diff upgrade?

**2001TransAm** · 09-16-2009, 02:19 AM

I have an 01 Trans Am with 166k on the drivetrain. The diff has alot of slack in it and im sure its about to go if I give it hell. I wanted to know if anyone has or if it is an option to put in a locker. I have checked and found several that will fit, but some say "not intended for high horsepower use" I only have 418 rwhp. I wouldnt think that would be over the limit for a locker. Has anyone done this or think its a good idea? Thanks

**JaycenK** · 09-18-2009, 08:11 PM

For a stock rear I think that is like pulling the pin on a grenade and putting it inside the rear case.

**2001TransAm** · 09-20-2009, 09:35 PM

So what do you suggest?

**JaycenK** · 09-21-2009, 09:00 AM

If you’re putting down 418 and your asking about a locker you better be racing only, and you better be talking about putting that locker in a 12 bolt or a 9inch. A locker is no good for the street. It is also very tough on the axles. The stock 10 bolt is way too weak for that kind of stuff unless you are running stock HP and then what’s the point? If you have as many miles as you say I would take it easy and save up for a 12 bolt or a 9inch That you can get a good carrier (posi) in it and have some fun on the street and the track. If you’re a 6speed car, shoot for the 9inch if you’re going to be on stickies and racing. If your and auto 12 bolt will be enough.
Some will tell you to just rebuild to 10 bolt and others will say don't waist the money on it. I say you make the choice but I would spend a little extra and be good to go for the future if you want to make more power down the road.

**2001TransAm** · 09-21-2009, 01:39 PM

I plan on upgrading the axles when I upgrade the rear end. I guess I will go for the 9". Thanks for the input.

**blackbirdbrain89** · 09-21-2009, 02:54 PM

dude theres a ton of guys that beak the stock rear under stock power... i dont now who the hell u make 418 and have not broke it yet? i broke mine with 342 hp and broke an axle at the track with street tires... put moser axles in and a mac diff cover with arp studs in the rear and broke not one, not two but three diffs b4 i hade the money to get a nine inch... if u going to spen the money on a nine inch u might as well get a m9... i wish i did.. just for aww factor and it comes with and adjustable tq arm

**JaycenK** · 09-22-2009, 03:53 AM

Originally Posted by blackbirdbrain89

dude theres a ton of guys that beak the stock rear under stock power... i dont now who the hell u make 418 and have not broke it yet? i broke mine with 342 hp and broke an axle at the track with street tires... put moser axles in and a mac diff cover with arp studs in the rear and broke not one, not two but three diffs b4 i hade the money to get a nine inch... if u going to spen the money on a nine inch u might as well get a m9... i wish i did.. just for aww factor and it comes with and adjustable tq arm

people make 600 and run them for a while with no problem but it is a crap shoot. around a 90% chance that it will break. even if you upgrade the axles the support cover on a stock 10 bolt seems to do more damage than good. They work great on biger 10's and the 12's and 9's.

**2001TransAm** · 09-22-2009, 04:27 AM

Yeah, I think the diff is about to go. Iv been nice to it the the past few weeks. Just driving grandma style. (which is killing me!) Where can I get an M9?

**INMY01TA** · 09-22-2009, 04:41 PM

Originally Posted by JaycenK

people make 600 and run them for a while with no problem but it is a crap shoot. around a 90% chance that it will break. even if you upgrade the axles the support cover on a stock 10 bolt seems to do more damage than good. They work great on biger 10's and the 12's and 9's.

Anyone making 600hp and using a stock rear is not someone I am going to look to for advice on my car.

**JaycenK** · 09-25-2009, 05:19 AM

Originally Posted by INMY01TA

Anyone making 600hp and using a stock rear is not someone I am going to look to for advice on my car.

Dude it all depends on the use. If your a young gun or even an old cocker looking to tear it up every corner, every straightaway yea your going to break it on stock HP and you would have broken it if a damn 4 banger came in the car.

If your in your 30's or any other age and money is tight, trying to build your car the way you want it, you will find a way not to break it even when you are putting 600 down and don't HAVE the money to go blow 2 to 3 K on a rear.

While I know it is hard to find self controll sometimes, some of us have to use it to continue even driving our cars because broken parts like that are just not an option. I would rather baby my 4 gen than drive a honda,yota or anything else for 6 months to a year till I can afford it.

**Naaman** · 03-25-2010, 06:24 AM

So what is the cost to upgrade to a 9" or a 12-bolt, installed?

Based on what I could find, the 12-bolt is WAY more expensive, but are there extra costs entailed in fitting a Ford rear end onto an F-body?

If my modding goals are 350-400 hp at the wheels, which between the two is the more appropriate?

Also, when talking about the reliability of the 10-bolt, are we talking about just the differntial, or the whole rear-end? Does swapping to a 12-bolt require a new axle as well?

**pajeff02** · 03-25-2010, 07:57 AM

I recently installed a Moser 12 bolt in our car. It was upgraded with 33 spline axles, welded sway bar brackets (in lieu of exhaust clamps), LCA relocation brackets, ABS/TCS compatible, and a True Trac. Total cost was $2,800 shipped.

**rc74racer** · 03-25-2010, 09:21 AM

Originally Posted by JaycenK

Dude it all depends on the use. If your a young gun or even an old cocker looking to tear it up every corner, every straightaway yea your going to break it on stock HP and you would have broken it if a damn 4 banger came in the car.

If your in your 30's or any other age and money is tight, trying to build your car the way you want it, you will find a way not to break it even when you are putting 600 down and don't HAVE the money to go blow 2 to 3 K on a rear.

While I know it is hard to find self controll sometimes, some of us have to use it to continue even driving our cars because broken parts like that are just not an option. I would rather baby my 4 gen than drive a honda,yota or anything else for 6 months to a year till I can afford it.

