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I'm not for sure but the 1 O housing I took apart had 28 spline axles. The other style 12 bolt uses 30 spline. Everything else seemed ok to run in a 12.50 4 speed car we had. With slicks and a heavy flywheel and non slip clutch back in the day it finally broke an axle.
Have a Olds rear 12bolt cover with 466's and Detroit Locker in my 67 bracket car... broke a few axles, best 12:10's in the quarter. Had Henry's Axles in it and broke one of those, replaced that with a Summer Brother's... Could go better but cant leave too hard thats when things break I found.... Anyway havent ran the car since 1992...
Curious about this as well. Can't 71-72 chebby 8.5" bolt in axles be used with the aftermarket modified 8.8 posi units? This would allow the available Moser replacements. Are the axles the main weak point at the track? There is a girdle cover but that doesn't sound like an issue. I also plan on running slicks and doing a 3.90 posi swap, which is not cheap. Brian Trick mentioned 500+ ft/lbs is no problem with a type O. He also mentioned the 70 oiled axles were better than the 67-69 sealed axle bearings and the 71-72 were the strongest factory.
Can't 71-72 chebby 8.5" bolt in axles be used with the aftermarket modified 8.8 posi units?
The early (67-69) rearends use different axle bearings than the 70 rearend, so you have to match the axle shafts to the rearend housing, not just to the carrier. The side gears in both versions are designed for the spline count and angle of the original O-Types, so assuming you change those to side gears that fit the Chevy shafts, it might work, assuming the axle bearings and seals are compatible. Wouldn't it just be a lot easier to get aftermarket shafts made correctly for the O-Type?
The early (67-69) rearends use different axle bearings than the 70 rearend, so you have to match the axle shafts to the rearend housing, not just to the carrier. The side gears in both versions are designed for the spline count and angle of the original O-Types, so assuming you change those to side gears that fit the Chevy shafts, it might work, assuming the axle bearings and seals are compatible. Wouldn't it just be a lot easier to get aftermarket shafts made correctly for the O-Type?
Yeah, I imagine the cost difference would be minimal. I realize the axles aren't swappable, oiled vs sealed. I was planning on reusing the axles, especially with my current plan 400 ft/lbs of torque 358 build. If I step it up, axles can be swapped when I finish the 374, if they are the pin in the grenade. My understanding is the stock necked down chebby 12 bolt are the weakest factory axle in these years. This rear can't be as bad as the 7.5", broke one twice.
Last edited by olds 307 and 403; June 13th, 2021 at 04:41 PM.
One of my issues was it was a stick car, heavy cars are tough on components on launch. Recently I was informed about slipper clutches, never knew they existed. They allow a bit of slip to ease the launch...
Broke a stock 30 spline in a sbc Chevelle 4 speed. Not an O rearend.Put 30 spline Strange and went about 5 years and pulled out to check and they were twisted 4 splines yet not broke. Could not believe it.
They are pretty durable overall, but they do break on occasion. I know someone who broke a 28 spline '69 O-type axle shaft on polyglas tires (13.3 quarter mile car)... it axle hopped, hit the sticky track, bang.
I was running 12.40-12.50 with my '70 O-type, had aftermarket 28 spline axle shafts from supercars unlimited in it and everything else factory original. Held up to a bunch of huge burnouts and 30ish passes. I just upgraded to a '68 31 spline O-type for durability/reliability.
Parts availability is minimal, so I'm not sure why you'd want to run one unless you have to (e.g., factory correct for the car). The only new gears available are 3.42 and 3.90, and they don't work with the factory hi-po carriers (need to mill them). The 8.5" 10 bolt rears with retained axles are the best bang for the buck out there. I probably should have just switched my H/O to that for racing... Could have any gear selection, aftermarket carrier options, etc. And if it grenades, it doesn't cost you another $2k to replace.
One of my issues was it was a stick car, heavy cars are tough on components on launch. Recently I was informed about slipper clutches, never knew they existed. They allow a bit of slip to ease the launch...
I have 2 hard core stick shift drag racers. There base weight pressure is 400 to 650 and with centrifugal weights it will keep clutch from slipping going down track. The low base weight allows high HP cars with small slicks to leave hard and slip the clutch enough yet not spin the tires beyond recovery. Now you can get a dual disc complete with flywheel to weigh in around 24 lbs. That's a huge rotating weight savings.
My 64 F-85 had a 68 Olds 31 spline axles with 4.33 ran 12 flat at 115 MPH 5 years ago. I traded the 4.33 whole housing for a 3.42 Olds rear the guy came from Canada to trade here in Calif.
Gerald
Mid 12's at #4200 with 3,08's 70 type O but I was using 71-72 8.5 axles and a mini spool in the type O open diff. No issues but it was automatic and also not over a 26" tire diameter helped. Obviously drag racing a 4 speed and or trans brakes can destroy every kind of axle or gear but also I believe a shorter tire is a parts saver as well . Thing of a using a 3/8 rachet vs a 1/2 drive breaker bar and its the same thing on your axle or diff...
Good comparison. What are your thoughts on the 71-72 axles for differences vs the 70 axle? Brian Trick just mentioned they are stronger but obviously the Moser replacement are better and with a spool or aftermarket posi, the 71-72 go right in.
Good comparison. What are your thoughts on the 71-72 axles for differences vs the 70 axle? Brian Trick just mentioned they are stronger but obviously the Moser replacement are better and with a spool or aftermarket posi, the 71-72 go right in.
Well in my case its was for the correct type of 28 spline axle to fit the mini spool. 90 degree 28 splines on a 8.5 or F 8.8 etc and the type O and the old 8.2 P axles 28 spl w 60 degree splines, the swap is simple as the 70 and 71-72 uses same seal bearing type on axle.
Ultimately and something I may do on my 28 spl Type 3.91 in my 70 Rallye would be a new style F diff in 31 spl like Eaten Tru Trac modified for Type O ring gear and some 31 spl Mosier axles with the same 70-72 seals and bearings.
ive twisted both axles in a 28 spline O type slighly lifting the front wheels in a low 12 65 f85 4 speed with 455 and 4.33 gear.29 x9 slick.no problem with 31 spline O type with 3.91s 2
9in slick
This makes my point above on using tall slicks and also on 4 speed drag racing on 28 spl axles.. 29 inch tall Plus with 4 spd launch .wont last long .. I lightly tweaked some 28 spline axles in a 11 second S10 used to run as well and it was on 29 inch slicks with automatic. Run a 26" race tire and with a automatic you can run 12's with longer life.
Last edited by GEARMAN69; July 7th, 2021 at 06:49 AM.
June 13th, 2021, 10:21 AM
