Can Stock Rear End handle 550 HP?
- Thread starter 84GNTTOP
- Start date
- Joined
- May 28, 2001
The HP won't be the culprit.. It will/can be the 550tq, the converter mult, and the rear gear mult.....
Add to that, the shock of leaving at elevated power, and the ol stock 8.5 may say "adios"..
In the FWIW dept: I ran a stock hsg, T/A cover, Moser axles, Det locker, 10.5" slicks, at FW over 850..NP.
Add to that, the shock of leaving at elevated power, and the ol stock 8.5 may say "adios"..
In the FWIW dept: I ran a stock hsg, T/A cover, Moser axles, Det locker, 10.5" slicks, at FW over 850..NP.
TurboWh1
Well-Known Member
- Joined
- Aug 12, 2002
Mine put up with it for years. Id say 6-8 years at that HP level. I eventually burnt up the posi unit and when I tore into it found the axles starting to twist. Probably a good thing the posi unit failed 
I would recommend an upgrade in the very near future!
I would recommend an upgrade in the very near future!for the most part yes, if the car is really hooking hard on a track over and over I would go with a set of 28 spline axles and an eaton posi.i went 1.5 60fts on radials years ago alot before i swapped axles and the stockers had a nice wave to them
bigballsbilly
Active Member
- Joined
- Mar 29, 2014
The c clips are also a weak point in the rear. Upgrading to c clip eliminators when you upgrade the axles would be money well spent.
robzombie
Well-Known Member
- Joined
- Oct 10, 2012
for the most part yes, if the car is really hooking hard on a track over and over I would go with a set of 28 spline axles and an eaton posi.i went 1.5 60fts on radials years ago alot before i swapped axles and the stockers had a nice wave to them
That was the axles just letting you know they were leaving. They usually wave at you when they are on the way out.
Just be thankful they are courteous and let you know when they are leaving. If you really tick them off they twist and shout!!
I gotta say they took a real beating
really should have swapped them out earlier with the what I was doing with them but hey I got smartI gotta say they took a real beating
Thanks for the info - I'll be looking into a rebuild in the near future.
- Joined
- May 26, 2001
What we have found with a few thousand track runs with many GN's, the weakest point of the stock rear end is the 28 spline axles. With most street cars in the 11-12 sec range they do hold up really well.
An upgrade to 30 spline axles is good insurance, but the posi must be changed as well. If 33 spline axles are used there is no posi unit for them, and a spool can be used.
With upgrade axles, the rear end then has 2 other weak areas.
The stock trans yoke will twist internally in a 11-12 sec. GN. With any more HP than that, it would be wise to change the yoke and U-joints to a 1310 or 1350 size.
When in the 9's, and lots of track time, all the above upgrades are needed, and the "weak link" becomes the ring and pinion. The only solution for this is to replace the gears periodically.
In my case, I learned the hard way, and after 3 or 4 disasters with teeth-less gears at the track, now the gears are replaced before 300 runs accumulate!
An upgrade to 30 spline axles is good insurance, but the posi must be changed as well. If 33 spline axles are used there is no posi unit for them, and a spool can be used.
With upgrade axles, the rear end then has 2 other weak areas.
The stock trans yoke will twist internally in a 11-12 sec. GN. With any more HP than that, it would be wise to change the yoke and U-joints to a 1310 or 1350 size.
When in the 9's, and lots of track time, all the above upgrades are needed, and the "weak link" becomes the ring and pinion. The only solution for this is to replace the gears periodically.
In my case, I learned the hard way, and after 3 or 4 disasters with teeth-less gears at the track, now the gears are replaced before 300 runs accumulate!
If the backlash is in spec and the gears have a good running pattern the stock ring and pinion will last a long time. I've got about 300 hits on one and it's still together. I don't plan on pushing it with any more hard hits since the next combo will be over 1000hp.
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thats alot of power for the 8.5.I ended up going right to the 9 inch after the 8.5 had enough, no regrets at all.not a single broken part in 5 years.i know guys go fast on the 8.5 but there is a lot of work to be done to it and its no fun breaking the 8.5 and heading to the wall.
It still takes a lot of work to a 9" to be able to withstand 1000+hp hits and 1.2x 60' times.
its not cheap by any means but the 9 inch will be much more reliable/safe.i went big $ on the 9 inch after my friend would run 1.10 60fts for 100's of runs on a heavier 7 sec car,our thought was after building the 8.5 up and if something did break, the cost of the initial 8.5 build then replacing the broken parts was not far off from a built 9 inch.the safety factor obviously is without a price.
20psiofevil
Active Member
- Joined
- Feb 10, 2013
Same boat here! Running the moser 28 spline axles in my rear with a Detroit ratchet locker. My next mod will be upgrade to a 31s axle/spool combo with 3.55 gear in an 8.8". Don't really know if I should do the ford 9" ends and eliminate the c-clips. I mean are the c-clips really that weak with a 31s axle? I've already installed 1350 u joints and a girdle.
that rear combo handled 1.4 60fts at 3800 lbs on my old combo.
its dangerous and expensive to find out that's the problem.
20psiofevil
Active Member
- Joined
- Feb 10, 2013
And that's the damn truth!
bigballsbilly
Active Member
- Joined
- Mar 29, 2014
We'll worth the investment. If you launch and a c clip breaks the damage can be very devestating to the car ... and worse for your health.
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