rear end and diff suggestions - F-Body Road Racing and Autocross Forums

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ReEntryRacer View Member Profile	Sep 16 2010, 05:42 AM Post #2
ReEntryRacer Group: Advanced Members Posts: 618 Joined: 8-December 04 From: British Columbia, Canada Member No.: 569	QUOTE (wastntim @ Sep 13 2010, 09:18 PM) considering going to a 10 bolt and a 3.90. I have been running that combo for two years, with an Auburn Racers Diff. I use a late 4th gen rear, with LS1 4th gen rear brakes, which are adequate. I have only found 3.90s from Motive Gear (made in Italy). All is fine so far!

Sidney View Member Profile	Sep 17 2010, 05:36 PM Post #3
Member Group: Advanced Members Posts: 181 Joined: 13-January 04 From: Bloomington, IL Member No.: 122	QUOTE (ReEntryRacer @ Sep 16 2010, 12:42 AM) QUOTE (wastntim @ Sep 13 2010, 09:18 PM) considering going to a 10 bolt and a 3.90. I have been running that combo for two years, with an Auburn Racers Diff. I use a late 4th gen rear, with LS1 4th gen rear brakes, which are adequate. I have only found 3.90s from Motive Gear (made in Italy). All is fine so far! Rob, You can't run the 4th gen rear in a 3rd gen in CMC. These are about 3 inches wider so be careful when picking one up used if it's already out of a car. Sidney

nape View Member Profile	Sep 22 2010, 01:50 AM Post #4
Veteran Member Group: Advanced Members Posts: 2,511 Joined: 14-November 04 From: Homer Glen, IL Member No.: 540	QUOTE (Sidney @ Sep 17 2010, 12:36 PM) Rob, You can't run the 4th gen rear in a 3rd gen in CMC. These are about 3 inches wider so be careful when picking one up used if it's already out of a car. Sidney It looks like it's allowed by the rules. Sidney is right about the width though, it requires 4th gen wheels. QUOTE 7.29 Rear axles 7.29.1 Any OEM stock differential housing that was originally offered in an eligible model car is allowed. Updating/Backdating of OEM stock differential housings is allowed. 7.29.2 Both GM and Ford cars may also use a Ford 9”, GM 12 bolt, or Dana 44 rear axle housing, but the housing must maintain both the exact OEM suspension pickup points and OEM rear end geometry as the originally equipped axle assembly.

Posts in this topic

wastntim rear end and diff suggestions Sep 14 2010, 04:18 AM

ReEntryRacer QUOTE (wastntim @ Sep 13 2010, 09:18 PM) ... Sep 16 2010, 05:42 AM

Sidney QUOTE (ReEntryRacer @ Sep 16 2010, 12:42 ... Sep 17 2010, 05:36 PM

nape QUOTE (Sidney @ Sep 17 2010, 12:36 PM) Ro... Sep 22 2010, 01:50 AM

trackbird QUOTE 7.29.2 Both GM and Ford cars may also use a ... Sep 22 2010, 03:37 PM

nape 7.29.1 should allow the update/backdate across the... Sep 22 2010, 06:24 PM

CMC #37 I know it is allowed to have 4th gen rears now in ... Sep 22 2010, 06:47 PM

GlennCMC70 It is a legal swap. The question was asked about ... Sep 22 2010, 11:24 PM

StanIROCZ I'd do a 4th gen rear and avoid the wheel spac... Sep 23 2010, 04:21 AM

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wastntim View Member Profile	Sep 14 2010, 04:18 AM Post #1
newbie Group: Members Posts: 24 Joined: 13-September 10 Member No.: 20,845	Hey all, new here. I'm looking for any and all helpful suggestions. Over the weekend, I broke my pinion on my borg warner in my 89 firebird LT1 running CMC2. I had been running a 3.45 gear but was considering going to a 10 bolt and a 3.90. Any suggestions regarding the rear end and differential is appreciated.