Blaen99

iTrader: (1)

Purchased an N/A RX-7 sport about a year ago, been working out stuff over that time (thanks to lots of searching at that!)

I'm down to one problem that even searching doesn't help with. It's in the brakes.

Now, as a prequel, the brakes used to work 100% perfectly. They were -mint-, no issues whatsoever. May as well have been brand new parts in the system when I finished up with it.

Then I swapped in a new engine because the old one had a coolant seal problem.

I swapped on a temporary hose from the lower manifold to the brake booster line, it had a slight leak and all that it started on the engine. Brakes didn't work worth a damn, acted as if it was a bad brake booster - but it should have been, considering there was a leak in the line/etc..

Here over the past couple weeks, I've had a chance to really start to try to work on the brakes. However, for the life of me, I cannot figure out how to get the brakes to work how they were before I swapped the engine. They act as if the brake booster is bad, with one addition: One day I was driving along, and the parking brake light was on. Checked the brake fluid, and the resevoir was completely empty.

However, this makes no sense. How could a car one day suddenly have brake booster issues after an engine swap, when it ran perfectly before?

I'm heading out to prepare to replace the brake booster, but I am hoping someone has some advice other than randomly start replacing parts and bleeding brakes.

clokker

iTrader: (2)

Is there a one way check valve somewhere in the vac hose to the booster?
Should be...it's internal in the stock hose.

If the reservoir went totally dry and you don't see any external puddles then there's only one place the fluid could have gone- into the booster.

In case you're wondering, that's not a particularly good thing.

At the very least you'll have to separate the MC from the booster and see if it's wet in there (ew!).

Blaen99

iTrader: (1)

On the N/A, is the one-way check valve in the s-shaped hose off of the manifold? Or the L-shaped hose going to the booster from the metal pipe?

And I'll pull off the MC right now to find out if that is the case.

clokker

iTrader: (2)

Assuming the stock parts, the check valve would be between the firewall hardline and the booster itself.

Good luck.

Blaen99

iTrader: (1)

Then yes, the line that's been there for 20-odd years is still there ><


Appears I'll need it. Not even trying anymore untill I get brake wrenches.

Blaen99

iTrader: (1)

Okay, finally finished replacing tons of stuff.

New brake booster
New master cylinder
Flushed + bled brakes
New hoses

No brake assist. None. It's like I have the manual brakes from hell.

Tested this by pushing the brake down, starting it up - it doesn't go down any further. Same as before I did all this replacing of brake system parts ><.

What could it be?

clokker

iTrader: (2)

Are you getting vacuum to the booster?

graniteguru

iTrader: (1)

I had the same problem on mine. Turns out I had reversed the line with the check valve in it. It is a one way valve and if you put the line on backwards, it will not give you boost. Try turning it around. Let me know.

Blaen99

iTrader: (1)

How would I check this?

clokker

iTrader: (2)

Pull the hose off the booster, cover the end with your thumb.
Have someone start the car and you should be able to feel the vac being pulled.

Blaen99

iTrader: (1)

If I can't feel vacuum, what is the next step?

clokker

iTrader: (2)

Check your connection at the engine?
Check the hoses and hard line between the engine and the booster?
Check the vac nipple you're tapping for vacuum?

ForsakenRX7

Check the vacuum source.

Blaen99

iTrader: (1)

Assuming there's no vacuum at the engine source, what would be the next step from there?

Moving the line to, say, one of the open lines on the throttle body?

ForsakenRX7

Correct.

Blaen99

iTrader: (1)

It -definitely- gets vacuum. Not the strongest vacuum I have ever felt, but it definitely gets vacuum. What's the next step?

RiCKoLA

iTrader: (3)

this happened to me a couple years ago. it kicked my *** for a couple days till i found something on the forum about the check valve. flipped the hose around and TAADAAA!! brakes worked!

Blaen99

iTrader: (1)

Check valve is working properly.

ForsakenRX7

So vacuum is correct, checkvalve is correct, and everything is new and bled right?
I'm lost after that frankly.
Out of curiosity, can you get us a pic of the vacuum hose, like where you have it hooked to on the manifold. The fact you said it was weak is the only thing I have to go on at this point.

Blaen99

iTrader: (1)

I've replaced both hoses leading to the brake booster, both the S-shaped and L-shaped ones. The S-shaped one leads directly to the standard place on the LIM on a N/A engine - a picture isn't possible atm, however.

In addition, I currently have the one-way check valve hose replaced with a hose that has no check valve to eliminate any chance of the check valve being an issue. However, both the hose without a check valve and with a check valve gave the same vacuum when pulled off and tested (I pull off the booster end, not the hardline end to test).

Blaen99

iTrader: (1)

Would adjusting the pushrod between the MC and the brake booster fix this issue?

Blaen99

iTrader: (1)

After more testing/working at it, I *may* have partial or full power-assisted braking for the first push of the pedal, then it goes for a bit (Say, 30 seconds or so) where I can't hit them if I want it to come back.

I'm stumped at this point ><. Would that imply the vacuum is too weak to build up the reservoir?

clokker

iTrader: (2)

Given that you've replace all the hardware, the vacuum source itself would seem to be the only thing left.

Blaen99

iTrader: (1)

Tracked it down.

It *does* have brake booster assist. The problem hails from the brake booster starts abnormally low in the pedal action - i.e., close to the floor

How do I adjust it so the brake booster starts closer to the top of the pedal's action? The pushrod near the master cylinder?

clokker

iTrader: (2)

Yes.

You'll have to be careful...if the rod is "over adjusted", it won't allow the internal valve to release, vacuum will just accumulate and the brakes will lock.

Jeez, you've really had a hard time with this.