Rear End Questions

Killa02 · Feb 20, 2009

Hello,
I've got an 03 Mach 1 and want to get into the 12s this year. I've run a best of 13.3 stock and with heavier 18" wheels. Since then I've added a BBK offroad x pipe and some Nitto DRs that I'll mount on my stock 17s. I'm thinking about gears and if I do it'll definately be 4:30s but here's my question:
If I run 4:30s with DRs, do you think I'll be ok with my stock axles? How do feel about just upgrading to Moser 28 spline axles or is this a waste and if I'd be better off changing the carrier to a 31 spline?
Obviously the 31 spline set up would be the strongest, but I'm not to excited about dumping $1200 into this rear. I've got a few other projects and would like to get out of this as cheaply as possible. Thanks-Jim

squeak93 · Feb 20, 2009

Stock axles will be ok. No need to upgrade YET.

Flghtmstr1 · Feb 20, 2009

Here's something I've always wondered: if I break my rear end at the track, can I upgrade to the 31 spline stuff without having to pay someone to basically re-install my gears? Asked another way, are the 31 spline carrier and axles drop-in items, or does such an install require the same expertise as a gear install?

I'm sure I'm capable of doing gears myself if it comes to that, but I'd rather have someone else do it so I can go back to them if it whines

Stan Weiss · Feb 20, 2009

Flghtmstr1 said:
Here's something I've always wondered: if I break my rear end at the track, can I upgrade to the 31 spline stuff without having to pay someone to basically re-install my gears? Asked another way, are the 31 spline carrier and axles drop-in items, or does such an install require the same expertise as a gear install?

I'm sure I'm capable of doing gears myself if it comes to that, but I'd rather have someone else do it so I can go back to them if it whines

YES such an install require the same expertise as a gear install. The pinion depth should not change. But the backlash and gear position need to be the same as before after changing the carrier.

Flghtmstr1 · Feb 20, 2009

Stan Weiss said:
YES such an install require the same expertise as a gear install. The pinion depth should not change. But the backlash and gear position need to be the same as before after changing the carrier.

Thanks for the info! I figured that was the case, but I thought there might be a way to "cheat". Hopefully, I won't find out for a long time.

snowb07 · Feb 20, 2009

If you look to Cheat then you will be cheating nothing else but yourself. Modding a car is expensive, butis more expensive when things are not done correctly the first time.

02nightmaregt · Feb 20, 2009

I did the 31 spline upgrade when my rearend bearings were going out and it was only 400 bucks. YOU should be good on your axles, but if you plan on going to the track and doing hard launches alot then why not upgrade it so it doesnt explode at the track

Shiroelex · Feb 20, 2009

Depending on the size of your drag radials, you shouldn't have to worry about your axles. I'm guessing you would be using a 245 to 275 wide DR on the stock rims, and those won't shock the axles as hard as a street radial or slick. I did a few launches on stock 28 spline axles with 315/35/17 drag radials, and they held up pretty good. For peace of mind, some aftermarket 28 spline axles would definitely cover the weak spot in the rear. If you plan on getting the gears done however, I would just save up and get a 31 spline carrier and axles to go in at the same time. My gear/locker/axle/girdle install costed me $350. With 31 spline in the rear, you don't have to worry about the axles anymore. You would have to worry more about ripping your battle boxes and spinning an axle tube at that point. It's a neverending cycle!

parrish5o · Feb 20, 2009

Until you get into the low 12s I wouldn't worry about the axles.

Flghtmstr1 · Feb 21, 2009

I'll be in the low 12s as soon as the track opens

Killa02 · Feb 21, 2009

Thanks guys for all the responses.
I guess the only thing to do is to bite the bullet and get it done right. If I'm willing to spend the money on 28 spline axles, I should just spend that money on 31 spline instead and get the new carrier. -Jim

02nightmaregt · Feb 21, 2009

Killa02 said:
Thanks guys for all the responses.
I guess the only thing to do is to bite the bullet and get it done right. If I'm willing to spend the money on 28 spline axles, I should just spend that money on 31 spline instead and get the new carrier. -Jim

Smokeurhonda · Feb 22, 2009

Man, it's hit or miss on your axles, especially with 4.30's. If your going to get the gears installed anyway why not just upgrade to 31 spline stuff all at the same time. FRPP 31spline diff with Carbon discs is 250 bucks, you can get moser axles for another 250. So an extra 500 bucks now will save you on the install time later down the road.

Mike97gt · Feb 22, 2009

it depends on how hard this car will hook.. On slicks I would say YEAH 31 spline now and weld the axle tubes.

You might get away with your 28 spline and unwelded tubes but in the long run you would be better served with a 31 spline unit

Killa02 · Feb 22, 2009

svttech77,
The best 60' time I could get with street tires was a 2.1. I've heard that Niito DRs are only good for a 1.8 -1.7 at best. I haven't tried them yet so I'm clueless, but that's what I've read from some of the other forums. Does that sound right to you?

My goal is to break into the 12s this year. I figured a gear swap would be the easiest way but it does seem pointless to do a ring and pinion and not upgrade the carrier and axles. I ran a 13.3 stock, so I think I might try getting there with the stock 3:55s and go the bolt-on route for now. Maybe wishful thinking but I've got an off road x and some Nitto DRs, maybe a tune and I'll be there?-Jim

Smokeurhonda · Feb 23, 2009

Dude, with gears and nittos you can def hit the 12's in your car.

Blackone51 · Feb 23, 2009

Just search ebay for low mile 03 cobra 31 spline diff and axles. The 03 cobras are always upgrading to an auburn set-up or compariable. I got my stuff used with only 9,000 miles for 200 bucks. I decided to upgrade while I'm in there changing to the 4.10 gears.

twogts4us · Feb 24, 2009

svttech76 said:
it depends on how hard this car will hook.. On slicks I would say YEAH 31 spline now and weld the axle tubes.

You might get away with your 28 spline and unwelded tubes but in the long run you would be better served with a 31 spline unit

I agree - it's all about the tires. On slicks, you'd definately NEED upgraded axles. Otherwise, they are certainly a nice to have and not overkill at all. It's a crap shoot, a catch 22. If you are able to get it to hook up well, you might break something. If you can't hook, you won't get the ET you want, but you'll likely be able to drive your car home.

Rear End Questions

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To hell with your Mustang, I want to see your HOG!

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To hell with your Mustang, I want to see your HOG!

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it doe snot

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