Rear ends are expensive. Modifying and upgrading anything beyond welding the spider gears adds up quickly. Gear sets, spools, bearings, set up kits, axles, braces, bushings, pinion adapters, axles savers, and pinion brakes…did I miss anything? I have always been one to budget these upgrades spread out over time instead of dropping three grand or more on a purpose-built rear end, and I am always brainstorming ways to save some dough. That is precisely what I did on this project.
I find that the age old rule of fast, reliable, and cheap (pick 2) is true in demo derby as well, but in building a demo car “fast” relates not to how fast the car is, but how fast it can be built. In order to do things quickly, unless you have a setup that needs no alterations to go in another car, that means spending time fabricating, ordering a bunch of prefabbed parts that will still need to be modified anyway, or $$$ paying someone else to build it for you. That means that the two that I try to pick most often is reliable and cheap, and I pay for that with more time spent building parts etc. on the car. Don’t get me wrong though, I’m not a #builtnotbought guy who won’t admit to buying parts. I buy parts all the time, but where I can easily learn the DIY and save some money I sure as shoot am going to try.
The original reason for this build was to put together a rear end that would be an upgrade from the stock c clip rear end in a 76 malibu for a limited weld class. My brothers and I had decided to put a car together for our dad for a once in a lifetime hometown show. A local guy decided to promote a derby as part of his wedding celebration and by golly he did it. Having never had a derby in my hometown before (to my knowledge) or since, we knew it would be special. Since dear old Dad doesn’t have much in the way of his own setup, that meant robbing drivetrain bits and pieces off other pre ran cars or using what was laying around.
For the rear end, my inspiration came from learning that the 28 spline GM 8.5 10 bolt axles are not only the same spline count as 8.8 ford rear ends, but that the splines are the same size so that they fit perfectly in the ford spider gears. I believe this to be true for most axle spline counts, no matter whether Ford, GM, or Dodge, 28 is 28, 30 is 30, etc. Let me know if this doesn’t hold in all cases with a comment, I love to learn.
With this knowledge I was able to put a plan together to build a rear end from pieces laying around the farm. Here was the recipe:
- 10 bolt bolt-in-axle set, leftover from my personal 10/12 bolt hybrid rear end build.
- Bare 12 bolt housing, left over from same build
- Mid 80s drum brake ford 8.8, there was a pile of them
I cut about 3” of the axle tube ends off the 12 bolt housing to get the bolt-in ends. Then I cut the ends off the 8.8 rear and test fit the 10 bolt axles. Sure enough, the splines fit nice and snug. The hard part was trying to figure out the exact length needed from the carrier pin to bearing retainer plate. I did my best to make it the same width as a stock 10 bolt-in-axle housing and equal on both sides, but I’m sure it wasn’t perfect. I didn’t know at the time to bevel the axle tube ends for better weld penetration, but that would be a good idea. I used some 1.5” angle iron and clamps to line up the tubes, and with the axle bolted in place, tacked each end on. At that point I removed the axles, fully welded up the tubes, welded spider gears, and went back and braced the new ends by welding on the very same 1.5” angle iron used to line them up.
The next thing to figure out was the pinion yoke. The ford rear end pinion yoke was a flanged style, but it was too small for the slider shaft /GM flange bolt pattern. Luckily, in the 8.8 pile, I saw that a different disc brake 8.8 had a larger pinion flange. I pulled it off and the bolt pattern worked fine to bolt up to the slider shaft flange, but the pinion gear splines must be different because it would not fit in the newly built 8.8. The workaround though was that the larger pinion flange also had the bolt pattern for the smaller flange on it; so I cut the large flange off of its pinion yoke, then bolted and welded the large flange onto the small flange 8.8 pinion yoke and voila we’re getting somewhere.
So, what I ended up with after all this effort was a ford 8.8 with 10 bolt bolt-in-axles, stock gears, welded spiders, and could bolt up to a slider shaft. My only regret on this project was not fully bracing the rear end, as after the derby (he got 2nd) the passenger tube was bent forward close to the carrier housing. I was hoping to use this rear end as a low-key upgrade in stock class ford shows, so that’s what I get for trying to be sneaky. I will probably build this rear end again when inevitably the need arises in the future.
derbytime.net 