Brake Booster?

[shotgunfatcat]

So everything has gone wrong at once on my truck. In the last 10,000 miles I have replaced a load of parts. In the last 1,000 miles, It is getting increasingly worse. I haven't even driven it in a while do to the fact that every time I start it up, something else breaks. Here is a list of things so far.

Trans, every u-joint (front needed a double cardan joint, all wheel bearings, front axle seals, which they gave me the wrong ones which fit and had to do the job again because they were leaking, sway bar end links (I know a big one), Exhaust, as well as a list of things that could be repaired, but I am holding off, just trying to get the thing back on the road.

Anyways, I started loosing brake pressure, and now I am about all out of brake pedal in general, no holes in the lines, newer pads all the way around, rotors seem fine. I replaced the master cylinder thinking that was the problem, to no avail. My last option I would think is the booster. Now I know you can test these. Can I do this with a mityvac? Or should I take it to a shop? Is there anything else I should check, I am running out of options in my own little mind.

Thanks in advance to any help, I will also take some comedy if you got it, just don't make fun of my mother.

 

[lametec]

All the booster does is make it easier to push the pedal down. If the pedal goes down when you push it, it's not a problem with the booster.

To test a booster, start with engine off. Pump the brake pedal 3 or 4 times until it gets firm and hard to push down any at all. Push and hold the pedal down, then start the engine. Pedal should now go further down. If it doesn't your booster is not working.

 

[jam0o0]

what truck? how old? how many miles? what engine?

what exactly is happening? is the petal going to the floor easily and the truck is not stopping? if this happens right after changing the master cylinder then you have air in the lines still. did you stroke the master when it wasn't full of fluid? doing this even once can ruin the seals. did you bench bleed the master? if not it might never completely bleed out. when was the last time the brake fluid was changed? water collects in the fluid over time and then when you try to stop it boils and the bubbles cause soft petal.

 

[shotgunfatcat]

It is a 2000 Chevy 1500 with 130,000 miles. I bench bled the MC, which got quite firm after bleeding it, so I don't think I got a bad one. When I press the pedal down, it damn near goes to the floor before it starts to stop, maybe an inch of pedal left, once stopped I can push the pedal all the way to the floor easily enough. I would think maybe I did something wrong, but it is doing the exact same thing before I changed out the MC. It is possible there is bad fluid, but I would like to be able to test the booster.

So I would have a hard pedal if the booster was bad then? I am not too familiar with the booster in general.

 

[Milton Shaw]

Sounds like You have air in the lines, bleed the brakes with a helper, pump three times, hold and then open bleeder valve on shortest line, repeat, repeat, check level in master cylinder and then repeat for each wheel. If that doesn't fix it you may have brakes too far out of adjustment or calipers in a bind where they are pushing the piston back in when you let the brake off.

 

[shotgunfatcat]

I bled the brakes after I put the master cylinder on, and it was doing the same thing before I replaced anything. I am just going to pump out the old fluid in general and see what happens, 7 dollars is better than 100.

 

[Eagle Point]

I was always told to start bleeding the corner further away from the master and work your way around to the master. Even though you bench bled the master I would still crack open the lines and pressure bleed the master after doing all the calipers. I don't know if you had the calipers off but make sure they are on the correct side. I worked on a Nissan truck one time where the owner replaced the calipers (along with everything else that it did not need) and had the right and left front calipers switched. The bleeders were at the bottom and he could never get it to bleed properly! He replaced the booster, rear cylinders, shoes, pads, proportioning valve, hoses, you name it and still had a soft pedal. He called me since I worked at the Nissan dealer at the time and was shocked when in less than a minute I told him the calipers were on the wrong side. I switched them, bled the brakes and all was well except for all the $$ that he had spent on inferior parts to the OEM parts that he replaced for no reason. Oh well live and learn.

 

[shotgunfatcat]

Ha, Yeah I only replaced the master cylinder and then bled the system, I always bled the way you are saying too until this job, both my mityvac instructions and the instructions that came with the MC said to start from the closest and work to the furthest, cunfused I was, but oh well. I am going to bleed the system out of the old fluid and see what happens. If something is still not right, I am just going to have to take it somewhere.

