OT: Carolla brake oddness

[Dogma]

Sorry if this doesn't belong here, but I know some of the mechanical gurus here don't read the OT forum.

My wife's 95 Carolla gave me a bit of a scare on Saturday. Immediately after I started it, I realized that I could pretty easily push the brake all the way to the floor. Pumping the pedal has no effect. The fluid level was good, but black. Almost coffee-like opacity. OK, flush time. Fortunately, I had just picked up a mighty-vac from HF in anticipation of rebuilding my 850's brakes. Some of the bleeder screws gave me trouble, so those got replaced before everything was flushed and bled. After all that, the brakes are only marginally better, I might even be imagining that. I estimate it's getting %70-80 of the stopping power it should have, and no amount of pumping can build any more pressure.

After scratching my head, and consulting my dad (trained as a mechanic with the Seabees, plus decades of self-maintenance), we agreed that the master cylinder is the likely culprit, though the symptoms are nothing we've seen before. So, before I spend time and money on a master cyclinder, are they any other theories out there?

[82Shafty]

Internal seals are most likely the culprit.

As long as there are no external leaks I would suspect the master.

Make sure all linkage through the firewall is still intact as well.


Masters are cheap and easy to replace.. make sure you bench bleed it and then start at the furthest wheel in the system and work your way up. RR,LR,RF,LF.

I've seen several things cause this in the past

1) a Master Res. Cap that has allowed moisture to enter the system

2) Wrong type of fluid added to the system (engine oil)

3) A brake job was done not too long ago, where a mech will fully pump the pedal to the floor causing the piston to run into the bore area that normally is not used and picks up grub which tears up the piston seal.

Mainly I see them leak down the booster from the rear or down the firewall and if it is manual, not boosted, you can sometimes find it on the inner cabin of the car as well.

[Dogma]

Arright. Now that you mention it, I don't have a lot of confidence in the cap. It's a rubber thing that doesn't seem convincingly tight. Thanks.

[Suzuki mad]

When I've had master cylinders go the brakes normally seize on. If its loosing pressure I'd look at the wheel cylinders or the lines.

Suzuki mad

[Dogma]

When I've had master cylinders go the brakes normally seize on. If its loosing pressure I'd look at the wheel cylinders or the lines.

Suzuki mad

It's not loosing pressure, it just can't build any more than it's got. I guess I wasn't clear on that. With the engine off, the pedal is firm, but very near the floor. I can hold it until my leg gets tired, but it never goes further. With the engine running, I can push it right to the floor.

[PAULYBOY]

Have you looked at the vacuum lines, specifically the one off the booster?

[Dogma]

Have you looked at the vacuum lines, specifically the one off the booster?

No. Should I? What would I be looking for there? Vaccuum running down the side of the booster?

[peterpressure]

Are you 100% sure you have no leaks?

I had a VW once, the PO had run a brake line INSIDE THE CAR...

Well after siting one winter I went in to take it for a ride and had almost no brakes. Rode it around for a day dumbfounded, then I realized the carpet was kinda wet, wait no, not wet, SOAKED in brake fluid... Removed the carpet and there was a rusted line with fluid slowly leaking ou underneath...

Just make sure you know you have no leaks..

[Dogma]

Are you 100% sure you have no leaks?

I had a VW once, the PO had run a brake line INSIDE THE CAR...

Well after siting one winter I went in to take it for a ride and had almost no brakes. Rode it around for a day dumbfounded, then I realized the carpet was kinda wet, wait no, not wet, SOAKED in brake fluid... Removed the carpet and there was a rusted line with fluid slowly leaking ou underneath...

Just make sure you know you have no leaks..

Well, I saw no sign of them while I was under the car and what pressure it has, it holds until my leg gets tired. Also, if it was leaking, I would be able to pump it to build pressure, right?

[82Shafty]

IF it was leaking your reservoir would be low!


VW's and their internal lines ughhh. If you pull the drums and the cylinders are clean, and the calipers are dry where the piston comes out and if you physically trace the brake lines and all are dry, then you should feel that without a doubt it's an internal master leak (bypassing).

If it is vacuum boosted, check the back of the master to ensure fluid has not entered the vac boost, fluid can take out the diaphram!

[rusty boltz]

I wouldn't worry about the booster or the vacuum line going to it, if the booster was causing an issue you would have to stand on the pedal to stop the car (no assist). Either you have air in the system or the rear shoes are way out of adjustment. Since you've already bled the brakes I would look into adjusting or replacing the rear brakes. The extra pedal travel you are feeling is likely the gap between the shoes and the drum. An easy way to tell is pull the parking brake while moving, if it has little or no effect you need rear brake attention asap. Inspect the shoes and drums and if they look acceptable (if you have the correct tools you should measure) then adjust them. The adjusters may be frozen and need to be freed (whick would explain the lack of adjustment, very common). Some cars can be driven in reverse at a low speed then slam on the brake this forces the brakes to adjust, some cars its not that easy. Fortunately Toys are very easy. If the rear brake adjustment does not help then I would look at the master cylinder.
You can disregard everything I said about the rear brakes if you have disc brakes since discs never need adjusting. Then it would definitely be air in the system or a faulty master. But I'm pretty confident based on your described symtoms that it is a drum brake adjustment issue. If you have the patience to work on a 30 year old motorcycle this should be cake. Good luck!

