five7kid

iTrader: (14)

I know, I know, first you're going to say "10-bolt and drag racing don't mix." Yeah, I know, but stick with me here.

I'll admit I am not a frequent visitor to this forum, but I did both search and read through the 10-bolt sticky before starting this.

I kept the '82 drum brake 10-bolt back in 2010 when everything else in my fleet had broken, and getting the LS1/4L60E swap done was the quickest way to get something running again. I had a set of 3.73 GM gears to put in while the engine/trans swap was going on. I don't recall the details, but I wanted a Detroit Truetrac, but they either weren't available for the 7.5 yet, or couldn't be delivered in time to support my need (back ordered, something). Whatever the reason, we went with an Eaton clutch posi unit. One big downside to me is I'm a synthetic lube guy, and Eaton frictions aren't compatible with synthetic gear lube. Like a good boy, I used petroleum gear lube and posi additive. I welded the axle tubes, already had a Summit support cover on it, and aftermarket 28-spline axles.

Previously I had done about the same to an '83 disk brake rear end for the other Camaro I had with LS1/T56 swapped in. It had 4.10 aftermarket gears, Eaton posi, welded axle tubes, and Summit support cover. It lasted through the 2nd launch with sticky tires, after which the gears started howling. It was replaced after 15 passes with a 9" (and I've since sold that car).

Fast forward to spring 2012. My son has an S10 Blazer with an LS1 clone swapped in. It had the "gov lock" posi, which is a disaster for drag racing. I took the Eaton out of the T56 car's 10-bolt, handed it to him, he found some 4.10 gears on line, and had it set up.

I started noticing last season that he had to put on the park brake in order to torque lugs with the wheels in the air, but I didn't have any problem doing that with the Camaro - until early August this year. Both still do the burnout fine.

A week ago, I decided to do a fluids change in the Camaro in prep for the last racing of the season, including a 3-days-of-racing that weekend. When I pulled the drain plug, and found these (the dime is in the pic to show the size of the pieces - it wasn't in the rear end...):



I had only planned on draining the gear lube and refilling, but after I saw these, I pulled the cover and took a closer look. I expected to find chewed up gears, but they looked fine, and I didn't see any other loose pieces. So, I put the cover back on and refilled with fresh petroleum gear lube. After trying to figure out what they were, a fellow racer put me on to this rebuild kit:



Apparently the outer tabs from a friction disk. But, each disk has 4 tabs, and I only found two. I showed them to the shop that did the install the next day, and without me saying anything, he said, "Looks like tabs off of a posi disk." Great. It was only one day before the weekend, so I decided to just do a gear lube change every evening, and hope to get through the weekend without anything getting caught in the gears or bearings (hoping the drain plug magnet would catch any such pieces that were liberated).

Which I did...

Oh, after seeing what I found, my son decided he'd better check his. When he pulled the cover, he found a chewed up bronze-colored piece like in the bottom row of the rebuild kit photo. He cleaned things out as good as he could, put the cover on, refilled, and went racing.

Friday after racing was done for the day, the drain plug had a few sparklies on it, but nothing significant. Saturday it was even less.

Monday I got the car in the garage and started pulling the rear. The gear lube was still clean, but as soon as I pulled the cover, I could see that one of those bronze colored pieces was on its way out of my posi. The shop explained that they go over the outer disk tabs, and then ride in slots in the posi housing. So, apparently the failure mode is those tab alignment things getting out of place.

The reason I'm posting this is to warn those who want a posi for their 10-bolt and want to race, you'd better stay away from Eaton posi units. What's in mine noe is a Detroit Truetrac, which the shop says they have installed dozens of (including in 7.5 10-bolts - they are pretty common out there in various platforms), and haven't had any issues with them to date.

Now, I've seen in various places here on TGO that if you want to upgrade your 7.5 10-bolt, to go with aftermarket gears. Well, the shop tells me exactly the opposite - if you have GM gears in the ratio you want, keep them! After abusing these for 3 years, including 3 seasons of racing and almost every day commuting, and having a posi unit spit out metal pieces, these gears still look fine and set up without issue when they put it back together this time, I'd have to agree. I do believe I saw a comment about keeping GM gears in the 10-bolt sticky, but it wasn't to the effect that GM gears are typically superior to aftermarket.

And, if you have an Eaton posi, either don't race, or don't do burnouts.

