junito1

OK. Before i go replacing EVRYTHING. Maybe your suggestions and experiences can save me some money.

I would like to hear what you guys have to say as to why my brake press is gone.

How and what happened: Was driving the car on friday when all of a sudden i started noticing when i came to normal traffic stops(and slowly got on the brakes they kept sinking to the ground). But when i jumped on the brakes hard and suddenly it would hold the pressure like they were supposed to.

So the brakes stayed working like that for a whole day.

The next day(saturday morning) my brakes got even worse and now they were sinking all the way to the ground everytime... no matter how i used the brakes.
SO now around evening time on sat. the brakes magically came back to NORMAL working order. THey worked!!! But after that 15 minute drive they were back to completely sinking to the floor everytime.



IS it the brake master cylinder? The booster?
And if i removed my ABS. DO i have to order the Brake master cylinder for a non ABS fc3s? Is there a diff in BRake Master cylinders between 4 piston equiped cars and others?

clokker

iTrader: (2)

Sounds like master cylinder to me but you can easily check the booster just to be sure (although I'm not sure if this test works if the MC is defective...).

With the car OFF, depress the brake pedal and hold it.
Now start the car.
The pedal should sink a little as vacuum is applied to the booster.
If it does, the booster is probably good.
When boosters fail the pedal becomes very hard to depress, it doesn't just sink to the floor.

Now replace the master cylinder.

Yes, the TII master cylinder has a larger bore than the single piston brake setup but the smaller master cylinder works fine if you swap to the 4-piston brakes.
The vacuum booster is different as well but again, the stock, single piston unit will be OK with the larger calipers.

I don't know anything about the ABS setups.

sharingan 19

iTrader: (16)

I've had a master cylinder go out, it just died (at the top of a hill ) and I didn't have any warning, but when it did, the pedal went down to the floor as you described, and it didn't come back up.

Now my ABS has a small leak and sometimes when I pull up to a light, if I keep steady pressure on the pedal it will continue to get lower and lower (never to the floor though) until I release it, then it goes back up to normal. Like you I never have that problem if I get on the breaks hard, only under constant light pressure. Its been like this for about 6 months.

I assumed this is an ABS problem (or maybe how that crap-tastic system is suppose to operate) but in any event it should be gone once I can complete my ABS removal.

The master cylinder is different for 4 piston set ups. You don't have to order the non-abs master cylinder (some consider the ABS unit an "upgrade") unless you want to also order non-abs lines, and make it a plug-in affair.

InsomniacFC

iTrader: (4)

Check your brakes down at the calipers and see if they need to be rebuilt. I had a similar issue and when I went to rotate the tires I checked out the brakes only to find the seals on the calipers were bad.

Other than that, you might want to bleed the system if you haven't already.

InsomniacFC

iTrader: (4)

Mods please delete this and all posts of mine below. The site froze and for some reason there's 10 posts here. Thanks.

RotaMan99

Sounds more like a leak to me then the master cylinder. Go around to all four wheels and check your calipers for dark damp area and around the brake lines and, Master cylinder etc..

junito1

I have an 88 TII. It originally had ABS, but it was leaking. Im not no mechanic, but i removed the MC a long with the 2 front brake lines of an 86 sports models that had 5 lug and 4 piston calipers, no ABS. On my car, I proceeded to remove the ABS pump, 2 front caliper,and the MC. The MC had to be changed do to brake line fittings being on wrong side for ABS. ANyways. I did this over a year ago and have not had any problems till now.

CLocker;

WHen my car is off and i depress the brake it will sink all the way to the floor, but it will always come back up, all the way.(never gets stuck on floor)


Also. WHen the pedal is pressed all the way to the floor it will actually stop the car a tiny bit.

junito1

brake pedal feeld like a clutch pedal.

When i am driving and i go to stop the the brakes will sink all the way in but when depressed to the floor they actually make a tiny bit of pressure and can make a very crappy stop. heh

still think its the MC guys>?


Oh And i checked all the brake calipers for wet spots and they are all fine.

clokker

iTrader: (2)

I do.

Medicj02

each master cylinder has 2 pistons .... when the first piston's seal goes out there is a spring behind it that will still let you pressurize the system using the 2nd piston....you need your master cylinder rebuilt.....very simple to do and takes max an hour if its your first time doing it.......then fork out the extra 5 bucks and put in new brake fluid (don't just pour the new stuff in, flush out the old stuff)

celbii

iTrader: (2)

Exact same thing happened to me. New master cylinder fixed it.

Edit: mine also had a tiny bit of stopping power all the way at the bottem of the floor, so I definitely think its the mastery cylinder.

junito1

rebuild?

I think i will buy a band new one.

thanx guys

pfsantos

iTrader: (1)

If there is no air in the system and no leaks, it's the master cylinder for sure.

Think of it this way. Without power brakes or with the engine off, brake fluid has no way to go with a good master cylinder and calipers. If the master cylinder seals are leaking, the piston just moves in the bore and the fluid squeezes around it when you apply the brakes. The brake pedal spring (have a look) brings the pedal back up and the piston spring does the same in the MC.

McHack

Having just gone thru brake woes, +1 this response....

Also, ya might want to start w/ just checking to make sure your fluid reservoir has the appropriate amount of fluid in it...

RX7MAVEN

There is a check valve or a port to let fluid from the reservoir fill the master cylinder when the brale is released, and prevent flow back into the reservoir when the brake is depressed.. Dirt, contaminated brake fluid, or wear can cause the fluid to leak back into the reservoir when pressing the brake. It is an internal leak with no loss of fluid. If nothing is leaking replace/rebuild the master cylinder. Brake system should be flushed every two years. Brake fluid collects condensation and dilutes.
Using brake fluid from an opened bottle that has been laying around for a while is not a good idea.

Medicj02

+1 to rx7maven's post.....last master cylinder i rebuilt i had to spend an extra almost 30 mins using brake cleaner and a pick to clean out the ports

RotaMan99

Actually thats not really correct.

There are 2 pistons but one piston pressurizes the front while the other does the rear. If one seal goes in one piston, say the rear piston, you will still have the front brakes but not the rear. Same thing happends if there is a leak some where in the break system say at drivers front caliper, you will have very little to no front brakes but will still have rear brakes. Pedal will still have lots of travel since you are now pushing either the rear piston against the front piston or the front piston against the front wall of the MC. The springs have nothing to do with the pressure in the brake lines, they are their to force the pistons and your brake pedal back to its neutral stance.

Now it is sounding like the MC. Disconnect the MC from the booster and you should see, if the seals are leaking, brake fluid between the MC and booster.

detonation

try getting the brake lines bled...might be some air in the lines...might help...

junito1

MY reservoir has not gone down in fluid. AT all. Checked it many times.

ALready checked all my calipers for damp spots and they are all nice and dry.

BUt on my reservoir when i press the brake pedal, for some reason the fluid in the reservoir is getting moved around with air or something.