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Discussion Starter #1
And by track I mean the kind with turns. The car has about 95000 miles on it, its got a cam and headers, coilovers, a front BBK, and I was running 265F/285R 100TW Federal FZ201s for tires.

The first time I felt it was doing a "casual" launch out of the pits (no clutch dumps just hard acceleration in first). I heard some popping, some tire chirping, and the rear passenger side axle had sort of a pulsing resistance to it. After easing of the gas and then easing it back on all was fine.

From that point, there were two turns at the track, one in particular was much more apparent, but while powering out of this corner you could feel the drivetrain lagging and could hear a pulsing dull pop noise from the rear passenger side area, and as I straightened out it almost slipped out of it, and the noise and drag on the power train disappeared.

The fluid in there is from the dealer, it has been in there for 9 years and 50000 or so miles, with at least 10 track days since then. Guess its one of those track car maintenance items I forgot about. So anyway, I have some Torco Type F Modifier and Red Line 75W140NS on order to see if that results in the diff behaving better.

My follow up question would be... what kind of diff is available for this car that would be good for road course/HPDE work? I know there is more than enough literature on drag car diffs, but were I to have to replace it I would want to get something that would behave well at the track.

TL;DR I think my diff is starting to go or the fluid was so bad that it was locking/slipping on corner exit and I'm curious if anyone else has had this issue and what a good replacement diff for HPDE/road course might be.
 

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Obviously, changing the oil would be the first step. If that doesn't fix it, must be you have worn out diff. Red Line 75W140 GL-5 is the oil that should go in if you are using Red Line. This is what I have in my diff. I remember calling Red Line and discussing oil options and that is what they said to use. Can't remember all the reasons any more but you can call and ask them. I do have Wavetrac in there instead of original cone clutch type diff.
Now, if you are driving around corners, original diff is not going to work the best and it will wear out fast. There will be bad one wheel spin. This is just how it is with these. Not worth rebuilding with original cone clutches IMO. Mine was roasting inside tire on autocross course while working as good as new driving around town.
Best upgrades for this rear end are Wavetrac and KAAZ.
Wavetrac is very good gear type all around diff. Quiet, works well, supports 1000+ hp, it has lifetime warranty no questions ask.
KAAZ is multi-disk clutch type drifting weapon. Not very civilized for DD, locks almost like spool.
If axle breaks during drag racing, with KAZZ you are looking at the wall, where Wavetrac keeps you going straight.
For turns racing like autox and roadracing, KAAZ will make your car push. Wavetrac may spin one wheel in case of inside wheel lift, it needs to sense some load to really work. They have some features in it to help prevent this but not sure it's 100% effective. But thing is, GTO doesn't normally lift rear wheel around corners unless going over curbs.
For fastest lap times on road racing course, KAAZ may have slight edge, it simply gives more traction on exit at expense of extra push on corner entry. We are talking one or two tenths difference per lap here.
If you end up rebuilding and upgrading, find someone that knows how to work on these and use all the best parts. Many do it twice trying to save few bucks the first time. It takes time, car will be out of service for a while. Way to do it is to find cheap core and build new diff, that way no downtime. It can be swapped out in one day that way.
 

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And by track I mean the kind with turns. The car has about 95000 miles on it, its got a cam and headers, coilovers, a front BBK, and I was running 265F/285R 100TW Federal FZ201s for tires.

The first time I felt it was doing a "casual" launch out of the pits (no clutch dumps just hard acceleration in first). I heard some popping, some tire chirping, and the rear passenger side axle had sort of a pulsing resistance to it. After easing of the gas and then easing it back on all was fine.

From that point, there were two turns at the track, one in particular was much more apparent, but while powering out of this corner you could feel the drivetrain lagging and could hear a pulsing dull pop noise from the rear passenger side area, and as I straightened out it almost slipped out of it, and the noise and drag on the power train disappeared.

The fluid in there is from the dealer, it has been in there for 9 years and 50000 or so miles, with at least 10 track days since then. Guess its one of those track car maintenance items I forgot about. So anyway, I have some Torco Type F Modifier and Red Line 75W140NS on order to see if that results in the diff behaving better.

My follow up question would be... what kind of diff is available for this car that would be good for road course/HPDE work? I know there is more than enough literature on drag car diffs, but were I to have to replace it I would want to get something that would behave well at the track.

TL;DR I think my diff is starting to go or the fluid was so bad that it was locking/slipping on corner exit and I'm curious if anyone else has had this issue and what a good replacement diff for HPDE/road course might be.
There is a lot of info on rears, you need Torco fluid and the F modifier.These use a cone type of lock up, it behaves differently than clutches, the harder the cones are forced the more difficult it is for them to unlock, that is the source of the "clunk in the trunk" Before I did the research I tried Royal Purple, that was a costly mistake. I know little about other combinations but I can say that Torco and modifier works, no question about it. A word of caution; do not go over board with the modifer, Search the forum for the amount to use, just a coupla ounces (I don't recall exactly). That number is with Torco, how it behaves with other fluids I can not say due to differences in chemical make up.
 

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spider gears might be taking a dump.

these LSD's aren't really made for abuse, either. cone teeth and the inside of the ring gear carrier case my be worn the smurf out, too. no amount of friction modifier or gear oil swap is going to fix that.
 