And, finally, after all the talk about how weak 7.5 10-bolts are, I run high-12's here at altitude, 12.0's/low-11's at sea level or with a 75 shot at altitude. While I still consider it the "weak link", it's holding up fine with the auto trans in front of it. Sure, I'd like a 12-bolt or S60 (didn't much like the 9" in the 3rd gen chassis - takes up too much of the available room back there), but for now, this is doing okay. I really expected the gears to show some distress, but, they didn't.

Of course, if you have a manual tranny and sticky tires, I'd say get the 10-bolt out of there as soon as possible...

Oh, one final note (and I mean it this time), Detroit is owned by Eaton now. In fact, the Truetrac box said "Eaton" on it. For what that's worth.

Atilla the Fun

Most of this post I've posted before, but the guys on LS1Tech are a great reference of what some 7.625 rears can survive. And I was using Richmond in my 7.5 when it survived a 10.21-second 1/4-mile in my old '88 IROC. Not GM gears. At the time, there was no Truetrac, and I still don't trust them for serious abuse, the spur gears look too delicate. Maybe for a rear that can fit larger spur gears, unless that larger rear is going in a heavier application. But as to the Eaton limited slip: Tom of Tom's Differential reportedly said that "when you start getting into some serious power (around 500-550hp) the carbon-fiber clutches will warp" BGH himself once posted this: "The original Eaton used the 18 disc steel set. I'm not a big fan of the carbon-fiber clutches. There are only 14 discs in that set. More discs means better lock up." And this: "The carbon-fiber plates seem to work well on the street. The only problem is that if you ever slip them real bad and get them hot they seem to glaze over and stop being as effective." And this: "The original Eaton Posi that was used in the '60s and early '70s Chevy muscle cars had 18 disc steel clutches and 200 pound springs. These are still working well in many of these cars 30 + years later. The new Eaton is designed to be smoother and last longer." ( More bite, less life, more life, less bite. The bite is the whole entire point. That's why the silly thing is rebuildable ) Here are other findings: "If you want the 800 lb/springs ( and that's kind of the whole entire point of buying a HP diff ) you can't combine them with the carbon-fiber clutches." "Additional traction out of a corner that you will get with the 800 lb springs." " I just rebuilt mine. Those carbon-fiber clutches were falling apart on it as well. They actually use 1 LESS pair of clutches compared to the more common all steel set. That's less surface area available and when that carbon-fiber falls off you lose a bunch of pre-load too. " "Carbon-fiber is great for road racing BUT drag racing stick with the steel clutches and they can handle more abuse. I have seen many carbon-fiber clutches actually peel from the plates they are glued to." "The natural lubrication (graphite) of the carbon-fiber clutch discs allows smooth low speed operation." ( Things that are lubricated don't have much friction, and those discs are there to create friction for traction, which is why posi's get friction-modifier additive to the gear lube ) "The new Eatons use carbon-fiber clutches. They don't last as long as the old steel ones did. Just about every one we put in the customer calls back in about 1000 miles complaining they only spin one tire. If I was going to buy an new Eaton i would take the carbon-fiber out and replace them with the old steel ones. We install about 10 a week and they still have that problem." "It does chatter, even thought the end user doesn't hear it. " "Use a Parifin based lubricant....... and since friction modifier, not the synthetic type like RedLine, is Parifin based..... it homogenizes much better and negates the chatter and inherent heat build up in the clutches." ( When you tear down engines every day, you begin to notice the problems are mostly in the ones that ran Parafin-based motor oils, like Pennzoil and Quaker-State. since it's not good for engines, why would I want it in my axle? To save the C-F clutches that still have every other problem listed above? Absurd ) "We try to push the Auburns. They don't have the clutch issue that the Eaton has. I have always used Auburns in my personal car and have never had any issues." "I used to have an Auburn Gear high performance series limited slip. It was a great unit. I was really impressed. The street driveability was pretty flawless, and it always seemed to lock up when I needed it to." ( I agree ) I'll let that suffice though there is more. To be fair, IF BGH spends 40 hours EVERY week playing with Eatons, then he SHOULD be able to get results that satisfy him.

big gear head

The Eaton Posi is an excellent differential for most street/strip use. The new carbon fiber clutch plates that they install in them are not the best. The clutch plates are not heat treated like the old steel clutch discs are. The clutch kit that you have pictured above is for the Gov Lock, not the Eaton Posi. That is why there are 4 tabs on those clutches. The Eaton Posi only has 2 tabs on the clutch disc. The old solid 18 disc steel clutches are still the best and should be used for drag racing. They will not break like the discs that you have. Get the 18 disc steel clutch set for the Eaton Posi that you have and rebuild it and you will not have any more problems out of it. Check this out. http://www.camaros.net/forums/showthread.php?t=211822

five7kid

iTrader: (14)

I see now that the rebuild kit pic I posted is for the Gov Lock (the title called it "Eaton", the description "Gov Lock"). And, I guess that explains why I only found 2 tab pieces in the Camaro (didn't find any similar pieces in the Blazer).

