brake booster question

[scrowley]

Well my cruiser brakes have always been giving me some trouble. Everything has been replaced except booster.

I did the booster checks out of fsm and it fails one test. When I pump brakes with engine off til hard then hold and start the pedal goes almost to floor. It is supposed the move "slightly". Operation 1 b.

I just 're bled brakes after not touching for a couple yrs. No air in system still. Brakes work good but not great. In a panic stop they work good on initial push but if you stay in it the pedal is hard with terrible stopping power like it fades away. If you 're hit pedal it is good initialy but does get hard again. Hard like it feels like a good pedal but not making enough stopping power. No way in helll I could ever lock up tires (37's) even with abs disconnected.

Anyone know what this means???

 

[DARKNESS]

That means your booster is fine. You'd have a hard pedal after the truck started if the booster was bad. Probably a bad master cylinder or air in the lines. I had trouble accepting this at first, but alot of master cylinders come bad right out of the box.

 

[98 SNAKE EATER]

does it pass the air tightness check?

Mine had the same pedal feel you're describing and didn't pass the 30 second residual air check test and the pedal would rise immediately after shutting down.

Swapped out the booster and now I have solid brakes again


*sent from my android string cup*

 

[Timpanogos Slim]

I am far from expert but that sounds like my experience with my brakes last year.

I had already replaced my master cylinder with a brand new Aisin unit at that point.

fwiw the booster i got from Centric is a good 100% identical rebuilt unit. I couldn't get the old one out until i took the nuts off the motor mounts and jacked up the engine a bit. This wasn't a big deal to do - just two nuts and a floor jack with a bit of 2x8 under the oil pan.

 

[scrowley]

does it pass the air tightness check?

Mine had the same pedal feel you're describing and didn't pass the 30 second residual air check test and the pedal would rise immediately after shutting down.

Swapped out the booster and now I have solid brakes again


*sent from my android string cup*

It did pass the air tightness checks. One problem is I bought the truck years ago and it came with no brakes. PO couldn't get them to work. So I never really have known what they should feel like. PO put on new calipers, LSVP, master, braided brake lines. Master is a Aisin. That was 4ish yrs ago and descent amount of miles.

I just converted to Part time 4x4 so I think I am going to order the stuff to delete the ABS. At the same time check my Master. I would hate to spend all the money for a booster if it's ok.

But it does fail that one test but listed above (1B) As Darkness said in first reply the pedal would get hard instead of pushing down so far. Which I guess makes since if the booster wasn't adding the assist then the pedal would stay hard.

 

[DARKNESS]

I'd get the seal kit to rebuild the master if it was me.

FWIW Mine had a soft feel. I adjusted the LSPV and it got way better. I think the front was engaging and the rear wasn't engaging at all until very late in the pedal travel.

Your symptoms sound more like a master cylinder. I've followed alot of brake threads and thats almost always the solution.

 

[Options20002001]

FWIW Mine had a soft feel. I adjusted the LSPV and it got way better. I think the front was engaging and the rear wasn't engaging at all until very late in the pedal travel.

Same symptoms in mine too. Adjusted the LSPV (truck is lifted) and immediately noticed an improvement. However, i am still going to replace the booster as i sometime hear a hiss, especially when starting the truck, cold. I take this hiss as an air leak (small) when the engine is cold....a failure somewhere in the booster. This "leak" either seals itself completely or is very small when the engine warms up.

The master cylinder (oem) is a new remanufactured one that was installed less than six months ago. I will replace this next if i don't get good, functioning brakes after the booster replacement. Everything else, rotors, pads, calipers and lines are all new now.

 

[scrowley]

Same symptoms in mine too. Adjusted the LSPV (truck is lifted) and immediately noticed an improvement. However, i am still going to replace the booster as i sometime hear a hiss, especially when starting the truck, cold. I take this hiss as an air leak (small) when the engine is cold....a failure somewhere in the booster. This "leak" either seals itself completely or is very small when the engine warms up.

The master cylinder (oem) is a new remanufactured one that was installed less than six months ago. I will replace this next if i don't get good, functioning brakes after the booster replacement. Everything else, rotors, pads, calipers and lines are all new now.

Well, mine has the same hiss when cold. Cooler it is louder the hiss. But the hiss does nothing to how the brakes work.
Also adjusting lsvp made a big difference with 4" lift but the more I move it up the better the brakes "feel" but the stiffer pedal with no brake power gets worse.

I will be deleting abs and lsvp in next couple weeks. I will inspect master at same time.

 

[blunderbuss]

@scrowley any updates?

 

[SUMMIT CRUISERS]

Just a couple of ideas...

Any hiss coming from the the pedal area at any time means bad booster. If you continue to drive with a bad booster you could burn a valve.
Last thought, if the master cylinder is thought to be bad, remove the cap/strainer and have someone step on the pedal. If the fluid squirts up in the reservoir, the master cylinder is bad.

 

[inkpot]

If we had thought of it back then , you could of test driven 5 or 6 other 80's for comparison on the day you rode along on Devil's Canyon. That is really the only way to know if your brakes are good, bad, or somewhere on between. John

 

[scrowley]

Well my brake issue has been resolved. I deleted my ABS unit and LSVP. My brakes where instantly better.....much better. Then I put on EBC yellows and the brakes are like WOW!!!!!!
Then pedal feels a little different every now and then and I dont know why but I am still guessing the booster is suffering. BUT I dont care anymore because I can lock them up and feel much safier driving it like I stole it.....well for an 80 anyways.