Brake pedal hard when car is off, then soft when the car is on????
 

2000 Integra GSR w/ITR brakes all the way around.

When the car is off and I bleed the brakes and the brake pedal is hard as a rock. As soon as I turn the car on, the pedal gets softer. There is still brake there, but it just doesn't feel like it should.

I replaced the MC last night and re-bled the brakes in the order Acura said to (LF, RF, RR, LR). Before I changed the MC out, I went through a whole bottle of ATE superblue just bleeding and it was acting up so that is why I changed out the MC. So after I did that and again used another whole bottle bleeding each caliper, the pedal is still softer when the car starts.

Any ideas? I don't wanna keep wasting fluid, but I will if I need too.


Just a quick thought lol... what if I bleed the brakes like I was bench bleeding the MC? Put 4 long hoses from the calipers back into MC and have someone hold the hoses in there and open the valves on the calipers and then pump the pedal until no bubbles are present? To me, that seems like it may work, but just a crazy though right now.

* brake pads are carbotech XP10 front and HP+ rear.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

I some how installed the front inside pad wrong and the backing plate would flex, ie inside pad bending. Still not sure how the hell I did it.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

If you still have a brake booster, that is normal. Turn car off. Press on brake pedal, and it should be hard. Leave foot pressed on brake pedal and start car. As engine vacuum adds force to the brake pedal via the brake booster, pedal will go down, and feel much softer, until you reach max pressure. Brake booster reduces required pedal effort, so it feels completely different when car is off compared to on. If pedal is hard when motor is off, goes down and is softer when motor is on, and goes back to hard when motor is turned off, everything is likely normal.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

also check that seal between the mc and where it "mounts" against the booster.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

This!

Re: Brake pedal hard when car is off, then soft when the car is on????
 

i believe he is saying they still don't feel firm like they should. he knows that a brake booster makes pedal effort easier when the car is running.

i think the problem he is describing is a sinking or soft pedal with the booster assist, though it pumps up firm and bleeds normally with the car off...


or, i may be off on his description...



my guess is a possibly a failed booster - the atmospheric check valve may be clogged, causing an overboosted and thus really soft/easy pedal. brakes will work normally, but pedal travel will seem long, and soft.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

First so the diagnosis steps on the booster contained in this document:

http://www.autoshop101.com/forms/brake05.pdf

The is booster operation seems OK, proceed to road test. You can just warm up the brakes with 5 gentle braking events and then do five hard snubs just avoiding lock-up on the road down from say 70 mph to 20 mph and time each braking event with the booster connected using a stopwatch. Then disconnect the booster, plug the vacuum line and do the same thing on the same stretch of road. You will have to push much harder on the pedal. Compare the times. If they are similar, everything is likely OK. If pedal starts to go to floor at any point, back off, take it home and try to diagnose the issue. Obviously only do this on an empty road without tight curves if you suspect the brakes of being defective. And don't do this if you don't have a hard pedal with the car off.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

Hey good to meet you today. I actually pulled the pads off and found that the top of the backing plate is actually hitting the top of the inside caliper body which is putting more pressure on the top of the pad and thus only using half the pad and the pads show the angled wear :( I'm not happy. It's the ITR brake setup. The issue is with the Carbotech pads as I tried on a set of OEM ITR pads and they fit perfect and allows the caliper to bolt on normally without putting any pressure on the top of the pads. I took a grinder to the top of the backing plate which helped a little but i still think the pad is sitting just a tad too high up. The bottom of the foot that slides needs to be like 1mm lower.

I will contact Carbotech and see what they can do.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

Oh, and now I have to go back and re-bleed all 4 calipers because after fixing the pads, I have no pedal. I bled the front calipers, but the pedal is worse now that before. It goes straight to the floor.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

Try bleeding them in the correct order and make sure there's no leaks.

Are you using swapped MC/Booster? If so, were they matched? I have a similar issue with ITR MC swapped in my Accord(stock Accord booster, rock hard with car off, but "sinks"/soft when car on), but it's simply due to the booster not being adjusted.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

If pedal goes to floor, problem is with hydraulics. Not a pad issue. If you have OEM ITR pads and they fit fine, then solve your hydraulic issues first using those pads.

