Caravan brake problem!

[Lee'sdaytona]

Greetings,
I was just returning from a nice 2 hour drive in my turbo mini. I start to get this bad shimmy, which I thought might be a flat tire. Nope. As I pull off the turnpike, I feel like my brake pedal is moving a bit further to the floor before it stops than normal, but maybe I'm going crazy. I take it the rest of the 20 minute drive home. 10 minutes from home, after test-stomping on the brake pedal a bit, it goes further to the floor, and the brake light comes on. Thank god I converted it to a stick, I just did engine braking, and some e-braking and made it home safe.

The fluid is a bit low, about 1/4" from the bottom of the fill holes. What should I check first? I can't see any obvious signs of leaking just yet. Should I pull the rear drums off and the front tires to check the calipers?

If the MC went bad, will a Daytona MC work fine or does the minivans have a larger bore MC?
Thanks,
Lee

[shadow88]

If you don't see an external leak, I would pull back the master cylinder and look into the booster for your loss of brake fluid. Finding where the fluid went should be priority #1.

[Lee'sdaytona]

Yeah, well, I did a quick look around the car, and found no brake leaks, IE, around the insides of the rims. But that doesn't mean there can't be fluid in the drum.

I suppose I could easily pull the MC from the booster without unhooking brake lines.
Most signs point to the MC since it is the oldest component in the entire system, but that doesn't explain the shimmying on the road? Would a MC going bad cause a caliper to hang up?

[Vigo]

No, it wouldnt.

The fact that you picked up shimmying and had a sinking pedal leads me to believe you had a dragging brake which overheated and warped a rotor or drum, and led to boiling brake fluid which caused a soft, sinking pedal.

Generally that would cause a noticeable pull if you let go of the steering wheel (you might not feel it in the wheel while holding it).

[cordes]

No, it wouldnt.

The fact that you picked up shimmying and had a sinking pedal leads me to believe you had a dragging brake which overheated and warped a rotor or drum, and led to boiling brake fluid which caused a soft, sinking pedal.

Generally that would cause a noticeable pull if you let go of the steering wheel (you might not feel it in the wheel while holding it).

And that would be easy to test because the brakes would work as normal once cooled down.

If you've got a leak you should be able to start the car and pump the fluid out pretty easily with the pedal.

I have had a bad caliper which would not bleed for anything. It was the seal around the piston allowing a little air to be sucked in without leaking any fluid. I would have not thought that possible were it not for perfect brakes as soon as I swapped and bled a new caliper.

[Lee'sdaytona]

Ok, so a bit of an update/another question

I checked the front calipers by removing the front wheels. The disks and calipers appear to be in great shape with no signs of leaks. The front calipers/pads/rotors were replaced in 8/2009. The rear drums, shoes and wheel cylinders were replaced in 1/2011, but I didn't pull the drums to look at them. I decided to replace the Master Cylinder, if for nothing else, but piece of mind. As far as I know, it is the original MC from 89. I did have much more pedal this morning moving it into the driveway, but still not the norm.

When removing the MC, I managed to get the lines off without damage. I took both nuts off which hold the MC to the vacuum assist. The MC is stuck on there. It appears the right side stud is free from the MC, but the left side stud appears to be frozen in place. I hit it with PB blaster and going to give it some time. Are there any tricks to get these off without damaging the vacuum assist?

Thanks,
Lee

[cordes]

I've only messed up the lines coming off of the MC. I've never had an issue getting one off of the booster.

[Lee'sdaytona]

Vigo, I think your absolutely right. I managed to finally get the MC free from the booster, but it took one hell of a fight. I installed the new MC, bench bled, and bled the brakes. The pedal is back to normal now. Took it out on the highway, and after a few miles started shimmying again just as bad as before. I decided to take it to my mechanic, as I won't have time to fix it myself. I'm not even sure how to diagnose this? How can you tell if a disk is slightly warped, or if a caliper is hanging up only at highway speeds? It kills me that the entire front brake system is only a few years old. The disks have no grooves whatsoever in them!
Oh well.
Thanks for all your help as always.
-Lee

---------- Post added at 09:01 PM ---------- Previous post was at 09:00 PM ----------

PS, the mechanic said it sounded like something was hanging up and heating up causing the fluid to boil, just like you said....

[Vigo]

The easiest way to tell would be to just see which way it pulls.. dragging front brakes pull hard to one side when you hit the brakes, back brakes dont pull as much when you hit the brakes.

You can also apply the parking brake lightly (keep your hand on the release!) while driving to see if the shaking gets worse. That would point to it being in the rear brakes.

[Lee'sdaytona]

I'm relatively certain it is the front brakes, because the front end is shaking the most. The rears are not even a year old. Also, the problem is intermittent. For example, I drove all around town on my test drive, no problem. Got on the highway up to 75mph, no problem. A few miles up the highway, it started shimmying like crazy. Pulled off, and kept it under 45mph, and all was normal again. The van also did not pull to any side, though when I let go of the steering wheel, it was not shimmying, so I guess that tells me nothing.
-Lee

[cordes]

I'm thinking you've got two independent problems.

[Lee'sdaytona]

Yeah, maybe. I am having them grease/replace the front wheel bearings. The driver's side wheel bearing started chirping back in the spring. Maybe that is an issue too.
-Lee

[turbovanman²]

You can't grease the front wheel bearings. Rear wheel cylinders don't stick on.

Figuring which caliper is hanging is cake, go drive it, when it starts to shimmy, pull over, now stick your hand on the front wheels or close to it, the one that burns your hand is the bad caliper.

[cordes]

You can't grease the front wheel bearings. Rear wheel cylinders don't stick on.

Figuring which caliper is hanging is cake, go drive it, when it starts to shimmy, pull over, now stick your hand on the front wheels or close to it, the one that burns your hand is the bad caliper.

+1 Most of the front bearings need to be pressed in too.