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Discussion Starter #5
Obviously, changing the oil would be the first step. If that doesn't fix it, must be you have worn out diff. Red Line 75W140 GL-5 is the oil that should go in if you are using Red Line. This is what I have in my diff. I remember calling Red Line and discussing oil options and that is what they said to use. Can't remember all the reasons any more but you can call and ask them. I do have Wavetrac in there instead of original cone clutch type diff.
Interesting, I was looking at the Truetrac as it had a reasonable pricetag. The other two are looking like $1000 to $1200? I get that they might be better but it sounds like "anything" would be better than stock?

Regarding fluid, I had heard bad things about the LS additive Redline oil and that our stock diffs like the type F modifier. I do like Redline Oils though, hence the combo of the type f modifier and no-slip additive redline.
 

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Discussion Starter #6
spider gears might be taking a dump.

these LSD's aren't really made for abuse, either. cone teeth and the inside of the ring gear carrier case my be worn the smurf out, too. no amount of friction modifier or gear oil swap is going to fix that.
Hmm okay. Well the only thing I have going for me is I don't do clutch dumps or power shifts so hopefully I drive it lighter than the typical GTO owner that burns out the diff super quick 😂
 

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Interesting, I was looking at the Truetrac as it had a reasonable pricetag. The other two are looking like $1000 to $1200? I get that they might be better but it sounds like "anything" would be better than stock?

Regarding fluid, I had heard bad things about the LS additive Redline oil and that our stock diffs like the type F modifier. I do like Redline Oils though, hence the combo of the type f modifier and no-slip additive redline.
Truetrac is one option but it does have some issues. From my research I found that people usually have too much slack on stubs when used with Truetrac. Especially with aftermarket stubs. And apparent they don’t go in as far, can come out. None of this is from my experience, never used Truetrac. And performance wise it is not as good as other two, not to say it doesn’t work just fine. IMO, rebuilding the diff is do it once do it right deal, and game changer performance wise. Worth spending some extra $ on it.

You may be right on oil plus modifier combo. Mine is Wavetrac (gears) so that works. I still think calling redline and getting some info from them may be beneficial.
As for Torco with F modifier, I tried that before building my diff. It made it little quieter. Did not improve on one wheel spin.
Also there is some info out there that suggest that diffs using Torco oil wear out quicker. Nothing I could confirm, just what I heard from guys that know more than me.
 

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Discussion Starter #9
Alrighty well I put in 1.5 oz of Torco Type F and then the rest of the way up with the Red Line 75w140NS. The diff did not fall out of the car, so far so good. On my quick test drive last night it did seem a bit quieter and not chattering. I gotta say though, what came out didn’t seem like as much as I put in.
 

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Alrighty well I put in 1.5 oz of Torco Type F and then the rest of the way up with the Red Line 75w140NS. The diff did not fall out of the car, so far so good. On my quick test drive last night it did seem a bit quieter and not chattering. I gotta say though, what came out didn’t seem like as much as I put in.
🤞
 

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There is a lot of info on rears, you need Torco fluid and the F modifier.These use a cone type of lock up, it behaves differently than clutches, the harder the cones are forced the more difficult it is for them to unlock, that is the source of the "clunk in the trunk" Before I did the research I tried Royal Purple, that was a costly mistake. I know little about other combinations but I can say that Torco and modifier works, no question about it. A word of caution; do not go over board with the modifer, Search the forum for the amount to use, just a coupla ounces (I don't recall exactly). That number is with Torco, how it behaves with other fluids I can not say due to differences in chemical make up.
Torco RGO 85W140, 2 quarts and 2 oz of the Type F modifier
 

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Alrighty well I put in 1.5 oz of Torco Type F and then the rest of the way up with the Red Line 75w140NS. The diff did not fall out of the car, so far so good. On my quick test drive last night it did seem a bit quieter and not chattering. I gotta say though, what came out didn’t seem like as much as I put in.
See if there is oiliness on the undercarriage and exhaust at the front of the differential. Pinion seal leaks a lot on those
 

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I have been doing HPDE for 11 years in the GTO. I change out the diff fluid at the beginning of the season and halfway thru, so that is March and July. I have Kaaz diff and only use their fluid. It has been in the car since 2010. I do not notice any adverse effect when driving on the street.
 

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I have been doing HPDE for 11 years in the GTO. I change out the diff fluid at the beginning of the season and halfway thru, so that is March and July. I have Kaaz diff and only use their fluid. It has been in the car since 2010. I do not notice any adverse effect when driving on the street.
I am curious if you know exactly your KAAZ is set up:

2.0 way or 1.5 way?

Standard or WPC treated steel disk plates?

Any special arrangement of disks and pressure plates to alter lockup ratio?

I assume friction modifier is still required with KAAZ oil? Which friction modifier you use and how much you put in?

I still have my old rear end that is perfectly good short of spinning one wheel around tight corners. Sitting on the shelf, collecting dust, so maybe I could just stick a KAAZ in it and have it ready to go in case I feel like it...
It was all these variables and need for oil changes that kept me from getting it in first place. With Wavetrac, it’s stick it in and forget, plus lifetime warranty.
 

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Discussion Starter #16
See if there is oiliness on the undercarriage and exhaust at the front of the differential. Pinion seal leaks a lot on those

Good to know, there probably is.

I guess the gear oil doesn't smell as strong as ATF. I swear ever since I did my clutch job and tranny fluid swap about once or twice a day I'll catch a whiff of ATF smell.
 
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