94 Accord Chump Car Brake pedal issues

The brakes work fine, the problem is the brakes don't engage until the pedal is almost to the floor. We've replaced the master cylinder (twice) with proper bench bleeding, replaced all 4 brake calipers, rubber lines with stainless steel, and adjusted the pedal slightly and still have the same issue. Brake booster is getting vacuum, but if those are bad you usually get a hard pedal right? Could I have gotten two bad master cylinders in a row? We are replacing the brake booster just for E36 M3s and giggles at this point but we are scratching our heads at this point. Didn't want to adjust the pedal too much with fears of screwing up the engagement of the master cylinder.

Any change in pedal ratio or caliper size?

Does this car have ABS?

Could be air trapped in the ABS pump or its lines.

Did you switch the front and rear brake lines at the master?

You say you replaced all four brake calipers, did you put the calipers on the correct sides? Had a similar issue with my Infiniti, turns out I switched the calipers in front and had the left caliper on the right and the right on the left. The bleed screws not pointing upward should have tipped me off. Felt like an idiot when I figured it out (L and R are cast into the caliper!) Switched them back and all was right again.

No ABS, went from standard accord calipers to nsx/legend calipers (just recently and the problem was before this swap), had swapped from drums to disc in the rear before as well but installed the appropriate master cylinder and proportioning valve to match (from rear disc non abs hondas). We've done 3 14 hour races, a couple PDXs, and a 3.5 hour enduros with a pedal that doesn't engage until it almost hits the floor. It's always been a little nerve wracking and I'm just ready to fix the issue.

I'm going to re bench bleed the MC and ill double check front to rear lines although I believe the bore sizes are different to prevent this.

Thanks for the help and sorry for brevity - from phone

Stepped masters aren't all that common, but the dual system does act weird if you swap front and rear. Really soft. Usually you want the front lines closest to the pushrod/booster.

Awesome thanks for the help Keith! I'll double check that tomorrow. Going to throw a new booster in while we are at it. The car still had the og one on it

sounds like air in the system or possibly an adjustment issue? can you try a non-slight adjustment? adjust the crap out of it!

I spent a lot of time going through the whole system last night. @keith the master cylinder is a stepped master cylinder but after researching the inter webs the stepped master cylinder is for an ABS car where we have no abs. Not sure it would make that big of a difference. No leaks coming from the proportioning valve and all the lines from the master cylinder to proportioning valve to the wheels are in the right place. Installing the new booster today, going to install a non-abs master cylinder, and bleed and hopefully I have a solid pedal.

You said you adjusted it a little.... is there more?

I'd investigate a little and see if the master is even being engaged until near the end of the pedal stroke. You might just need a longer rod or equivalent.

Bench bled the MC again, new booster is in, bled lines and master cylinder on car, adjust pedal (about 8mm of adjustment). Pump it up a few times feels great. Let the car sit and idle for a second and press on the pedal and it goes almost strait to the floor.

There's still air in the system someplace.

I've had this problem on other cars.

Try a reverse bleed to see if you can force the bubbles one way or another.

The trick is to do the "pump it up, hold it down, crack the bleeder" method but pump the pedal like you're blowing up a life raft on a sinking ship during the pump the pedal part, as fast as you can. BTDT a couple times on cars that had blown a line and ran completely dry.

There are no leaks and the cylinder isn't losing fluid over the course of time. I might switch back to the old prop valve. I've made number adjustments to the pedal, new parts, manual and power bleeds to try to dump air out of the system and it still won't hold a pedal. The only thing we haven't replaced is the proportioning valve.

Perhaps the system is missing a required residual pressure valve. Usually they're only required for drum brakes (~10 psi) or when master cylinders are below the floor (~2psi) but I bet it would solve your problem.

Maybe just one (in either front or rear) would suffice or possibly one in both (before they split)

Here is an example: http://www.speedwaymotors.com/Speedway-Disc-Brake-Residual-Valve-2-PSI-Purple,5312.html

I've had prop valves lock one way or another (they are actually often safety valves that latch one way or another to keep the system from emptying completely)

Some times you have to bleed at each fitting along the system to ensure everything is bled and not letting air into the system (which won't necessarily show as a leak)

Thank you guys so much for all of the help. Do you think even though the MC is mounted to the firewall a residual pressure valve will help? I'm going to change the prop valve tomorrow evening. I put a new master cylinder on it today, bled it about 6 times total, adjusted the pedal as I stated above, bled each line in the current prop valve. The one thing that I found before the wife ordered me home was that I kept getting a lot of air coming out of the front right caliper at the end of the pedal travel.

After reading reviews on speedway it's worth a shot with those pressure valves.

Sounds suspiciously like a reaction disk issue inside the booster. Do the brakes come on hard when they finally do?

Given how much other stuff you've tried it makes sense to try the booster.

Also, to save a E36 M3load of fluid you can run a clear hose from caliper to master cylinder which will also let you see if any air is coming through.

Put a new booster in today as well.

i'd really work at making sure that the air bubbles are out, and since the prop valve is the only thing not swapped out, i'd try a new one too. if the problem persists, throw a 2 psi valve (or two) in there and give that a shot!

DirtyBird222 wrote: Put a new booster in today as well.

Did it make any difference?

daeman wrote:

DirtyBird222 wrote: Put a new booster in today as well.

Did it make any difference?

Negative.

Will try out the 2psi residual valves today. If those don't do the trick. Old prop valve is going in. If that doesn't work, retractable boat anchor.

Also this is how the funky early 90s prop valves flow. http://s172.photobucket.com/user/JKao234/media/d_g2_integra_abs_removal.jpg.html

Well one of the other guys from the team came over to help me diagnose tonight. Apparently the calipers from an Acura Legend GS mount on the other side of the rotor. So we did a quick swap and got a nice pedal! Took it for a drive and it felt like the booster was bad. Check valve was on backwards. Took the car back out and pedal engages about 3/8 of the way down. Make a slight pedal adjustment and it felt much better. It's still a slightly spongy pedal but it feels way better than it has ever before. So maybe the old master cylinder or booster was bad. Pedal is good for this race.

Plan for after this upcoming race is to ditch the Honda prop valve all together. Devised a plan to run a line from the first port of the master cylinder to a T that goes to the two front brakes then the same thing for the rears just with an adjustable prop valve.