abs pulsating
 

My 1988 560sl pulsates the brake pedal when I pull out of garage in the morning or (abs is being activated)
The brakes , rotars ,hoses , are all new
calipers are rebuilt, fluid is new
when I purchase the car this summer the motor relay for the abs was missing
I replased it and thats when the abs started working . maybe too much
The sensors are all cleand up front and back
I also checked the resistance of each one and they are are within spec.
the abs sometimes comes on at a slow speed stop during the day
but this is happens hardly at all
Is there a problem or thats something normal for that model?
Some of the old threads say this action in reverse is a test, but I can't see how the abs knows when to test itself at least in that year.
Any help would greatly appreciated

Not normal. Our old 190E had the same exact symptoms, and the speed sonesors were "in spec" and I cleaned them. Nothing worked, and then the ABS sensors were replaced and problem solved.

I may have to go that route.
Did you have to replace the rear one also?
Thanks for the help

actually it is quite a normal problem. this is one of the things that have been a problem throughout the years. it is a little pricey to fix. the pedal pulsates at a low speed? same problem here... at least you know that the ABS is working. not something that has to be fixed and not something that will fail as a result... has been a problem on the 190E all the way up to the S500 but not too sure of the newer ones. this is for the 80's and early 90's models.

Actually, it is not normal ABS operation. It might be a common problem, but that is very different from "normal." The ABS system is not functioning as designed, and eventually the sensors will fail, lighting the ABS light and disabling the system. If you don't mind not having ABS, no problem.

However, if you want to have the system functioning as "normal" than you'll probably have to replace the front wheel speed sensors.

Some people live with the ABS slow speed pulsing and don't care if the ABS fails at some point. If you are one of those (I rarely use ABS, even on black ice) then don't bother spending the bucks to fix the problem.

It's up to you, and no I didn't replace the rear sensor. I would have left them all alone but the buyer for my 190E wanted it fixed.

I was wondering if there are any other ways to tell which one is bad I hate to change good parts.
But again changing both will end this problem
Its worth it , all the rest of the brakes are new now.

i said it was a normal problem... maybe i should have spoken your language and described it as a common problem... and the only reason i spoke up on this thread is because i had a long talk with my mechanic about this and i feel he knows much more than you so i will be glad to take his advice. he told me not to worry about the sensors... he never mentioned the abs failing as a result... he explained that it is not a problem with the abs at normal operating speeds but only an issue at low speeds. read your manual... it specifically states in the manual that you might feel violent (and yes they use the word violent) pulses from the brakes during a hard stop... it goes on to explain that that is the abs working and not to worry about it... just in case... it is in the section about the abs brakes in the owners manual.

"(I rarely use ABS, even on black ice)" i cant believe you said this... what do you mean you rarely use ABS... if your car has ABS and you press the brake... you are using ABS! dont think it only works when the wheels start to slip or when the brake is slammed to the floor... it is working everytime you press the brake.

Maybe you don't understand how ABS works, or what it is. IT's not "normal" braking. The ABS system is only used when the tires exceed the threshold of traction and apply and release the brakes in rapid succession in order to keep the wheel from locking.

If the ABS system is working everytime you push the pedal, I'm in serious trouble, since the ABS system in our 190E was disabled by the failure of the speed sensors. If you love your manual, you should read the part about the ABS warning light and the fact that your brakes will work without ABS operation. ABS stands for:
Anti-Lock
Braking
System

The key word is "Anti-Lock."

And while it might seem like semantics, your using the word "normal" sends a message that this how the system is designed, and the flaw is a design fault, not an actual equipment failure. It is an equipment failure and NOT normal. Yes, lots of older MB's have the fault, and it's not critical that it be dealt with, but if you are trying to have the system working as designed, then you will need to make repairs. As to the system NEVER failing to operate at higher speeds, sorry, untrue. If the speed sensors fail completely, you will have no ABS operation, regardless of speed. How do I know? Experience. 800,000km's of MB driving and many repairs on many cars with over 350,000km's. On the 190E I just sold, the ABS was not operating at ANY speed thanks to the complete failure of the front speed sensors. I tried cleaning them (sometimes works) but not in this case.

