upgrading to 33 spline 930 chromoly stub shafts

so last year i started drag racing my car. for those not familiar, its a late 85 944 with a chevy 2.2l ecotec thats making right around 500hp to the tires, and its backed with a corvette transaxle. on the 5th pass on this combination i met my goal for the season and that was an 11 second pass, running an 11.97 at 123mph. the very next pass came a drivetrain failure, the very last original porsche part in my drivetrain, the stub shaft, gave up and snapped.



after talking with a couple others i concluded this wouldnt be a one off failure with what im doing with the car, so i started working on a stronger solution. there isnt a stronger bolt in option, nor is there a bolt in stub shaft with a 930 cv joint flange to eliminate my adapter flange (something that could have attributed to the failure).

what i came up with has been 3 months of research, problem solving and machining. the solution to the failure point was found in the sand car market, moving to whats referred to as a "micro stub" axle. they make them in several different configurations, the strongest being a 33 spline shaft, the same spline size used in 1 ton truck front wheel hubs, and it uses a 930 cv joint flange.



the biggest hurdle to the whole thing was the wheel bearings. with the larger diameter of the splines the thickness of a hub where it presses into the bearing would be dangerously small, necessitating a bearing with a larger inner diameter. after exhaustive searching i found no suitable single wheel bearing to fit in our control arm. my solution was to go to a pair of tapered roller bearings, much the same arrangement as an early arm, or our front wheel hubs (just larger).

next thing was the hub. having splines broached is a giant pain and huge expense so i decided it would be best to start with an existing wheel hub. i tracked down that a dodge 1/2 ton truck front wheel bearing used the correct splines and was a large enough outer diameter to accommodate our wheel bolt circle (many hubs exist in this spline but with small bolt patterns and an outer diameter thats too small to drill the 5x130 bolt pattern). after many hours at my lathe nearly every surface on the existing wheel hub had been machined (many of those surfaces being case hardened, making it a long process). the porsche 5x130 bolt pattern was drilled in, you can note the dodge 5x5" bolt circle that is not used.









no pictures, but spacers were machined for the back of the hub to set the wheel bearing preload. preload isnt adjustable, the nut stub shaft nut (the giant 1 3/4" one) gets torqued to 250ft/lb and preload is set at 10 in/lb. the preload was set by trial and error, assembling and disassembling to sand the spacers till i got it correct.

right now ive got one side complete and back on the car. luckily the cv joint flange ended up only 1/32" further out that the stock stub shaft and my 930 adapters, allowing my existing axles to fit with no changes. there is a slight offset change in the hub, its 0.100" further out meaning i had to shim the caliper to make the brakes fit. luckily my rear caliper swap (rx7 fronts) allowed me to shim the calipers to go further out.

before i get asked, no i wont be producing any of it for sale. i did consider it but there is too much stacked against making it viable. it only would work on 85.5-86 cars, and you have to be running a cv axle with 930 joints. right now there is way too much machining time and hand fitting, im sure i could get a machine shop to make a run of parts, however i doubt there are enough people to make it worthwhile. my point of posting this was just to share a unique solution to a problem most wouldnt even think of.

I'm surprised it didn't shear off the 8mm axle bolts first. I've broken several of those, but never the stub axle. You are making some very good upgrades though.

i was running an adapter on the stock stub shafts to allow me to run a 930cv joint. they use a shorter 8mm grade 12.9 cap screw, and the 930 joint bolts to that with 10mm bolts. this whole setup i always saw as another failure point. funny enough, a few days prior to twisting off the stub shaft i broke all 6 bolts of the 8mm bolts in the adapter on the opposite side. i believe these bolts had worked their way loose causing the failure.

They do work loose. I got to the point of checking them every time we came off the track. We were doing road course with ours. Even loctite wouldn't keep them from getting loose.

Hotrodz of Dallas wrote:They do work loose. I got to the point of checking them every time we came off the track. We were doing road course with ours. Even loctite wouldn't keep them from getting loose.

over the years ive read a lot about cv axle bolts coming loose on these cars. i periodically checked the bolts when i was running a stock/stock style axle and i never had them be more than a slight bit loose. with my 930 axles i ran a set of arp bolts and they were torqued to 51ft/lb, never had any issues there. really i should have checked my adapter bolts more, but it requires pulling the axle out to get to them.

i have started using a new (at least to me) loctite product on the problematic bolts. its orange, its designed for bolts smaller than 1/2". its stronger than blue, really closer to the strength of red, but you can remove bolts without heat. i used this on the adapters after the failure and while i didnt get that much mileage on it those bolts for sure wernt coming loose.

I had used these to lock my CV bolts.  AWESOME.  Never had a problem.

https://www.lindseyracing.com/LR/Porsche/LA-CVLB-085024.html