Locked rear end on dedicated Autocrosser? - PeachParts Mercedes-Benz Forum

t walgamuth · #1 07-06-2007, 01:36 PM

Anbody have experience with a locked rear on a race only car? I would love a torsen or a quaiffe but don't want to spend the $ on such an expensive device for a seldom used autocross only car.

I can get it welded probably for not too much money but I am wondering if it will work well for my purposes?

Tom W

Hatterasguy · #2 07-06-2007, 01:56 PM

I don't know how advisable it is, but I have seen people weld them.

OMEGAMAN · #3 07-06-2007, 03:06 PM

The torsen still provides unequal speeds in a corner with out wheel spin. If you weld it up they are gonna both spin at the same speed all the time. I think that would make the rear of the car want to come around on you wouldnt it?

Chas H · #4 07-06-2007, 03:22 PM

I've tried welded rears and was not impressed. The tight corners you'll have in auto-X are gonna make for a lot of scrubbing and loss of speed.
I would go with stiffer springs and larger sway bars and leave the rear as is until or unless you start to get excessive wheel spin.

mzsmbs · #5 07-06-2007, 03:48 PM

yeah, welding it is kind of the redneck way to go.

t walgamuth · #6 07-06-2007, 04:27 PM

Quote:

Originally Posted by Chas H

I've tried welded rears and was not impressed. The tight corners you'll have in auto-X are gonna make for a lot of scrubbing and loss of speed.
I would go with stiffer springs and larger sway bars and leave the rear as is until or unless you start to get excessive wheel spin.

I have excessive wheel spin unless I feather the throttle a lot. I have short springs already. I have not found a source for a larger antisway bar. The car feels pretty flat in the corners. I could exit them a lot faster if I didn't have to feather the throttle so much.

Tom W

t walgamuth · #7 07-06-2007, 04:28 PM

Quote:

Originally Posted by mzsmbs

yeah, welding it is kind of the redneck way to go.

Well until I have an extra $2,000 around to fit a torsen I won't mind if you think I am kindof redneck!

Some of my best friends and closest relatives are rednecks!

Tom W

Chas H · #8 07-06-2007, 05:40 PM

How much would another rear cost if the redneck modification doesn't work?

t walgamuth · #9 07-06-2007, 06:03 PM

I have several to choose from. A 369 like what is in there, a 346 and perhaps others but at least the two.

Tom W

Chas H · #10 07-06-2007, 06:12 PM

It could be worth a try.
Sometimes excessive wheel spin can be caused by a too short shock absorber pulling on the inner wheel. Just something you can check on cost free.
Have you looked to some European tuners for sway bars?

Old300D · #11 07-06-2007, 06:18 PM

Welding works for drag racing. Anything involving turns requires a differential, limited slip or or otherwise.

t walgamuth · #12 07-07-2007, 08:07 PM

Just got back from the autocross. Wow! I was really close to some pretty fast cars. I am pretty sure all of the cars that beat me had limited slip.

FTD was by a '70 911 porsche with very wide wheels and a late model 3.6 motor equipped with carburators. He ran a 33.4 or so. My best time was a 37.476 iirc.

My car was lumped in with a whole passle of lightly modified classes who had no opposition in their class. They used a pax time to determine trophies. I finished fourth in that group with a pax time of 30.5 or so. Sixteenth overall by pax time, probably about the same on raw time. There were 43 competitors all together.

The guy with the above mentioned porsche won on pax too.

He was running hoosiers too. That car just acceleratied like crazy out of the turns and didn't slip or slide at all.

The extra negative camber from my racing alignment helped I think. I was able to run less air in the fronts and still avoid running them over on the edge. I used finally about 30 psi in front and 26 in back. After a run the rubber temps on front were about 143 and the backs were about 120. I don't know if that is appropriate or not. I think I will call Hoosier on Monday and ask.

ON my last run my clutch fan failed and it started running a bit warmer. 90 degrees c.

So that will need to come off.

I am going to do some more lowering of the rear, I think and also install some urethane bump stops inside the front shocks that I have left over from my BMW days.

I have not found very many folks who think welding my diff is a good idea. But I have not yet found anybody who has actually tried it.

It was over 90 degrees. I didn't get burned much and drank about 6 bottles of water and am presently thirsty so I am going to go drink some more!

Good clean fun.

Tom W

OMEGAMAN · #13 07-07-2007, 11:47 PM

I wonder if there is a way to add friction discs the the rear end you have with some machine work. You say you have a few to play with. It might be worth a trip to the local junk yard for some experimental parts.

t walgamuth · #14 07-08-2007, 07:00 AM

Yeah, maybe that is possible. My favorite machinist can set up a rear, and knows others around town who could do any machine work he lacks the equipment to do (not much actually).

I have been pondering it.

I have this vision of the Miata of one of the guys (it has a turbo, a full zoop suspension but still street driven some, and a turbo motor) laying two nice strips of rubber coming out of the 180 degree turn. (he beat my time by a second or so). He also had a really cool racing seat with sides about 8" deep which required a removable steering wheel to get out of. He got his seat off the internet.....I am going to look for one like it. His was 17" wide. One of the things stopping me from shelling out the bucks for a new one has been the width thing. I don't want to buy a seat off the internet and find I am too wide for it. His was 17". I think a 16" would be a perfect fit for me. Thiis guy is my age more or less and has a zz tops beard and a ponytail that is about two feet long!

You meet some interesting folks at the autocross.

Tom W

t walgamuth · #15 07-08-2007, 11:13 AM

Anybody know if the BMW rear ends have any interchangibility with MB?

Tom W