So im trying to clean up my engine bay and i was just thinking, can i relocate the vacuum line for the brake booster? id like to delete the line that goes along the firewall so i was thinking of welding the hole shut an adding a fitting either in the back of the UIM or on the bottom of the UIM.... can i do this or does it have to be at a specific location?

thanks in advance

 

I've never seen it done on an FD but yes it doesn't have to come from one specific location, as long as it it's a good sized line. On the USDM turbo FC the brake booster line comes from the back of the plenum area (FD UIM basically has no plenum), closer to the throttle body. On the JDM FC the brake booster comes from a hole on the back of the rear secondary runner. That hole appears to have been drilled and tapped at the factory.

 

cool, thanks! will try it out!

 

Yea, as long as it is behind the throttle body and like arghx said the line is large, I see no problem with relocating it. Seems like a good idea to clean up the look of the UIM.



John

 

Just don't forget to put a check valve in the line so you don't pressurize the booster.

 

I taped my brake booster line into the secondary runner of my intake. Works perfectly fine.

 

On an unrelated note, anyone know what would cause loss of brake assist when a car stalls? I noticed this on my RHD when I was initially tuning it that if it stalled coming to a light, I would "lose brakes" and have to push harder. In my blue FD or any other FD I've driven it doesn't do that. Could the brake booster be leaking?

thewird

 

Could be a small leak in the diaphragm that still lets the booster work normally when it's running. Could also be the check valve leaking I think, I don't remember if it is in-line in the hose, or built in to the body of the booster. Should hold enough vacuum inside for at least two strokes of power assist after the engine is turned off.

 

Oh! Maybe that's why. It has an silicone hose on it instead of the OEM one. So if theres a check valve in it, that would explain it. Can anyone confirm this?

thewird

 

The engine isn't running so no vacuum=no brake assist.

 

is that necessary since the stock line doesnt include one?

 

The stock line has one it's stuffed inside the vacuum line so you can't see it.

 

Yea, the stock line does have the valve built into it, if you look close at the line and squeeze it you can feel it. Wird, the reason you are losing your brakes when the car shuts off is because of no check valve. The check valve is a one way that keeps vacuum in the booster after the car is shut off. I only know this because last year I had made my own booster line and when doing my burnout at the track without the line lock the pedal would push back on me with boost. Also, when the car shut off I lost assist. So I bought the new factory hoses from malloy and all is good. I believe the check valve is in the hose that attaches from the metal tube to the engine.

 

Thanks guys. The FSM had no mention of it.

thewird

 

the LHD cars got a recall for this, they moved the check valve from the engine side to the booster side, because of this problem.

 

tricky mazda! awesome. thanks for all the help guys

last question, does anyone know the size of the hose for it?

 

Got a quik question... Would this chk valve failing or the booster sporting a small leak cause idle issues??

 

It's a vac leak of a closed system. Yes, it will cause idle issues.

 

Yeah, I made that mistake. It would also sometimes loose assist while driving. Get a new OEM one from Ray.

 

And btw, the check valve is in the hose from the booster to the hard line, not the hose from manifold to hard line. At least it is in my 94.