PONTIAC ZONE TECH FORUMS
 

Go Back   PONTIAC ZONE TECH FORUMS >
Engine Tech
> Suspension
User Name
Password

Suspension Some times the most over looked

sponser links

Reply
 
Thread Tools
Old 11-03-18, 02:50PM   #1
john23
Registered User
 
Join Date: May 2016
Posts: 5
Default 12 bolt street/strip with tru trac rebuild

This was originally posted in GTOforum.com

Hi Everyone. In the fall of 2016 I shelled my 12 bolt, holing the cover from the inside with some sheared-off ring teeth. I never knew it Ďtil I got home, then the oil on the garage floor was a dead giveaway. Full disclosure? It was an abusive relationship. The rear end treated me really nice. It was always there when I needed it. And in return I beat on it over and over and over. And for that I feel bad. But not enough to change my ways. Time for another rebuild. Counting rebuilds this will be the 7th rear end Iíve had under the car.

I rebuilt the 12 bolt as follows. I went with a Detroit Tru Trac differential. I like the fact they donít require rebuilding like clutch style differentials, and they seem to do what I needóstreet durability and usefulness and straight line traction at the track. I kept my ratio 3.73. I bought the gear set, the rebuild kit, the bearings, the axle ends that positively retain the axles, and 31 spline custom length axles from Mark Williams Enterprises. They are right up the road from me in Louisville, Co. My builder was Pat at Pat Condon Race Cars. He did a good job. Both Pat and I know some of the folks at Mark Williams and they are knowledgable and friendly. The left main cap was replaced with a steel unit. The ????? were welded to the housing. The positive retainers were used at the housing ends, new 7/16 in studs were installed and the rear end was shortened by ĺĒ on each side. The yoke was replaced with a heavier unit as was the driveshaft yoke and the drive shaft was shortened accordingly.

More on narrowing the rear end. As you folks know, there is precious little room for tire under the rear of early A-bodies. Mine is a í65 gto. I run 15 X 26 X 11.50 LT Hoosier DOTs on 8 inch Weld aluminum rims with centered offset. They are 26.5 inches tall. The 12 bolt before the shortening put the edge of the tire barely inside the fender lip even with the inside fender edge cut. For years I used airbags to gain clearance but they adversely affect the launch. Without the bags the tires rub when cornering. With the shortened rear end the tires are nicely centered in the wheel well with about ĺ in. clearance on both sides. The Hoosiers put about 10 inches of tread on the ground. Iíve thought about trying for 11 inches on the ground, splitting that inch and a half clearance I have, but it would require custom rims and new tires and the $1000 plus price tag doesnít seem worth it. I was able to bend the brake lines to accommodate the shorter backing plate to backing plate distance, no cutting required.

I was surprised to learn the Tru Trac requires conventional lube. I used synthetic in the old clutch pack differential because of less friction loss when the rear end cools at the track. The synthetic is too slick for proper performance with the Tru Track.

My impressions after running the new rear end for 2 shortened seasons: I think the new package is slightly heavier and there may be a small increase of thru loss due to friction and heavier rotating weight. However my 60 ft times have stabilized. The car seems to repeat the 60 ft easily. Provided of course the tires donít spin at the launch. My best previously with the old 12 bolt was a 1.68 60 ft. But that was once. Usually it was a 1.72--1.75 and maddeningly inconsistent. The 60 foots now are all around 1.70 and repeat over and over. The time honored laying 2 black stripes down the street seems to confirm that both sides are working equally. The price for the rebuild was well north of 2 grand. But the package will be bullet proof at my power level for some time and the consistency is welcomed.

One more thought. My car should 60 ft better than it does given its e.t. I have tried various shock packages, without much success. It does not seem to transfer weight on the launch. I might install a rear sway bar one of these days, though I hate to add weight to the car. Deeper gears than the 3.73 would also help the 60 ft, but that ratio is a good compromise with the short DOTs on my street/strip car. I donít own a trailer and those same DOTs are on the car all season long. The street manners of the TruTrac are impeccable. I am pleased with its performance, both street and strip. Thank you all.
john23 is offline   Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Hughes Performance Rebuild kits Superchief Transmission TECH 3 04-25-09 03:05AM
76 10 bolt confusion! damonrink Grape Vine - General Discussion 5 12-03-07 07:54PM
Rebuild 1975 350 strickrodt70 1958 - 1981 Pontiac Tech & Restoration 3 01-06-07 02:50PM
Need help with 400 turbo rebuild crazyfrank Transmission TECH 8 08-11-06 09:55PM
8.5 in 10 bolt diff upgrades for street/strip use Johnny406 1958 - 1981 Pontiac Tech & Restoration 3 01-31-06 12:03AM


All times are GMT -3. The time now is 11:33AM.

Featured Ads
Ken's Speed & Machine
Mayhem Turbocharging

Carter Cryogenics.  What can we freeze for you?

Pacific Performance Racing

Central Virginia Machine Service.  Home of the Injun Engine!

All Pontiac Engine Kits

Larry's Auto Machine.  Full serivce auto, marine machine shop, domestic and foreign.

Powered by vBulletin® Version 3.6.8
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
2001 - 2007 PontiacZone.com
Page generated in 0.05627 seconds with 17 queries