Ive got a 1988 Toyota pickup with a SAS and for some reason i cant get the brakes to work. you can pump them up several times and they will have pressure and continue to have pressure but as soon as you release the pedal they almost instantly loss all pressure. It has a new master cylinder, front calipers and rotors. It doesnt leak any fluid or anything. any help would be appreciated thanks.

 

how's the booster? or even just the check valve and the line running to it?

 

yeah i think the booster is fine because i had this problem before on my other cab and i've tried 3 different master cylinders and i took out that check valve and ran it directly to my holley carb (has a ford 302) and still doesnt make a difference! its always had this problem and i've asked a ton of people and still noone can figure out what the problem is!

 

Rear brakes?

A classic sign of 'pumping up the brakes makes them work, but letting off the pedal makes them get squishy' is improperly adjusted or improperly bled rear brake cylinders.
So,
(A) bleed the whole brake system starting from the farthest wheel from the master cylinder and work your way to the closest. If you've any doubt about which is closest or furthest, grab your tape measure
(B) Adjust the rear wheel cylinders properly.

If you still can't get them to work, take them to Mineke, Midas or Big-O or somewhere that does free brake inspections. Let THEM tell you what the problem(s) is(are).

 

So the booster is still the old one from 88? What is leading you to think the booster is fine? Sounds similar to an older car that does not have booster assisted brakes; they need constant pumping as well.

Try this; take a drive and use the brakes with the vacuum line hooked up to the booster, then unplug it and cap it off and see if there's a noticeable difference.

It will be pretty much like driving an older style car that has drums all the way around and no booster, but you will have to vigorously pump the peddle to get the pressure up for disc brakes for the front (why booster are used), so stopping distance will increase, so obviously, DRIVE VERY SLOW AND FAR AWAY FROM OTHER TRAFFIC, LITTLE KIDS, AND SO ON!!!

If there's no or very little difference, then you know where your problem is.

True what abecedarian says too; pull the drums off and take a look at the shoes and cylinders in there. If you're not loosing any fluid though, the cylinders are probably fine, but the shoes could be completely shot.

 

Wait a minute... theres a 302 in that Yote?

Have a cam with a high lift in it?

If you do, that may be the source of your problem; not enough vacuum...

If it's stock though, I'll go back to my previous post, lol

 

Regardless of what's going on, if you pump it up and it works, but let off and it stops working, get those rear DRUMs adjusted properly. "Pumping it up" takes nearly all of the blame away from the booster and front end and lays it squarely on the rear, where the brakes don't "float" like discs and have springs to pull them back.

 

X's 2

I'd probably start there 1st

 

no it doesnt a big cam just a comp cam 280H which is .456 lift. yeah we just readjusted the rear brakes and its not leaking any fluid in the seals because im not lossing any fluid. i'll try the vaccum trick and see what happens and get back to you. thanks for the help i appreciate it

 

Just be VERY careful when doing this, I don't want to be the cause of you wrecking your Yote, lol. Take it slow and easy, and lets us know what you come up with.

oh yeah, welcome to YotaTech!

 

Are you bleeding the LPSV? Did you bench bleed your master?

 

where is the beer in that diagram?

 

it's not in the diagram 'cause it's already been drank.

 

lol good one abe