Really need some help with my brakes

[Curly]

my mechanic said that the booster is too small and my engine doesn't produce enough vacuum level to support the dual booster.

That doesn't explain the slow pedal return.

Curly

[Stuka]

You have air in the master cylinder. It has to be bench bleed.

[tara]

You have air in the master cylinder. It has to be bench bleed.

i will bench bleed it tomorrow and check if there are no bent hard lines

[Stuka]

You have air in the master cylinder. It has to be bench bleed.

i will bench bleed it tomorrow and check if there are no bent hard lines

Cool, should make help a lot.

[Stuka]

my mechanic said that the booster is too small and my engine doesn't produce enough vacuum level to support the dual booster.

A dual diaphragm does not require more vacuum than a single.

[tara]

i have to do a test to check the booster. if i disconnect the hose and it works better, then it is the booster which is faulty ?

isn't a dual 7" booster to small for my car ?

[44bz]

i have to do a test to check the booster. if i disconnect the hose and it works better, then it is the booster which is faulty ?

isn't a dual 7" booster to small for my car ?

I don't know that it's too small, your problems seem to be caused by issues other than the size of your booster. I have a 7" dual diaphragm booster in my gladiator with 35s and it stops just fine.


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[RamJetFSJ]

Definitely bench bleed your Master cylinder. I didn't think it was needed either, but I struggled with my brakes a lot and it wasn't until after I bench bled it I had any success. I had slow pedal return also. But that doesn't necessarily mean thats your only problem. Ive heard of a lot of reman master cylinders being bad right out of the box (but again, that could just be because they didn't bench bleed it). It took me a few R&R and bench bleedings to get ALL the air out. Also, make sure your rear brakes are adjusted correctly, and the whole system is properly bleed. Start at the MC and crack fitting all the way back one at a time while bleeding to bleed air out of every component.

[Stuka]

i have to do a test to check the booster. if i disconnect the hose and it works better, then it is the booster which is faulty ?

isn't a dual 7" booster to small for my car ?

The dual diaphragm boosters do not need to be as large of a diameter because there are two diaphragms. This is what gives you better braking with them when everything is working properly. You can actually get away with having less engine vacuum as you have double the assistance. But unless you are running a cam with a lot of overlap, or a turbo, vacuum is not an issue.

[Tatsadasayago]

You don't have to remove the master to 'Bench-Bleed' it if you already installed it.
Remove the hard lines, install the bleeder fittings and drape the hoses over the lip. The person working the brake pedal needs to be gentle and slow else fluid goes everywhere.

The hard braking, slow pedal return and accompanying residual braking is worrisome. Sure sounds like a soft line's inner liner has come loose and the split/flap is acting as a bi-directional check valve. I just can't think of any other component that would cause this.

[tara]

MC bleeded. did a test for the booster : and it seems to work. but noticed that there is no seal between MC and booster , is it ok ?

[Tatsadasayago]

There is no seal or gasket between the MC and booster. The booster usually has a thin foam gasket between it and the firewall, but it's mostly for sound deadening.

You can often spot a leaking MC by the fluid running down the forward face of the booster. This is possible because the factory never put anything in between.

[66stepside]

How did you bleed the brakes, and did you bench bleed the master cylinder?

not bench bleed, but it doesnt look that my issue could be cause by a bad MC

If you did not bench bleed the MC, its going to be very difficult to get the brakes to work. I HIGHLY suggest you do this. You can't get all the air out in the vehicle as the plunger wont be compressed in far enough.

X2

When I installed a new booster set up I had a similar experience and it was caused by not bench bleeding the MC. I took the MC out, bench bled it, reinstalled it and it all worked out.

I had to search da net for a YouTube a video on how to bench bleed as the written instructions that came with my set up weren't too clear for a brake novice like me.


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[tara]

YESSS ! bench bleeded has changed everything and after a few miles and brakings, the car begins to stop well .
i shortenend too the rod of the booster which was little bit too long.
there is may be another probleme which explain the low pressure at the rear wheel cylinders : an old rubber brake line which could be "ballooning"

may be a bigger booster would have done the job better a 8" dual or 9" dual...


anyway, huge thanks for your help !!!

PS : do you know how i have to clean used master cylinder and brake lines before storage ? with brake cleaning spray ?

[tara]

bad news, it seems that when car is cold it works not well and more and more i drive, braking becomes better. sound weird, no ?
i noticed too that after a while not braking, the disc are "cold" compare to the drum which are very hot...

[Stuka]

bad news, it seems that when car is cold it works not well and more and more i drive, braking becomes better. sound weird, no ?
i noticed too that after a while not braking, the disc are "cold" compare to the drum which are very hot...

You still have air some place in the system. As the air gets more and more compressed, it will compress less.

It sounds like the drums may also be adjusted too tight, which is why they will be hot without any braking.

[tara]

we installed self adjusting kit at the rear

[Stuka]

we installed self adjusting kit at the rear

You still have to set the base adjustment though. They should be tight enough to just barely feel them when you spin the drum by hand. If you cannot turn it, use a brake spoon to adjust the pads in more.

[tara]

i might have still some little air... i will replace tomorrow the brake line which is ballooning and see ... but as far as i can see, the brake pedal is still hard to press and slow to come back to position , which i really wonder wouldn't a sign of a bad booster

[tara]

i spoke with an old mechanic guy who said that he thinks that the problem is that my engine doesn't produce enough vaccum for dual booster and that the original 9" single booster require less vaccum. so he advised to installed a 9" single or add avaccum electric pump to help, what do you guys think ???

another possibilty : i got a vaccum leak somewhere before the booster so the vaccum is not strong enough and the booster cannot work correctly