have trans or diff coolers and I always get high trans temp warnings at track days. It usually happens near the end of a session so I never worry about it since I'm always slowing down and heading in when I get the message. I do have a DRM radiator with integrated oil cooler. That thing works great. Water temps max out about 225, oil temps about 255.

Oh, I use Amsoil.

Dog

ZR1 MK

Yes, its a partical issue as you state, not a breakdown issue.

Keep in mind, major sychro wear is due to full throttle shifts. I did most shifts at the track in my other cars like that, but my current car rarely gets them. One of a few reasons why my 19 year old trans is original and still going strong.

froggy47

Yes, true, and (in my case) whenever the car is autox/track it's full throttle shifts. Street pretty easy shifts. Dual use car with low annual miles.

I guess for about 60 bucks & 1 hour of my time it would be silly not to chg both 2x a year.

Thanks all.