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sparky · Joined: 27 Nov 2002 Posts: 772 Location: Malta

Hey guys.

So the 951 brake/suspension upgrade was working great until I went to get the wheels all aligned. They put some bar on the brake pedal to hold the brakes down while they were doing the wheel alignment, im not sure if it is coincidental or if it effected something but ever since, if i go for a drive now, all the brakes seem to jam on after about 10 mins of driving and braking. It gradually gets worse during the drive until the brakes are jammed on too much to even drive.

If I leave the car for a while, the brakes release and the same happens again if i go for another drive. If i dont touch the brakes, they dont seem to jam.

What could cause this problem?

The car has a 951 brake/suspension upgrade with a 951 MC and Booster.

Cheers,
Mark
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When the checkered flag drops... The Bull$hit Stops

1976 Euro 924 (The 945)

- Full 951 Brakes/Suspension

1998 Boxster with goodies
2002 3.0 Xtype 4wd sport

fiat22turbo · Joined: 18 Jan 2006 Posts: 4040 Location: Portland, OR

How old are the brake hoses and master cylinder?

The lines could be collapsing internally.
_________________
Stefan
1979 924 Carrera GTS (clone-ish)
1988 944 Turbo S (Silver Rose)

Ozzie · Posted: Fri Sep 03, 2010 1:17 pm Post subject:

sticking calipers?
were these new or refurbished?
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Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
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Engineer of Electro/Mechanical Systems Maintenance

daniel · Joined: 18 Jun 2009 Posts: 686 Location: Sydney, Australia

Had this problem once with a Formula Vee, tiny metal filings in the fluid due to the master cylinder running off square. Blead a little fluid of each caliper and see what it looks like
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Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

ic932 · Joined: 11 Feb 2005 Posts: 1104 Location: UK

+1 on the flexi-hoses collapsing internally, if old...

Brembos of this type can suffer "plate-lift" The stainless plates that the pads ride on get warped due to corrosion developing behind them (alloy - steel - bad reaction)

The quick fix is to shave a mm or two off each side of the pads' steel backing plate to loosen them up.

The proper way of course is to remove the plates and scape away the gunk the replace with new ones.

Always heat the allen bolts that hold the plates on until they are cherry red, they are tight and locktited too!

sparky · Joined: 27 Nov 2002 Posts: 772 Location: Malta

Hey guys,

The Flexi hoses are brand new and the calipers are newly refurbished. All the brake lines are new on the car.

Its not 1 brake that is sticking on after some use, its all the brakes equally jamming themselves on. I went to a test run this morning, after about 10mins they started to apply a little and after then when i braked it was just getting worse until it was hard to pull into the drive. I just went out now (2hrs later) and they are completly free again.

I had the problem of the metal backing warping on my xtype but that made more of an annoying squeeking sound and no noticable brake force, this is more like someone is putting reasonable force on the brake pedal.

When this happens the brake pedal is stiff as a rock right at the top.

Considering all 4 wheels are locking up at the same time, its hard to imagine it being related to a sticking caliper or a collapsing hose isnt it?

Hopefully the above info helps shed some light onto this

Thanks,
Mark
_________________
When the checkered flag drops... The Bull$hit Stops

1976 Euro 924 (The 945)

- Full 951 Brakes/Suspension

1998 Boxster with goodies
2002 3.0 Xtype 4wd sport

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

check your vacum one way valve...maybe you've installed it backwards?
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sparky · Joined: 27 Nov 2002 Posts: 772 Location: Malta

Hey buddy,

Checked/Tried.
The first time this happened I thought there may have been a vacuum lock and undid the vacuum hose but it made no difference. The brakes use to work fine with no issues until I went to the wheel alignment guy. Im guessing this was just coincidental.

This is really weird.
_________________
When the checkered flag drops... The Bull$hit Stops

1976 Euro 924 (The 945)

- Full 951 Brakes/Suspension

1998 Boxster with goodies
2002 3.0 Xtype 4wd sport

924RACR · Posted: Fri Sep 03, 2010 9:36 pm Post subject:

Then the next remaining weak point would be the master cylinder sticking. Perhaps you'll need to rebuild it? Would make sense, as the alignment guy probably pushed it down further than you normally do when driving.
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

sparky · Joined: 27 Nov 2002 Posts: 772 Location: Malta

Aight ill get onto taking it out tomorrow. What should I be looking for when its out and taken to bits?

Do you think a good cleaning will do the trick, I cant seem to find any master cylinder rebuild kits. Im guessing it is all dependant on what condition the bore/piston is in.

Many thanks for the pointer,
Mark
_________________
When the checkered flag drops... The Bull$hit Stops

1976 Euro 924 (The 945)

- Full 951 Brakes/Suspension

1998 Boxster with goodies
2002 3.0 Xtype 4wd sport

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

Since you swapped your master cylinder and booster, I am wondering if your brake actuating rod is adjusted correctly.

Go under the dash, and undo the locking nut at the pedal. Then back out the rod, and screw it back in BY HAND until you can just feel it touch the cup it rides in inside the master cylinder.

Good luck!
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

!tom · Posted: Sat Sep 04, 2010 1:38 am Post subject:

As Rasta says, it sounds as though your master cylinder isn't returning to the full "off" position.

When the master cylinder is in the full pedal up position, fluid can flow past the pistions. When you apply the brakes, this passage is blocked off so that the pistons can build pressure.

This bypass is there so that as the fluid heats up and expands, it can go into the brake fluid resivoir.

If your master cylinder never returns to the full "off" position, as your brakes heat up, they'll apply more and more as the expanding fluid builds pressure.

You'll have problems bleeding your brakes without this adjusted properly too.
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78 924 NA
5-lug

sparky · Joined: 27 Nov 2002 Posts: 772 Location: Malta

Cheers guys!

Ill get onto this at first daylight tomorrow and let you know how it goes!

This does make perfect sense though

_________________
When the checkered flag drops... The Bull$hit Stops

1976 Euro 924 (The 945)

- Full 951 Brakes/Suspension

1998 Boxster with goodies
2002 3.0 Xtype 4wd sport

sparky · Joined: 27 Nov 2002 Posts: 772 Location: Malta

Fiiiiiiiiiiixed

What seems to have happened is the metal which the brake pedal rests against when the brake is not pressed got bent forwards, most likely from the wheel alignment guy paying no attention to where he put the thing that holds the pedal down. It was causing the problem that you guys described with the piston not fully retracting.

Ive bent it back up and there seems to be no problem at all now

Next up is fixing a few electrical gremlins and "the man" is coming round at the end of the week to sort that side of things out

Its finally a car!

I will take it to a bodyshop next time im abroad for a while and get them to reduce the size of all the gaps in the body panels, mainly the boot area, wings and hood. The sunroof is pointless and annoying, its too hot here to ever open it up. Considering a delete on that too.

So I dont start a new thread, are there any upgraded alternators I can run on the car that are an easy swap? When my lights are all lit up and my amp is on, it falls to 11v

Thank you all so much for help with the brake problem!
_________________
When the checkered flag drops... The Bull$hit Stops

1976 Euro 924 (The 945)

- Full 951 Brakes/Suspension

1998 Boxster with goodies
2002 3.0 Xtype 4wd sport