I just got a 94 2wd pickup. I've noticed a couple of problems relating to the brakes. First, they fade (pedal goes to the floor) under constant pressure. I feel like there's air in the lines and will bleed them tonight. Other thing is that sitting at a light with pressure on the brakes the engine rpms drop from near 1000 to 500 or so. It'll just drop for a second, then back up, and a few seconds later back down again. It will sit and idle fine, it only does this when holding pressure on the brakes. I'm going to pick up a manual tonight too.

Thanks

Greg

 

If you pump and hold and the pedal goes to the floor, it is probably your MC going out. You may also have an issue with your brake booster, but I would focus first on the MC.

You can bleed them and see if that works, but it sounds fishy that you are essentially losing hydraulic pressure on a whim. Air could be in the lines if your reservoir dropped down too low, and while on a decline or incline air got sucked in.

 

I guess it could be air, but it really does sound like the master cylinder may be going bad. My camry started doing that it until it failed completely. Be careful driving and don't brake at the last minute. If it fails completely, you won't be able to stop at all.

Mine started to fail when I changed the brake pads. I don't know why, maybe it was because the new brakes pads were making the MC work harder.

 

Thanks guys,

I bled the brakes which seemed to do the trick for about 1/2 mile. I was stopping hard during that 1/2 mile again and again. No fade. But then it started again and the idling issue was more pronounced.

I am not losing any fluid. I drove it over 200 miles yesterday (just to get it back home) and didn't lose any. The cap on the master cylinder is messed up and doesn't stay sealed. I strapped it down to keep it on tight. It will hold pedal pressure when the engine is off. Only goes to the floor when the engine is running.

The idle speed drops kind of like it does when you pull the dipstick. That's why I was thinking some kind of vacuum issue.

Thanks for your help already. Looks like I found a great resource.

Greg

 

I found this thread which seems to sum up the idling issue, and attribute it to a vacuum leak. Being that mine is accompanied by brake fade, am I being reasonable to assume the most likely scenario is a leak in the brake booster?

 

Just a question - if your pedal feels like it goes down further than it used to, and then it feels like something is almost "Pushing back," like the brake booster is kicking in or something, does that mean the MC could be going? My brakes have gotten sorta weird lately. It's like they're not as responsive as they were when I got the truck (I'm pretty easy on my brakes so it's not as pronounced, but when I hit the brakes a little harder I notice it). It's it doens't go all the way to the floor, but it goes farther than I'd like it, and suddenly it's like something kicks in and the pedal gets rock solid firm and the brakes work great all of a sudden. Thoughts?

 

After a little tinkering the problem seems to be with the coolant. Sounds far fetched but when I get to the same point in my test drives the brakes start fading, and the idle starts fluctuating. This point is on a hill at a stop sign. So I thought about the air in the radiator problem I heard mentioned. Checked the radiator and it's a little low. Added a little, went back out, and came back and it was all coming out the overflow. So maybe a thermostat?

Who knows. I'll post a solution if I find one.

Greg

 

I am willing to bet you have two separate problems here. Under no circumstances should the brake pedal go all the way to the floor - unless the MC is bad, or you gave a leak/air in the lines. Toyota would never design a brake system that was dependant on the idle staying consistent. Yes, the brake booster could have something to do with this, but the pedal would not go to the floor, it would just become really hard to push; in other words, you would still have brakes.

 

yeah, the brake problem is a separate issue...i also think MC...it can leak internally without any fluid ever being lost.

the fluid makes it's way past the seals inside and just ends up on the other side of the piston, but still inside the cylinder or resevoir.

 

That's what I'm thinking too. I let it idle for about 30 mins. last night as I added coolant trying to get any air out. For most of this time the brakes were soft, but held. I was alternating between heat and a/c. Then all of a sudden (with the a/c on) the engine idle started fluctuating again with the brake pedal and the pedal goes to the floor. There has to be some correlation, although it's probably just a contributing factor.

I really appreciate you guys helping out so much. The input has been valuable.

 

I think I've got it fixed. Here's what I did:

1. You guys were right, replacing the master cylinder took care of the fading brakes.

2. Parked it on a hill and let it idle with the radiator cap off. Seemed to burp out a lot of air. This helped the fluctuating idle problem tremendously (only does it when the a/c is on now).

3. Lowered the engine idle speed. Just about knocked out the fluctuating idle problem. Still does it a little. I think the problem is with the a/c on idle speed which seems to be high at around 1350 rpm. Soon as I figure out how I'll lower this to the correct speed.

Thanks for all the advice.

Greg