Brake booster push rod - 3000GT/Stealth International Message Center

ProwlerGT · 05-06-2008, 08:37 PM

So far the closest thing to what I want to know I found here:
Brake booster trouble, or is it?

All its says is what I've realized is that the booster push-rod is too far back causing my brakes to drag. I have 2 boosters (my old OEM one and a used one with lesser miles which is the one installed). Both apparently have the push-rod too far back because both are doing the exact same thing and a pedal test while watching the mc fluid with the reservoir top off shows that the push-rod isn't engaging the MC till about 3/8" or a tad more into pedal push.

The question I have is this:
Should I be able to pull/push the push rod freely with ease back and forth with my fingers or should it be firm in place? Please. lol... no jokes.

I am guessing of course it should be firm and I'm talking about on the end that pushes into the mc and not the pedal side. I went to adjust it tonight and found that turning it in either direction does nothing but SPIN IT. It is spinning FREELY and I can move the rod up and down freely. It seems broken to me, but as I've never dealt with booster's before I figured I'd ask someone who may know for sure. I'm pretty sure its broke because "how could you adjust something that moves freely" like that

Last question: Does adjusting pedal height affect the push rod on the other side?

ProwlerGT · 05-08-2008, 03:35 AM

Well for future readers here's some interesting detail on the push-rod:

The summary:
It may be wise to readjust your power booster push-rod cap nut +/- every 50k miles depending on driving habits. It may also be a good practice to put a 7mm nut behind the cap nut so that it does not move in the future thereby eliminating the need for future adjustment after much use.

The details:
That 3/8" I wrote about ... well I believe I've figured out where I lost it. The little cap nut that is the tip of the push-rod that pushes the master cylinder is almost exactly 3/8" long. It is actually about 6.5/16 long which comes to 3.25/8" long.

Whats this mean? Before the fluid in the reservoir moves (top of reservoir off pushing pedal ever so slowly) the pedal travels 3/8" down. The cap nut is adjusted or I should say PUSHED BACK OVER TIME DUE TO USE 3/8" back and thus the delay of braking and loss of ability to use fully available brake power.

Each successive push of the brake pedal moves the cap nut EVER EVER EVER EVER EVER so slightly backwards in a clockwise motion due to sheer forward pushing force. Over many thousands of miles; probably over 60k the cap nut gets far enough back to where it affects the braking performance.

I found this stuff out I went to adjust the cap nut on my old OEM booster which is off the car. The cap nut would not budge at all. It was jammed all the way back and I had to use the vice grip pliers to hold the rear grip portion in place while i turned the cap nut counter-clockwise.

The only thing that bothers me though is if the cap nut is 3/8" long and the brake pedal engages the fluid movement at 3/8" push down then this would mean adjusting the cap nut outward nearly its full length, which I believe would damn near push it right off the end of the push-rod threads. Though on the car vs using the spare I had to work on may make a difference since its all connected up to the pedal etc.. Though I also have to see the back of the master cylinder push plate too and see if it is worn inward though that would've been taken care of during the mc rebuild I do believe.

Idea: A 7mm nut behind the push-rod cap nut tightened good against it may eliminate the need for future adjustment.

I haven't been able to will myself to work on the car yet cause I don't want to set myself up for further disappointment even though I'm confident about this fix, but now having done this on the spare booster I've got some reference experience for doing it on the car.

ProwlerGT · 05-09-2008, 09:34 PM

My bad: The cap-nut is physically part of the threaded push rod that engages the mc. I had thought the cap-nut came off, but it does not. So my idea of using a lil nut to hold the cap-nut in place assuming the cap-nut was separate from the threaded part won't work. What about thread locker? Is that a bad idea to use in this instance?

ProwlerGT · 05-10-2008, 05:08 AM

Spent what turned out to be all of last night (all AM hours till 6am) adjusting the push-rod, cleaning my mas (then a wonderful fight at the very end with the connector/harness that refused to stay clipped together), and finally bleeding the brakes.

I started bleeding without the car on cause I have no ABS, but later I realized the booster makes it hard for you. I guess I wasn't thinking though and could've pulled the vac line off the booster instead of starting the car. That would've been a much better way since I had the garage all nice and A/C'd and now we're getting our wonderful 80%+ humidity days and nights here. I finally realized that due to not having a good seal between the bleeder hose and the bleeder valve I was getting on the spot air coming into the line so I'd try to press the bleeder hose as hard as I could till all I saw was tiny tiny tiny bubbles to no bubbles. That was the best I could get it.

After all that time I think the brakes are going to work wonderfully as just pulling back and forth in the garage it now seems to have that DEAD stop stopping power that I have been missing for way too long. I could not however go take it for a test drive yet as my broke ass van is parked behind the garage on ramps and today I have to take an exhaust pipe in somewhere for a custom weld job. It is probably better I drive it later today anyway because I have not had any sleep.

I hope cleaning the MAS does something GOOD. It did not look at all dirty (used flashlight) like the one on my van did. Though the Mitsu one seems to be designed such that debris would not touch/hit the element. We'll see. Going to sleep now at 7 AM !!!!

