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Old 05-25-2018, 03:39 PM   #1  
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Time for new rearend - Questions

My 2001 Trans Am only has 49k miles, but has had a hard life. It was used for autoX and HPDE track days for the first 45k miles of its life. The rear end was hurt at BBORR in 2008. The race for the pinion bearing spun. It has been rebuilt twice in the last 3k miles, and is making terrible noises. I'm not spending another dime on the 10-bolt.

With the history out of the way, I do not plan to autoX or HPDE the car again. I might do BBORR again. I would like to be able to drag race it, with drag radials. I figure the 10-bolt would break on the first hard launch. The car only makes ~420 rwhp, and that probably won't change in the near future. But I plan to own this car when I die, so who knows what is next.

I see that Hawks Thirdgen has an 8.8 option now. Speccing one out, it doesn't seem any cheaper than a 9" or 12-bolt, although I haven't priced them in a long time.

What are the pros & cons of each? Where would be a good place to look for a decent used rear-end that will hold up? Or should I just buy new? I really don't want to spend $3K plus, but am not sure I have a choice other than a junkyard 10-bolt.

Thanks in advance.
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Old 05-27-2018, 08:43 AM   #2  
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Re: Time for new rearend - Questions

The 8.8 and the 12-bolt are very similar in terms of strength and weight. The 9” is stronger and heavier, but with that option comes a MUCH wider array of gear ratio options. There is also a Dana 60 — Strange has a version that bolts up to an F-body called the S60. It’s a little heaver and much stronger. Gear ratio options are similar to the 12-bolt. 8.8” has a slightly better set of ratio options.

Some guys prefer the 12-bolt just because it’s a GM design. The 8.8 and 9” are Ford, and Dana rear ends were used by Mopars. If you like to take sides in that way, maybe that matters to you.

At your power level, all are strong enough. If you think you’d ever go north of 600rwhp, you might want to go to one of the stronger options. Over 800 and you DEFINITELY want to skip the 8.8 and 12-bolt. I don’t know what power level it requires before you need to seriously consider whether a 9” is strong enough, but I suspect it’s at least 1500.

If I remember correctly, the 9” services from the front, and therefore requires you to disconnect the driveshaft in order to service it; the others have rear covers that unbolt like you’re used to. I’m not sure if that’s true of all varieties of 9”.

In all cases, be mindful of how the torque arm attaches. Some aftermarket torque arms use four short bolts that thread into the rear — two top and two bottom. The factory arrangement with two long through bolts is generally viewed as the superior design — especially when it comes to removing those bolts if they are being stubborn. I’ve heard horror stories of MANY hours spent unsticking those top short bolts.

Personally, I’ve become an HPDE addict, and I’m saving up to do this 9”-based IRS swap.

http://www.heidts.com/part/irc-401-k...-firebird-irs/

Last edited by JakeRobb; 05-27-2018 at 11:26 AM.
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Old 05-28-2018, 08:47 PM   #3  
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Re: Time for new rearend - Questions

Thanks. And wow, that IRS is cool, but expensive. You can buy a nice E36 M3 for that much, ans do an LS swap. I love F-bodies, and terrorized the local BMW chapters DE's for years, but there is a point where factory IRS makes sense.

Anyway, after doing a bunch of reading, I'm leaning towards a Moser 9" with a Wavetrac diff, 3.70:1 gears, aluminum center and gundrilled axles; if it will work with stock LS1 rear brakes. If I have to buy Wilwoods or similar, not sure what I'll do.

It seems the 12 bolt has issues with a torque arm and hard launches on slicks. There are too many posts about issues with the S60, and Strange not supporting them, to keep me from buying from them.
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Old 05-28-2018, 11:02 PM   #4  
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Re: Time for new rearend - Questions

I've had my Strange 12-bolt/3.73 for 20 years. At one point, when the car was still an M6, I was doing 5,000+ RPM clutch dumps, through a McLeod Street Twin, on full slicks, well prepped track. Admittedly, did not run it every week, only made a few passes on a weekend once in a while, and not much of anything for the last 5 years. 12-bolt is still intact, although eventually I switched to a TH400 trans and 4.11 gears. Strange customer service was faultless.

