1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

Rear Axle Strength

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Old 11-21-07, 07:58 PM
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Rear Axle Strength

So I'm going to be dropping the S5 TII into the FB soon with the TII tranny but I'm worried about the axle. How much power will it handle before I'll snap it? I searched for about 45 mins but could not get some real answers about it.

Just want to know if the ford rear end is would be a good idea even though its a huge expense.

Can someone give me a decent estimate as to how much the axle can take, and make it archive worthy.

Thanks guys
Old 11-21-07, 09:24 PM
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Its been covered a million times.

Its all about how you apply the power.If you pop the clutch,drift,drive hard and/or run slicks then you can break the stock rearend with the factory 101HP.Its commonly agreed that the 84-85 units are a bit stronger due to their larger axle shafts,but the 3rd member is basically the same.
If you start with a good condition rearend,give it the best oil and regular attention.....then they can take a lot,for a long time, under high HP applications so long as you dont abuse them.
Ive put 300hp through a stock GSL-SE rear axle for 50K miles and almost 7 years and it had 100K when I got it.Daily driven,not abused but I do use full power and keep her on boil regularly....... 245-17" tires out back.
Basic rule of thumb.....if you stick with the stock TII ECU,your power levels shouldnt exceed what the stock rearend can handle.

Here are my components,torn down last year to replace a noisy pinion bearing.....no worn teeth,no twisted splines.


Old 11-21-07, 09:57 PM
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Originally Posted by steve84GS TII
Its been covered a million times.

Its all about how you apply the power.If you pop the clutch,drift,drive hard and/or run slicks then you can break the stock rearend with the factory 101HP.Its commonly agreed that the 84-85 units are a bit stronger due to their larger axle shafts,but the 3rd member is basically the same.
If you start with a good condition rearend,give it the best oil and regular attention.....then they can take a lot,for a long time, under high HP applications so long as you dont abuse them.
Ive put 300hp through a stock GSL-SE rear axle for 50K miles and almost 7 years and it had 100K when I got it.Daily driven,not abused but I do use full power and keep her on boil regularly....... 245-17" tires out back.
Basic rule of thumb.....if you stick with the stock TII ECU,your power levels shouldnt exceed what the stock rearend can handle.

Here are my components,torn down last year to replace a noisy pinion bearing.....no worn teeth,no twisted splines.


***deleted images for thread sake***
I plan on making more than 300 well,.....I hope to make more than 300hp. So is it safe to say that anything over stock S5 TII power, makes the Ford rear end a necessity?
Old 11-21-07, 10:11 PM
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Originally Posted by HIM_Tattoos
I plan on making more than 300 well,.....I hope to make more than 300hp. So is it safe to say that anything over stock S5 TII power, makes the Ford rear end a necessity?
Stock S5 makes 200HP.....stock S5 ECU can handle near 300HP before it runs out of metering ability.Ive proven that the stock rearend can handle 300HP for long durations given the best conditions possible.There are plenty of stories about the stock rearend holding more power than that,but if you dont want to chance it or have to worry,then do the upgrade.

If you want to make more than 300 crank HP,then youll need a standalone ECU and a TO4 family turbo,or better.Once you get into that territory,then money flies out the window anyways,so the cost of the Ford rearend swap shouldnt be an issue.
Old 11-23-07, 01:26 AM
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It all comes down to how you apply the power. I've known people running a lot more than 300rwhp with the standard LSD but if you plan on doing high rpm launches at the track with sticky rubber you're bound to break something. I'm running about 300rwhp with the S3 LSD but I don't abuse it so I should have any issues.
Old 11-23-07, 07:21 AM
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"dont fix it unless its broken"

im BIG on overkill. do it right and go big or go home. i was going to do a 8.8 swap into my car but changed my mind. im certain the 7" can hold up fine if treated properly. iyoure going to be running drag slicks and doing high rpm launches, get the 8.8. if youre not, dont.

i have faith that with the moser axles the rigidity of the stocker is beefed up drasticly. if anything else brakes, theres a solution to those problems as well. cryo the gears, reinforce the housing, stronger LSD, etc etc.

pus, i dont like the fact of loosing so much power in the drivetrain when i dont have to.
Old 11-23-07, 07:38 AM
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http://www.mrcmfg.com/respeed/catalo...246fc5ed6d7adf
Old 11-23-07, 09:58 PM
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these are your ticket... I am at 350 rwhp and climbing (waiting on new injectors) on Bwaits moser axles, while I do not do the 0~400 (1/4 mile for the metrically challenged) I do time attack and road racing, and have not had any problems sofar. knocks ((slams))(head) on wood

once more for effect:

kenn
Old 12-26-07, 12:36 PM
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Originally Posted by HIM_Tattoos
So I'm going to be dropping the S5 TII into the FB soon with the TII tranny but I'm worried about the axle. How much power will it handle before I'll snap it?

Just want to know if the ford rear end is would be a good idea even though its a huge expense.

Thanks guys
the ford 9 is overkill for what your doing..i drag with a toyota 8"..axles are30spline and have not broken one as of this post..and i run a BP 13B with 200 NOS on a plate.
oh and 26x8.5 slicks...

The fella who built it for me gave me both 5.29"s with spool and 5.71"s with spool to use..
I recomend the toyota..oh and it weighs aprox 75-100 less than a mustang8 or ford 9.
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