Need an opinion please----> Rear Axle

drilzzz

New Member
Mar 22, 2010
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Hey everybody! I know I know I haven't been on here for a while but school and work have consumed my life but I'm back to make some upgrades on the Stang. And as always thank you for taking a look at this thread.

I have a 1997 Mustang GT basically stock all around. I was told by a mechanic that I need new rear axle shafts and bearings. Also, they told me that the work would include some exploratory surgery (not what you want to hear from a mechanic lol) in order to see what else needs to be replaced while the job is being done. I was quoted $800 for this job.I have had the car for 6 years without doing any rear end work/replacement except for fluid change. I have also found a complete rear differential on Craigslist for $1200. The assembly is stamped M4006-B373. The seller had it built at Steeda and has receipts to prove it. The assembly is 8.8 with 3:73 gear ratio purchased new from Ford Parts and upgraded at Steeda with Auburn locking differential 28 spline and Yukon axles. When I looked at the set up I shook the end of the axle shafts to see how much play there was. There was a little play when moving the shafts. Is it acceptable to have a bit of play or are the axle shaft not suppose to move at all? Also, does this deal sounds like a winner or would it be wiser to have my rear diff built?:shrug: Purchasing and installing the assembly would run me about $1500. Any advice would be extremely helpful.
 
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Question, do you need an upgraded rear end or is the stock one strong enough?

Remember that a re-built rear end is as good as a new one (assumng the person doing the rebuild sets the gears up correctly).

Here's my point. Buying a used rear end is a risk. Esp one that might have lived a hard life. So if you were to purchase the used unit and then have it rebuilt, would you still consider it a value?

So my vote is if you do not need the upgrade, have your old unit re-built.

OBTW, the fact the half shaft moves up/down is not necessarily a problem. To truely find out, pull the half shafts and inspect.
 
Thanks guys for taking a moment and looking at my long add.

Burns- I don't really need an upgrade. I just thought that while I'm spending the money I might as well spend a bit more and get something that would be higher in performance. But from the posts I'm seeing that this would not be a good deal and that the set up is not that great. I am afraid that my rear diff is totally shot and that I would have to rebuild the entire thing and that the cost will exceed $1200. The guy selling the rear diff says he only put 7,00 miles on it.

So as a confirmation, you guys would rather rebuild the rear diff on the car and not deal with the used set up?
 
31 Spline Axles=$220
3.73 gears=$150
31 spline differential=259
Bearing kit=$80
Fluid=$30

You have a grand total of $739 plus shipping.

If you brought all these parts to a shop and asked them to install them, you could come out less than $1,200 and have a built 31 spline rear instead of a 28.
 
yea but your an almost stock stanger, do you really need 31 spline axles? ive seen 550hp go through the sock 28 spline axles without breaking. further more $800 is kinda steep to put axles and bearings in. theres a thread in talk rite now you may find interesting. you can find even stronger 28 spline axles for around $100, the trac-lock is fine up too around 350-400hp if your a weekend warrior. so my point is if your not having gears installed, your spending $400-$500 in labor that can take someone with some shade tree mechanican a few hours to do it on a saturday. a good mechanic, it shouldnt take him/her an hour-hour and half just to replace axles, bearings, and seals. unless it the dealer, then youll pay out butt for it. labor rates here in denver nc run around $75-$100/hour. but thats just me though.
 
If you have the money, you might as well upgrade while you have it apart. Even if your car is stock right now, I'm sure you plan on doing some more performance stuff to it in the future. When you do that, you wont have to worry about breaking a rear end.

Some people might have saw a 550hp car run on 28 spline axles, but I have a seen a bone stock 4.6 break 28 spline axles also.

I am just one of those people who plan ahead. If my transmission broke on me and I had to pull it out, it's going to get a 26 spline input shaft, and carbon syncro's, and probaboly a spec stage 3 clutch. I just see no point in spending money on parts/labor right now, when one day you might want to upgrade to 31 spline parts. At that point you have to spend that money again on parts/labor.

