So I was driving down the 405 yesterday and went to stop in a hurry, pedal to the floor with little response. After the momentary heart attack, I was able to pump and get her stopped without incident.

All of the braking power was at the back, the fronts are not working. So I limped it down to the shop today and had them do front brakes (calipers, rotors, bearings, seals, pads, hoses) as it was time for those anyway.

After I got it back, I still have a crappy pedal and they are telling me that's all the pedal it will give them. It doesn't feel to me like the front brakes are working at all, still. The fluid is not leaking out anywhere and the master cylinder is full of fluid. Part of their service included a brake fluid flush, so I don't think its that either.

Do I need a new master cylinder? What else is there between the master cylinder and the hoses?

 

Could be the master cylinder or the flexible lines going to the wheels. If you've never changed those lines or it's at least been a few years, do it regardless. The easy way to check the master cylinder is to pump the brake peddle a couple times then hold down on the peddle. If it starts sinking and continues to the floor, the master cylinder is gone.

 

You mean the hoses, right? They run from the lines to the calipers. Those were already done with the brake service.

I'll check the MC tomorrow. No way to change that thing without bleeding the brakes again, is there? I only have me here and am out of state at the moment, hate to drag it to the shop for something that is so easy to change just for them to mark up on labor.

 

Sounds like a M/C to me, too. It's pretty cheap and easy to fix. I'll be doing mine, and a new booster and vacuum hoses, when I get back from Montana after Thanksgiving.

 

That's correct. Sorry, I missed them in your first post.

If you'll Google "one man brake bleeder" there's allot of info on the process. You can do it yourself but it can take a bit of time.

 

Pardon my ignorance, but I work at a production shop and Im sure that none of my guys would have any idea to bleed the abs module/block/thing on the frame behind the axle if so equipped. Just something you may wanna look at before condeming the master. Good luck!

 

Sure enough, it sinks to the floor but it does so slowly. So the leak therein must be slow and small. How hazardous is it to run it like this for a few days? I really do not have the time to get it to shop here for a couple of days and I have some stuff that I have to get done. Am I at serious risk of having no brakes at all when I need them?

I have had an occasional problem that has not been flaring up much recently, but occasionally the rear brakes did not release correctly after a hard stop. Could this be MC as well? I always attributed that to the parking brake sticking, so I stopped using the parking brake and it hasn't really been an issue since.

Because the rear brakes are such a job with the full floating axle and they were recently done, I hate to go back in there again.

I don't think these have ABS, do they? Pardon MY ignorance, lol.

 

"I don't think these have ABS, do they? Pardon MY ignorance, lol. "


They sure do!

 

keith1992- your master cylinder is likely bypassing internally, showing no outward signs of leakage, yet not building the pressure necessary to apply the brakes. That could well be due in no small part to the fact that most people dont flush their brake systems every other year (or ever), which I think is a good preventive measure. Nonetheless, you DO run the risk of having more pucker power stops (or lack thereof) in your future with your current master cylinder. My experience with reman master cylinders has not been good- I have one on my W350 I need to return under warranty. After that, I will get a NEW one. Your mileage may or may not vary.

 

Well now, don't I feel like an idiot? So there is other stuff that could be acting up, i.e. the ABS controller/computer. Where is that thing at and how do you test it? I am gonna get the MC anyway, the one under there is definitely OE and time to be replaced.

Well, I cannot speak for the previous owner, but flushing brake systems is a part of my yearly PM. Most people also never flush the ATF then wonder why the tranny starts acting up at 150K. Don't change the oil in your engine long enough, and it will start acting up, too. That said, oil changes every 3K miles is overkill. I do mine every 10K miles now and I add a full gallon of Lucas Oil Stabilizer.

As for the M/C, where do I get a real new one? Dealer? I know that nothing you buy at Kragen/Autozone/Advance/Oreilly's is ever really new.

 

Exactly what he said! Had the same issue but my rear circuit was pooched and was only stopping with the fronts. Stock MC went so I replaced it with a rebuild and it was no better than the stock dead one I had. It was by-passing on the inside right out of the box but it would actually pressure up under the lid and barf out fluid from the lid seal. Put in a brand new one about a month ago (I prefer Raybestos but I hear Dorman and Cardone are really good too) and flushed out the whople system. She stops like a freakin sports car now, especially with the 1-ton guts in the rears.

 

Does anyone think I also have a bad brake master cylinder? About 2-3 weeks ago I had the brake pedal go closer to the floor when pressed, accompanied by the brake and ABS light coming on at the same time in the message center. I have checked all over the truck and found that I have no hydraulic failures (meaning no bad lines or leaks) and even tried bleeding any possible air out and still have the pedal going closer to the floor with both lights coming on each time the pedal is pressed. The brake pedal is clearly not as tight as it has been the past 25,000 miles I've put on the truck in about a year's time. Would the ABS light be coming on because I have a problem with the ABS in the rear or is this diagnosis a bad master cylinder? Any chance it's a bad check valve in the brake booster? How reliable are those and do they usually pose a problem in the 89-93 diesel trucks? I haven't had any problems with the brakes up until this point, brake pedal has always been tight, and no lights ever came on no matter how many times I'd press the pedal. Looks like I'll be doing some brake work on my truck here pretty soon and thanks for any help.

Sal

 

I wouldn't wait any longer than I had to. A bad master cylinder can take a dump at any time.

 

My truck is driving me nuts!! I had two bad masters in a row(leaking out of the rear, one reman one brand spankin new) and Ive only had the truck 2 weeks!! I have to pull the rear drums next, dont trust the guy who did em last and i cant get this thing to bleed. Blocked all the hoses and rock hard pedal. released the rear and straight to the floor... No leaking that I can see but I cant get my right rear to adjust up at all... Now I have an excuse to avoid socializing again on Sunday!!!!

 

Well, I am gonna do the MC but for some reason I have a feeling that wont be it. I hate anti-lock brakes. They are the worst invention ever and the folks who made them standard equipment should have been strung up by their fingernails. Is there any way I can eliminate that system and just have normal brakes without replacing all kinds of stuff? I used to have such a nice pedal and it stopped on a dime, this weenie pedal just ain't gonna cut it!

Prior to this, I only drove AMC stuff and none of them had ABS on them and the brakes worked great. Simple to fix, too. You either did pads/shoes, or you looked for leaks, or you bought a new MC. Real nice and simple.