1987 560SEL problems with jerking when accelarating
 

Hello i was directed to repost this in here as i mistakenly put it in the wrong section before. I own a 1987 560SEL my problem is as an example if i get onto the highway and go 1-60 it will shift very smooth. Then release the gas the breaks will apply themselves (which i assume is by design? quite annoying rlly tho). So it will drop to like 45-50 when i go to give it gas again it will jerk the car quite aggressive im assuming its the transmission shifting into a new gear? Im just not sure if this is considered normal or if im breaking something by driving it around.

The brakes should never apply themselves. Are you sure you just aren't stuck in a low gear and the engine RPM is slowing the car down? If so, it's entirely possible that you get an abrupt shift when you hit the gas again. Check for vacuum leaks, barring that sounds like time to have the transmission checked out.

The brakes applying themselves is not part of the "ABS" system in the car? I dont have a book on this car im kind of clueless. It may of been a stupid try on my part but i did take the 2 relays out of the ABS system and the brakes did not apply themselves and the jerking motion while accelerating went away during a test drive. But the next day the brakes were back applying themselves along with the jerking and thats with the 2 relays out still. I figured it must of been a coinincidence that the problems stopped for the 1st test drive and put the relays back in. I was under the impression that the brakes+jerking was related. This only happens if im on and off the gas if im already on the gas and accelerate more its not a problem.

The ABS system on the W126 is just that.....Anti-Lock Brakes. If you hit the brakes hard enough to lock the wheels, it pulses the brakes to keep the wheels from locking and sending you into a skid.

Self-applying brakes on Mercedes didn't come around for over a decade after your car was built, and only to prevent a crash! The brakes should never apply themselves on a W126.

Since the jerking happens when you accelerate, let off the gas, then accelerate again, it sounds like you have a transmission sticking in a gear or stumbling during a gear change. If you're not technically inclined, it would be well worth having it checked by a reputable shop before you do any permanent damage to it.

Actually, 126s with ASR do have self applying brakes; the symptoms described by the OP are consistent with either correct ASR operation with mismatched tire diameters, or, a fault in the ASR system with same diameter tires all around.

As a first step, the circumference of each tire (aka, "tire roll-out") should be measured and compared.

Thank you for your response Frank i went and checked the tires they were all the same size 205/65 r15 i hope that what you were referring to. Is there a way i can just disconnect the whole ASR system i don't actually like the self-applying brakes. Im slightly confused when you say ASR system i was talking about the ABS before these are separate or all controlled with the same part?

Have a look at the data plate on the crossmember in front of the radiator. (See thumbnail). Does the code 471 appear in the list of three digit code numbers? If so, the car is equipped with ASR, which, although it includes ABS in its functions, is also a form of traction control.

471 does not appear in the codes i dont currently have a camera to upload a picture so i will try and write it out with the correct format.

6501160 9
126039 12
52 1
274 412 581
109564 M442 806
494 872
2 172 G519 873
551

Edit:the formatting gets changed when i post i guess but the 3 digit codes it has are 442,491,519,551,581,806,873