Brake Vacuum booster rebuild oddity

[kauboi]

So, my brakes have been troubling me since I took my car out of long term storage. First, they dragged, then I replaced two calipers, and now they don't drag. Bleeding has been difficult, so I bought a HF pneumatic power bleeder, but the rears seemed to give endless air, and I noticed my idle would surge when I pump the brakes, so I've now rebuilt my booster with the kit from autoricambi. One of the seals was the wrong size. They offered a refund but I had already put the booster back together. Curiously, the kit didn't include the "plunger" seal, which seems critical. I wanted to try rebuilding myself for education purposes, but don't recommend it. I reinstalled the booster and now it seems as the idle dips just slightly if I pump the brakes. I'm going to check the compensator valve tomorrow, and bleed the system.

[DieselSpider]

So, my brakes have been troubling me since I took my car out of long term storage. First, they dragged, then I replaced two calipers, and now they don't drag. Bleeding has been difficult, so I bought a HF pneumatic power bleeder, but the rears seemed to give endless air, and I noticed my idle would surge when I pump the brakes, so I've now rebuilt my booster with the kit from autoricambi. One of the seals was the wrong size. They offered a refund but I had already put the booster back together. Curiously, the kit didn't include the "plunger" seal, which seems critical. I wanted to try rebuilding myself for education purposes, but don't recommend it. I reinstalled the booster and now it seems as the idle dips just slightly if I pump the brakes. I'm going to check the compensator valve tomorrow, and bleed the system.

Is that the one that pressurizes the master cylinder and pushes fluid through the system or just a powered vacuum pump attached to each bleeder individually? You will get air using the vacuum models unless you use bleeder screws with thread sealant on them to prevent it. You may want to use the power bleeder initially and then just let them gravity bleed for a few moments afterwards to ensure the air is out of the system. Just be sure to have the rear axle loaded to keep the compensator valve open (if its still in place) or you will have problems. My 78 is probably the fastest flowing system I have experienced yet when gravity bleeding.

[spider2081]

Did you clean the check valve at the booster? Have you measured your vacuum. I think most boosters need about 18" of vacuum to operate properly. I would think if your vacuum is stable the booster is not causing the idle change.

How did you get the booster open to install the kit. I have a spare booster and purchased a kit but have not tried to open the one I have.

[kauboi]

Is that the one that pressurizes the master cylinder and pushes fluid through the system or just a powered vacuum pump attached to each bleeder individually? You will get air using the vacuum models unless you use bleeder screws with thread sealant on them to prevent it. You may want to use the power bleeder initially and then just let them gravity bleed for a few moments afterwards to ensure the air is out of the system. Just be sure to have the rear axle loaded to keep the compensator valve open (if its still in place) or you will have problems. My 78 is probably the fastest flowing system I have experienced yet when gravity bleeding.[/quote]

it's the one that draws from each individual bleeder. I'll try the thread sealer idea, thanks!

[kauboi]

Did you clean the check valve at the booster? Have you measured your vacuum. I think most boosters need about 18" of vacuum to operate properly. I would think if your vacuum is stable the booster is not causing the idle change.

How did you get the booster open to install the kit. I have a spare booster and purchased a kit but have not tried to open the one I have.

I replaced the check valve, as the kit had one. I will check vacuum. The booster is pressed together and twisted to engage the peened bits that retain it together. I believe you'd need a fixture and tooling to open and close it that way. I actually pried mine apart and back together.

[Turbofiat124]

I never had any luck with those vacuum bleeders. I have had really good luck using the Gunson easy bleeder.



You fill the bottle up with brake fluid, install the cap on the reservoir and connect the air hose to a spare tire and when you open the bleeder screw it forces new fluid from the bottle to the calipers or wheel cylinders. Even if you replace the MS, you don't have to bench bleed it.

I would recommend not going any higher than 15 lbs on the air pressure. The bottle tends to leak so be sure to wrap the threads with teflon tape.

The kit doesn't come with a cap to fit the master cylinder reserviour but if you can get a cap that fits the clutch reserviour from an X 1/9 it fits both the brake MS and clutch MS on all models.

[kauboi]

Thanks for the suggestions, but it appears that neither the motive or gunson bleeders will fit the 40mm cap on my (our) car(s). So, I enlisted the gf and bled the brakes today.Also did a bit on the master cyl. Brakes are better, but as I also opted to replace the rear pads, I found one caliper piston that wouldn't turn in to open up for the new pads. I guess I'll have to replace it, too, unless I can free it somehow.

[DieselSpider]

Thanks for the suggestions, but it appears that neither the motive or gunson bleeders will fit the 40mm cap on my (our) car(s). So, I enlisted the gf and bled the brakes today.Also did a bit on the master cyl. Brakes are better, but as I also opted to replace the rear pads, I found one caliper piston that wouldn't turn in to open up for the new pads. I guess I'll have to replace it, too, unless I can free it somehow.

Check that the parking brake cable is fully releasing on that side before you go too crazy with it. If the cable is sticking then the auto adjuster screw stud will be held out by the parking brake actuator and will prevent the cylinder from going to its fully rested position.

[spider2081]

If parking brake cable is releasing have you opened the bleeder to be sure you do not have a hydraulic blockage preventing the piston from turning into the caliper housing.

[kauboi]

Oh, ok, I'll check the cable adjustment and the bleeder idea today, thanks guys!

[kauboi]

So, I ended up removing the parking brake cable from the caliper to rule out the piston being held up, with no luck. I also tried opening the bleeder to no avail. Next I removed the caliper and held it in the vice where I was able to wind it in, but it was incredibly stiff. I had tried and failed to rebuild the other side, a few months ago, and ultimately replaced it. I took out the parking brake mechanism, and tried to push the piston out and it is stuck, so I've just ordered one from partsgeek. It was so cheap I'll take a chance on them. Seemed like the park brake cable was much harder to remove than the other side, and I noticed my lug bolts had some evidence of getting hot, though it didn't seem to be dragging. I also noticed the adjustment rod was slightly bent, and the nuts were very nearly as "loose" adjustment wise as possible. I think maybe I've been dragging in back for a long time. I've now replaced 3 out of 4 calipers, and am hoping I don't have to do anymore brake work, as I'm over it.

[DieselSpider]

Note that best practice is to replace brake parts in pairs so it you replace/rebuild one caliper you do the same on the other side the same for rotors and brake pads.

[Turbofiat124]

Thanks for the suggestions, but it appears that neither the motive or gunson bleeders will fit the 40mm cap on my (our) car(s). So, I enlisted the gf and bled the brakes today.Also did a bit on the master cyl. Brakes are better, but as I also opted to replace the rear pads, I found one caliper piston that wouldn't turn in to open up for the new pads. I guess I'll have to replace it, too, unless I can free it somehow.

Yeah you need a X 1/9 clutch reservoir cap. I ordered a used cap off Ebay.de for my Trabant just so I could use the tool.