PurpleZ28

so we just picked up an 88 rx7 non turbo, but the car has a hard time stopping. after replacing the master, the booster, the proportioning valve and check valve it got slightly better.

the vacuum to the booster was reading 20psi ( or whatever vacuum is). the first pump of the pedal makes the car want to stop fairley quick but not where it should be. the second pump firms up the pedal and then stops the car 50% less and last but not least the 3rd pump the car has only 10% stopping power while the pedal is completely firm.

In other news when we disconnect the check valve line from the booster after starting it, it does hiss out out air. but if you disconnect it with the motor running the idle stays the same ( no idle change).

no air in the lines we've bleed them about 8 times.
no leaks anywhere
we've gone through 3 boosters

our only question would be is there a way were not getting enough vacuum?

CrimsonPride

iTrader: (11)

If you disconnect the vacuum line going to the brake booster with the car running it should cause a vacuum leak to the engine probably so large that the car will stop running or at least idle up a lot if it does stay running.

I don't remember where the check valve is in those cars but if you disconnect the vacuum line between the check valve and the engine the booster should not suck in any air. If you disconnect between the check valve and the booster, the booster should suck in air.

Are you sure you are getting engine vacuum in the line going to the booster?

I would also check for swollen flexible hoses at each wheel while pressing the brakes and check the brake pedal linkage and booster pushrod under the dash for excessive wear.

PurpleZ28

Yes I am getting vacuum through the lines. The only logical thing I can think of is the motor not creating enough vacuum. I'm going to re plumb all of it this weekend and see

CrimsonPride

iTrader: (11)

Not sure if you suspect primarily the engine or the plumbing to the booster but if you want to check it a vacuum gauge like these is really inexpensive. IIRC around 16 - 18 inHg warmed up at idle is normal vacuum. If the engine isn't producing enough vacuum your engine won't be running very well generally but it won't hurt to check.

PurpleZ28

Thanks for the reply

the weird part is the vacuum gauge is reading 20 psi to the booster at idle fellas I'm fully out of ideas

PurpleZ28

Another question where the brake booster hose plugs in to the block what is supposed to be right next to it, looks like it should be held on with 2 bolts. Seems like a lever that rocks 90 degrees

CrimsonPride

iTrader: (11)

At this point I would make sure I have inspected everything. If it was my car I would put it up on 4 jackstands with the wheels off, idling and inspect everything while someone presses the brakes. See if you have any give anywhere like at a caliper that isn't bolted on properly, flex hose bulging or maybe one of the rear caliper pistons sitting on one of the nubs on the backside of the pads if someone didn't install the rear pads properly.

When you say 20 psi which is a pressure reading I am assuming you mean 20 in hg. If so your engine vacuum is good.

PurpleZ28

Vacuums good brakes re bled calipers work. New booster coming Tuesday but no brakes. Could the boosters piston and calipers female be different diameter

CrimsonPride

iTrader: (11)

I can't think of anything else to suggest.

You might want to rephrase the above question in more detail in case some else will give you some input. The booster doesn't interface with the calipers directly so I think the above is hard to follow.

PurpleZ28

What I ment was the boosters rod? Be binding in the master cylinder? Sorry I'm on mobile and my train of thought is jumping around

marsredr100

I can't really think of anything else base on what you have posted. Is there a check valve or should it be a check valve on the booster vacuum line that could be missing or malfunctioning?

CrimsonPride

iTrader: (11)

I wouldn't think so, but not entirely sure.

I believe the pushrod from the booster just hits the piston of the master cyl in the middle so if there was any binding I think it would be the piston within the master cyl or something within the booster with itself.

But, sounds like you have replaced both already.

There is such a thing as bench bleeding a master cylinder but I don't know how important that is. Since you have bled multiple times think you would have had all air out of it by now.

PurpleZ28

The check valve is in the hose to the booster and is working correctly. The master was bench bled like I said I've never experienced anything like this.

misterstyx69

iTrader: (142)

OH!..I think I may know what is going on.
the Rubber Hose between the Booster and the Steel hose that attaches to the firewall..It has a CHECK valve IN IT.,(that little rubber shaped hose)
IF the hose has inadvertently been reversed then you can get brakes..BUT the Brakes will feel like Manual..and I mean"grab the wheel and use your whole body weight to stop the Car"brakes!..Been there/Done that..Screwed me up for 3 weeks!

Check that hose..it actually has an ARROW on it to show direction of how the hose should be installed.If you can't see the arrow then you need to have the air flow go from the booster to the Engine..(Vacuum)..

PurpleZ28

Could it be The booster again my buddy's 89 hondas booster, when you press the peddle with your thumb over the booster hose creates pressure my booster does not

PurpleZ28

So I made a vacuum cannister and now I have brakes... thanks everyone for your help

DC5Daniel

iTrader: (10)

So you vacuum bled the system? I have have the same issue/troubleshooting to a T.

PurpleZ28

Look up pvc pipe vacuum cannister or vacuum reservoir. I'm on mobile otherwise I would post a picture.

DC5Daniel

iTrader: (10)

I took the car somewhere that had a BC pressure bleeder, air and dirt came out that never dislodged from traditional 2-man bleeding. Brand new reman calipers all around, several master cylinders, new prop valve, booster, the whole 9 yards. I've never had a firm pedal until now. Vacuum/pressure bleed is the answer.