BUILD THREAD 86 GP 2+2~Blown 6.0

[81cutlass]

Yep thats the worst of it. Just broke that axle as far as i can tell. I will have to see the carrier bearings and gears to see if anything got thrown through there or if the posi got cooked when it broke.

If the gears and carrier look good, its going to get moser 30 spline axles to GN width and I'll cut 4" out of this housing and get a proper set of 15x10's on the rear. Probably go with c clip eliminator 9" ends. I didnt spit the tire out since it had disk brakes and the caliper bracket kept everything in (like i always thought and said it would) but when its apart and needs ends anyways i'll tackle it.

If the gears and bearings or posi are trashed, it's getting a 9". New gears, carrier, axles, install kit and all the other needed upgrade parts are like $1000 and I can scrounge up a 9" for not much more than that.

This happened on the 2nd pass of the day. 1st pass was a 11.79 and it spun a bit. Took a psi out of the tires, launched, shifted to 2nd, hit rev limit, made sure i didnt miss a gear, let clutch out again, didnt move. Luckily all the oil stayed inside the diff so the track was happy.

I searched locally for 3hrs for a zr2 being parted out or something but nobody got back to me. No luck. Threw it on the trailer and went home.

 

[Texas82GP]

 

[81cutlass]

Loaded on my buddies pickup and trailer to haul home last night. Unloaded it today.

Pulled the diff (not easy), there was a TON of preload on the bearings keeping it from coming out easy. The drivers side axle was also stuck in the diff and i had a hard time getting it out. I basically had to remove both sides shims and turn back and forth with the carrier to get it out.

So yeah

My posi didn't do THAT good of a job moving the car with the one broken axle so i question how good my posi actually is. Its got like 5k miles on it and looks useable but I'm tempted to throw a spool in it and see how it does. I might see if i can get new clutch plates and inspect it a bit more to see if they are bad or not. It did move the car on flat surfaces with the broken axle but it wouldn't move up even a slight slope. Not sure if that means the posi is wasted and if i put it back together if it would spin both tires or not.
https://www.speedwaymotors.com/GM-8-5-Inch-10-Bolt-Steel-Full-Spool-30-Spline,46899.html

So for sure I need axles and a bearing kit.

 

[81cutlass]

Bought another zr2 rear for parts today. Plan is to convert this one to 9" ends and moser or something axles. In the mean time I stole the shafts out of this one that im putting in the rear I have in the car now to get it back on the road.

 

[TexasT]

11.75 at 120. It's sure making power to trap 120. And that's on only 11 degrees of timing. It slowed down to 117 when I put 13 degrees in it which seems wrong but I'm not sure.

Racing starts at 10 tomorrow!

Pretty salty picking up 28mph in the second half. Lots of top end!

This is the first ls swap I have interest in. I dig the blower and the speed density. Keep up the great work we are ready for a 10 sec slip.

I think I'd have jumped straight to the 9" if you have the fundage. I'm an 8.5 believer but that drive it like you stole it six speed is a lot to handle. And you don't even have it dialed in yet. That thing will give a ten sec slip sooner than later.

Great stuff. Loving the pix and story! Makes me jelly and think how much fun it was when I was single and did as I pleased.

Added: Question while I'm at it. A few pages back there was a pic under the front end with a bar that seemed to tie the frame horns together. IS this a Pontiac thing or a 2+2 thing? I have the MCSS bars that go from the cross member under the engine to the horns but this looks like some thing I might need if I can fit it with the slic I run. Thinking it would tighten up the f/e a bit.
TIA

 

[64nailhead]

11.75 at 120. It's sure making power to trap 120. And that's on only 11 degrees of timing. It slowed down to 117 when I put 13 degrees in it which seems wrong but I'm not sure.

That's not wrong, that's expected IMHO. You'll need better fuel, cooler intake temps, meth injection or a combination of these.

That axle looks like the stock 28 spline giddyup. If that's the case, then I'd say it's expected with what you're putting to it. A 30 spline diff and set of Moser or Strange axles will stick together.

