Have new(used) toy need help.
 

Recently I purchased a 300 CE "92.
Have a problem with the brakes, They seem to have a mind of their own.
After driving approx 45 miles they LOCK UP.
It seems to be some kind of vacuum problem as the brake pedal gets
gradualy stiff,it goes in to a violent shake (abs?) and if I let it go
it will lock up the front wheels right front first (if it makes any difference)
I have adopted a new driving style (STAB the brake pedal hard)once in a while and they seem to unlock or not go further in to lock up.
That is until the pedal starts to stiffen up again.
It is not the most pleasurable way to drive and very disconcerting to my fellow drivers on the road. I have a '88 260E , had a 89 300E and never
experienced this kind of problem.
Any help ideas will be greatly appreciated.Thank You very much...

Answer:
 

DANGER:

This is a SAFETY issue!!!

Please have it towed to the nearest Mercedes Benz dealer for diagnosis.




This car is not safe to drive...

Of course it is a safety issue. I understand that very well.
This problem rears its ugly head only while driving on the
highway. In town it seems to be OK.
As I stated before I have other vehicles thankfully it is NOT
my only mode of tranportation.
As an x factory trained mechanic (Porsche,VW, Audi,Mazda)
and current Aircraft A&P licenced mechanic,I think I know about turning wrenches a little bit,This auto as stated before is my toy and all I was
looking for was some ideas about how to solve this problem before
I dove head down in to it. Towing it to the nearest dealer was not
my idea as to how a do it yourselfer operates.Perhaps the time will
come and I will wave the white flag but I think it is a little premature.
Thank You very much for your relpy and your concern for a fellow driver
on the road is appreciated. Thanks Again Mr-tuanis........

I hope this helps you some. I had a very similar problem recently with a "76 model Corvette, mine turned out to be a faulty brake master cylinder. The vaccum brake booster may also be suspect on your Mercedes but I'd start with the master cylinder. I wonder if someone here has a test method for the msater cylinder?
Al

Answer:
 

The issue sounds like failed brake hoses acting as one way valves plus contaminated fluid.
By this point there is a 90% chance the calipers and rotors are junk.

Brake:
http://www.peachparts.com/shopforum/showthread.php?t=142411



As a new member, there is no way anyone would know your DIY level...

My concern is for you and other innocent people that may be maimed and/or killed.

Note:
The following is FYI data for the education of younger members, as to how serious the issue can be.

The car is not safe to drive on public roads, as per your description, and depending upon how the prosecutor views your credentials, the charge would be gross negligence as to amount to a willful or depraved indifference to human life, (if anyone died) Vehicular manslaughter or Murder charge in the state of Michigan.

One of my co-workers wife used to have a geo i think that exhibited similar symptons as yours. After a bunch of work that didn't make a difference, they discovered that the brake fluid has transmission fluid in it from someone who didn't know what they were doing. the power brakes would allow the fluid to be pushed to apply the brakes but the brake fluid collapsed the lines to where the brake fluid wouldn't return and would lock of the brakes at any given moment. so new brake lines and all new componets plus fluid cleared up that problem.

Thanks to All for the replies. In special to Whunter (super Moderator)
the worn brake lines acting as a one way valve is a problem I heard of before and perfecly plausible and /or applicable on this case.
Yes you are right the R/F disc is almost gone and the pads are approx
60to75% worn. I have NEW disks, pads,hub bearings and caliper rebuild kit
soooo this auto will go in to my garage and will not come out on the road
until it is repaired properly.I will look in to bleeding the system and will
most likely replace the brake lines with steel braided ones(perf prods)
I do not want to replace all the brake parts mentioned above and have the new rotors ruined.It is ALL I was trying to avoid. Such as an ABS egaging
when it is not supposed to (common on some aircraft).
As for the dealer tech's, mechanics,I'm sure they have their place and no
doubt SKILLS. But the nearest MBZ dealer wanted $1800.00 to fix a miss on My Ladyfriend's 280 ce and I was able to repair it for approx $350
quite a substantial savings (not to mention fringe benefits).
Well thanks to all again and keep those ideas coming.Mr-tuanis

