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mgatlag · Joined: 02 Aug 2007 Posts: 647 Location: Avon, IN

Hey all- I had a post started on the parts forum looking for rear drum parts but it's turned into a q and a. So I'll bring it over here. My 77.5 924 has spongy brakes and I can't lock them up if needed. The front cals and rear cylinders were replaced a few years ago. I've tried bleeding them repeatedly and get the same response, better (but not perfect) after bleeding and then spongy shortly after again. I used the clear hose from the nipple into a clear glass method and did notice the fluid coming out was a murky greenish color. Should I flush the fluid from the system completely? What's the best method?
I've also adjusted the rear drums but don't know how much drag/rubbing the drum should make when I spin it by hand. Should there be much if any? I do know that the spring pin thingy that clicks on the adjusting wheel is broke off and I've suspected that to be a cause but don't know. Any help is appreciated.
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Michael
'77 1/2 924 N/A- 5 speed Audi box
'04 Ford Taurus - gone!!
'92 Jeep Cherokee Laredo - gone!!

Porsche... better than tea with Miss McGill
(Slap Shot)

DOCO · Posted: Fri Sep 21, 2007 12:33 am Post subject:

howde!!! when you adjust the rear brakes you want to adjust one side at a time.tighten ONE adjuster till the brake drum locks up.then back off on the adjuster till the drum just breaks free.do this on all 4 adjusters you will then have the brake shoes evenally adjusted to the rear drums.the spongyness that keeps returning after bleeding, is probly a worn master cylinder.not nessasarly will you see an external leak on a master,they can have an internal leak that lets the fluid bypass between front and rear ports of the master.try bleeding at the master cly.at the lines and see if there is any air trapped in the master.be careful when trying to open the lines if there seized or rotted you may break them.use pentrating fluid and tighten the lines just a little first,this helps in breaking them free.hope this helps
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Doco "where am i going and why am i in this handbasket"author unknown
79 924 N/A "Webster"
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[+]___[+]
\0 924 0/
[__]..[__]
"WEBB STR"

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

YES, get rid of that brake fluid!!! To flush/change it out, I recommend a power bleeder.

They have a good price HERE.

Use your "furthest from the master" technique, and bleed each wheel til the fluid runs clear.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

My local auto parts shop lets you "borrow" tools like this. You pay for it up front and they get your dough back when you return it. I used their vacuum bleeder and I will never pump another pedal again! Just keep the reservoir topped up and pull fluid through the caliper by attaching the vacuum to the caliper valve.
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1980 931S
15psi boost, MS-II, EDIS, 951 IC, custom intake, Ford 5.0L throttle body, Forge BOV, WB o2, G31 w/LSD, 964 wheels, 968 rear sway, Bilsteins, 200# Welt. springs. A laptop, and a partridge in a pear tree.
1991 964 C4 Cabriolet

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Not to be a complete contrarian, but the pressure bleed I think is better for two reasons: one, the system is designed for pressure, not vaccuum (seals, etc), and two, with the power bleeder you don't have to worry about the resevoir, as it adds fluid as you bleed.

My .02!
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

mgatlag · Joined: 02 Aug 2007 Posts: 647 Location: Avon, IN

I've been thinking about repacing/rebuilding the master cylinder. I know there are rebuild kits out there, but are they any good? Or is it better to buy a new/rebulit one from the store? I know that I'm gonna start with flushing out the fluid with good stuff. Gonna look into the power bleeder too.
_________________
Michael
'77 1/2 924 N/A- 5 speed Audi box
'04 Ford Taurus - gone!!
'92 Jeep Cherokee Laredo - gone!!

Porsche... better than tea with Miss McGill
(Slap Shot)

Smoothie · Posted: Fri Sep 21, 2007 5:35 am Post subject:

The rubber brake hoses may be due for replacement too. Old ones can be another cause of spongy feeling brakes. As a general rule, replace about every 10 years.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

mgatlag · Joined: 02 Aug 2007 Posts: 647 Location: Avon, IN

I have a new set of brake lines ordered. I found a new master cylinder that I was wondering if anyone knows this part #. It's Beck Arnley # 072-6380. I found a price of $60 and this seems very low since all the others I've found were at least $150. I just don't want to buy something crap or wrong.
_________________
Michael
'77 1/2 924 N/A- 5 speed Audi box
'04 Ford Taurus - gone!!
'92 Jeep Cherokee Laredo - gone!!

