long pedal after sport-brake swap
 

I put sport calipers up front and now I have a long pedal.

Specs:
1991 car and master
big sport brakes up front
standard 1.8 rear
wilwood valve

pedal drops 1 inch then gets firm on the brakes
bled the brakes all the way around, multiple times
bench bled the master


confused Time for a tilton pedal box?

you has leak. abs?

does the sport package have the same brake cylinder as regular?

I'm pretty sure I don't have a leak. No ABS. I have budget brake fluid in it because I'd rather use that to fix bleeding issues. I doubt that is the problem because the pedal is still firm after it drops. It feels like I have a really big air bubble (had this problem once before).

Targa Miata

negative. I can handle more pedal movement, but not the 1" dead zone. I've read that the 1" drop is an air bubble issue, not master cylinder displacement issue.

Hustler,get a power bleeder,it will makes things alot easier to bleed air out of the braking system.

It sounds like you have a big air bubble trapped somewhere.

I agree spike, most likely in some of the funky fittings or wilwood valve. I've had this before where it seems like I have to drive the car for a while, then the air bubbles migrate to the bleeders...is that crazy?

Can anyone confirm this symptom to NOT indicate inadequate master cylinder displacement?

this happened when i would bleed my ABS equipped miata. Air pockets would get stuck in the ABS unit, I would have to cycle the unit a few times before i could bleed to force the air out.

I think the turbo is thugging the brake parts. I'll ask it nicely to stop.

On a side note, anyone have a link to good, affordable heat shielding for the brake lines and something to wrap around the valve?

You can head down to BEGi and ask them to make you a custom heat shield.

or search. since it's been covered in multiple threads.

"heat sleeve" was the magic I needed. buy buy buy

If you had the master off, it could not be adjusted properly to the pedal. IE-pedal "falls" till it takes up the slack and makes contact with the master, then it's brakes like normal.

Or you still have air in the master, which is my second guess. I doubt you bench bleed it well enough. +11113232 to a hand-held vac pump, as these make bleeding shit a lot easier. (read-you'll never do it without one after you try it)

Also since you changed calipers, they could still have air in them. You should gravity bleed those too.

I had this 1 inch slop before with the stock brakes, and the same one inch slop with the sport brakes.

Its like 1 inch of nothing, then firm pedal. From what I remember it was the same with another MT netters car, so I just learned to live with it. Braking performance has always been very predictable and consistent.

Maybe I should lengthen the master cylinder piston and see what happens with the slop.

I thought that was only possible with the clutch master?

pop the master off (two bolts and a tug-job) then take the black rod sticking out the back and spin it. Then you have a longer or shorter engagement height.

Hustler,I suggest you get one of these,once you use one,you will never bleed brakes without one again.

Motive Products

I have the miata specific bleeder.

I have one for my vw, just need a miata-compatible cap.

I pressed in the cylinder, slowly by hand multiple times, then with a wood clamp thingy that compresses the piston really slowly. What's this pump you speak of?

Can anyone confirm this?

better one at harbor freight. That one you linked to won't hold the pressure unless you are still pumping it.

Harbor Freight Tools - Quality Tools at the Lowest Prices

or... sigh... same thing but cheaper at sears. Oh well, sears is 10 miles from me, and HF is only 2 :)

http://www.sears.com/shc/s/p_10153_1...7058000P?mv=rr

The Sport brakes use larger pistons in the calipers and a larger master. Putting the front pistons on and leaving the rest of the system alone is going to give you more pedal travel, no matter how well you bleed the system.

Will the increase in travel feel like a 1" dead-spot, or should there be some pressure throughout the travel? My buddy with a 94 has the same brake set-up and no dead-spot. I'm about to switch to 1.8 fronts because of the drama. However, after about 50-track hours owith the standard 1.6 brakes, I don't mind a little extra travel.

fyi, I do not think this is related to the brake valve.


Thanks for chiming in.

Summit Heat Protective Products

There is tape on that link as well. I might have some scraps if you come South of the River.

Same with me. It is annoying. I adjusted some of the play out with an adjustment to the Master, but didn't want to do too much and have them dragging. Might do this next time the car is up in the air.


Chris

I'll swing by next week. I'm stuck in Houston again this weekend. Wanna hold my car over the weekend?

Kill the engine, pump the brake pedal till all the vacuum is gone. Now, do you STILL have the 1" of slack before it gets hard? If so, you have slack before the master. If it's now hard as soon as you touch it, air.

Sure, but there's no room in the garage.

Chris

:confused: So no slack after the dead pump means slack in the master/pedal connection?

Chris

Looks like I am a winner!

I don't understand what you're asking. Reread what I said above. With bigger calipers and not a bigger master, there will be more travel. But that doesn't mean there will be a "dead" inch in the pedal by any means.

Re-read.

You have air in your system.

correct, firm from the top...another reason why I think its air and not the master.


edit: If I pump it, its rock hard, instantly.

Air. Get the hand held vac pump I linked you to. They got them at any autoparts store. Bleed that shit. /thread

Also get a screwdriver and tap on the calipers with the handle. Helps to get tiny air bubbles stuck to the sides of the cylinders to "let go" and float to the top where they can be bleed out.

I don't understand the need for the hand-pump.

You do now.

I love you.

:ugh2:

I meant that if you pumped it while the engine was off, and there's no slack then that would mean that the freeplay while the engine is on needs to be adjusted with the Master/pedal lever.

That confirms what I thought.

More detailed explanation: Sport Compact Car: Technobabble: December 2002

"Fifth thing to remember: Bigger pistons in the calipers mean more pedal movement."

Sorry, had to link the old SCC article. SCC used to have some good information every couple issues.

Chris

Hustler,you might want to try using your penis pump to get the little air bubbles out.

I'm pretty sure I'll need a bigger one for the 8mm bleeder.

fixed

This brings up a few questions I have about bleeding brakes. Should you have the engine on (i.e. pressure for the booster) while bleeding? I feel satisfied with the pressure when bleeding, then turn the engine on and it gets a little too soft for my liking.

With the Wilwood valve, should I bleed with it all the way open or closed? (open is unscrewed, closed is screwed in, correct?)

And again with the Wilwood valve, if I go from all the way open to closed or closed to open, the first pump of the pedal is just a titch softer than every pump after that, is this normal?

I was expecting to be able to lock up the rear brakes first pretty easily with the valve all the way unscrewed (the opposite direction of "less brake") but even with it all the way open, I seem to be barely getting the even pressure between front/back that I was hoping would show up somewhere in the middle of the valve's travel. This was tested in the wet and dry, if it makes a difference.

You don't need the engine running. The booster simply increases the amount of pressure in the brake system for a given pedal pressure. You don't need much pressure to bleed the brakes, thus there is no reason for the booster.

The Wilwood setting shouldn't make any difference - again, you don't need significant pressure. I can see how the first pump after adjusting the Wilwood might be slightly softer, but I wouldn't worry unless it's causing a problem.

If you don't get rear lockup even with the Wilwood set all the way to "more brake", then you either have a mechanical problem with your rear brakes (check those slider pins) or your setup is so unbalanced that even running even pressure won't give you rear lockup. By the way, the rears will become more prone to lockup as traction increases, so if they don't lock in the dry they definitely won't lock in the wet.