Poor brake pedal feel

[7Mboost]

Brakes go almost all the way to the floor but still work and work at the least, decent there. With the car off the brakes feel fine, but right when I start it up brakes feel poor and go to the floor. The brakes have been bled several times by 3 mechanics so I'm gonna have to rule that out. I also put on a new master cylinder today with no luck. (the car was bled after this as well) Any ideas on what could be causing this/similar problems?

Its on a 91 turbo with abs if you need the info, and the ABS light is not on.

 

[Doward]

Verify that your brake booster is working correctly - check that it doesn't leak, and that the one way valve is working correctly.

That's where I'd start.

 

[7Mboost]

Verify that your brake booster is working correctly - check that it doesn't leak, and that the one way valve is working correctly.

That's where I'd start.

Will do, how freakin' unlucky can I get with this thing.

 

[Doward]

Also:

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=BR&P=5

I doubt your booster has any problems (brakes would be stiff then) but check it just for piece of mind

 

[7Mboost]

John, where is the one-way valve located?

and: my dad played with the pedal a little bit and it didn't do anything, I'll make sure its set to those specs though.

You gonna be avail this week sometime?

 

[IJ.]

pedal......

there's air in the system

 

[7Mboost]

pedal......

there's air in the system

Lol my bad.

But seriously, we've bled it several times. My dad (don't worry he's a mechanic) just bled it earlier today (like 2 hours ago) and said there was no air in the system.

 

[IJ.]

Pedal CAN'T go to the floor if there's no air in the system as fluid in noncompressible.

There's air in there somewhere.

Either that or the Master is stuffed.

Do a pedal height retention test to confirm.

Engine off pump the pedal 4>6 times to exhaust the booster then press the pedal and hold the force hard for a few minutes, come back and let us know what happens.

 

[Doward]

Ian, I had the same thought, but I bled the system myself. Yes, I did get a bunch of air out of the system, but the pedal literally sinks to the floor when you step on it.

The car DOES slowly stop, and there is SOME pressure buildup - but nothing like I would expect. Pumping the pedal also does nothing to build pressure. (usually a sure sign of air)

That said, I do wonder if having the two connectors to the ABS actuator crossed, could have somehow introduced air into the actuator?

 

[IJ.]

Dunno John haven't had much to do with ABS/a70's but I'd imagine the hardpipes can only go one way/place.

Pedal height test I've asked for will reveal a lot.

I stand by fluid doesn't compress though

 

[7Mboost]

Dunno John haven't had much to do with ABS/a70's but I'd imagine the hardpipes can only go one way/place.

Pedal height test I've asked for will reveal a lot.

I stand by fluid doesn't compress though

Will check the pedal height first chance I get tomorrow.

Just did some brainstorming with my dad, he agrees with air in the system, he thinks its in the ABS box. How do I go about checking or bleeding that, I hear its a bitch!

Also John on the one-way valve, my dad thinks having the one-way valve backwards would make the pedal harder to compress? either way it will be checked though.

 

[easternguy2005]

You might want to see what pressure you're building/holding at the distribution box at the driver fenderwall. Then work your way to the ABS.

The ABS light should come on at first then after car starts the light goes out.

When I changed out my M cylinder the autozone one had the back caliper plunger installed backwards so it wanted to pull a vacuum and hold it there. You can tell that problem cause nothing sprays out when you bleed them. After you tighten the nipple the brake pedal pusher was reporting the pedal wouldn't come back up.

 

[tekdeus]

I have a similar issue. I just flushed and replaced my brake fluid with Dot 4. The previous owner removed and bypassed the ABS system. I used both a Vacuum bleeder as well as the pedal pusher method. My brakes still seem a little soft. With the engine off, the pedal is stiff, and doesn't move. How can I tell if there is air in the system?

 

[supraman87]

I had the same problem

 

[Muzy]

Was the MC bench bleed? As somtimes the pedal will not alow full stroke
thus can not push all the air out of the MC itself. Muzy

 

[boostinsupragirl]

air in the system, broken brake line or a bad brake master

 

[7Mboost]

Could my brakes feel weaker due to my FFIM? I have a 5/16ths or 3/8ths fitting hooked up the brake booster and when we pinch the hose to the booster with vicegrips the brake petal gains more resistance like I feel they should, what is the stock input size going into the intake manifold (on a stock one)?

 

[Doward]

The ID of the banjo bolt is 1/4" (measured) and the OD of the Banjo fitting coming off is 5/16" as near as I can tell (.335").

 

[RiyadYar]

i had similar priblems with my brakes and ppl kept saying air .. make sure the master cylinder was bench bled. and make sure that the booster pin is touching the MC piston. also it can either be your calipers or proportional valve. my problem turned out to be the calipers being seized open

 

[7Mboost]

Ok, pedal still feels the same with 1/4" hooked to the booster like stock. The brake pedal is within spec according to the TSRM, what should I try next?

Also I should mention the pedal feels like normal (stiff) when not running but loses its "resistance" should I say when the car is on. (running)