costas

iTrader: (1)

Hi to all ! will the 84-85 GLS-Se differential hold around 300 whp? it will never have slicks just street tires ,if it does break what will go first ? the axles ,gears or LSD? the reason I am asking is I am planning an N/A 20B swap and I want to keep the factory diff
one of the reasons beeing it's lighter weight compared to a ford 8.8",8" and 9" (less unsprung weight)
Thanks

stuchizik

iTrader: (2)

From what i've read here - no direct experience with the 20b - you should be fine with almost double that horsepower level unless you have slicks and like hard launches. Check out the drag times thread. There are people doing sub 10 sec. 1/4 miles on stock rear. This requires lots of power, a good hard launch and the traction to handle the power. Make sure to use a TII trans. If it was me i'd save my money and use it for the ecu to run the 20b.

mjm4jc

Yeah, there seems to be plenty of people using the stock rear with 300 + hp. As far as I know the diffy is not the issue, but the trans. One friend of mine has a little over 300 hp in his SE and has to get the trans rebuilt every now and then. The diffy has held up well however.

costas

iTrader: (1)

Thank you for the responce that's what I thought as well plus I will be using Moser axles because i have them.

thunkrd

iTrader: (1)

i think it depends more on maintenance with those higher hp outputs. if you look at lwnslw's thread, he destroyed his rear end with 440 hp

bad 83

iTrader: (3)

Alot of it depends on how you drive it. I have put 400hp through my rear without it breaking. One of my buds can't get his to take 250hp. He loves spinning tires and hard launches. He has broken the ring and pinion, axles, axle bearings, etc. It's really going to depend on your right foot

Hyper4mance2k

iTrader: (40)

it also depends on the type of driving you do and the clutch you run. I've distroied 2 rear ends and 2 transmissions now. The last diff the lsd took a **** then the pinnion bearing failed. I'm only making 190whp NA. I'm actually stuck tearing down my rearend today because i think the torsen I installed 2 weeks ago is already dead...

thunkrd

iTrader: (1)

hope it isn't dead, waiting to find out.

i need to replace my stock SE diff

jeepinoffroad04

i dont know if mine is stock or not honestly, i haven't opened it up, but i dont think my car should have had LSD in it... but if i take off and spin i have 2 black trails... but i've got a 5.0 litterally in my car and hooking it up this week, so i may weld my spiders and try it out.... if all else fails... oh well.. swap time... but i'm hoping 300hp will not kill it

elwood

iTrader: (1)

Man, I've asked this same basic question before, and the real answer is that it depends . . .

As you can see from the other replies, there are a lot a variables:
- How well you hook up at launch
- How rigid your driveline is, including your clutch
- Mass of your flywheel
- RPM you launch at
- How sticky your tires are
- How sticky the surface is
- How often you launch the car hard
- Weight of the car

Then comes the question of the condition of the rear end before you start beating on it. Are any of the parts already overstressed and work-hardened? Do some of them already have cracks?

You get the idea.

In general, from what I've seen with the average driver, under average conditions (whatever those are for a gearhead), the rear should last for a while (whatever that means).

I'm running 350RWHP and I've probably put 10K miles on a GSL-SE rearend that had 210K miles on it before I began beating on it. Might break tomorrow, who knows?

Not going to write you a novel, but I want to share some general "rules of thumb" for power ratings:

1. Powertrain components are usually only rated to the power level that the OEM requested. For example: Mazda needs a rear end that will handle X torque and Y HP. The rear axle engineers design a unit to meet the specs, then begin durability testing. They run it through dyno and on-road testing while monitoring temps -- this validates the HP rating. They run it through "drag cycles" where they take the car to a strip with street tires and launch it -- over and over again until they reach the number of cycles that Mazda deems the lifetime of the vehicle. This establishes the torque rating of the rear end. The rub is that nobody really knows how much extra torque or HP the unit can handle. Once it passes, they pat themselves on the back and move on to the next project. That rear end can handle maybe twice the torque for a full lifetime, maybe three times -- chances are nobody really knows.

2. If you do happen to have a component that is rated to its full potential -- i.e. a rearend that's rated to 312 lb-ft of torque because somebody paid for the extra testing to find that out -- the life expectancy is cut in half for every 10% you exceed the rating. If we take the hypothetical example above, suppose you try to put 468 lb-ft through the rear end (50%) above the rating. Also suppose the "lifetime" was 100K miles. If you manage not to break it catastrophically, that 100K will be cut in half 5 times, for an expected life of 3K miles.

