hinchcliffe

I've replaced the rubber lines front and rear now the pedal goes to the floor. I've used my motive power bleeder. Tons of air in the front came out but not much in the rear. I changed from Super Blue to Gold fluid so I know the fluid went through. With the engine off the the pedal stiffens up but if I push hard I can get to the floor. I did bleed the master cylinder and all is well.

I'll check to see if there is any leakage again, but there was none earlier. The fluid is topped in the master cylinder as I checked that first. Clutch is fine and brakes engage, albeit not hard, at the floor.

Anything else to look at? To me the fact that the pedal hardened means the booster is fine. Can't imagine the seals in the master went just when changing the lines, but stranger things have happened.

Mrmerlin

is the MC original?
Did you do a pedal bleed that is push the pedal to the floor?
if so then the seals have gone over the unused portion of the MC bore and been cut by the corroded bore thus cutting the seals.
More than likely you need a new master cylinder and right now your wasting fluid

chrisjbell

Its air or a leak and since the pedal does harden up I'd lean towards air. Not too many things that can cause those symptoms... they can be hard to find though. Make sure none of your new lines are letting in air at the connections. Mrmerlins thought makes good sense.

hinchcliffe

No with the power bleeder it pressurizes the system and fores the new fluid into the space of the old fluid.

I'll have to bleed again , yes original MC. Although I go near the floor on the track with the pedal when I work it, I've never had brake issues. If bleeding again doesn't help a MC will be on the list. Looks easy enough to replace, considering I've completed my Timing Belt, replaced the shocks and now the brake lines.......

Nicole

You may want to look-up the ordeal we went through with my car when the brake lines were replaced.

In a nutshell: We bled the system many times, with multiple techniques, replaced the master cylinder (no difference), cycled the ABS (SharkSkin had built a special device for this) and replaced the bias valve (big difference); Eventually, Greg Brown replaced the rear pads with original Porsche and adjusted the brake pedal. I recently drove a low mileage 91 S4, and confirmed that my brakes now feel pretty normal.

dr bob

I had a lesser case of what Nicole described. I tried the power bleeder, pedal bleeding, vacuum bleeding, etc, and nothing seemed to firm the pedal up to where I thought it should be. The brakes still stopped the car OK, the pedal just seemed a little low and soft.

So I was doing a maintenance rebuild of the system with new hoses, pads, rotors, and rebuilt the calipers. I took significant care when removing the brake hoses to IMMEDIATELY cap the ends of the steel sections so they wouldn't drain out. I used short pieces of vaccuum hose slipped over the flared end of the steel line section, pinched with a hemostat to 'stop the bleeding'. Seemed like an appropriate use at the time.

After rebuilding the calipers, I filled them with fluid and bled them individually off the car with the pressure bleeder. That way I could push fluid through the hose, gyrate the assembly to make sure there was no way that there would be any air trapped in a high spot, and make sure the bleeders were high to get whatever air was left in there pushed out through them.

For the steel brake line sections, I isolated each section and used a combination of a vacuum bleeder and the pressure bleeder to push/pull fluid from the low end to the high end of each section of steel line individually. Section by section, I worked my way up to the ABS unit from either side. From the wheels through the ABS unit, then from the MC up through the ABS. Always lower to higher, so air bubbles would always be moving uphill with the fluid flow. Pressure on the low end, vacuum on the upper end of each section of line. It took the best part of a casual afternoon to flush and bleed do the whole car this way, not including the caliper rebuilding, but the results are certainly worth the effort IMHO. The pedal is high and extremely firm now. There's some benefit from going from 20+ year old original brake hoses to the Goodridge hoses from 928 Int'l, but getting ALL the air out really made the biggest difference.

I casually cruised through 3 quarts of Valvoline DOT-4 synthetic fluid (less than $30 with tax at the POLAPS) during the operation.

I started doing the bleeding this way as an experimental exercise. I probobaly should have taken the extra day to document the whole thing with video, pictures with circles and arrows on the back of each one, and a Duane-like narrative description that might make it look as painless as it wasn't. (sorry Duane...) Stuff like this is therapy, not work, right?

hinchcliffe

Pretty straight forward to remove/replace the MC? Remove the fittings/reservoir, remove the clip on the brake pedal and loosen the booster. Then pull the old one out?

Really can reach everything? Bench bleed the new one, fill reservoir and open fitting push rod close fitting and do again?

I found a new ATE one for $240 shipped from a reliable source so I'll be tackling it this weekend.

Any other gotchas? I've searched and only see that some remove the backside line at the check valve from the abs? This is an 87.

atb

When I replaced my stock brakelines with stainless I had a weak pedal, although I re-bled many times both with the power bleeder and two man method.

I unbolted the calipers one at a time and raised them up out of the wheel well so the brake line extended upward with the caliper being the highest point, and then rotated them around in my hands. The idea was to get any air that might have been trapped in the brakeline or caliper to the nipple. Re-bolted and and rebled. Pedal pressure was fine afterward.

dr bob

Bench bleeding uses hoses or steel line from the outlet ports back into the reservoir. I have a collection of plastic fittings and hose for just this purpose. Or you can buy a couple sections of flared steel brakeline, cut them in half, and screw the pieces into the MC ports. Tubing forms OK with your fingers, but avoid kinks obviously. Then MC clamped level in the vise. Add fluid to the reservoir. Pump GENTLY with a screwdriver, until no more bubbles come back through those lines. Leave it all connected as you install, or put the plastic shipping plugs back in if you need the room for MC installation.

MFranke

You don't need to unclip the pedal. Just unbolt the MC from the booster. You may want to disconnect the ABS and brake pad wiring so you can move it out of the way to prevent accidental damage to the aging barrel connector as you try to deal with the MC fasteners.

kawi825

Hey Curt, just a suggestion.. check the rubber grommets under the fluid reservoir too. Mine were all dry and cracked. Just ordered from Roger.

MFranke

A new ATE MC should come with new rubber grommets for the tank.

Mrmerlin

If your installing a new MC get some dow corning 111 and put it on the outer edges of the new grommets this to assist in keeping water out of the MC grommet bores

supercedar

I never see any mention of pressing pedal firmly with power bleeder on. and open nipples.
Thomas

dr bob

Not sure it buys you much, plus letting the pedal came back with open bleeders will cause back-flow into the calipers. Put the receiving bottle at each wheel above the caliper, with a hose sloping continuously and the bottle end submerged in the fluid, and it reduces the problem IF you take the time to allow any bubbles to work their way up the hose before you release the pedal.