If pedal goes to floor, 99.99% chance you have air in the system.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

Are you sure that order is correct? Usually when bleeding the brakes you want to start with the caliper furthest from the MC, so you would be bleeding the front brakes last - not first.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

^ The helm manual says the opposite. Start closest to the MC and work your way out.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

Re: Brake pedal hard when car is off, then soft when the car is on????
 

That's splendid, but still doesn't change the fact that the manual still says the opposite.

Here are a few things you can possibly check. Bench bleed your master cylinder, diagnose for a faulty brake booster and check valve. Check if you have any cracked lines from overtightening the fittings, and of course rebleed the system.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

I had the exact problem last year, and it ended up being a broken brake booster. It was the last thing I replaced but it fixed the problem.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

That's what I am thinking too. I will be ordering a new one.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

Also, try driving the car (carefully) around the block if you feel the brakes have pressure but just more "squishy" and see how it really feels. The "car off" will feel stiff as a board but I've had times where once I drove around and came back.. some air worked itself around and I was able to re-bleed the system and find the trapped air.

Also, are your left and right calipers on the correct side? Bleeder should be on the top of the caliper... I know I had to swap my legend 2pistons from left to right for this reason (castings are stamped with an L and an R)

Good luck!

Re: Brake pedal hard when car is off, then soft when the car is on????
 

Please let me know if the new brake booster fixes your problems. My gf car is doing the same thing, Ive replaced the MC twice and bled the brakes about three times but still goes straight to the floor when the vehicle is running but while bleeding with the car off gets rock hard.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

ok, i've been through this for an entire summer and have replaced EVERYTHING more than once.
first thing's first, make sure you bench bleed that master. this is very important. otherwise you are just introducing air into the system that may get stuck somewhere.

1. isolate your problem. do the front brakes work? Do the rear brakes work? i removed the brake lines and nut, bolt & washered them. its not the best but if you have a bad caliper, u can isolate them out this way. use crush washers.

-if the pedal is still terrible-

2. check for brake line swelling. for this, hook the lines back up (or check for this before u unhook them) and have a friend pump the pedal while you look for a swolen line. you can also feel for a soft spot in the lines.

-if the pedal is still terrible-

3. make up a couple of port blockers to block the 'out' on the prop valve. there is a company that sells fittings to do this. we made them with an old brake line and just welded it shut. try the back, then the front.

if none of this works:
bleed the entire system from the master all the way out to the calipers. crack the lines coming out of the master till u get no air. then do the lines INTO the prop valve. then the lines OUT of the prop valve. then the lines out at the calipers, then the bleeders. there is air trapped somewhere. you just have to find it.

also, if you messed with the rod length on the booster or lost the pad that goes into the brake pedal for the brake light switch and replaced it with a nut and bolt, that will cause an issue.

good luck.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

Did you bench bleed the master cylinder yet? It does sound liek there's air int he system still. Also, how did you bleed the brakes (helper pumping the brakes, vacuum pump, pressure bleed)? If you had a helper helping, did he push the pedal all the way to the floor?

Re: Brake pedal hard when car is off, then soft when the car is on????
 

According to the Acura Factory service manual, you bleed in the order: LF RF RR LR, so the Helms is correct.

And on page 19-15, it gives the procedures to test the brake booster.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

I bench bled the MC before I put it on till there were no bubbles present then some more. There could well be some air in the system, but I have literally gone through 3 big bottles of brake fluid. I had a helper. He is a Honda technician and he pumped the pedal.

I haven't tested the the brake booster yet because I'm working on my clutch as I busted a spring from the clutch disc while at Road Atlanta on the 2nd day.

Re: Brake pedal hard when car is off, then soft when the car is on????
 

i bled 5 GAL of fluid through my car 4 different ways and didn't get it out will we went through the system, found where the issue was and methodically bled it section by section.
https://honda-tech.com/forums/road-racing-autocross-time-attack-19/looooong-brake-pedal-2828912/

Re: Brake pedal hard when car is off, then soft when the car is on????
 

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