Willie

iTrader: (1)

Is there a way to check a brake booster? Here's my problem. I'd say that my brakes functional normally as long as mild to moderate pressure is applied. But when I really need to STOP, the pedal is very hard. I performed a search on this but only found cases where the pedal goes to the floorboard or is spongy. Mine does not go to the floorboard.

This is a problem that's been going on for a couple of years. I think it's the booster. The check valve has been tested (good) and also swapped from a known good working car. It made no difference. So is there a way to test the booster before spending the time and $$$ to replace it?

Willie

MrDude_1

actually, that sounds kinda like it could be bad flex brake lines..


the booster is a pretty simple vaccum device... im thinking about it in my head and unless its gunked up so that the air cant get in there fast, i dont see how it would do that..


when the car is idling and you push the brake fast and repeatedly, do you hear it sucking in air or not??

Willie

iTrader: (1)

It's funny you should ask that. I believe you can hear it but I'll have to double check. Haven't driving my car in a while.... If you can hear it, does that mean the booster is leaking?

Willie

MrDude_1

no.. when you push it in rapidly and the engines under a decient vac (like at idle) then you should hear the air going in.


assuming its holding the vac to begin with ( you could check that with a vac pump/gauge... or even just T-ing a gauge in after the check valve..) then the other half of the system, is letting the atmospheric pressure in to assist with breaking..

if the air isnt entering the booster, then its not helping you press the brakes down.


while you probly get it willie, im sure ive confused atleast one person reading this... heres how power brakes work for thoes who are intrested...

Chickenman35

That could very well be a booster problem. A small pinhole or crack in the diaphram would give the the problem you describe.

Poor pad material could also be the problem, as could glazing of the rotors.

Have you tried other brands of pads? I've found that Bendix Titanium are particularily good. Excellant cold stopping and modulation, plus they really haul the car down from high speeds. The Titanium coating will scour the rotor surface of any deposits left from other pad material. This is an important issue that is often overlooked.

I used the Bendix TI pads for hillclimbs where they had to go from high speeds ( 80 to 100mph ) to 20 mph several times within 2 minutes. Never a fade issue.

Contrast that to Raybestos "Sure Stops" ( an Oxymoron for sure ) where I nearly went through a tire wall at the finish line because the car would not stop. Couldn't lock the fronts no matter how hard I tried.

Interestingly, with the Raybestos pads, the pedal feel was as you describe. OK on light or medium stops, but you really, really had to lean on it when making an all out stop.

If you've been using the same pads MFG for years then that might be the problem. If you've changed pad MFG's and the problem remains consistant then I would be looking at a new booster.

Hope this helps.

Matt_Ky

Wille,
My '91 Camaro recently developed similar problem ie brake pedal hard to depress and gets harder each time you feather the brakes to the point of barely stopping (3rd time you hit brakes). Installed new power brake booster, no change problem is still there.
Drive short distanc vacuum recovers then repeats the hard to depress brake pedal with hardle any stopping power. Scary! Went out into major intersection when light turned red on me
How much vacuum should you see between check valve on booster and I believe it is a filter that the 8" or so rubber line goes to from check valve?

Chickenman35

Full manifold vacuum. Should be no restriction. Filter should not restrict flow. Mkae sure that there is no restriction or blockage in line. Check hose and fitting leading to booster for leaks or cracks. Did new booster come with a new check valve?

If you have a huge Cam in the car, that could be the problem. In that case an Auxilary Vaccum Cannister, such as those offerred by Comp Cams should provide additional vacuumm reserve.

Matt_Ky

Chickeman35,
Thanks for the quick reply. I really need to get brakes fixed today and go out of town (relative admitted to hospital). Yes, the new power brake booster came with check valve.
Stock engine ie no big cam.
The 8" rubber line from check valve, is that a filter on the other end right by intake manifold?
So, I should disconnect rubber line from check valve and measure vacuum between check valve and filter?
Thanks again!

Chickenman35

Yep...vaccum at that point should equal manifold vaccum. Note you could have a restriction in the line or fitting ( partial blockage ). That would still show full manifold vaccumm, but would not allow reservoir to recover fast enough.

If vacuum checks out OK, I'd carefully check the fitting and line for any clogs. Make sure that hose has not deteriorated internally. May look OK on outside but could be falling apart on inside and blocking flow. Has hose ever been replaced with something other than OEM? Booster hose must be thick wall, reinforced vaccum hose so that it will not collapse. I've seen guys use cheap fuel hose ( non reinforced ) as a booster hose and the danged thing collapses. Not good.

Power steering hose will work fine ( heavy wall, reinforced ).

PS: You can thank insomnia for the quick reply. It's 3:48 AM out here on the West Coast.....Yuck!! Going back to beddy-bye now.....ZZZZZzzzzzz

Matt_Ky

Son of a gun, problem solved this morning! An $8 filter between intake manifold and check valve on power brake booster. After I installed power brake booster yesterday.
Local Midas Shop yesterday said brakes were good all the way around, power brake booster bad.
Local Ken Towerys today said I need brakes done all the way around $500.
F^&*% can't trust anybody these days!
:rant off:

Thanks Chickenman!! You were right had plenty of vacuum yet it was not revovering quick enough.

fastlapster

After about 3 weeks of looking for help diagnosing what I think is a problem with my booster I finally found what appears to be the Lexus Brake Booster Training Manual. This is excellent even if a little technical. It will help with understanding any manifold vacuum boost system and describes double piston boosters.

http://www.autoshop101.com/forms/brake05.pdf

customblackbird

iTrader: (15)

sry dont mean to hijack but it seems u fixed your problem. i have a simular problem. wat is the filter u used and where did u get your filter from?

hes my prob. my car 87 formula 350 has the BW 9bolt and 4 wheel factory disks. car never had good brakes, car seemed to stop normally under low to mid pedal. Once i go above its like theres no pressure. The pedal doesnt go to the floor but its just the like wheels just keep turning through the brakes. I can never get the front wheels to lock up , even in the rain. its been 3-4yrs since ive had the car and this is what ive done to try and fix it.

replaced master cylinder( bought rebuilt for 4 wheel disks) got new booster as well. replaced all rubber lines with braided stainless, replaced rear calipers for stocker rebuilt/new, put on ceramic pads. replaced front rotors with drilled/slotted, also replaced front calipers with SSBC aluminum force 10 upgraded calipers, came with ceramic pads. also took out stock proportioning valve out, connected the front brake hard lines with a T fitting. rear brake hard line has SSBC adjustable proportioning valve.

after all this... i still havent fixed the problem. i even connected a SSBC brake pressure tester to the calipers to see wat pressures i was getting at the calipers. fronts showed like 600psi normal stop and something like 900psi panic stop. these seem really low. engine vacume was good i believe so idk what else the prob could be. any ideas?

gregsz-28

iTrader: (1)

You could probably get that filter at any auto parts store, or from a junkyard car.

customblackbird

iTrader: (15)

i dont even kno what filter your talking about. he never stated the part# or anything, just said filter

gregsz-28

iTrader: (1)

the filter in the vacuum line to the brake booster.

customblackbird

iTrader: (15)

yea i got that. but wat kind of filter is it!!!! am i not being clear? like an oil filter lol or a fuel filter like what?

gregsz-28

iTrader: (1)

More like an air filter, it filters gasoline fumes out so that they don't damage the booster diaphragm.

IROCmenace

iTrader: (1)

Do TPI cars have that filter? I just have a line from the plenum to the check valve. Never heard of a filter???