GA brake trouble

[VGJONO]

Ok now ive been working on the GA's brakes for the last week, got them from not working in the slightest to working and now to sticking on. i managed to get the car to go on a 40 minute drive yesterday from the local transport office to home with no troubles, now today i cant even make it 5 minutes up the street until they stick on. The system is Disc up front and drums on rear and the fronts are boosted by a remotely mounted booster, i have pulled apart both front calipers cleaning all sorts of muck and crap out of them as well as clearing blockages in the L/H brake line, and had all the dirty old fluid flushed from them, the rears have only been bled and topped up with fluid, now as you drive they start locking on and the more you drive the worse it gets until you finally come to a halt. the brake pedal goes rock solid when this happens. anyone have any ideas?

Cheers
VGJONO

[fridgeGB]

I guess it could be a few little possibilities. Process of elimination seems like the best way to get to the bottom of it. First thing I would try is disconnecting the vacuum line from the brake booster so it's just running like the stock system. If it works fine them its the booster. If not then we cancel that out and move on

[C_Fernance]

I had the same problem once in a Scorpion. Exactly the same symptoms. Starts off fine, then the more you drove and used the brake the more they stuck on till basically the car wouldn't move. I would then release one of the bleed valves to release the built up pressure and it would be ok for another 5-10 minutes. Kept doing this till I got home.

The problem was in the master cylinder itself. I'm not exactly sure which seal was causing it, but replacing all the seals with new ones in a rebuild kit solved the problem and the brakes worked perfect afterwards.

Cost for the rebuild kit at the time was under $50.

A whole new master cylinder cost me $130 2 years ago so that may be a better option if you are worried about the current one being in reasonable condition to suit a rebuild.

[Decrepit]

The problem was in the master cylinder itself. I'm not exactly sure which seal was causing it, but replacing all the seals with new ones in a rebuild kit solved the problem and the brakes worked perfect afterwards.

[VGJONO]

Cheers guys, i was fearing that the master cylinder would be the case, i have a spare here but it is from a drum brake on all 4's setup, could i get away with using it if i swap out the reservoir to the larger one suited for the disc front end or are they different internally??

[C_Fernance]

The problem was in the master cylinder itself. I'm not exactly sure which seal was causing it, but replacing all the seals with new ones in a rebuild kit solved the problem and the brakes worked perfect afterwards.

I'm sure you and mum used to get sick of all the calls "Come and save me" every time I broke something.

[shuggy]

they are completely different ratios

I had this problem, it was that the master wasnt retracting all the way to allow the piston to open up the return valve. I put a washer between the master and the booster on both bolts and all sweet now

[VGJONO]

fair enough, well looks like i will be stealing the master off of my project for the time being.

sadly just putting washers inbetween the master and booster wouldnt help being remotely mounted


next question is, the master cylinder i can borrow from my project is a GD boosted setup, will the master cylinder from that work in this?? seperated from the original booster?

[Scorpma82]

Doutbful....Unless the partnumbers are the same, i wouldn't recommend that.

The chances are, the master clyinders would differ internally so u couldn't see with the naked eye.
Bore size,Crack Point psi's, pushrod length etc

[shuggy]

that setup is ridiculous

get rid of the booster all together!

[VGJONO]

Unless that setup is the cause of my issues it will be staying, if it was my car, maybe I would just get rid of it. But seeing as this car is my sister's I will be leaving it, as the better the brakes are the safer she can be while driving it.

[LukeAussie]

Not sure if the internals are different, but I'd err on the side of caution with brakes... You could pull the two masters off, compare visually and maybe check with a brakes guy for their thoughts. Having said that, a new master should be easy to get. Got one for the GC a few years back. I reckon PBR had them in stock...

And you'll definitely need a different master for front discs/rear drums than for all drums. The discs and drums run on a different circuit (hence the two reservoirs), so such a system won't work. You'd also need the proportioning valve for the front discs (which you should already have, since you've got front discs).

Good luck!

[VGJONO]

cheers guys, had another drive of it in my street and jacked it up to figure out exactly which wheels were locking up, turns out both fronts are and only the rear right hand brake are locking up, leaving the rear left functional. does this mean i can rule out that it is a master cylinder and maybe try other things? i know it had very bad fluid in it when we first bled the brakes and we only flushed out the calipers themselves, not the lines, so my thoughts now is the brake fluid is contaminated with mud and water causing it to boil. that is if the master cylinder is working correctly, i was told if it was the master cylinder it would be All the brakes that had issues correct?

[geezer101]

I'd be undoing the brake lines and performing a full line purge. I've seen brake fluid go really bad and some people don't realize you need to refresh brake fluid at some point (it can absorb a lot of water and once that happens the brake fluid is near useless). I would also get the master cylinder reconditioned - the full deal. Bored out, stainless steel sleeve - the works. It is over 40 YEARS OLD and it's the only thing stopping your car.

[VGJONO]

Could only find a New listing for GC-GD master cylinders on ebay, this would fit correct (image on the ebay ad is a stock image i beleive)
http://www.ebay.com.au/itm/BRAKE-MASTER ... 725&_uhb=1

[mitsushed]

Brake fluid is incredibly hydroscopic *cough* paint stripper *cough* who said that?

If you had water in the lines and it boiled while you were driving the opposite would happen. Your pedal will slowly become softer and the brake effect weaker until the pedal hits the floor. Air compresses, and when your watery lines have boiled and you push the pedal all you do is compress the steam in your lines, not apply the brakes.

Discs needs a massive amount of fluid and pressure compared to drums. If you pop open your drums and look at the slaves, compare them to the size of your caliper pistons and it gives you an idea...

I agree with either recondition or replacement if you don't want to rebuild it yourself. Better safe than sorry.

hope this helps!

[davetrees]

Could only find a New listing for GC-GD master cylinders on ebay, this would fit correct (image on the ebay ad is a stock image i beleive)
http://www.ebay.com.au/itm/BRAKE-MASTER ... 725&_uhb=1

A GC/GD cylinder will bolt up to the GB firewall, BUT :
- it's the wrong diameter cylinder for the brakes (I think GC/GD is 7/8" ?), and
- you will have to get your brake lines remade/modified because the pipes attach to the M/C in different places.

You need a 11/16" Nabco cylinder. NLA in Australia - I scored a NOS one on eBay a couple of years ago from the USA. You can still get rebuild kits for them though (I've got the part number somewhere).
Just get it reco-ed

The GC/GD master cylinder cylinder is designed for boosted brakes, and different calipers & wheel cylinders. Alternatively, I guess you could always bolt a complete set of GC/GD brakes into the GB !

(What Geezer said about fluid maintenance too ..... I completely replace the brake fluid in mine once a year).