Good luck.

Portland82GSL

iTrader: (2)

Don't mean to thread jack, but what about a stock 12A GSL rear end?

3rd and final 7

iTrader: (9)

300 whp is ok on GSL rear end , Steve has been doing it for a few years now

rotorholic

iTrader: (53)

It will hold 500hp as long as it dont hook up or bite the floor, At 300hp the car should spin the tires. I had a gsl-se with a stock turbo making 300+hp and it never broke anything out back, After I bolted on street slicks I started breaking 3rd gear in the tranny when it come on boost. I had friends break the carriers, drivers side axles launching at the track with stock engines and full slicks.

sen2two

iTrader: (10)

you can always cryo the gears and upgrade to stronger axles. that will allow the SE rear end to take a beating for a little longer...

speedturn

iTrader: (1)

I have been running that much power for years on my 13B PP road racer. I have not broken a diff yet, but then again I am not drag racing. I have twisted and broken rear axles, but have not had a diff failure yet.

notveryhappyjack

iTrader: (4)

I sheared the teeth off my ring and pinion, it was a se diff and I did a 20mph stomp on the gas in 2nd manuver.

Make sure to warm the drivetrain up for about ten miles before you think about launching it, thats what I did wrong

Hyper4mance2k

iTrader: (40)

true true. I run a 7lb flywheel adn a 6 puc race clutch and disc, so my rear end takes quate a jarring all the time.

B6T

iTrader: (2)

My GSL-SE makes, at the most, 180hp from a street ported 13B and my diff just went.

I'm running Falken Azenis ST615s, an ACT street clutch, a 7lb flywheel, and worn OEM engine mounts. After doing a short burn-out at the track, I launched from about 5000rpm. The car spun hard off the line and then hooked hard at about the 60' mark. After looking into it, the limited slip wasn't locking up, allowing only the passenger side tire to spin. The car hooking at the 60' mark was actually the diff itself jamming up.

The spider gears inside the differential have seemingly locked up. The car now drives like it has a spool, or a welded diff.

WTB: GSL-SE differential

sen2two

iTrader: (10)

one thing to think about. remember these rears have been taking a beaten for 20+ years. and im sure a lot of times with crap fluid that hasnt been chagned to often.

they are worn. cryo treat them and a rebuild wouldnt hurt if you plan on using them for racing.

B6T

iTrader: (2)

It really bugs me how 'cryo' treat it has become the internet-wide automatic response to any gear strength related problem.

The company I work for makes gears for the aerospace and I've never heard anything about cryo treating there. Never heard about it in any of my engineering courses either.

I have a feeling that some guy a while back had a tank of liquid nitrogen he had to get rid of.

forrest[fb]

i figured i would ask since this is a 1gen post,, whats the best motor oil to use for a 12a?

sen2two

iTrader: (10)

its not an "internet" sensation. in certaian regulations to race, all parts must be in stock form. so (especially in road racing) racers cryo treat all rear end gears and tranny gears. it is NOT good for everything though. if you cryo treat a crank shaft if becomes to stiff and can make it brittle and break because it has no flex...

but for giving gears/syncros some added strength and longevity. cryo treating is highly reccomended among race teams.

B6T

iTrader: (2)

I just don't know much about it, and this is partially because I've never *had* to know anything about it.

I suppose its a good idea when your limited by race regulations.

tasty danish

iTrader: (5)

not actually. The jury is still out on cryo treating. It makes no difference in hardness/brittleness. proponents claim it make the atomic distribution more even but no one's quite sure. There are no changes that can easily be tested.

If it does make a difference it's marginal.

I recommend you look into WPC coating (fancy shot peening), nitriding, and case hardening. Those ARE validated.

As for the weak point of the axle... it's the gears. Diffs are pretty tough, -se axles are strong and moser replacements are bullet proof. It's the gears that are the biatch.

B6T

iTrader: (2)

^ Ring and Pinion gears, or the spider gears? I'm certain I've destroyed the spiders in my diff. Then again, launching from 5500rpm on one wheel probably wasn't good for them.