Hey all I have just come across a 1973 Firebird rear axle which I’m considering putting in my 53 Chevy. The guy doesn’t know what the gears are and is unsure of its running condition, but the price is just north of zero so I think I should get it. What I’d like to know though, is whether these diffs are exactly the same as the Camaro diff of the same era? Are all the parts interchangeable? It should be 8.5” 30 spline setup. I’ll probably need to get a new ring and pinion as I’m specifically looking for 3.73 ratio. Hoping not to spend more than $500 on the whole transaction. This sounds like the right diff to buy yes? Sent from my iPhone using The H.A.M.B. mobile app
Firebird, Camaro should be the same but i believe they both would have 28 spline axles not 30 Sent from my iPhone using Tapatalk
I thought they changed from 28 to 30 spline in 1971? Sent from my iPhone using The H.A.M.B. mobile app
I’m reading different things. I have read that GM stopped making the 8.2 10 bolt and 12 bolt diffs in 1971 and went for a compromise - the ‘corporate’ 8.5 diff for just about everything. A lot of what I’m reading says that 8.5’s can be found under 71-81 Camaros and Firebirds but I guess that’s not conclusive Sent from my iPhone using The H.A.M.B. mobile app
Thats rite, and after all the 12 bolts lve rebuilt nuthin has ever been 30 spline....and 10 bolts definately not.... Sent from my SM-G900V using Tapatalk
That 10 bolt is a really strong rear axle, only lacks the "glamour" of the other's names. There's a lot of 8.8 Ford parts that will interchange, seals, some bearings, etc. If you're gonna run it hard do the c-clip eliminator gig. Well worth the time and $$.
I’m only pushing 300hp max. I will get it regardless but obviously hoping it’s a 30 spline. Luck of the draw Sent from my iPhone using The H.A.M.B. mobile app
All 8.5" "corporate" 10 bolts were 28 spline. However, current GM 1/2 to pickup trucks use an evolution of the 8.5 - it's an 8.625" ring gear and 30 spline. The differentials / ring & pinion will interchange, note you do need to use different bearings & races to install the later diff into the early axle housing. Those bearings are readily available. I think for the most part when any aftermarket company sells a 30 spline differential for an 8.5" its really the new design diff with the hybrid bearings anyway...junkyards are full of GM 4x4 trucks that have limited slip diff's and 3.73 or 4.11 gears, might be a good way to get your 8.5 set up inexpensively.
Ahh right that’s interesting. I always equated 28 spline with being an 8.2” diff. But all these 28 spline axels people are talking of at actually 8.5” 10 bolts? This is good news. Nice to know you can still find a good strong GM diff out there for scrapyard prices. That’s what hot rodding is all about. Thanks a lot for that info Jarrett. Really useful. I’ll get to hitting up some wrecking yards. Best to avoid the catalogues where ever possible Sent from my iPhone using The H.A.M.B. mobile app
Jasper....1971 to 1981 Camaro and Firebird rears are 8.5" and the same. If your looking for 3.73 gears might be kind of tough..manual trans equipped Z28s had 3.73s....id say early 1971 to 1974 or so and late, like 1980 1981 because of the smog motors. 3.42 gears might be easier to find...as that was an automatic gear ratio for Zs...and will include some Trans Am 4 speed cars in there too.
Incidentally...the later stuff does swap in...later 90s cars like Roadmaster..and trucks used the 8.5" rear.....the 3.73 gears probably pretty commonly used in trucks. The only drawback is the 30 spline axles.....im sure someone sells 30 spline axles to fit the F body rear...
That Firebird rear is likely a 2.73:1 as that was standard on most all V8 Firebirds that year. TransAm and some Formula Firebirds might have 3.08 or rarely 3.42 to 1. KK
I don’t mind getting a lower 2.73 or some such thing so long as they are all changeable. I know that Holden Salisbury diffs with a 2.73 ratio won’t accept 3.73 ring and pinion, but I haven’t read anywhere that the 8.5 diff has the same problem with gear interchangeability Sent from my iPhone using The H.A.M.B. mobile app
Have you looked into hub to hub distance? I had a later ('78-80?) 70's FireBird disc rear under a TF truck, and it was a bit wider than I'd liked with the wheels I was using, tires kept rubbing on the fender lips. Just something to look into before you spend the dollars to go through it.
Most of those rears cud do up to the 3.90 range then a different carrier was needed.....like a 3 Series vrs 4 Series in a 12-bolt Sent from my SM-G900V using Tapatalk
The car in question runs a 61” diff at the moment. These are 61.5”. There are no troubles with clearance right now so I think I’ll be just fine. Lots of real estate under the ‘53 Sent from my iPhone using The H.A.M.B. mobile app
I only did the chassis, suspension, steering, brakes, and interior sheet metal on this. Tony Parker perfectly executed the chop. His work is Gold.
I saw a similar build in Bakersfield California this year. Chopped,channeled, sectioned. But a tad over the top for me. I like the one you worked on better. Sent from my iPhone using H.A.M.B.
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