924Board.org

porschetroy · Joined: 30 Dec 2002 Posts: 32 Location: Sacramento

I just replaced my brake hoses last week on my '82 931 with Goodridge stainless braided hoses from Weltmeister. At the same time, I replaced all my fluid with Ate Super Blue, rebuilt my front calipers, replaced the front rotors with drilled Zimmermans, and replaced the front pads with Porterfield R4-S's. The new pads seem to grab pretty well - once they grab. I have about a 1/3 of free brake pedal now though that wasn't there before. The problem definitely seems hydraulic though I bled my lines twice and there are no leaks. I didn't touch the master cylinder other than replacing the tank and grommets.

A Porsche racing buddy of mine claims he had the same problem when installing braided hoses on his 928. He actually put the old hoses back on and the problem went away. Has anybody else experienced a spongy pedal by switching to braided hoses or Super Blue fluid? I'd like to think there is still air in the lines because I don't want to replace the hoses again. I've already bled the lines twice though and there was no air in them the last time I bled them.

I'm assuming the Ate Super Blue fluid is not as compressible as the crap that's been in my car for three years. Anybody have any problems with this stuff?

-Troy

wdb · Joined: 02 Nov 2002 Posts: 2024

a vacuum leak in the vacuum booster or the line can make the pedal feel soft , try bringing up the rpm's to increase the vacuum and see if that changes the feel of the brake pedal . if the pedal gets harder ,you may have a problem with the booster ,or the vacuum line to the booster .

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

When you replaced the master cylinder reservoir, you introduced air into the master cylinder that is very hard to get rid of.

What order did you do the work in? Reservoir, brake lines, then brake pads? You should have replaced the reservoir first, then filled it with fluid, and allowed the air to bubble up through the fluid. Then flushed the old brake lines before replacing each one with a new line. Immediately after installing the master cylinder side of each new brake line, allow the fresh fluid to run though the line to fill it and flush any air down and out of the new line. connecting the caliper end, and reflushing each line at the caliper with the old pads in place. It is much easier to flush the brake fluid with old brake pads still installed, because the pistons are extended, and the bleed valve is not obstructed by the caliper piston. After flushing at least 4oz of clean fluid (without debris or air) from the caliper, close the bleed valve, replace the brake pads with the new ones and move to the next caliper.

Did you replace the pads before you flushed the fluid?

How much fluid did you work through the brake lines after you finished replacing the reservoir and the brake lines? I usually use a 40-48oz of fresh brake fluid to bleed and flush the lines with a MityVac, in my cars, and I never have spongy brakes.

Don't be afraid to pump lots of fresh brake fluid through the system. brake fluid is cheap, considering it's importance, and as the saying goes, you gotta break some eggs to bake a cake.

It is very difficult to remove all of the air from the brake system with the old pump and wait, open and close the bleeder valve with a partner system. Buy a MityVac vacuum pump, and the job becomes easier and faster, with better results.

porschetroy · Joined: 30 Dec 2002 Posts: 32 Location: Sacramento

Actually, I am using a Mityvac. I bled all four again yesterday and don't think I pulled any air out. I did have to put some teflon tape on the bleeder threads though 'cause I kept pulling bubbles through from the outside. It's hard to tell what's going on when that happens. There may have been air in my right rear caliper. They feel better today; I might just be getting used to it though.

I may have introduced air into the MC when replacing the reservoir but I don't think so. I left pools of fluid in both inlets while replacing the grommets and tank. I never depressed the MC while the tank was off and filled it back up as soon as the tank was on.

What you say about bleeding the calipers with the old pads kinda makes sense. I may try that next weekend. What a PITA! I "loaded" the calipers when I rebuilt them, then attached the hoses, then installed the calipers, and then attached the hoses to the dripping brake lines. Finally, I bled them. I went through one liter of fluid to do all the lines - it's all blue now. I still need to bleed the clutch cylinders though.

Thanks for the input. -Troy

924RACR · Posted: Tue Jul 01, 2003 10:12 pm Post subject:

I use stainless braided and ATE fluid in my racecar - no issues. You should try bleeding the traditional (2-person) way. Mightyvac will give a good start, but not a good final bleed.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

78porsche924 · Posted: Wed Jul 02, 2003 1:28 pm Post subject:

Someone also mentioned this tip, air gets caught in the brake light switches. Bleed them. It might help your problem. Also check for the play with the car off. If it is still really far with the car off, you mgiht need to adjust the little rod between the pedal and MC.
_________________
90 944 S2
78 924 NA <---now sold and killed by new owner
snailshell trans
Bae turbo kit
to check out my 944 S2 http://www.cardomain.com/member_pages/view_page.pl?page_id=388139

Joes924Racer · Posted: Wed Jul 02, 2003 8:45 pm Post subject:

I have braided metal lines waiting to be put on with the rest of the brake upgrade hope dont have this happen.I also got a set of those speed-bleeders for the disc calipers though my girlfriend doesnt mind sitting in the car helping me bleed the brakes.Shell drive it too now that the she can shift it.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.