 

[35mastr]

Does not sound like its the booster. You have air in the lines. Bleed the lines at the master to start with. Then go to the furthest wheel and work your way back.

 

[KrisKustomPaint]

New master cylinder or reman? Pedal going to the floor is most likely a whole lot of air in the system. 2nd would be a massive leak. 3rd would probably a bad master cylinder leaking fluid past the piston. A brake system is just a simply hydraulic circuit. Not really a whole lot going on there.

You could make your own vacuum bleeder with a mason jar. If you don't have anyone to help. just T into engine vacuum. run that line into the top of the mason jar lid. run another line from the bleeder through the mason jar lid to the bottom. Make sure the mason jar gets emptied before you **** brake fluid into the engine. You can seal the lines trough the lid with silicone, or what every you have laying around. It won't take much to seal a vacuum line.

 

[shotgunfatcat]

It is a new master cylinder, not reman, when I bench bled it, it pumped up nicely. I bled the system well. There is no leak, all of my hoses are good (not spongy), pads are all like new, none of the calipers are hanging up or leaking. I am thinking the fluid is shot, because before I touched anything, it was just as bad as it is now. I know air and contaminants can get in the fluid even with the system being sealed.

It isn't my first rodeo on bleeding brakes, I know I did them properly, or at least well enough to have more pressure at the pedal than I do now. I didn't know much about the booster. And I wasn't thinking about there being a spring in it to give pressure without vacuum help, so this I am sure is ruled out as well.

I am down to bad fluid or air, I bled the system well, so either there is a pocket of air that is really not playing nice, or I have bad fluid. either way I am going to have to bleed the system out to fix both, or my new MC is bad, it came with a lifetime warranty, so at least I won't be out that.

 

[jam0o0]

it really sounds like bad fluid or air in the system.

for the 1 in 100 possibility: i had a power booster go bad in my bronco. it sits a lot and the booster rusted out on the inside mechanism. the booster would **** the petal to the floor by it's self. i had to pull up on the petal to move the truck. i swapped in a new booster and everything was fine again. so boosters can do weird things, but i would bleed all the old fluid out of the system first.

good luck.

 

[monte433]

Most of your newer ABS systems need to be bled with a scan tool capable of cycling the abs solinoids while you are bleeding the brakes (ask me how I know LoL)

 

[shotgunfatcat]

Most of your newer ABS systems need to be bled with a scan tool capable of cycling the abs solinoids while you are bleeding the brakes (ask me how I know LoL)

I did look into this, I don't think my truck needs this done, but I will look into it again, it is possible. I guess sometimes the valve for the ABS can get stuck as well, which is something I need to check now too.

 

[Ohio Auto]

Are the rear brakes drum or disc?

 

[shotgunfatcat]

Are the rear brakes drum or disc?

Disc.

 

[pgreen]

It is NOT "bad fluid". Fluid that goes bad when moisture gets absorbed into the brake fluid. This is not an issue until the fluid gets hot when the brakes are used and the caliper gets the fluid to the boiling point. If it is a soft pedal after you bleed the brakes and before you drive, it is NOT a fluid issue. It is almost for sure air somewhere in the system.

It is not a bad idea to change the brake fluid on occasion, especially if it is old and/or dark. But, do NOT empty the system and start over. Pump it through the right rear caliper until the MC is very low, but do not allow the system to **** any air. Then add new fluid a bit at a time as to not dilute the old **** into the new too much. Keep doing this until you get new clear nice fluid out of the right rear caliper.

At this time, do the left rear. It should be able to be done with 4-5 pedal pump cycles. Then go right front, then left front. Make sure you get nice clean clear fluid out.

I have done race cars many times, as the high temperatures make the moisture a lot bigger issue. In fact, the fluid I use in the race cars is $80/liter (Castrol SRF), because it has the highest "wet" boiling point. Or the boiling point after moisture is present in the fluid.

