Glen McCartney

Just got back from a nice long trip with the car. Noticed on hard acceleration taking off in 1st gear on the way home that the tranny felt like it was slipping or the tires breaking loose (they weren't). But, it shifts fine, if I accelerate easy, doesn't fell like any slippage. Could the LSD be slipping? The LSD was installed by Steve Cattaneo when he rebuilt my trans in April 2008 (49000 miles ago) with new friction plates in the LSD.

Can it be tested while in the car?

If it is the friction plates, how hard to change out the friction plates with the trans in the car?

GlenL

It feels like one wheel spinning. That's what a "limited slip" limits.

jpitman2

If its not the tyres breaking loose, but you feel you are not going fwd as you should, that would sound like internal slippage in the box IMHO . Check the fluid for smelling burned due to slipping bands...
jp 83 Euro S AT 55k

Dave928S

^^ Sounds like the auto to me too ... slipping feeling/loss of forward progress but no wheel spin. Hard acceleration on pavement with a properly functional LSD (and transmission) will give two stripes and no throttle steer .... failing LSD's will often give massive throttle steer (back end snaking around) as you take off, as one side or the other gives drive.

GregBBRD

Yup, not the limited slip, if the tires aren't slipping on the pavement.

When a limited slip goes bad....only one tire will spin....like with an "open" differential.

You can check your limited slip by jacking up the rear of the car. Leave the transmission in park. Take off the emergency brake. Turn one wheel. You should "feel" resistance and the other wheel should turn in the same direction. The "amount" of "resistance" is the amount of limited slip action you have. 7-25 ft. lbs. for a "single" plate limited slip...like yours.

dr bob

** deleted **

85euro928

So if you put a torque wrench on a lug nut set to 7 ft lbs and turn the wheel using the wrench is that close enough? I'm thinking you could start at 7 and work your way up to where the wrench no longer gave way?

Glen McCartney

Thanks for the info, I fear it's something in the Trans. I will have to get it up in the air and check out fluid, fluid in fill tank looks bright red. Will drop pan and filter to see if it shows anything.

Dave928S

Pop the wheel cap and put a socket on the axle nut to check torque ... on a lug nut won't give a correct reading as it's off centre. Make sure there's no brake drag at all, as that will influence the reading you get.

FredR

If you take off hard and/or only get smoke/rubber deposit on one side you know the LSD ain't working- correct?

Regards

Fred

Glen McCartney

Found some information on troubleshooting from Mitchell's -
"Transmission Slips When Starting Off In 1st Or 2nd (Reverse Is Okay)
• Band B-2 shift valve sticking. Band B-2 piston worn or damaged. Band B-2 adjusted incorrectly or worn or damaged. Adjust brake band B-2 by installing a longer thrust pin (if necessary)."

Have to find information on longer thrust pins if this is the problem.

I have to test if reverse is OK under hard acceleration. Normal driving wouldn't even notice an issue.

Glen McCartney

Well, took car out to do some road testing. Felt some slippage taking off, once shifted up out of first gear everything felt normal. Got close to home tried hammering it in reverse, left two nice black rubber strips, drove about two blocks and then wouldn't move forward at stop sign. Reverse works perfect, drove it home 4 blocks in reverse.

So it is either worn or broken brake band B2, hard to believe it is worn as it was replaced 60K miles ago, why would it break? Or does it just need a longer thrust pin? Where is the thrust pin and can it be removed with the trans in the car? What are the options for lengths? Are the readily available in different lengths? How do you determine the proper length?

Thanks!

GregBBRD

Sounds like either the B2 piston broke or the B2 band broke. Either occur. The piston is more common and can be removed and replaced from the outside.

The "original design" B2 piston is a notorious failure item. They superceeded this piston a couple of times, but the "final" updated version occurred in about 1989. I can't speak for Steve, however, I will not rebuild one of these transmissions and leave the old design piston in, regardless of what it looks like. Makes no sense to leave in a part that is a known failure item.

Mercedes and Porsche part information claims that the piston change is a multiple supercession, with the band and the band "shock absorber" also needing to be changed at the same time, however, I know that many people have replaced the piston and let these original parts in, without issues.

When I'm rebuilding one of these, the B2 band virtually always gets replaced and the piston gets updated.....so I also update the "shock absorber" on the other end.

There's 3 or 4 different lengths operating rods, to set the dimension that the piston moves to active the band. All of the rods have to be ordered from Germany....so it is a bit humorous to think that people commonly check and correct the length of this rod.....where do they get the different lengths? At any rate, this dimension needs to be set-up, when the transmission is rebuilt. It would be very tough to determine the correct length, unless the entire valve body and separator plate were removed.

Glen McCartney

Thanks for the feedback. I would think Steve would have replaced piston too. In the itemized parts from the rebuild he lists Part # 1262701862 - Band - Brake Band and part number 1262721131 Piston. Any idea if that is the B2 piston P/N and if it is the new version?

Glen McCartney

Going to get under the car later this week and check the B2 piston. Anyone know the new part number for the updated B2 piston? Should be available from Mercedes or a transmission parts company like Transtar?