Hello gentlemen, I was wondering if I can find help with my brakes. So here is the background info. I drive a 1994 Discovery 1 and about one month ago I started having brake issues, my brake became squishy taking more travel distance to slow down, and sometimes I had to pump the brakes a least twice to slow down. I have got a new master cylinder and replaced the old one, bleed the system entirely, where now there is only new brake fluid running through the system. After doing the process I had my brakes again! but.... as I started driving the distance to no brakes to full bakes became shorter and shorter as all of my brakes slowly were getting clamped around my rotors. It does take a good amount of braking to get to this point but when it does my disco goes to 5,000 rpm in 1st gear just to get moving. The pressure releases after a few minutes when the car is turned off. I have runned into a wall when it comes to fixing this problem, I've thought it could be the non-returned valve on the booster but I can't get it off to see if it working. I'm asking for your help so I can get some insight on how to fix this problem. Sorry for the long thread and bad English.

 

Fluid level dropping at all over time? Check your calipers very very carefully to make sure they aren't leaking slightly and causing air to get into the system. The pressure releasing sounds like a stuck caliper to me. You could always upgrade to D90 front calipers and vented rotors for better stopping power FYI.

 

sounds like at least one of the wheel bearings is loose

 

Also check and inspect all your brake pads/calipers again, very carefully. Make sure everything is in 100% order. I've actually had it happen where a pad (rear I think) became dislodged and was sitting in it's 'bed' crooked (the friction material was rubbing). It can happen. Ensure all the brake sliding components are not binding (with rust, etc) and are lubed up well. I would remove each caliper and carefully (and slowly) run the pistons in/out about 3x times each (with a C-clamp/pedal back out). To ensure they are running fairly free.

Does the 94 have ABS?

 

I went through a few master cylinders with the same issue, I had one installed and the next day when I picked it up, no brakes. aftermarket master cylinders have never worked well for me. Also check brake lines just below drivers seat. They tend to corrode there and leak.

 

Yes my 94 does have ABS

 

Well, the first thing to do, if you haven't already, is put it on jackstands and CAREFULLY, and thoroughly re-inspect for:

a) BEFORE you remove the rim/tires: Check wheel bearing looseness. And, that each wheel is spinning freely (and which one isn't rotating freely). Activate your brakes a few times. Try to determine if there is a particular offending wheel/brake. Then you have narrowed it down.
b) Any oddities with the brakes/pads at each wheel .
c) There's always a chance it could be a faulty front/rear brake hose. This is one of those things you read about every once in a while, but they can come apart inside. It's real rare, but I recently had a hose in my Trans Am that did fail internally (or something became lodged inside the hose). I'd press on the brakes and the F/L wheel would go real tight and not release. But would rotate fine if I released the hydraulic pressure (bleeder screw) on that wheel. I popped the piston out of the caliper to see if it was rusty inside. Nope! Looked like brand new inside. I replaced the front hoses (they were original '78) and that did the trick. I haven't dissected the hose yet. The point is, a whacked-out hose COULD definitely be the problem.

Could also be a sticking caliper. If you find the offending wheel that's going 'stiff' you could pop the pistons out with air pressure. Put a couple pieces of wood of different thicknesses between the pistons and work the pistons out slowly (like 1/4" increments). Don't try to pop them out in one shot. And don't put your fingers betweeen them!! You want give some air pressure ...then remove a thickness of wood and keep repeating till the pistons are nearly out. Then remove by had. If you CAREFULLY remove the dust boots with a small screwdriver or gasket scraper you can probably put the same parts back in. I almost always can re-use the brake piston/O-ring/dust boot.

Oh, and if your fluid was REAL dirty, there could be crud in your caliper bores. Like I say, easy to pop out the pistons and clean/re-install. If you find a rusted or gummed-up caliper bore, or sticking piston, then you've found your problem. Often you can clean and re-use. Sometimes maybe you'll need a new piston. (or a rebuilt caliper)

There's also the possibility it could be in the ABS valving, but standard mechanical troubleshooting is to begin with the basic items first (simple things first). Because that's where the problems usually lie.

 

Superx03,

Thinking aloud here... does your brake pedal fully return to the "up" position? In our '96 Disco, the clutch pedal sometimes gets stuck and then finally returns all the way up. If your brake pedal doesn't fully retract the plunger in your new master cylinder, it might be covering the port inside the bore that allows the fluid back into the MC. Then, of course, pressure would remain in the system and possibly build up each time you press the pedal. Check that the pedal is coming all the way back. Another possibility is that your replacement MC has a slightly different design from the original where the push rod is actually the wrong length by a few millimeters or so. This can make a big difference in how the system works.

Cheers, Pavel.

 

*update* Yes, The brake pedal does go all the way up. After a certain time, I can't press the brake pedal down. Also just thinking I was looking at parts and at the end of most OEM or genuine parts have a plastic part at the end of the master cylinder with a notch, the one that I got don't have that notch nor that piece. So I was thinking I may got the wrong type of master cylinder which would also make sense because the new one didn't come with a resavore and my old one wouldn't fit. so right now the res. is in the master cylinder but sticking out just a bit but the fluid is still going through the cylinder. Also, I have found no leaks of brake fluid anywhere.

 

It is quite possible your new MC is different enough to be causing your problems. Permit an aside comment/recommendation: If you still have your original MC and can get a rebuild kit for it, it is possible to have it "sleeved" in brass or stainless steel. (Attempting to hone the aluminum cylinder insides will likely not be successful, you need a new internal surface of correct bore.) This is pricey but would restore the internal bore to a pristine condition and might solve your brake problem fully. Many owners of really old vehicles use the sleeving attack as the best way to fix brake components that can't be replaced with new. Cheers, Pavel.