The 12-bolt weighs less, although your aluminum case and gun drilled axles will reduce the difference. Power loss through the 12-bolt is 7% vs. 10% for the 9-inch (source - National Dragster article by Evan Smith, Technical Editor).

The Spohn torque arm attached to the 12-bolt has been problem free for at least 15 years. As I recall, the torque arm problem was unique to the Moser 12-bolt, because unlike the Strange, the Moser torque arm attachment used 4 individual bolts, threaded directly into tapped holes in the housing. The bolts tended to come loose. The Strange version uses two meaty through bolts on the torque arm mount, similar to the stock design.

Just wait ‘til you see the massive torque arm contraption on the Moser 9-inch. I'll post a picture in the a.m. when I'm on my PC. That may require some hammering of he tunnel, because the 9-inch carrier housing is not centered on the longitudinal axis of the vehicle, but is offset to one side.

Buddy of mine did pretty much what you are doing (except a spool) in his 1997 30th SS convertible, but he was making 1,350 HP at the flywheel, and running low 8’s at 166 MPH. If that's what you're planning on, a $4,000-5,000 rear axle assembly is the was to go. 12-volt won’t take that kind of abuse.

Last edited by Injuneer; 05-28-2018 at 11:05 PM.
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Old 05-28-2018, 11:07 PM   #5  
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Re: Time for new rearend - Questions

And yes, the 9-inch can be ordered for ABS, ABS+TCS, and for the 98-02 rear brakes.
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Old 05-29-2018, 05:40 AM   #6  
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Re: Time for new rearend - Questions

Thanks Fred. I appreciate the feedback.
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Old 05-29-2018, 12:39 PM   #7  
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Re: Time for new rearend - Questions

Moser 9-inch in a 97 SS:

Rear view shows 2 of three tube/bolts added to the housing, to support the torque arm mount. Front view shows the third tube/bolt, and the massive torque arm mount. One advantage of the 9-inch is a quick ratio change, with an extra carrier. The TA mount complicates things. We did it laying on the ground at the track, and it took two hours.

The third photo was taken before the TA mount was powder coated. The sensor added to the pinion flange is not part of the Moser package. We wanted to log driveshaft speed so we could keep track of transmission slip.
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Old 05-29-2018, 03:20 PM   #8  
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Re: Time for new rearend - Questions

Thanks. After more reading, I'm back to leaning towards the Strange 12-bolt.

The 9" gets expensive quick, and it seems you have to assemble the Moser yourself. Doesn't look like a hard task, but I prefer a bolt in.

1. Will the Strange 12-bolt work with my LG Motorsports torque arm, LCA's and PHB?

2. Require no bending of the floor or tunnel?

3. Work with my ACPT carbon fiber driveshaft (New U joint is fine)?

4. Hold 550-600 rwhp (hypothetically, I doubt this car will ever have a motor making more than that, if that)?
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Old 05-29-2018, 05:38 PM   #9  
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Re: Time for new rearend - Questions

1 - if they all bolted to the stock 10-bolt, they should all bolt to a Strange 12-bolt. As I recall, a tiny radius had to be ground off the sharp corner of either the upper or lower plates on my Spohn torque arm. But I've had at least three different Spohn TA's (he sometimes used my car for prototype installs and test fit-ups). The current one had to accommodate the unique combination of the TH400 trans, Gear Vendors O/D, and a significantly shortened driveshaft.

2 - No alterations of the body at all. With the optional (recommended) LPW aluminum cover, I had to rotate the stock sway bar U-bolt assemblies slightly to move the sway bar back slightly, so it wouldn’t hit the bottom of the cover. Now with the Spohn 1-5/16” solid chrome moly “drag” sway bar, and his u-bolt mount kit, no longer a problem. Also had a couple friends advise me to make sure the stock panhard rod upper brace didn't contact the cover preload bolts when the rear squatted, but it was never a problem on my car.

3 - I will give you one word of advice on the ACPT CF driveshaft..... NO ! I tried one, a 4” heavy duty unit. It was behind my T56. The shop that built and installed my stroker, and the McLeod Street Twin set my car up with a limp-mode tune in the MoTeC M48 Pro ECU, so they could drive the car less than a mile to a nearby body shop to have the SLP Ram Air hood installed. The ACPT driveshaft broke, separating the metal front yoke assembly from the CF tube - bonding failure. Yet this thing was supposed to be capable of standing up to 762 HP/752 lb-ft at the flywheel.