Porsche... better than tea with Miss McGill
(Slap Shot)

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

That does seem a bit low. . .OEM manufacturer for your master was ATE.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Smoothie · Posted: Sat Sep 22, 2007 2:37 am Post subject:

That BA part # cross references to this UP (distributor - United Brake Parts) master cylinder from "Schaefer Brand Units", which sells for $269 at NAPA - http://www.napaonline.com/MasterPages/NOLMaster.aspx?PageId=430&OEMPartNum=072-6380

Oh, scarey - the other one that pops up for your car is $480.89

- http://www.napaonline.com/masterpages/NOLMaster.aspx?PageId=470&LineCode=ATM&PartNumber=P9401&Description=Brake+Master+Cylinder+-+New

Your rebuild kit is only $27 - http://www.napaonline.com/masterpages/NOLMaster.aspx?PageId=470&LineCode=BA&PartNumber=0717673&Description=Brake+Master+Cylinder+Kit
,but if you found a whole new MC for $60, I'd say go for it. Even if it needed new seals (not likely if it's actually new, unless it's been sitting on a shelf for a very long time), it'd still only add up to $87 (plus tax and/or shipping).
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

RC · Joined: 25 Mar 2007 Posts: 2637 Location: Australia

Since your car is a 77 it will have a 21mm master cylinder, while the later 80+ ones are 23mm. I am sure the earlier ones cross reference to a VW part. When I was chasing a rebuild kit at a reputable BRAKE SHOP the guy quickly offered a brand new one for an excellent price compared to the kit alone. IIRC it was probably equal to US$60 and made in Brazil but have had it for many years now with no problems.

Warringah Brakes (and clutch) at Brookvale (Sydney) if any aussies are interested.

Roger

mgatlag · Joined: 02 Aug 2007 Posts: 647 Location: Avon, IN

Ok I think I'm getting somewhere now. I flushed the fluid and got good clear fluid all over but I noticed that when I got to the left rear drum, air was oozing out of the bleeder nipple after I bled it. I have a clear hose connected to the nipple and going into a glass jar. When I stopped pumping the pedal and went to tighten the nipple, lots of VERY small air bubbles were flowing through the hose from the nipple. Does this mean that the cylinder is shot? All the other wheels seem to be holding ok. After I was done, I went for a drive and after braking a few times, I'm back to spongy, AGAIN!!
_________________
Michael
'77 1/2 924 N/A- 5 speed Audi box
'04 Ford Taurus - gone!!
'92 Jeep Cherokee Laredo - gone!!

Porsche... better than tea with Miss McGill
(Slap Shot)

Ozzie · Posted: Mon Sep 24, 2007 7:20 am Post subject:

You have to keep bleeding until there is no air.
If you keep getting air in that line then there must be a leak somewhere- usually noticed by the pedal slowly going to the floor after it gets hard.
Check all the lines and hoses, inside the drums etc.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance

mgatlag · Joined: 02 Aug 2007 Posts: 647 Location: Avon, IN

so I guess that means that the master cylinder is probably ok then? I'm sure the 30yr old rubber brake hoses could stand to be replaced. I have new drum cylinders on order just ot be safe too. So if there is still air bubbles coming out of the nipple on the lf rear right now, the problem will be with that drum, right? It shouldn't have anything to do with the master cylinder if that's the case, right?
_________________
Michael
'77 1/2 924 N/A- 5 speed Audi box
'04 Ford Taurus - gone!!
'92 Jeep Cherokee Laredo - gone!!

Porsche... better than tea with Miss McGill
(Slap Shot)

Ozzie · Posted: Tue Sep 25, 2007 7:28 am Post subject:

The master cylinder sounds ok.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance