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Back right wheel keeps seizing up! Help!

4K views 8 replies 6 participants last post by  jfoj 
#1 ·
Hi everyone,

I recently purchased a 2001 330ci from someone who i can only describe as a "corner-cutter". it has a welded rear diff(idk if thats part of it or helps). When I bought it, the thing was maxed out to the ground for the front coilovers AND rear lowering springs...I mean maxed out. I first heard the "skid/stutter" sound and thought easy fix, I'll raise it, which is what i was gonna do anyway. Raised it and bought new brake pads, No Dice. Still does the same stuff.
when I turn off the DSC, it doesnt do #2. but problem #1 is constant


Problem #1 - When im stopped and I begin to accelerate while turning, my back right rear tire skids in quick little jerks. I thought it was both tires but it only seems to be the one. I can drive through it no problem as far as resistance goes, its not locking the whole car down but its definitely not a good thing so i haven't been driving it-(No dash lights blink or are on)

Problem #2 - When i take a sharper turn while moving, my DSC light blinks and the car goes limp. It doesnt die and everything stays on (radio,lights) but it loses all power throttle-wise. Once I straighten out enough I get power in my pedal back instantly and everything works fine.

Ive recenently had suspension work but it was done professionaly and the problem was occuring
 
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#3 ·
+10000000 on the diff causing this.

The tires have different arcs -- distances to travel -- when making a turn, so something has to slip on the pavement, this should be the inside tire because the weight transfer is to the outside. But the tires will ultimately decide which one will slip.

The diff is wreaking havoc on the DSC. The skidding tire is going too fast compared to the front tires, that also have different arcs -- distances to travel -- and the chaos this creates makes the DSC kick in to apply the brakes to the offending tire, and the throttle to drop out in an effort to regain control of the spinning tire.

You bought a car built by Dr. Frankenstein, it will be work for you to stay on top of. You bought a car that has been modified for a purpose, the result is that it has behaviors that you detect as symptoms of failure, but they are affects of the work done by the good Dr. Frank. Your monster needs a wife. Or a mechanic that knows how to keep this stuff running.
 
#5 ·
+1 to what jd said.

To clarify, a welded diff will force both tires to rotate at the same speed under all conditions. This is desirable when drifting but very impractical for everyday driving. The wheel skip you're experiencing when turning is from the inside wheel wanting to turn at the same speed as the outside wheel.

DSC is not designed to work properly with a welded diff. You're burning up the brakes and DSC unit because every time you turn, DSC senses the inside wheel is turning faster than it should be. DSC wants to brake the inside wheel but due to the welded diff it's basically impossible to do that independently of the outside wheel.
 
#7 ·
Let's explain this another way...

For the sake of discussion, your tires are 25" in diameter. Multiplying by pi (3.1419), the circumference is 78.5". Now, let's say you are making a right turn next to the curb. The left side tire has to travel 15 ft to make the turn, the right side tire only needs to travel 6 ft. I have not worked out the radius, but let's assume these numbers to be accurate for the sake of illustrating the problem of a welded diff -- also called a spool in some circles.

The tire that goes 15 ft, goes 180 inches, the one that goes 6 ft goes 72 inches.

The outside tire rotates 180 / 78.5 = 2.29 times, the inside tire only needs to rotate 0.91 times (72 / 78.5 = 0.91), but the spool forces it to go the same as the other tire. The inside tire is forced to rotate almost 1.5 times more than the distance it needs to travel -- it has to slip on the pavement or snap the axle shaft for this to work.
 
#9 ·
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