First time being at the track with the new motor. I knew the rear end was the weak link in this car.

Went up for the first pass of the day. Did a quick burnout, which I could feel the posi not hooking for the second half of it. Rolled up to stage, all excited might I add to finally see what the car will run. Held the rpm's at 2300 or so. Yellow, Yellow, ohhhhhhh Yellow!!! Drop the clutch and roll into half throttle. Hooks decently, for 10 feet at least when I was when I was greeted by a shoulder shrugging SNAP. "Really..." I thought to myself. I wasn't expecting it to break THAT easily. A spinning driveshaft in 1st gear confirmed it is the rear.

S60...12-bolt...9"...M9... or something else here I come. Just wish they weren't so expensive.

Hypothetically, if I was to run a 1.6 60' with 400whp what would I need for a rear. I'm all set with the 7.5" 10 bolt. There is a good possibility that the car will be much faster in the future so upgrades should be available.

 

I sold Moser 12 bolt rear ends for years and I never had one break. They are lighter than the 9 inch and 60, but the 60 might be a little cheaper.

 

I don't think my car is capable of breaking any of the rears listed above, including a 12 bolt. I think it is all going to come down to what kind of deals I can get. What do you think about buying one used? I have never re-built a rear end but I could easily learn to replace worn components if necessary.

 

I have a used 12 bolt in my SS(500rwhp) and it has held many 5k clutch drops.

I am in the process of putting a 9" in my Iroc. Check my build thread for pictures and information!

 

I went with a Moser 9" Yes they weigh more then a 9" and take more hp to turn but it gives me alot of room to grow aswell.

 

A used rear end can be a good deal, but you have to ask yourself why are they selling it. REplacing worn parts in a rear end can be tricky. If you don't get the pinion depth, bearing preload and backlash right then you will have problems.

Sometimes the Dana 44 rear ends come up for sale. You could use one of them.

 

I exploded a stock Ford 9" case with 4.11's and a stock LS1. I still recommend the 9", but get a nodular case. I also went with a 4.30 gear, and the car launches MUCH better with no bog and is way easier on parts. Literally, the 60' feels effortless compared to the 411. Not sure about the tko's overdrive, but if its anything like the T56 you can run deep gears and cruise all day on the interstate.

 

I will def. follow that thread NufNuff.

I have read that about the M9, I will admit that those things look great. Form following the function of being bullet proof.

Good tip on the nodular case UnstableAviator. I have a very low geared 5th. IIRC it is a .82... with the 3.23 gears it did 135mph in 4th and 65mph at 2100 rpm in 5th.

I would definitely be cautious if I was to look at any used. Obviously I could turn the pinion yoke and see if the axles rotate, but what other indicators are there? I know there should be a certain "backlash" or slop between the pinion and ring gear. How much? That may be a tough question to answer I realize.

 

Inspecting a used rear end can be hard. If you can't take it apart and inspect the parts or at least set up a dial indicator and check the backlash then you really don't know what you are getting. You can cgeck for smearing or excessive wear on the gear teeth, and metal in the oil.

 

My friend has a Moser 12 Bolt in his 95 Z28 with a 385 LT1 and a 6 speed and it has been problematic. He wore out the Eaton posi it came with in about 2k miles. He has now worn out the Truetrack he upgraded to in another 5k miles. He is now putting a spool in it. His car makes 450 whp and 450 wtq. He really regrets not getting the 9in now. He purchased the rear brand new from Moser so it is not a used piece he just picked up either. For the second posi he had a shop that has been in business for 45 years set it up so we know it was done right both times. It has never broke a ring or pinion either if it matters. Also he does run slicks on it a few times a year, but mostly the car is a street car. I will be putting the Strange S60 in my car when I upgrade it over the winter. 6 speeds are just hard on rears if you plan on running sticky tires and launching it hard.

 

Sounds to me like he has been doing something that he shouldn't be doing. This had noting to do with it being a 12 bolt. What ever he has been doing would have caused the same problems if it was a 9 inch, Dana 60 or anything else. The Eaton Posi is a very good differential, and so is the Truetrac. There is no reason that they should have caused any problems unless he was doing something wrong.

