924Board.org

porsche_reg · Joined: 19 Jun 2016 Posts: 62 Location: Boise, Idaho

hey all - I'm changing my brake fluid ('79 n/a), it's a been a bit, but not more than a few years. Everything was going fine (I've never done myself before) with fluid flowing from passenger side just fine, then on to the drivers side.

Fluid was pretty dirty, could see grit in there. Also the reason I'm changing (other than something to do and learning to do it myself) is that during the winter (worst winter in Boise I've ever seen with single digits and snow since Dec, now it's like spring though) I had some soft pedals. I could re-pump and pressure would return.

So now I'm trying to refill and get all the air out, but the passenger side only isn't flowing again. So I'm unable to return the car to service. I can build pressure up with a pump (Schwaben pressure bleeder) and it flows air and some spittle of fluid, but doesn't build or flow normally...

Any ideas or recommendations? I'd suspect if it was a bad master cylinder nothing would have some from the drivers side.

Thank you in advance.
_________________
Prev: '81 BMW 320i
'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback

Ozzie · Posted: Mon Feb 20, 2017 7:17 am Post subject:

Sounds like an overhaul of the system is required.
Any dirt or grit will damage seals and something akin to snot builds up in the pistons.
there are small ports in the MC and one could be blocked
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

porsche_reg · Joined: 19 Jun 2016 Posts: 62 Location: Boise, Idaho

dang it...

_________________
Prev: '81 BMW 320i
'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback

porsche_reg · Joined: 19 Jun 2016 Posts: 62 Location: Boise, Idaho

thanks Ozzie, when you say rebuild, just the master cylinder or do I need more?

I'm finding a wide range of prices. Stoddard has 477-611-015-A Master Cylinder for <$150, others are showing $200 - $300. Those might be for M471 options though.
_________________
Prev: '81 BMW 320i
'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback

Fasteddie313 · Joined: 29 Sep 2013 Posts: 2596 Location: MI

First I'd take the break lines and resivoir off of the MC, brake lines off calipers, blow all the lines out, throw a rag over the MC and blow it out from the lines inputs etc.. Compressed air ofcourse..

Then put the MC back together and fill it up, walk around the car like duck duck goose putting the lines back on he calipers once fluid was dripping from them nicely. Let it gravity bleed like that untill all are back together then pump the brakes bleed them and see what you get..
_________________
80 Turbo - Slightly Modified

porsche_reg · Joined: 19 Jun 2016 Posts: 62 Location: Boise, Idaho

thanks Fasteddie, good idea!
_________________
Prev: '81 BMW 320i
'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback

Fifty50Plus · Posted: Mon Feb 20, 2017 9:13 am Post subject:

A couple likely possibilities on one caliper are that the rubber hose is swollen and clogged or the foot of the bleeder screw inside the caliper is clogged with rust.
_________________
1979 924 NA race car H-Prod SCCA
1982 924 NA race car - Sold
1981 924 Turbo sold
1982 924 Turbo sold
1972 911 E race car - traded for Cayenne Diesel
1975 914 1.8 Building for H-Prod SCCA

porsche_reg · Joined: 19 Jun 2016 Posts: 62 Location: Boise, Idaho

I tested the line out to the hard metal lines connecting to the rubber ones connecting to the actual brakes - only air came out with the pressure pump.

Master cylinder was removed (I'm not that familiar with the workings, but looks pretty simple) and the front two ports or holes were pumping fluid when I pushed the pump, the back single port spurted a little, but not flowing like the front ones.

This leads me to believe something is wrong with the MC along the way.
_________________
Prev: '81 BMW 320i
'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback

Ozzie · Posted: Mon Feb 20, 2017 12:29 pm Post subject:

Master cylinder kits are available.
I have a Girling kit here but it is for a smaller diameter bore (19mm?) than mine which is larger. (22mm?)
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

Scott Sanda · Joined: 10 Jan 2006 Posts: 68

Pardon me if this question is insulting, it is not meant to be. Did you re fill the brake fluid reservoirs?

The only way you are going to get air out of a bleed valve if you have positive pressure on the top of the reservoir is if it is empty. If there was a leak upstream to the caliper, you would not get air from the valve, you would have fluid squirting out somewhere else.

I've accidentally pressure bled a race car dry before. You need to stop frequently, remove the air source, and top up the res.

Again, apologies if you have been refilling, and don't kick yourself too hard if you have not.

porsche_reg · Joined: 19 Jun 2016 Posts: 62 Location: Boise, Idaho

Hi Scott - no insult taken, sometimes the most obvious things are overlooked and it takes another to see it.

But yes, I did have the reservoir refilled. The drivers side bleeder was letting fluid flow, just the passenger was not. Air would flow through the lines fine, which led me to believe the original recommendation from Ozzie (overhaul) is the right course of action. New one on the way from Stoddard (paid a pretty penny to get it here overnight...)
_________________
Prev: '81 BMW 320i
'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback

Paul · Posted: Tue Feb 21, 2017 8:36 am Post subject:

Rubber brake hoses should have a date on them, replace when 10 years old.
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

porsche_reg · Joined: 19 Jun 2016 Posts: 62 Location: Boise, Idaho

thanks Paul, certainly could be a problem... I have received the MC from Stoddard (kudos to them for the NDA, got it today!)

Now, next problem is the seal to the booster - need an o-ring, but somehow I got 911-355-922-00 which apparently is for the reservoir (but not a 924 one).
_________________
Prev: '81 BMW 320i
'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback

porsche_reg · Joined: 19 Jun 2016 Posts: 62 Location: Boise, Idaho

hey Paul, any thoughts on where to source the brake lines? Looks like most of them are for five lugs, I'm at 4.

I see Ideola has the Goodridge, but I'm trying to stay a little under that price wise. I'm sure they are very nice.

Thanks,
_________________
Prev: '81 BMW 320i
'05 997.1 C2
Current: '79 924 n/a (family owned since new)
'12 Subaru Outback

Paul · Posted: Wed Feb 22, 2017 1:50 pm Post subject:

Front ones here:

http://www.autohausaz.com/pn/477611071A

I also checked Sunset they want $83 each:

http://www.sunsetporscheparts.com/?p=catalog&mode=search&search_in=all&search_str=477611071a
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.