brake bleeder valve on 84 GSL
 

I can't seem to find the bleeder valve on the master cylinder. The haynes manual refers to it on the left side, but there is not one on it at all. It also says that there is only one bleeder for the back brakes, but there is one on each wheel. The brakes are "spongy" and I bled them today without any change. Any ideas?

what kind of fluid are you running? DOT4 or DOT5?

fluid
 

DOT 3. The brakes work fine, except when depressed they will slowly drop to the floor. Air must be getting in somewhere, but fluid is not getting out. I want to fully bleed the system before I start changing hoses...

I have the same problem... except mine doesn't quite "slowly drop to the floor". It's just not real hard to push down... I wanna have a nice firm feel to it... i hate sponges.

Btw, what's the best DOT to use? 3 4 5?

I just got done bleeding my mothers brakes. If you think you have air in the master cylinder then you can use a pressure bleeder. I know you don't have one. I made a make shift pressure bleeder using 1/4" plate with rubber gasket material on the bottom and an air fitting threaded into a drilled hole through the plate. The only problem using it is that there is a line coming off the bottom of the master cylinder which is not typically on boingers so it can't be clamped in place. I used this to bleed the brakes by opening the bleeder screw on the wheel I started at and then held the plate on the filler after taking off the cap. Air pressure was set just to where I could here air flow. You watch the reservior level and fill as necessary. If you had this you could crack the fittings at the master cylinder and pressurize it. That would push any air out of the system if it is there. One other possibility is your master cylinder is old and the seals/bores could be wore. This would allow pressure build but the fluid would slowly leak back to the master cylinder.

I had the same problem in my truck. I didn't have the contraption needed to bleed the master cylinder on a ford explorer with anti lock brakes. I was working the rear brakes and it got air in it. I tried bleeding it over and over at the back brakes with no luck. It didn't return to normal until I did the front brakes. Turns out I didn't have to do the master cylinder. I guess the air travels around. I don't konw if it will work in your case, but it may be worth a try.

The short answer, probably DOT4.

The longer answer, DOT5 is not compatible with DOT3 or DOT4, do not mix them. You have to totally purge your brake lines of DOT3/4 before installing DOT5. I have heard that running alcohol through the lines is one technique. I have also heard that you need to completely rebuild your brake system too if you go to DOT5. DOT4 has a couple of significant advantages over DOT3, one, it does not absorb water as readily as DOT3 and two, it has a higher boiling point than DOT3. Also, beware, DOT4 eats paint! So be sure to clean off any you may spill.

I hope this helps.

I just swapped my master cylinder and had to bleed it. I did not find a bleeder on the master cylinder and it did not have any special tool. I just bled the brakes like normal, except that I bleed them until I got the master cylinder bubble out. The first time I did it the proportion valve was pushed off balance and I had to bleed them again to center it.

My GS rear has only one bleeder and it takes a while to get a master cylinder bubble all the way through. I just put in a GLS rear and it has two bleeders.

As far a brake fluid, I use Wilwood 570. It is a DOT 3 fluid but has a dry boil temperature about twice as high as regular brake fluid. I only put this is because I have a track day coming up and last time I boiled my brakes so bad them went away three times. I had to stop and let them cool, while I could have been on the track.

Hope this helps.