I have a 47 with a 1994 S-10 Front clip (disk front, drum rear). The truck has a GEO Metro Booster and Master Cylinder with all new brake components however the brakes are very spongy. I have run a lot of brake fluid through the lines, bench bled the master cylinder, install a wilwood adjustable proportioning valve along with new plumbing, still no luck. I'm looking for suggestions, since I'm almost sure the system does not have air however the brakes are very soft. I have also checked the master cylinder by plugging the ports and pressing on the pedal, results hard pedal with no pressure drop. I assume the GEO master cylinder bore size is to small, therefore I need a larger master cylinder, does anyone have a suggestion for type of master cylinder which will work with a GEO booster?
Basic Brakes What rear brakes do you have ? . Just for grins , try adjusting the two adjusters in each rear wheel until the brakes drag heavily then try to pedal - maybe the rear shoes are not fully bedded in , that will cause soft pedal .
My set has self adjusters only. I don't know the doner for the rear end however it is a GM. I did not build the truck so I'm at a loss for the histoy. I did not know GM made a rear drum brake with NO star gear. The self adjuster seem to work on the truck, the rear wheel has a small amount of drag, which is good. Maybe I have air traped in he calipers however I have never bled the calipers any different than the complete system and not sure how.
Pressure is pressure no matter how you look at it. how ever if you have air in the lines you can have spongy brakes. Rear brakes adjusted to loose or worn out front pads can give you a low pedal. Here are some things to check for..... 1 All bleeder valves need to be pointed up because air bubbles float to the top. If your bleeder valves aren't strait up you can trap air causing spongy brakes. Some times the builder can unknowingly install the calipers on the wrong side and end up with the bleeders on the bottom of the calipers. The calipers are also right and left so make sure you have 1 of each. If the bleeders are pointing up but not strait up you can remove the pins and put a block of wood between the pads and while making sure the bleeder is pointing strait up bleed them then put them back on. 2 make sure you have about 1/4" of pedal play, you want the piston in the MC to return completely and there to be a little play between the push rod and the piston in the MC, if not it can cause the brakes to drag, heat up and fade. 3 You want to adjust your proportioning valve at about 90 percent so that your rear brakes don't lock up before the fronts. Also and this is very important if you have mounted your booster MC combo underneath the cab this will turn your MC around. Meaning check the routing of your lines. the front brake line mounts to the front of the MC so that when you step on the pedal the front brakes engage first and of course the rear line mounts to the rear or booster side of the MC. Here's a link just scroll down to the diagram. I hope this helps you solve your problem Big Tim http://www.chevytalk.org/fusionbb/showtopic.php?tid/275422/
Is your master cylinder frame or firewall mounted? Sometimes I reverse bleed a stubborn one by using the pressure ball line on the bleeder screws till the master cylinder over flows. Do so at each wheel. Since you have m/c plugs for bench testing screw one in to block the front brakes and then the rear brakes. This might isolate which end is causing the sponginess. What kind of mechanism turns the adjusting screws on the self adjusters if there are no star wheels? Something HAS to turn them or the brakes are forever in one position.
Self Adjusters & Bleeder Screws Evan ; Some of the post 1970 vehicles I have worked on , had a triangular shaped wedge thing that went between the brake shoe and the park brake linkage , it had a very weak spring to pull it downwards each time there was any free space to do so so the wedge filled up the space and served to keep the brakes adjusted . Weird (to me) but it worked very well . Maybe this setup has a similar thing . Also , many older British cars had dual blind brake cylinders connected by a pipe , the brake hose went to the top and the bleeder nipple is on the bottom ~ needless to say , these are bugger all difficult to bleed out . Older Brand 'F' Cab Overs from 1957 ~ 1992 all had vertical hydraulic clutch master cylinders, those too were no fun to bleed . So did millions of Corn Binder Cab Over trucks . I always try " The Stick Trick " on problematic jobs, this is where you jamb a stick between the brake pedal and seat , dash board etc. and leave it sit for 24 hours then remove the stick and wait 10 minutes before depressing the brake pedal . This method allows atmospheric pressure to do the work of getting those few tiny bubbles or foam out of the system . It works ,believe it or not .
I'll be darned, might even be better with no male threads to sieze up in the female threaded sleeve. We do have two REALY LATE MODEL (for us) cars in right now; a 69 Firebird and a 70 442 so I better look them over. For years I've told people if they have more than two vacuum hoses, one for wiper and other for distributor advance, we don't work on them. As the old song says: Times they are a changen.
Big Tim. That's a very good 'How To' on troubleshooting this brake problem. It all makes sense, at least to me.
Everyone had great feedback, at this point, all bleeders are up as suggested, I recently GRAVETY BLED front and back. This was a great help, brakes are not the best but they are better than ever. I just ordered a master cylinder with a larger bore to see if it will help. I have a car show in Ocean City MD. this weekend. I think the current brakes are safe so I will wait until I return to install the new master cylinder.