[Dogma]

I wouldn't worry about the booster or the vacuum line going to it, if the booster was causing an issue you would have to stand on the pedal to stop the car (no assist). Either you have air in the system or the rear shoes are way out of adjustment. Since you've already bled the brakes I would look into adjusting or replacing the rear brakes. The extra pedal travel you are feeling is likely the gap between the shoes and the drum. An easy way to tell is pull the parking brake while moving, if it has little or no effect you need rear brake attention asap. Inspect the shoes and drums and if they look acceptable (if you have the correct tools you should measure) then adjust them. The adjusters may be frozen and need to be freed (whick would explain the lack of adjustment, very common). Some cars can be driven in reverse at a low speed then slam on the brake this forces the brakes to adjust, some cars its not that easy. Fortunately Toys are very easy. If the rear brake adjustment does not help then I would look at the master cylinder.
You can disregard everything I said about the rear brakes if you have disc brakes since discs never need adjusting. Then it would definitely be air in the system or a faulty master. But I'm pretty confident based on your described symtoms that it is a drum brake adjustment issue. If you have the patience to work on a 30 year old motorcycle this should be cake. Good luck!

I just put shoes on the rear a few months ago. It was one of those deals where Firestone was offering to check everything over for free or cheap, and then told me that the rear end needed drums and shoes. They wanted a ridiculous amount to do it, so I bought the parts and did it myself. They seemed dissapointed. Oh well. There was still some fiber on the shoes and the drums were fine, so I took the drums back. Funny, Firestone didn't offer to take $100 to flush the brake fluid, like they wanted for the Grand Prix (the brakes of which are currently working quite nicely). Anyhow, new shoes in there, and everything in good shape (including the adjusters).

However, I can't do your emergency brake test because the cable broke when I tried to set the brake for the oil change. It was working, just not as well as I wanted. I attributed that to the cable being about to break and stretchy. I didn't really pull on it that hard. I don't want to deal with this cable, but I should. Working on old motorcycles is so much less hassle in my mind. You don't have to crawl under them.

Anyway, unless something strange has happened in the rear end since I was in there, I think it's good. On to the master cylinder then (picking it up tonight). Unless there is some way that breaking the parking brake could cause the rear end problems you describe. But I've had cars without parking brakes before, with no ill effect on the hydraulic system. Thinking back, the pedal has been soft on this car for a quite a while.

[82Shafty]

After you did the rear brakes, everything was fine correct?

Did you bleed the brakes after you did your rear brake job?

Did you squeeze in the rear wheel cylinders in at all causing all of the crap to back flush into the system and damage the master cylinder?

For any of you who ever do a brake job on an ABS equipped car...even a Ford truck with just the rear ABS... crack open the bleeder before compressing! I cannot begin to tell you how intricate the workings are of the ABS solenoids are and how vital it is to never back flush crap into the unit.

I know many people over the years who have successfully compressed calipers and wheel cylinders with no ill effects whatsoever, me being one of them, but I've also seen the one out of ten come through the fleet which would require a master replacement. Then came ABS, no more back flushing and no more master replacement.

My point was not that he has a vac boost problem, obviously when Dogma described when he started the car, the additional multiplication of the vacuum boost allowed him to easily push the pedal to the floor. My point was that to always check the rear of the master when he takes it off to ensure there wasn't any fluiding leaking into the vac boost which will weaken the rubber diaphram. I know brake fluid is not supposed to swell rubber like other petrol products, but I've seen vac boosts get taken out by leaking rear seals on masters.

So, if it's dry, your golden. Instructions should come with your master on how to bench bleed the new master.

Also, fluid is cheap, by a fresh bottle and flush the entire system after you install the new master. After all, you certainly don't want to have to monkey around with the car when you can be out riding.

[Dogma]

No, I didn't bleed it during the rear brake job. I didn't open the system, so there shouldn't have been air in it. I should be slapped for not checking the level and noticing the color though. I don't remember how much I compressed the cylinder, but it's certainly plausible that some gunk was dislodged. No ABS to worry about. I'll have to remember the tip for future reference though.

I'll be sure to look around when I have the master off. SOP when disassembling anything.

[Dogma]

Update

OK, I've put the new master cylinder on it and fooled around bleeding everything. I can't get any more pressure to build in the system. I've put enough time into this thing that I'm frustrated and actually losing billable hours. That is, I'm so busy with work, I don't have any more time to fool with it.

So, I took it to CaRx to see what "experts" can find wrong with it. First, they tell me the hand brake cable was not broken, but the drums were way out of adjustment. No theories were offered on why it went bang when I pulled on it and there was no more tension. Perhaps things were so far out of whack that something came apart when I pulled on it, but it's hard for me to accept that I screwed up the reassembly that badly when I had the drums off. At any rate, the hand brake is supposed to be working now.

Now for the fun part. They tell me that when they blocked off the line to the front end, the master cylinder was able to build normal pressure. The theory is that a blockage in the front half of the system prevented me from bleeding the air out. I've pushed an awful lot of fluid out past htis blockage. They want nearly $700 to replace the front lines and calipers (oh, and the rotors are below spec, which have never been turned AFAIK). I can check and deal with the rotors myself.

Any opinions on a blockage causing my symptoms? Any reason I can't just replace lines and rebuild non-ABS Carolla calipers instead of paying $130 a whack for new ones (that come with pads I don't need)? It's not going to cost $700 more for Wendy to drive the Grand Prix if I have to wait to work on this myself.