OH yes how could I forget...... BLESS MY SISTER FOR HELPING ME BLEED THE BRAKES SINCE FOR WHATEVER REASON THE SPEED BLEEDER GODS HAVE CHOSEN TO OPT ME OUT OF BEING ELIGIBLE FOR USING THEM!!! My sister was a huge help. The speed bleeders I ordered from 3SX simply got their threads ruined on the new calipers. I have a feeling though that whoever remanned these calipers screwed up the rethreading. BLESS MY SISTER! I should treat her out to eat!

NIght... morning... good day... however you wanna look at it.

05-08-2008, 03:35 AM	#2 (permalink)
ProwlerGT King Detail Join Date: Oct 2003 Location: New Orleans area Drives: 95 3000GT Base DOHC Trader Rating: (11)	Re: Brake booster push rod Well for future readers here's some interesting detail on the push-rod: The summary: It may be wise to readjust your power booster push-rod cap nut +/- every 50k miles depending on driving habits. It may also be a good practice to put a 7mm nut behind the cap nut so that it does not move in the future thereby eliminating the need for future adjustment after much use. The details: That 3/8" I wrote about ... well I believe I've figured out where I lost it. The little cap nut that is the tip of the push-rod that pushes the master cylinder is almost exactly 3/8" long. It is actually about 6.5/16 long which comes to 3.25/8" long. Whats this mean? Before the fluid in the reservoir moves (top of reservoir off pushing pedal ever so slowly) the pedal travels 3/8" down. The cap nut is adjusted or I should say PUSHED BACK OVER TIME DUE TO USE 3/8" back and thus the delay of braking and loss of ability to use fully available brake power. Each successive push of the brake pedal moves the cap nut EVER EVER EVER EVER EVER so slightly backwards in a clockwise motion due to sheer forward pushing force. Over many thousands of miles; probably over 60k the cap nut gets far enough back to where it affects the braking performance. I found this stuff out I went to adjust the cap nut on my old OEM booster which is off the car. The cap nut would not budge at all. It was jammed all the way back and I had to use the vice grip pliers to hold the rear grip portion in place while i turned the cap nut counter-clockwise. The only thing that bothers me though is if the cap nut is 3/8" long and the brake pedal engages the fluid movement at 3/8" push down then this would mean adjusting the cap nut outward nearly its full length, which I believe would damn near push it right off the end of the push-rod threads. Though on the car vs using the spare I had to work on may make a difference since its all connected up to the pedal etc.. Though I also have to see the back of the master cylinder push plate too and see if it is worn inward though that would've been taken care of during the mc rebuild I do believe. Idea: A 7mm nut behind the push-rod cap nut tightened good against it may eliminate the need for future adjustment. I haven't been able to will myself to work on the car yet cause I don't want to set myself up for further disappointment even though I'm confident about this fix, but now having done this on the spare booster I've got some reference experience for doing it on the car.

05-09-2008, 09:34 PM	#3 (permalink)
ProwlerGT King Detail Join Date: Oct 2003 Location: New Orleans area Drives: 95 3000GT Base DOHC Trader Rating: (11)	Re: Brake booster push rod My bad: The cap-nut is physically part of the threaded push rod that engages the mc. I had thought the cap-nut came off, but it does not. So my idea of using a lil nut to hold the cap-nut in place assuming the cap-nut was separate from the threaded part won't work. What about thread locker? Is that a bad idea to use in this instance?

05-10-2008, 05:08 AM	#4 (permalink)
ProwlerGT King Detail Join Date: Oct 2003 Location: New Orleans area Drives: 95 3000GT Base DOHC Trader Rating: (11)	Re: Brake booster push rod Spent what turned out to be all of last night (all AM hours till 6am) adjusting the push-rod, cleaning my mas (then a wonderful fight at the very end with the connector/harness that refused to stay clipped together), and finally bleeding the brakes. I started bleeding without the car on cause I have no ABS, but later I realized the booster makes it hard for you. I guess I wasn't thinking though and could've pulled the vac line off the booster instead of starting the car. That would've been a much better way since I had the garage all nice and A/C'd and now we're getting our wonderful 80%+ humidity days and nights here. I finally realized that due to not having a good seal between the bleeder hose and the bleeder valve I was getting on the spot air coming into the line so I'd try to press the bleeder hose as hard as I could till all I saw was tiny tiny tiny bubbles to no bubbles. That was the best I could get it. After all that time I think the brakes are going to work wonderfully as just pulling back and forth in the garage it now seems to have that DEAD stop stopping power that I have been missing for way too long. I could not however go take it for a test drive yet as my broke ass van is parked behind the garage on ramps and today I have to take an exhaust pipe in somewhere for a custom weld job. It is probably better I drive it later today anyway because I have not had any sleep. I hope cleaning the MAS does something GOOD. It did not look at all dirty (used flashlight) like the one on my van did. Though the Mitsu one seems to be designed such that debris would not touch/hit the element. We'll see. Going to sleep now at 7 AM !!!! OH yes how could I forget...... BLESS MY SISTER FOR HELPING ME BLEED THE BRAKES SINCE FOR WHATEVER REASON THE SPEED BLEEDER GODS HAVE CHOSEN TO OPT ME OUT OF BEING ELIGIBLE FOR USING THEM!!! My sister was a huge help. The speed bleeders I ordered from 3SX simply got their threads ruined on the new calipers. I have a feeling though that whoever remanned these calipers screwed up the rethreading. BLESS MY SISTER! I should treat her out to eat! NIght... morning... good day... however you wanna look at it.

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