jaguar13

I'm FRUSTRATED! Having replaced dozens of brake pads over the past 25 years, I've never experienced this problem. 1988 560SL. After replacing pads, I can't get fluid to the rear. I inspected the lines, even isolated the rear calipers by disconnecting the T-joint where the line goes to the two rear calipers. Absolutely no fluid pressure. Fluid pressure is excellent in the front. Bad Master clyinder? That's what I thought when I replaced it however, symptoms are the same. Out of the side ports on the clyinder, I get maximum pressure. The front port however, I barely get a squirt. This is true on both the new and old master clyinder. What am I not doing? What am I doing wrong? Please help. I don't like technical things kicking my butt!

Nektopoli

Maybe the rear caliper are siezed(sp?)?

NP

jaguar13

NP....Thanks for your timely response. Rear calipers being seized doesn't appear to be the case. I'm not getting fluid that far. I'll pull 'em off and check again. Any other possibilities?

wagger

does it have a load sensing valve in the brake line to the rear
usually located around the rear axle.
the valve will normally have a linkage going from it to somewhere
on the rear axle/suspension. if you have the car jacked up then
it will be almost fully closed due to the linkage pulling the valve
closed. if you find the valve (if fitted?) work the linkage so that
it forces the valve open.

regards wagger

jaguar13

Wagger. I appreciate the advice. I couldn't locate anything. I did level the car, with no noticeable difference...still no fluid. I am wondering now if there is a vapor lock of some sort in the ABS control. That's really the only other thing I see in the line???

patrick

Jaguar13,

I guess you tried to bleed the brakes manually?

jaguar13

Patrick.....Manually until my hand wore out with a vacuum brake bleeder, then until my wife's leg wore out. All I get is AIR and ocassionally a dribble of fluid.

patrick

If you do it "manually" (or by your wife's foot) it is possible that the brake fluid does not flow quick enough from the "common" part of the fluid container to the part especially for the rear brakes.

If you bleed the (rear) brakes with a "brake bleeding machine" (I am not English speaking so forgive me my mistakes or the use of rather uncommon language while trying to explain rather technical things) there is a bit of pressure in the fluid container that makes the fluid flow faster to the rear part of the container so you cannot pull air with (or something like that, I just hope you understand this weird explanation).

jaguar13

Patrick, Thanks, I understand what you're saying. I'm going to bleed the ABS and see what I get.

patrick

It has nothing to do with the ABS. The problem may be in the plastic fluid container.

Do not you know anyone who has such a "brake bleeding machine" (I do not know how to call it)?

jaguar13

Patrick...Actually it prove to have quite a bit to do with the ABS. Once I got the air out of the ABS, I developed 60lbs of pressure and brake fluid shot to the rear breaks. Then, however, the pressure drops because for some reason the master cylinder output port loses its prime. Not only do I know some one with a brake bleeding device. I've been using mine all along. Once I remove the master cylinder and bench bleed it, the same sequence will repeat...plenty of fluid, lots of pressure than poooof...nothing. Now what???

patrick

OK, it seems that you have air in the ABS hydraulic unit too now.

I guess before you only had no fluid pressure to the rear brakes, but since you worked on other parts like the master cylinder, you have to follow a certain procedure to bleed the brakes correctly(and use the brake bleeding device ofcourse).

But I type this from home and I do not know the procedure by heart. I do know that you have to use the nipple called "SP" (on the hydraulic unit) and at a certain point you must put on the ignition until you hear the hydraulic pump run and then continue bleeding as you should normally do.

I have to look up the correct procedure at my work. I am almost sure there is nothing wrong. Does the car has ASR too? This is important for the procedure.

jaguar13

Patrick.....First I want to say how sincerely I appreciated your guidance and advice. I was aware of the "SP" port on the ABS. All I can say to anyone who reads this, at least for an 88 560SL...DISCONNECT THE NEGATIVE BATTERY TERMINAL! When I found out that had to be done, the brake bleeding procedure was completed in 15 minutes. Too bad that I have to feel so stupid not finding this out until I was on the verge of placing a hand grenade in the fuel tank. Thanks again Patrick:

John Mansch
Major, USMC Ret.