ACPT insisted I ordered the shaft too long, causing the failure when the slider bottomed out in the trans tailshaft housing. They determined that without seeing the shaft. I was able to prove, using the retailer I bought the shaft through as an independent third-party, that the shaft was ordered with the correct length.

ACPT sales refused to assume any responsibility. Claimed they never had a failure. Was like talking to a wall. I did my homework, researched the metal/CF bonding process, bypassed sales and contacted ACPT engineering. I was able to have a one-on-one discussion with their chief engineer - I am a licensed professional (mechanical) engineer - and he was convinced the failure was due to contamination of the metal/CF bond.

I got my ~$750 back for the shaft, but they refused to cover the shipping. From that point, I have only used Mark Williams 3” chrome-moly.

Long-winded.... maybe they have improved since 2000.

4 - The Strange is good for at least 700-750 HP at the flywheel. We measured about 12% losses at the rear wheels, based on comparing the 762 engine dyno HP to the 670 chassis dyno HP. The people who have had issues with the 12-bolt/T56 combo are those who spend every weekend at the track, with a dozen+ passes. If that's what you envision, I'd consider the S60.
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Old 05-29-2018, 06:59 PM   #10  
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Re: Time for new rearend - Questions

Thanks. I bought the ACPT in 2006. It has held up better than a 10-bolt, and been 170mph.

You sold me. I think I'll order a 12-bolt tomorrow. Now to figure out who to give the business to. And which drag tires to buy lol.
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Old 05-29-2018, 10:22 PM   #11  
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Re: Time for new rearend - Questions

The shop I bought my 12-bolt from is no longer in business. Take a look at Spohn Performance for pricing. Honest with good customer service.

https://www.spohn.net/shop/1993-1997...-12-Bolt-Rear/
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Old 05-30-2018, 04:42 PM   #12  
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Re: Time for new rearend - Questions

I bought direct from Strange if you want to bypass a middle man. Customer service is pretty good, but honestly they don't like answering questions for weekend mechanics.
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Old 05-31-2018, 10:03 AM   #13  
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Re: Time for new rearend - Questions

Quote:
Originally Posted by DrewHMS97SS
I bought direct from Strange if you want to bypass a middle man. Customer service is pretty good, but honestly they don't like answering questions for weekend mechanics.
Yeah, I tried calling Strange, and emailed them my "weekend mechanic" questions. No answer to either.

I realize I'm waffling more than Waffle House, but I'm back to the 8.8" Ford from Hawks now. The main reason is for the same price delivered, maybe a little less, I can get an Eaton Wavetrac diff with 33 spline axles, compared to a Yukon clutch posi in the Strange. Plus, Hawks was great on the phone. Not only answered my weekend mechanic questions, but volunteered some things I hadn't considered, like the e-brake bracket install. And the 8.8 appears to be just as strong as a 12-bolt, as long as the axles are the same.

The rear from Spohn is $2887, plus "high $200 to high $300 range for shipping". The Wavetrac diff 8.8 is $2995, plus $200 shipping. So the 12-bolt is either the same price, to $100 more, delivered to my house.
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Old 05-31-2018, 10:12 AM   #14  
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Re: Time for new rearend - Questions

I have had great customer service from Hawks. They took awhile helping me with a steering column issue, but they still got it resolved.

I have no experience with the 8.8, but I thought it was only slightly better than the 10 bolt. If I recall, my 12 bolt was about $2500 shipped, and that was with new caliper brackets (they have an option to send yours to them). My biggest issue with the Strange is their **** poor ABS sensor. It is a hollow bolt with the sensor in the tip and the two lead wires popping out the top. I had my wires break, and had to buy another sensor. If you end up with the Strange with more waffling, make sure you make some sort of strain relief if you keep ABS intact.
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Old 05-31-2018, 10:56 AM   #15  
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Re: Time for new rearend - Questions

The Fox year 8.8's have the same size 28 spline axles as a fourthgen 10-bolt, but the center is basically identical to a 12-bolt. With upgraded axles, in this case the same as a the Strange 12 bolt @ 33 spline, they are equally strong.
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