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Author Topic: mixed and matched GM 7.5 2.29, hunting 8.75" 2.28  (Read 2974 times)

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Offline thirdgear

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mixed and matched GM 7.5 2.29, hunting 8.75" 2.28
« on: November 30, 2016, 03:35:00 PM »
Hey folks,
 I've been here before, I left because of the Bonneville rulebook, but I've been driving an '83 RX-7 I completely rebuilt with no Mazda parts remaining.
The relevant bit being I got the rear axle assembly from a 4WD '94 S-Blazer, took the guts out, got 2 LH 28-spline axle shafts from late-'80s Bronco 2s, got a 2-series 28-spline Auburn from a '95 Z28 automatic, with the standard 2.73:1 ratio, and I got some 2.29:1 7.5" gears off eBay for $60 shipped. I also got a 2.41:1 set just in case.
 I tried this with the 3.8L V6 and T5 from a '96 Camaro, that T5 has a 3.75:1 first and a 0.72:1 fifth.
 Only now I'm turbocharging it, putting the closer-ratio V8 gearset in the T5, and going to some 2.73:1 gears. This car is on 225/45R15 BFG Rival S autocross tires.
 So I no longer need, and am willing to part with, both my 2.29s and my 2.41s.
Now, I'm putting together a turbocharged 454 in my red '86 Camaro hardtop, backed by an SM465 with the rare 1.5" input shaft, I just ordered it a new 12" clutch yesterday. If it slips I know where to find a dual-disc from a '69 L88 'vette.
 Anyway, the big-input SM465 is heavy and poorly geared, but it is unbreakable. And it has no OD.
 I was googling the 8.75" axle, and plenty of references to GM '70s big cars, but no details on exact year/model/engine?
 I don't need that for crawling under, but I do need it for phoning around. I already crawled under every car in every yard around, that lets me pull my own parts.
 I'll be welding the diff, once I get a 30-spline version. At the dragstrip I'll be trying 345/40R17 Toyo Proxes TQs on 11s, and at TRC I'll try Bridgestone Scuderia 345/35(Y)R19s on 12s
 

Offline SPARKY

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Re: mixed and matched GM 7.5 2.29, hunting 8.75" 2.28
« Reply #1 on: November 30, 2016, 05:40:37 PM »
So is this a 12 bolt 8.75 a 10-12 8.75 or a 8.8 you want to play with for the 2.28 gears?

  I have some of the Caddy 10-12s 2.28s
« Last Edit: November 30, 2016, 05:42:35 PM by SPARKY »
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Offline thirdgear

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Re: mixed and matched GM 7.5 2.29, hunting 8.75" 2.28
« Reply #2 on: November 30, 2016, 06:54:33 PM »
the12-bolt used in things like a '69 Camaro 427 are 8.875" ring gear with a1.625" pinion shaft. The truck 12-bolt was 8.875/1.437"
I'm failing to find the 8.75" 10-bolt assembly with the12-bolt ring gear.

Offline SPARKY

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Re: mixed and matched GM 7.5 2.29, hunting 8.75" 2.28
« Reply #3 on: November 30, 2016, 11:52:58 PM »
the 10-12 are most commonly found in Caddys  they have 45 degree splines the chevy 12 bolts have 60 deg splines
Miss LIBERTY,  changing T.K.I.  to noise, dust and RUST!!!

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Offline oj

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Re: mixed and matched GM 7.5 2.29, hunting 8.75" 2.28
« Reply #4 on: December 01, 2016, 12:01:53 PM »
I thought he was asking about how to set up a 'hunting' gear set, one that does not divide the pinion into the gear evenly.

Offline SPARKY

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Re: mixed and matched GM 7.5 2.29, hunting 8.75" 2.28
« Reply #5 on: December 01, 2016, 12:36:03 PM »
The 10-12 sorta evolved into the 8.8 that Ford uses--there is a thread on here about them-- they have a hard to find 2.26 ratio---the caddy 2.28 is not that hard to find---the 12 bolt is virtually impossible to find other than a special run some guys in CA had run and they are PROUD of them..
Miss LIBERTY,  changing T.K.I.  to noise, dust and RUST!!!

The # 1 issue is: TO KEEP THE REPUBLIC      
           tncsg.org     mrspowell.org

ELECTION  INTEGRITY  PROJECT
eip-ca.com  EIPAz.org  eipnv.

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller

Offline SPARKY

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Re: mixed and matched GM 7.5 2.29, hunting 8.75" 2.28
« Reply #6 on: November 12, 2019, 04:51:13 PM »
I just had a 1350 30 spline yoke made for  Ford 1/2 ton PU 8.8 with 3.08 gears by Phoenix Rack and Axel for El Miriage.  It has to have several machining operations but it fits nicely. They adapted a yoke from a GM 9.5.  You can have one made and shipped for around $125-130.  Contact me on list or Steve McKimmons at 602-252-8255
« Last Edit: November 12, 2019, 04:53:42 PM by SPARKY »
Miss LIBERTY,  changing T.K.I.  to noise, dust and RUST!!!

The # 1 issue is: TO KEEP THE REPUBLIC      
           tncsg.org     mrspowell.org

ELECTION  INTEGRITY  PROJECT
eip-ca.com  EIPAz.org  eipnv.

"Security is mostly a superstition. It does not exist in nature, nor do the children of men as a whole experience it. Avoiding danger is no safer in the long run than outright exposure. Life is either a daring adventure or nothing."   Helen Keller