OG BBF

Hi guys

Wanted to run this by you as having an issue with my new brake setup.

I've installed big brakes all around 356mm fronts and 330mm on the back. Deleted the abs and made new lines all around and have a wilwood proportioning valve installed. I used also the larger 929 non abs master cylinder for the install. Here's the thing. I bench bled the MC and installed. The. I bled the system. The pedal felt rock solid. When I took it for a test drive, upon turning the car on the pedal sinks, it still stays firm at the bottom, it doesn't hit the floor and the brakes still work great but the pedal travel is very excessive and soft. I've noticed that the front brakes are dragging, you can spin the front wheels by hand but it takes a lot of effort and of course the fronts are getting very hot. I'm not losing fluid anywhere the reservoir stays at the same level.

Any ideas? Would I need to adjust the push rod? I thought these master cylinders were identical in piston rod length and depth. I have also got the prop valve all the way out so least pressure.

Any help ideas would be great. I've read a few things that there could be an issue with the MC sucking in air somehow but bench bleeding it seemed perfectly fine.

Thanks.

rx7jocke

Go dual mbc without brake booster, you will never get it perfect otherwise.

OG BBF

Don't want it perfect, just don't want the front brakes binding.

TomU

iTrader: (11)

Sounds like you may a couple things going on at once. On the brake pedal, simple physics there. If you are pushing a non-compressible fluid, the fluid moves. On that point, the fluid could be moving through a leak, either a hose or inside the booster. Since you said the level hasn't moved, that rules that out. That would mean it's not non-compressible. You may still have air in the system. Another possibility is what you replaced the ABS system with. Did you replace the hard lines with rubber hose? If so, rubber will expand (less so with braided hose, but it will still expand). Are the brake lines to the calipers braided?

As for the sticky caliper, either the pressure is not consistent, or there's something mechanically binding. Are the pad depths consistent with the other side? It could be the pistons. You may want to try rebuilding it.

ptrhahn

iTrader: (9)

You say it only seems to occur when the car is turned on? What happens if you turn it back off, does the binding go away, and pedal height return?

All turning on the car does is push pressure in the tank. Usually the pedal is a LITTLE softer with the car turned on than not, so it sounds like a little too much of whatever than phenomenon is, is what's happening. It's "vacuum assist"-ing the brakes on.

OG BBF

Thanks for the reply gents. So the whole system is brand new. I replaced all the hard lines with new polyarmour lines. All the flexi hoses are stainless steel braided lines.

When I turn the car off the pedal builds pressure. When I turn it on it sinks almost all the way down. No fluid leaks. Checked the booster and looks fine. Adjusted the push rod length back so I know it's definitely not keeping the MC piston pressed. I removed both front calipers, pressed the Pistons back into the calipers no issues, reseated the pads and wheels spin freely. Press the brake pedal and the are binding again. The calipers are brand new so it can't be a fault with both of them. I unscrewed the brake line from the caliper to see if it relieved pressure off the disc but it didn't. At this point I am baffled, it's a very weird problem. I spoke to wilwood to see if the prop valve could be at fault but they said there is no way they would cause binding of the front brakes as they are only passages for convenience. All the pressure changes are on the rear pads.

Can someone confirm that the rear brake output on the MC (closest the firewall is for the rear brakes. And the other port is for the front.

One thing I think it might be. In using the Mazda 929 cylinder with abs for the upgrade. Since I deleted the abs unit maybe I need the non abs MC? Would this even make a difference?

ptrhahn

iTrader: (9)

I don't think you need a "non ABS" MC, though you might swap your OE 93 MC back in to eliminate it as a cause. I got a 929 MC years ago brand new from, Mazda, and it was bad... wouldn't bleed out. Took it back, swapped it for another and it was fine, so occasionally new parts can be bad.

P

BLUE TII

iTrader: (9)

I don't know the design of the Wilwood rear bias proportioning valve, but...

If the proportioning valve incorporates a check valve like a "safety braking" proportioning valve, it could be as simple as you have the clutch pedal to master rod adjusted too long and it is only affecting the front brakes because the residual hydraulic pressure is low enough not to push past the check valve in the rear brake proportioning valve.

OG BBF

I've tried 2 MCs and the original one back in, still having the same problem. Blue TII, I'm not running the clutch master off of the reservoir for the brakes. I've given the clutch master its own reservoir and I'm using the 929 MC reservoir without clutch master nipple.

Fritz Flynn

iTrader: (263)

I'd check the front brake lines themselves. One could be crimped or blocked with some debris.

If the fluid can't flow freely you'll have this type of issue.

OG BBF

Thanks fritz, I will give them another look. I did undo the banjo bolts at the back of the caliper to see if that relieved the pressure on the rotor but no such luck :/ this problem is very very bizzare indeed. Brake issues are usually very logical but this has me stumped

OG BBF

The issue may have been solved gents, turns out these calipers (Ksport 8 pots) are no good with 18mm brake pads. I've ordered some 17mm ds2500s which I have been assured will cure the binding. Thanks for all your help.

ptrhahn

iTrader: (9)

I was going to say—if you undo the banjo at the back of the caliper and it doesn't relieve the pressure, it's the caliper. Hope this does the trick.

OG BBF

Hehe thanks man, tried this before and it done nothing lol. Thought it would be weird if both new calipers had the same issue. If the discs don't fix the problem I shall be back with a review on which calipers not to buy lol