Thanks for the link. That de-mystifies a lot of things.

Now the dumb question: Where to get the "good" 18 disk kit? Eaton's application guide (http://www.eaton.com/ecm/groups/publ.../ct_128302.pdf) only shows it for 8.2" and up. The only thing available for the 7.6" is carbon.

As for Auburn, I had one of their standard posi units in the 8.2" I had in the '57. It lasted about 2 months, then it was one-wheel burnouts. I heard the Auburn Pro units were better, but I've gone 9" and locker in that car, so it's OBE now.

With regard to aftermarket gears, Richmond has been bought by Motive. The shop here refuses to put in Motive gears because of their poor quality. That doesn't bode well for Richmond.

cosmick

I rather like the traditional Detroit Locker, and while it's not the friendliest for daily commuting, it is a proven design that seldom fails even under extreme abuse. And they do make one for our axles. All the drop in lockers that fit a stock open case are based on the DL, but they look to have far less tooth engagement. For you driving that car to the drags every weekend, I'd say the DL would be the best.

big gear head

You might try the Raybestos clutches from Randy's Ring & Pinion. I wasn't aware that the 18 disc steel clutch set was not available for the 7.6 Eaton Posi.

five7kid

iTrader: (14)

You left out the part about "...driving the car to work 5 days a week, and to the airport when going out of town on business..."

We'll see what my son decides to do with his posi. He may go for a different unit himself, although being a college student, funds are a bit tighter for him. If we can get enough good parts between the two to make one good one, he may go for that.

Got the rear back in and took it for a little test drive. I didn't have much of an opportunity to test out its posi-ness, so I guess we'll have to leave that for tomorrow at the track. At least it seems to drive and run smooth, and nothing fell off on the way home.

cosmick

Best is a problematic term. But best would be one of those limited slips that can be electrically locked, if they're strong enough, and if they were made for our axle choices. Second might well be an ARB, those are really well made, but not available for our choices. I'm still young enough, at age 37, to be willing to put up with a DL for daily commuting all year long. But up in the canyons, the DL is more problem than help. I expect the same when I get ready to try autocross.

five7kid

iTrader: (14)

Not sure how "best" got into the conversation. Pretty sure I didn't use it.

I'm really in a rock & hard place situation with this 10-bolt. I didn't like spending money on it 3 years ago, and didn't want to now, but it's a situational thing. Ideally I'll get the '57 running next year so I can run it at the track, and concentrate on getting this car cleaned up, painted, AC running, etc. For a driver, a 10-bolt is fine. And, I'm sure, the Truetrac friendlier than even an Eaton.

Atilla the Fun

My fault, apologies for creating problems other than those I intended to create.

five7kid

iTrader: (14)

lol, I even searched the thread and couldn't find the word...

Well, mostly I was expressing my disappointment in the Eaton unit, giving kudos to GM gears, and a little amazed that this little 10-bolt is keeping up with the rest of the car.

Yesterday was a race day. I didn't have a very good view of the burnout, and no videographer to document it. I rolled through the water as usual, stepped on & held the brake (which has the 2-step switch in the pedal), shifted to 2nd (it starts off in 2nd gear when the shifter is put in the 2nd gear position), engaged the line lock, brought RPMs up to the 2-step engagement, and let go of the brake pedal. It would spin up to 5500-6000 RPMs without any more throttle until the tires dried off, at which point I let go of the line lock and let it grab. I thought I was getting smoke out of both tires, but couldn't see well. 1st round of eliminations my son was right behind me in line, I asked him to watch if he could, he said he thought the left tire started turning first but then they both spun (equally as best he could see).

The first couple of 60' times were right for the DA, and improved as the night went on. I only made it to 2nd round (had a poor RT), for 4 passes total. It picked up on me beyond what the weather station predicted based on last weekend's data in the last pass (double break-out - I should have dumped him). The last 2 60' times were the best I've seen in several weeks.

And, it drove home nice and smooth.

I think I'm going to like this Truetrac. I'll be racing again tomorrow afternoon, so we'll see how it goes this time.