I just wonder how often the fluid was flushed from your car?(brake) Sounds like another system that was not cared for, for a long time. JNT

To JNT and all concerned,
As I stated on my first post I purchased the auto recently
Have very little info as to the maintenance records.
The price was right and as an avid Do It Yourselfer (Junkie more like it)
I decided to make this auto MY New project.
I think the bodylines are very classy and sporty at the sametime.
Just got done doing my 944 Porsche suspention mods,a little eng mod
installed a newer engine actually,resealed the rear window (pricey on this
model)if done by the dealer,
Soooo the idea on this car is to park it for awhile and do some mods to it
nothing radical just the traditional stuff,lower suspention gas filled shocks,
new headlight assemblies,I already have a set of BRABUS 17 in Rims,update
the stereo system etc,,,,
As for the car History all I know is it came to calif,originally from Canada
and it has never been involved in an accident,It has a very srtaight body.
The car as I see it has potential, only the BRAKE Problem kinda got to me
as it is not consistent.(when I'm driving it I can not reproduce the problem consistently) That is why I decided to register and visit this forum.
Once Again THANKS TO ALL......Mr-tuanis

Master cylinder
Brake fluid expands when getting hot. Normally, without pressure on the brake pedal, there is an open connection from the brake lines to the brake fluid reservoir through the master cylinder. If for some reason (pistons in master cylinder not fully return) this connection is blocked the fluid expansion leads to pressure on the pistons in the callipers and eventually to locking up of the brakes.
Restriction in the movement of the pistons is caused by worn seals, corrosion of the cylinder, or contamination of the fluid. In any case the master cylinder has to be overhauled or replaced. Note that there are several different models of the master cylinder.

Brake lines.
Collect al brake fluid in a clean jar, if there is any sign of contamination all flexible brake
lines have to be replaced. If not inspect the lines for small cracks and replace if you find them.

Callipers.
Since your car is not very new and you like to wrench , I would strongly recommend to inspect/overhaul the callipers. It only requires some cheap rubber seals and some time. Make sure you have the right seals for your calliper, again there are different brands. If the bores or pistons are scratched the whole calliper should be replaced. Also make sure there are no signs of overheating of the piston (discolouring).

Rotors.
If the rotors have overheated or worn thin, you should always replace them. Not to expensive and essential for your (and others) safety.

Rob

Thanks for your reply, the sugestions make a lot of sense and I think
Mr Al Parker sugested something similar along the lines of the master cylinder.Part of troubleshooting is to correct the problem with the least amount of steps (change one thing at the time).I found my friend hitting
the starter on his van the other day to get it to start,I asked him have you
checked the battery? turned out to be a weak battery.I think a complete rebuild of the brake system is in order. From the sounds of the sugestions
I will replace the brake lines first,new brake fluid of course,next I will look in to the master Cylinder,as stated berfore I already have rotors,pads and caliper rebuild kit, will replace the wheel bearings at the same time(preventive maintenance) The brake lines I heard both good and bad things about the steel braided lines loss of pedal feel etc.Does anybody have an opinion on this? Should I go steel braided or factory (OEM) replacement?
THANKS Mr-tuanis..........

I third (fourth?) - master cylinder. But while you're at it, you'll probably need new hoses and fluid. And check your pads/rotors for damage and wear.

Answer:
 

Stick with the OEM, they are tough enough for racing.

PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1992 Mercedes Benz 300CE 24-Valve
Part: Brake Hose
Note: Front
36.5 cm in length : male and female connector.

N7000-26865 Brake Hose Corteco/Freudenberg IN STOCK



PART NUMBER SEARCH RESULTS WITH PRICES
Vehicle 1992 Mercedes Benz 300CE 24-Valve
Part: Brake Hose
Note: Rear
30.5 cm in length : male & female connectors

N7000-26863 Brake Hose PBR IN STOCK

FYI...after-market rotors do not always mimic oe in vented fin placement, angle or number.
Buy pads and calipers anywhere, but buy oe rotors.

Have had many BMW's, Mercedes and Audi exibit brake shake and pulsation only a few hundred miles after some shop ..( Does MIDAS mean anything...) fitted 'new' rotors etc..


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