Need HELP. Brake pressure building up, but won't release.
 

We swapped my coilovers from my Z to a friend's 04 G35 coupe.

Everything went without a hitch last night. Drove home 20 miles with a mix of street and interstate roadways.

This morning, after trying to diagnose a brake light switch issue on my Z by borrowing the switch from the G, the problem arose. (Neither vehicle was turned on while doing this)

The switch that I pulled was the lower switch since there's two switches on the brake pedal assembly which I'm thinking may have been the ASCD switch. (The one that disengages cruise control when brakes are applied.)

^^This switch work may not have anything to do with this as it may be coincidental with timing.

The brake system in the G is building vacuum pressure, but not releasing. It will build pressure on its own or when you press the brake pedal. This is causing the entire system to apply the brakes and stop the car.


This happened as soon as we left the house and we didn't make it but five blocks away. In order to get home, we had to pull the vacuum line to release pressure a couple times on the way back home.


04 G35 coupe, 6mt, with oem brembos that have never been touched and brake lines were not kinked during installation of coilovers.


Does ANYONE have any ideas??

Wow, almost 100 views and no one has experienced this issue? lol

No one in my area has either. I've even checked with a shop that specializes in z32's since he's does work on z33's and G's as well. After he consulted with a tech of 19 years at a local Nissan dealership (both of whom have not experienced this issue,) they both suggested replacing the brake booster thinking the internal spring/diaphragm was causing this to happen.

So, unless anyone has any ideas, we're looking for a cheap brake booster to fit a z or g that has oem brembos. (It's going on the 04 6mt g35 coupe)

helpsies?

It's definitely a booster issue since pulling the vacuum line off it releases the brakes.

When you were under there fiddling with switches, did you adjust the rod from the pedal to the booster at all? It's quite picky about adjustment, and if you get it a bit too long, the booster won't release completely and cause the problem you describe.

If you didn't move the rod at all, something in the booster started sticking. It may be worth a try to loosen it a bit, like a half a turn, and see if the problem goes away.

Here is something to check: with the engine off, pull off the vacuum hose from the booster to empty the vacuum. Climb under the dash and see how much freeplay the shaft has. There should be some, I'd guess an 1/8" or so. I've not adjusted the system on this car before so I'm not sure. My older car needs 1/8" or so.

Boosters aren't cheap and I've not had any luck with rebuilt ones. Your best bet is a junkyard.

Asterix

When you say "no luck with rebuilt" I'm assuming you've tried a couple reman's and have had them go out shortly after?

Cause I'd rather give a $250 reman a shot a time or two before I dump $700+ at Infiniti for a new one. LOL

Actually, I tried 5 rebuilt boosters from the only place that carries them. None of them held vacuum for more than a few hours, which my 20-year-old Toyota one does as long as it's not too cold. Sure, they boosted, but so does my old one. I'm not paying $250 for a rebuilt booster that really doesn't work any better than a 20-year-old one.

My recommendation is still to look in the junkyards for a Z that has been rear ended. That booster will be far better than any reman and may cost less.

Asterix

Oh, I have my feelers out EVERYwhere for a used one. Problem is wrecked 03-04 G's with Brembo's are harder to find sometimes than you might think. lol

Are you sure the booster isn't common between an '04 G with Brembos and one without? I'd suspect the master cylinders are different, but maybe the booster isn't.

Asterix

From all we can tell the booster AND MC's are different. At least different mounting points.

They are two separate part numbers for Brembo's, and non-Brembo's.

Now, I would be curious to see if the Track Z's have the same booster and mounting points. That would expand my search a small percentage.

btw, thanks for all the input. :)

-T

I don't think it is your booster or master. It is probably in the switch. Test the switch with a meter make sure it is working and the correct normally open or normally closed switch. If the car has VDC and a switch is not adjusted correctly that may be your problem. the symptoms you are describing would not lead me to a booster. If the booster is not working then you get no power brakes. You don't get more brakes as you drive.

Since I only touched the ASCD switch (only disables cruise control) on the G, it would be weird that the brake switch went out at that time. (I don't doubt that could've happened, lol)

The question I would have is, if the brake switch was bad, would it not activate the brake lights too?

While the car is applying it's own brakes, the rear tail lights are not illuminating. They only illuminate if you actually press the brake pedal.

Oh, extra question. From the discussions with a local z shop and local dealership, they mentioned a spring/valve inside the brake booster that could have weakened over time and it causing it to hold pressure when it should be releasing. They couldn't give a solid reasoning as they wondered about the rod pressurizing the master cylinder to push the fluid into the calipers, but they thought that it might be holding enough pressure to do it on it's own. Does that sound anywhere near plausible?

When you say switch, do you mean the brake light switch? Like, on the pedal?
I'll certainly pull the thing off and check.

If you want to know what's inside the booster and how it works, read this. It's from Toyota, but they're all the same.

So, I see from the catalog at Courtesy Parts that there are 10 different boosters for the Z from '03-'08, but only 3 master cylinders. That's rediculous.

My next check would be www.car-part.com. It shows many boosters for an '04 G35 available, and 7 of them state they're for the one with Brembo brakes. $75 ain't bad either.

turbotoy, a booster certainly can fail in such a way that it doesn't release the brakes. The fact that when russ713 pulled the vacuum line off the booster it released the brakes says it's the booster. Either it needs replacing or the shaft from the pedal to the booster needs adjusting.

Asterix

wait... you found brake booster in that list on c-p.com? I need to look again, I didn't see it yesterday. LOL

Then again, I'm a little tired and ragged right now. 0_o

It's under P for "power brake booster".

Asterix

Yeah, I went back after I posted and it hit me while I was typing it up. :gotowned:


f*ck me, I feel :icon14:

I had the same problem when I changed my brake light switch. When installing the switch do not push forward. Just back off about 1/4 inch.

Wow I had the exact same problem as the OP. Found out ^^^ THIS was the reason. There's suppose to be a minor gap when installing the switch which I did not know. This fixed it thanks man. Took me days.