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  #1 (permalink)  
Old 01-19-2005, 09:52 PM
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Axles

In the near future I plan to rebuild my 12 bolt in my chevelle and i was wondering how much power/torque the stock axles will handle and how many splines are on the stock axles before i tear it down?

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Old 01-20-2005, 02:41 AM
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not the axles

Its not the axles you have to worry about. Its the C-clips that hold them in. This is the week point.

NHRA general rules 2.11
Any car running 10.99 or quicker cannot use stock C-clips or stock axles.

This would be in the vicinity of 500 hp.
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Old 01-20-2005, 09:46 AM
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Your axleshafts have 30 splines, and either came with the 12-bolt special ordered, or was installed behind a big block (most likely a 396) and those engines were rated at a high of 375 horsepower, the 12-bolt was also installed in Chevelles equipped with the 425 horsepower 427, and the 450 horsepower 454.

That was back in the day of gross horsepower ratings and they were known to be as much as 25 percent low on the advertised ratings.

One source in a search I just did asks whether the 12-bolt axleshafts are retained by c-clips or bolt on bearing retainer plates.

Last edited by M&M CUSTOM; 01-20-2005 at 09:48 AM.
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Old 01-20-2005, 10:45 AM
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Actually it's not the c-clips or the axles you have to be concerned about. it's the spider or differential gears that go first. I spend many many dollars trying to get a twelve bolt to live in a heavy, fast bracket car.. Spiders go first! No matter if they are Moroso "break proof" (lasted 6 passes) or stockers..
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Old 01-20-2005, 06:16 PM
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I am not sure anyone has answered Derkyb's question. However, it is a difficult question to answer. The torque an axle will withstand without breaking could be calculated based on the smallest diameter and the ultimate tensile strength of the material. You would probably find that any axle will take a huge amount of torque before it breaks. A given instance of torque is not what breaks axles. Axles break due to repeated applications of torque which leave the axle permanently deformed and work hardened. Axles, like any other part used in a high performance application, should be inspected regularly and precautions should be taken to anticipate the worst case scenario. One old trick was to run a piece of masking tape down the length of each axle and spray paint the axle with high temp paint. Subsequent inspections would show how much the axle had be permanently twisted. The reason you don't want to use c-clips is due to the fact that if an axle breaks there is nothing to prevent it from sliding out of the rear end housing, dropping the car on the ground on that side. A pressed on bearing may not prevent this from happening, but it is a whole lot more likely to prevent it than a c-clip axle. Moral of the story, buy new axles suited to the application (race axles for the strip / street/strip axles for the street - there is a difference) and use a c-clip eliminator kit (better would be to use housing ends designed for press on bearings).
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Old 01-20-2005, 06:23 PM
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Cheapest and best solution to the problem is put a 9" Ford in it!!
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Old 01-20-2005, 06:56 PM
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9" Ford

The 9" Ford is the only way to fly.
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Old 01-21-2005, 06:48 PM
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Thanks Guys

All of your replies have broadened my knowledge, but the trophy goes to redsdad. That is a great idea about painting the axles, i'm going to try it. Yea I could go wit the ford but I want to try to keep it stock looking yet kick *** at the light. I'm going to leave the axles stock wit eliminator kit until I can afford slicks, figure I'll spin the tires before theres enough torque to break the axles. : ) What do YA THINK?
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Old 01-21-2005, 09:26 PM
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DerkyB,

HERE is a good article concerning where to beef up the 12 bolt to it's fullest potential.

HERE is a good article about 12 bolt vs. 9". The 9" is not at all up to snuff from the get go as everyone seems to think it is. It just has the most potential of the two to handle higher torque.
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Old 01-22-2005, 07:03 AM
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Two excellent articles Wildman. Thanks for supplying the links.
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Old 01-22-2005, 09:08 AM
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Being a moderator here in the Trans/Rearend forum, I do a lot of internet searching for information to answer questions.

And while I have much more experience in axles than transmissions I leave the trans questions to the more experienced members than I, and the axle and driveshaft questions are anything from cakework for me to- only the older members know this stuff.

I knew quite a bit of the information in both of those articles, but ended up learning quite a bit more.

I believe those articles both deserve a place in my axle information sticky post, with credit to wildman926 for bringing them to us.
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Old 01-22-2005, 11:25 AM
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Wildman

Thanks for the articles good information.

Ok one other question. Why do you need to add posi trac additive to the gear lube?
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Old 01-22-2005, 11:52 AM
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You guys are very welcome. I learn so much from this site, when I can contribute, I do if no one beats me to the punch!!

It is used to quiet the chatter of the clutches of the posi rear, as they disengage/engage when going around a turn, etc.
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Old 01-24-2005, 12:21 AM
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Quote:
Originally posted by wildman926
DerkyB,

HERE is a good article concerning where to beef up the 12 bolt to it's fullest potential.

HERE is a good article about 12 bolt vs. 9". The 9" is not at all up to snuff from the get go as everyone seems to think it is. It just has the most potential of the two to handle higher torque.
Wildman, you seem to know quite a bit about final drives. This is my first try at building up a car. I love the car but I want to modernize it so that I can enjoy driving it without going through a full body workout everytime I take it out.

I have a '48 Chevy Aerosedan in which I plan to install a 250 ci inline six backed up by a TH350. I already have the donor vehicle, a '79 Silverado which has a 12 bolt diff. My questions are: Since the torque tube/diff. will have to be replaced and the truck diff. is too wide for the car, what might I do to complete this swap. The car will be a daily driver (pleasure not hot rodding or show) so I need something for economy. The rails are 48 inches wide in the rear.

Al
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Old 01-24-2005, 07:09 AM
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I think the truck rear end was still different than the pass. car version in 79. I know the late 60's/early 70's rear was different. You would probably have to narrow it and that would be a bunch of money to put in a one off rear. I would figure how wide the rear needed to be based on the tires you were going to run. Then head to the salvage yard with a tape measure. For your engine/tranny combo, a Chevy 10 bolt or a Ford 8 inch would work well. Find one the correct width and gear ratio. Since these rears are less sought after than 12 bolts or 9 inch, they may cost you less.

You will want to replace the rear springs. The stockers, which were prone to break anyway, were not designed to absorb the axle wind up. The torque tube did that. Chassis Engineering and Posies make replacements. Of course, based on your comment about the full body workout, you may want to go with air bags and a four bar set-up.
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