Any one who throws money at a 600hp motor without updating the drivetrain and suspension to handle it is just plain stupid, it's ass backwards. If you have the money to invest in that kind of HP than you have the money for a rear end. The problem is people just want power first and are totally focused on HP instead of reliability/driveability. Why would you want a high HP car that you can't use the power in?

To OP the entire 10 bolt is a POS, center section, axles, housing, etc...if you get a 12 bolt you need the entire assembly.

**INMY01TA** · 03-25-2010, 02:48 PM

Originally Posted by Naaman

So what is the cost to upgrade to a 9" or a 12-bolt, installed?

Based on what I could find, the 12-bolt is WAY more expensive, but are there extra costs entailed in fitting a Ford rear end onto an F-body?

If my modding goals are 350-400 hp at the wheels, which between the two is the more appropriate?

Also, when talking about the reliability of the 10-bolt, are we talking about just the differntial, or the whole rear-end? Does swapping to a 12-bolt require a new axle as well?

9 inch is maybe slightly cheaper. You're going to be loooking at around $2,500-$2,800 installed. Shipping will be around $200, as will an install. A Moser 9 inch for the F body is a bolt in piece. No modification required. As for your car, I'd say depends on if you have an M6 or A4 and what your goals for the car are. If you have a 6 speed and will be launching it at 6,500+ on slicks, I'd go 9 inch w/Detroit Locker. (I have a 6 speed w/Strange 12 bolt and do launch it this way, so far so good. If I could do over, I'd go Moser 9' tho) For an auto, 12 bolt will do just fine.

**Knight** · 03-25-2010, 03:00 PM

Originally Posted by rc74racer

Any one who throws money at a 600hp motor without updating the drivetrain and suspension to handle it is just plain stupid, it's ass backwards. If you have the money to invest in that kind of HP than you have the money for a rear end. The problem is people just want power first and are totally focused on HP instead of reliability/driveability. Why would you want a high HP car that you can't use the power in?

Guess I'm stupid then... or maybe I never knew the rear end couldn't handle the power until after I built the engine. And I did upgrade the suspension and carrier/axles/bearings/gears in the rear end. I had never dealt with a gm rear end before, and seeing as no one I talked to said anything about the 10 bolt being unable to handle my build, I didn't know it would blow up. Maybe I didn't do enough research and maybe I figured GM wouldn't have been so stupid. My first car (72 Roadrunner) had a stock 8 3/4 rearend and it took everything I threw at it - like about 600 hp worth - never a problem. Glad there's places to find out about this stuff now though. Just because someone does something doesn't mean they're stupid, maybe they just don't know.

**rc74racer** · 03-25-2010, 03:42 PM

Originally Posted by Knight

Guess I'm stupid then... or maybe I never knew the rear end couldn't handle the power until after I built the engine. And I did upgrade the suspension and carrier/axles/bearings/gears in the rear end. I had never dealt with a gm rear end before, and seeing as no one I talked to said anything about the 10 bolt being unable to handle my build, I didn't know it would blow up. Maybe I didn't do enough research and maybe I figured GM wouldn't have been so stupid. My first car (72 Roadrunner) had a stock 8 3/4 rearend and it took everything I threw at it - like about 600 hp worth - never a problem. Glad there's places to find out about this stuff now though. Just because someone does something doesn't mean they're stupid, maybe they just don't know.

Ok you have a point and I was a bit harsh. It just seems to me everyone is so focused on how much HP they can get out of their cars instead of making them driveable and reliable. They fail to do the research and plan properly blow their entire wad on engine upgrades only to find out their suspension and drivetrain can't handle it. It's pretty easy now to research a build with sites like this.

**Knight** · 03-25-2010, 03:50 PM

Originally Posted by rc74racer

Ok you have a point and I was a bit harsh. It just seems to me everyone is so focused on how much HP they can get out of their cars instead of making them driveable and reliable. They fail to do the research and plan properly blow their entire wad on engine upgrades only to find out their suspension and drivetrain can't handle it. It's pretty easy now to research a build with sites like this.

Agreed. I didn't even use the internets when I started building this car. Wish I would have though. Would've saved me a lot of headaches. But I've managed to go a while with 450 hp on my 10 bolt. Just gotta be easy on the launch. Next upgrade is a 9 inch for sure. Live and learn.

**Naaman** · 03-26-2010, 04:27 AM

Originally Posted by INMY01TA

9 inch is maybe slightly cheaper. You're going to be loooking at around $2,500-$2,800 installed. Shipping will be around $200, as will an install. A Moser 9 inch for the F body is a bolt in piece. No modification required. As for your car, I'd say depends on if you have an M6 or A4 and what your goals for the car are. If you have a 6 speed and will be launching it at 6,500+ on slicks, I'd go 9 inch w/Detroit Locker. (I have a 6 speed w/Strange 12 bolt and do launch it this way, so far so good. If I could do over, I'd go Moser 9' tho) For an auto, 12 bolt will do just fine.

Well, let's say that it won't be a track car, but might make an occasional trip to the drag strip. It's a daily driver, M6. I understand that the 12-bolt results in less drive train losses, while the 9" is more stout. At 400 whp, would there be a difference in reliability, or would it just make sense to go with the 12 bolt since it soaks up less power?

**INMY01TA** · 03-26-2010, 02:36 PM

Originally Posted by Naaman

Well, let's say that it won't be a track car, but might make an occasional trip to the drag strip. It's a daily driver, M6. I understand that the 12-bolt results in less drive train losses, while the 9" is more stout. At 400 whp, would there be a difference in reliability, or would it just make sense to go with the 12 bolt since it soaks up less power?

I don't think you'd notice a difference in drivetrain loss of power. Get whichever you prefver.