This stuff is not even close to necessary in a street car or truck. The best stuff for the money is found at a Ford dealer. They have some high temp stuff that was used in their pick up trucks. Lots of racers use this because it is very good for the money.

 

[99LeCouch]

Long-time lurker joining up to have a say...

My 1999 Buick LeSabre had the exact same symptoms. The pedal went down to the floor with no braking power when the engine was running, and was high/hard with the engine off after a few pumps. Like the OP, the MC was bench-bled, got replaced, and the lines bled out 3 times. After the 3rd bleed the booster was disconnected and the vacuum line unhooked. The brakes worked fine as manual brakes after the booster depleted its vacuum reserve. One new booster later the car stopped just fine.

Test the booster by unhooking the vacuum line, capping it off, and pumping the pedal a few times. Then, properly support the rear end of the truck and try to move a wheel with somebody standing on the brake pedal. If the brakes work fine with no vacuum boost, it's the booster.

It might be a "1 in 100", and here's somebody else who was that 1!

 

[cdenton]

Ok, I have been using a mityvac to bleed brakes for 15 years. 1st, remove the bleeders from all calipers and put two wraps of teflon tape around each. This will keep air from coming in when they are cracked and better allow you to bleed out the abs.
Second, bleed the master first at the master and then as others have said start the furthest from the master.
I do this annually on all of my cars and it has worked fine for abs and non abs. Also, I pull all of the fluid out and put in all new fluid, so there is air everywhere and I have no issues.
Brake booster failures are very unusual. One of mine is 38 and still works fine.
Oh, and hunt down some ate super blue. It has a dye in it so you can see where it is making it. Could prove very helpful.

 

[35mastr]

I have also seen sticky caliper pins. Go to each wheel and remove each caliper and pins to make sure they are free. A frozen pin will give you poor brake pedal. Its a real common issue.

 

[dadsEH]

I did look into this, I don't think my truck needs this done, but I will look into it again, it is possible. I guess sometimes the valve for the ABS can get stuck as well, which is something I need to check now too.

So what was the outcome??

 

[shotgunfatcat]

Ha, well, I had it bled a few times by a few different people other than myself. Nobody really got any air out of it. One of those guys was a Gm mechanic.

Let me get a little story out of the way first. My truck was out of commission for about 2 months with various problems, I was driving my dad's f350, which we just completely went over all the brakes on it (calipers, pads, rotors, etc.), and that pedal pretty much engages the brakes within the first inch of pushing on it (stops on a dime, well a very large dime, but it is a f350).

Anyways, my mind was so used to that that when I got in my truck it didn't feel right. But I guess it was all in my head, which I am sad to admit, although one of my abs sensors is bad, which I kinda knew already, and it still isn't fixed.

GM's brakes will go to the floor if you push on them once stopped, it is just how they are, this combined with the abs tripping, and my ignorance about the brakes made me believe there was something wrong. But I have been driving it for about 3 weeks now, and although still doesn't feel right, I know, it stops just fine, and only every now and then the abs kicks in (which I make sure I stop early). I will get to this this weekend with a a little cleaning of the sensor, maybe a new one. My exhaust broke again, so I have to fix that as well. The problems just don't seem to stop.

 

[Milton Shaw]

If you are still having the problem, with all the wheels off, and a few lug nuts tightened back up. Have someone pump the brakes while you look for each caliper movement. You may have a stuck caliper or stuck pins and moving a piston a lot to get the brakes to work. In normal brake caliper operation each piston would move .002 or so as it operates. You may have one moving a visible amount and that one is causing the low petal. The little movement that pistons move is why someone ridding the brake petal on disk brakes really heats them up fast. The pistons when the pressure is off retracts just couple of thousands from the relaxing of the square o ring inside the caliper. That's also why when you just do pads only and push the pistons back into the caliper if dirt,salt,rust has gotten on the piston (which is on every piston) the caliper sticks and then the brakes drag and overheat.