Why is your mechanic not in a rush to fix this? Not a critical element and it's a fairly expensive repair.

Why don't I use ABS (you can tell, as the pedal pulses during ABS operation) very often? Well, even on ice, I anticipate the low traction and usually don't even come close to threshold braking. Sometimes I do, but not often.

Read up...

http://auto.howstuffworks.com/anti-lock-brake.htm

http://www.autoshop-online.com/auto101/abs.html

http://www.e-z.net/~ts/hybrakes.htm

http://www.abs-education.org/abcs/abctips.htm

I agree with what you are saying about the abs
I believe the last owner was too cheap and figured why spend the money and took out the motor relay for the unit.
He had the vechicle for 2 years and did not make as many repairs and maintenance as I did in 3 months
I want to get it back to original with abs working
thanks for the help, I will be ordering the sensors soon
maybe I take a chance and buy one ,go from there.

I had the same problem with my '88 300 sel. ABS would pulse after first brake application after initial start up and ocassionally when coming to a stop at low speeds. Both wheel sensors and differential sensor checked out as within spec. I remember reading somewhere that for some illogical reason the right front sensors seem to fail at a higher rate than the other two. So I replaced the right front sensor first. That was about 4 mos. ago, the problem has not returned.

brgds,

BENZSTER

Thats a good idea
That way yuo cut the cost in half
maybe???
Right side might be the lucky side

"Why don't I use ABS (you can tell, as the pedal pulses during ABS operation) very often? Well, even on ice, I anticipate the low traction and usually don't even come close to threshold braking. Sometimes I do, but not often."

this isnt a question about ABS anymore, this is a testament to your insanity...

you just proved my point... YOU CANNOT SEE BLACK ICE... anyone that tells me that they dont need ABS on ice is in my opinion an idiot that should not be trusted.

im stopping this conversation as i can see that you are not making any sense and i am wasting my time... i never intended to have a chat with you... all i wanted to do was tell the person that started the post about the issues i have had with the problem he is having. if you cannot respect that than you can kiss my a$$.

How on earth did we ever live past 18 before ABS was invented? :eek:

shear luck...

Well, replacing the speed sensors isn't too difficult a job, and I'd offer to walk you through it, but we'll let icetrey the knowledge-god take this one.

One more point in the checking of the sensors is that they may check out good with the wheels straight. Try turning the wheels both sides and make the measurements. Intermintinent problems in the cables may be eliminated. Just a point to consider.

now i understand why you are so angry... not my fault america runs the world.

you wrote...

"Interesting...

http://pabaah.com/modules.php?name=News&file=article&sid=706

Could backfire for the Repubs, as Clinton could come back..."

canada never has a say... eh?

ABS problem
 

One other possibility to consider, if the ABS warning light is either coming on during normal braking, or if you are getting ABS operation even during light braking on dry roads, etc.:

The pick-up of pulses from the ABS sensors on the front wheels can be disrupted or intermittent if the wheel bearings are not adjusted properly (too loose).

I had my car in for front brake pads and new rotors, and when I got the car back the ABS warning light came on at the first application of the brakes. I took the car back, and the mechanic "isolated" the problem to the right side ABS sensor, and replace it. They said that they weren't sure how the ABS sensor got damaged, but they concluded that they must have done it during the rotor replacement.

Only problem was that they problem came back. So, I start poking around myself, and discover that the wheel bearings aren't close to being adjusted properly, following the front rotor replacement. I tightened them up to spec., and the ABS problem went away. The play in the wheel bearing disrupted the spacing between the rotor and the sensor. Replacing the sensor with a new, clean one probably helped the sensitivity of the sensor a little, but the problem was the loose wheel bearing all along.

Bob Schleicher
1991 420SEL, 174,000 miles

Oh, now I get it. A neo-con troll from the BW board. Should slap radunegru for sending you here. Don't bother posting any more "open discussion" stuff here, it's not welcome. We had an OD forum and came over to wreck your place. M B Shop is strictly technical. Not much "bling bling" kinda crap here either. Just good tech knowledge.