Just My Opinion....
 
My take. This is where an honest assessments of your goals, priorities, resources (both in money/time/abilities) should be done.

Priorities: there is a major difference between budget and then HP verses HP over budget.

It also makes a big difference if you are doing the work yourself. Because if the labor is free, more money can be spent on parts before blowing the budget.

A stock rear-end can be rebuilt with all new seals and bearings for $650-750. For that you get for all intensive purposes a zero mile rear end complete turn key.

If doing the work yourself, the rebuild kit is less than $150. Note, rear end rebuild can be a difficult job. Not recommended for the beginner. Do your homework before starting!

If the stock rear end will not fit your future plans, and money is not an issue, then upgrades should be considered.

This is where the order of the priorities matters. What is the correct decision for one person may not be the best decision for another.

Good luck.
 
Wow great information everybody. I am without a doubt way under educated when it comes to my Mustang.

How many spline are in the car right now (all stock rear end)?

My priority is to get the car back on the road but at the same time upgrade to something a bit stronger while I'm already spending the money.
 
00gt here in NC is running the the new trickflow topend kit, 324hp plus a 150 shot on a nice tune. (the bottom end is built as well) aprroxamitly 500-525hp. we're running 28spline moser axles, stock style trac-lock with cobra clutchs, and mickey tompson ET streets, no borken anything yet and been that way for a while. it is a DD and sees a lot of track time. yea if your gonna build the mess out of the car then, by all meens hit it up with the good stuff, but note anything under 550hp the moser axles are fine as i mentioned earlier. but its how you spend your money and how wild youll get with the upgrades to the engine etc.
 
I bet that 500hp car is an auto.

why no its not, its a built t56 6spd. so ninja your saying my car with 250hp will break an axle? no it wont i dont have enough HP or TQ to do it. so there for your statement is WRONG. ive launched mine with the same ET slicks that are on the 00gt of my buddies rickys car now and @2800rpm and left like a scalded dog. so you have to have enough HP and TQ to snap axles. his input shaft in his tranny will snap first or his clutch will explode first. if he has a grippy enough clutch the input shaft will go before the axles. and thats from experiance.
 
Just a few thoughts:

First, the engine's peak torque output at launch isn't nearly as important as the energy stored in the flywheel. That's what you're really leveraging with those stratospheric launch RPMs, not how much torque the engine is actually making. In fact, the engine is probably making less torque at 6000 than it is at, say, 4000 (well, street engines, anyway...) Don't underestimate the energy stored in a 30-pound piece of steel spinning at 6000RPM. If you've ever tried to stop even a bicycle wheel spinning at a decent clip -- 20, 30 RPM? -- with your hand you might still have trouble scaling up to that steel disc at thousands of RPM.

And even though the input shaft to the trans can be hurt by this, especially if a solid-hub clutch disc is employed, it's really the axles and spider/side gears in the differential that are really at risk and it's largely to do with the torque multiplication through the trans and final drive.

A TR3650 (for example) with a 3.38:1 first gear multiplies the input shaft torque 3.38 times. If there's a set of 3.73 gears in the back then it multiplies that torque an additional 3.73 times. In other words, the axles and side gears will see 12.6x the torque presented to the input shaft of the transmission. At the engine's torque peak (say, 300 ft-lbs), that's 3782.2 ft-lbs of torque at the axles. This the reason things get heavier and heavier-duty as you move back through the drivetrain: the input shaft to the trans is comparatively tiny compared to the beefy pinion and axle shafts and it's because of torque multiplication and the forces involved at each stage. In differentials like the Traction Lok, think about the spider and side gears: they are what's transferring all this torque to the axles and they're doing it with just a few teeth's worth of engagement. It's amazing the beating that hardware withstands...

And when you side-step the clutch at 6K and add in the energy contained in the flywheel in addition to the torque the engine is making, it wouldn't surprise me to see instantaneous torques many, many times this value. Add in sticky tires and a prepped track and it's no wonder **** breaks when you don't have rear-end hardware up to the task.