 

[MC96]

Added: Question while I'm at it. A few pages back there was a pic under the front end with a bar that seemed to tie the frame horns together. IS this a Pontiac thing or a 2+2 thing? I have the MCSS bars that go from the cross member under the engine to the horns but this looks like some thing I might need if I can fit it with the slic I run. Thinking it would tighten up the f/e a bit.
TIA

Pontiac thing "Grand Prix bar"

 

[81cutlass]

Pretty salty picking up 28mph in the second half. Lots of top end!

This is the first ls swap I have interest in. I dig the blower and the speed density. Keep up the great work we are ready for a 10 sec slip.

I think I'd have jumped straight to the 9" if you have the fundage. I'm an 8.5 believer but that drive it like you stole it six speed is a lot to handle. And you don't even have it dialed in yet. That thing will give a ten sec slip sooner than later.

Great stuff. Loving the pix and story! Makes me jelly and think how much fun it was when I was single and did as I pleased.

Added: Question while I'm at it. A few pages back there was a pic under the front end with a bar that seemed to tie the frame horns together. IS this a Pontiac thing or a 2+2 thing? I have the MCSS bars that go from the cross member under the engine to the horns but this looks like some thing I might need if I can fit it with the slic I run. Thinking it would tighten up the f/e a bit.
TIA

Thanks! Yeah that top end trap speed really pleased me. Just want to get the launch tuned in.

I am like 50/50 split on keep the 8.6 I have or go 9". A 9" that handles what I want is like 2 grand. I can get this 8.6 20% or so healthier for ~500. I have heard people running to the 8's on turbo novas and 2nd gens on good 8.5's I just dont know if I had a poor axle or if its THAT mean to the rear. I havnt spent much money on it yet that i wouldnt get to patch the car back together for the fall so i'll access again this winter.

And yeah, as mentioned it's the grand prix bar. It kinda interfears with a cutlass jounce bar setup but if you use a few washers they space out enough and you can run both. Something I need to do still is find some jounce bars for this.

 

[81cutlass]

That's not wrong, that's expected IMHO. You'll need better fuel, cooler intake temps, meth injection or a combination of these.

That axle looks like the stock 28 spline giddyup. If that's the case, then I'd say it's expected with what you're putting to it. A 30 spline diff and set of Moser or Strange axles will stick together.

Reason I was surprised it slowed down with more timing is many LS tuners say 10PSI and 10 degrees of timing is safe for boosted LS world and you wont blow up. Should pick up 15ish hp per degree of timing. Gen 3 5.3's often take 18 degrees and 18psi on pump gas and alky or so before the rods get bendy. I was only at 11 psi and 11 degrees with 130ish iat's at the top of the track. I am on e85 too. At 11 psi I should be able to put at LEAST 15 degrees in with those IAT's. The "bad" news though is my computer didnt connect that pass so I didnt get any data. I could have bumped the rev limiter or shifted early on 2-3 shift and had something happen I wasnt aware of. I tried getting my launch sorted out the next day (since that higher timing pass was the last of the day) and before I got a pass where I could put more timing in it blew that axle. I might have ran lean or somehow ended up taking timing out of that pass I guess, I cant really be for sure. I probably shouldnt put much thought into that one fluke pass at the end of the day.

It's a factory 99ish 30 spline GM axle. I actually have a 99-03 zr2 s10 8.5/8.6 in the car I built a year and a half ago. I would have expected to blow up a 28 spline but was a bit surprised to blow up the 30.

I hope the stock 30 splines are just not to the quality of a moser or strange or whatever.

 

[MC96]

Fun tidbit I picked up. Axles are on a 24 pitch spline, meaning 30 splines is 30/24ths of an inch, or 1.25" That also means a 28 spline axle is 1.166.

Axles also supposedly gain 1% strength every .002" of diameter. By that math a 30 spline is 42% stronger than a 28 spline axle.


According to that math (if I did it right) , a 31 spline axle (like most ford 9"s) is 104% stronger than a 26 spline 10 bolt, 35 spline is 188% stronger than that same 10 bolt.