This started out just trying to get some information on speed sensors
Can't believe we are getting into a tizzy.
I believe the bearings I repacked and set are ok
The sensors are probably bad or I hope there bad because I don't want to purchase new ones and still have the problem

I agree with myanoch.
Keep it nice, follow the rules.
That is why the open forum was removed, and I believe some people were banned.
Going at each other does not help the problem, nor anyone of you 2.

I was reading my manual, and it states that a pulsating brake pedal when starting to move (while having some pressure on the pedal) is sort of a self-test.
My car does it often (6 years of ownership), when I first start the car in the mornings, specially if it is very humid.

Why don't blackmercedes and icetray meet in the nearest mercedes parking lot and open up a can of wup-ass and see who comes out on top.

After reading all of the above threads on A.B.S can some one tell me,how do i know if my A.B.S is actually working.

Go down a dirt road about 30mph and lock up the brakes. If the brakes lock up and slide the abs ain't working.

The same thing happens to my car each morning as well. I know my ABS works (as they activated this evening in a panic stop). I thought this is normal for the car. Like he ABS is going into stand by mode (for lack of a better term). Have we decided that this is not normal? My car as been doing this for as long as I can remember with no side effects as far as I can tell.

I can't believe I am confused on the answers.
Either there are a lot of cars out there doing a so called test mode ???
or there are a lot of pre 90's with speed sensors bad.
If the unit is not working the ligh comes on the dash
If the speed sesors are bad the light won't come on because the unit
thinks the brakes are locking up. ( when there really not)
If there is a intermitent break in a wire you get abs at times with no set pattern of failure
Am I thinking correctly on this
Plus the only test short of going to a dealer is a resistance check to see if the sensor is bad????
I can't believe there is an intermintent break in the wire and it cuts out every time I back down my driveway in the morning?
but I can believe the sensor could be bad and the longer distance plus down hill cause it to act up.
I was never a parts changer without defining the cause of the problem but in this case I may have to change my way.
Again thanks for the help

you are such a silly person... i take pity on you.

What is the exact specification for the tightening of the the wheel bearings in the front. Car is 300SEL 89.

My ABS light comes on on the first few feet of driving and I have just ignored the issue. Brakes were done in the front and maybe it is the distance of the sensor to the teeth. Need to check this.

Does everyones Light come on? Mine just does the pulse / standby thing at the exact same spot on the driveway each morning. As far as I can tell, it does not do it again through out the day (weird) and there is no light that comes on ever.

The plot thickens.

Mine does the pulsing first thing in the morning after going a few feet. It never did that before so something is wrong or is going to be wrong soon if we don't find the problem.

My guess is its the rear sensor. With the diff weeping and all the debris that goes past there it wouldn't suprise me if the thing is on its way out. If it threw a light I could check the code using my make shift code reader but it doesn't. It does it for about a couple of seconds sometimes accompanied by a springing sound (boooiiiiiiiiinnnng) and its done for the day. :(

My light came on twice in 2 months of driving, goes right off after a restart.
I think thats not the problem that I am concerned about
My light does not come on when it pulsates.

When you say that it pulsates, are you talking about constant or periodic ulsating or just that one time when you start up in the AM and roll a few feet and then that's it?

I drove it to the resturant tonight , had not driven it in 2 days
when i backed out of the garage it pulsated twice while backing down the driveway
That was it it worked perfectly all the way down and back
no pulsating ,not lights,
no nothing
thats the way it acts.

Can someone give me an idea where the ABS sensors are.... I can't seem to find them on my handy dandy shop manual.

1989 300e

Thanks

found the info in another section of my manual....

where are they?
 

Lee, I have an 87 300e but no shop manual. Could you please advise where the front speed sensors are located & how to get to them. thanks

speed sensors
 

two bolts into the front calipers... snakes back up to and RCA connector.. I believe there are one or two plastic ties that keep them wrapped with the "brake pad worn" sensor and something else.

I have two spares and am going to replace the right side one tonight and see if that solves the problem... if not I will replace the left... if not...I guess I will have to buy a rear one....

Had two good speed sensors..so I know at least what direction to go on..

Lee