 

Do a quick google search and start reading about all the people who have problems with their Moser 12 bolt, this is hardly an unheard of occurance. I am not doubting that either posi is good, but if you are going to use the car and use it hard then a 9" may be better suited for the OP. If you cant do a burnout or run Mickey Thompson ET Streets on a built rear then apparently he is doing something wrong and I know drag racing voids the Moser Warranty. His gears are really noisy and have been since new. This is probably rthe reason for that link. It was broke it exactly how we were told to do it both times. His also has a wierd vibration now that it did not have before the installation of the Moser rear end. He has a PST aluminum driveshaft that has been verified to be balanced by 2 different shops. Moser has never stood behind this product since it was new after numberous calls. Just trying to give the OP some info to help him since his car is also a manual.

 

I'm not trying to defend Moser, all though I sold more than a hundred Moser 12 bolt rear ends and as far as I know none of them ever broke. What I'm trying to say is that the Eaton Posi and Truetrac are not made by Moser and would have done the same thing if the guy had them installed in a stock Chevy 12 bolt, Mark Williams 12 bolt, Strange 12 bolt or a Currie 12 bolt. It wasn't a Moser problem because Moser didn't make the differential.

As far as the 9 inch goes, it wouldn't have made any difference. If this guy had a 9 inch with a Truetrac, Traction Lock or Auburn he would have had the very same problem. He is doing something that is not normal for the use of these differentials. If he is doing a lot of water burnouts then that is what is killing the differentials. They are not made for that kind of abuse and no matter if he has a 12 bolt, 9 inch, Dana 60 or anything else, a clutch type differential is going to fail with that kind of use. A Detroit Locker would have been a much better choice if this car is being used for drag racing and water brunouts are done. If it's a race only car then he needs to use a spool. It's not the fault of the rear end, it's the bad choice of differential.

 

The more opinions I hear the better. I guess I need to think of whether I would rather have a locker or a posi. In the S60 two posi's are offered. the Truetrac and the Strack. I had a S60 quoted and was told this "The Trutrac and Strac are internally identical, the STrac is 8lbs lighter and a little stronger. (no cost difference)" Why would anyone want the Truetrac if that is the case? Unless it doesn't last as long? I really hate an unpretictable lock up of the rear wheels. I also have never ridden or drove in a car with a locker. I do drive the car pretty hard, but would only make it to the track once a month at most. I wouldn't really care about any noises like I've heard the lockers make.

At what point do you choose a locker over a posi?

 

Like the posts above, if you do a lot of drag racing with water burnouts then you need a locker. A clutch type differential just won't hold up to water burnouts. If you are building a car that is mostly for street with a few trips to the track without water burnouts then use a Eaton Posi or other clutch type differential (just not a Auburn). If you are building a car for serious drag racing that will also be used on the street then use a locker. If you can put up with race car behaviour then you can handle the noise and jerks from the locker. If you are building a car for drag racing that will not be used on the street then use a spool. If you are building a car for auto cross or road racing then use a Truetrac, Torsen or one of the other gear type differentials. If you are building something with 1200 HP or more then use a Wavetrack.

 

Good information. What is it about water burnouts that ruins a clutch type diff?

 

I don't have a good explaination for that, I just know that it happens. If you go to a drag strip and watch the street cars do their burnouts you will see a lot of them start spinning both tires, and then after a while one tire will stop spinning. When this happens the clutches start heating up and the oil gets hot. This leads to quick destruction of the clutches. A clutch type differential can be built to handle this, but it also requires regular mainanance, just like changing valve springs and rod bearings.

 

Yea, at this point I am leaning towards a locker just to get rid of wear components. Do you have any idea which is lighter, locker vs clutch type? Isn't there some rule of thumb about X amount of rotating mass= X amount of hp?

 

You have to be getting real serious about racing before that tiny amount of power makes any difference. I built a 9 inch for a guy a few years ago that was ultra light weight. A stock 9 inch chunk weighs about 84 pounds. When I got done with this one it weighed 42 pounds. He was running a little over 200 MPH with this car and trying to get everything he could out of it. He even had the ring gear bolts gun drilled.

 

Wow, he really went all-out. Every little bit helps. An interesting discussion I was reading about hp vs rotating mass and sprung vs unsprung weight...

http://forums.5series.net/e60-parts-...ncrease-71631/

 

Good info here, thanks guys!