1991 R32 GTR Brake Booster

[Jjtxaz24]

Hey guys, 

I hope you are all doing well. Seeking your wisdom on something that has me puzzled.

The OEM brake booster on my GTR was bad. So I decided why not clean up the bay and get something new in there in place of it. I replaced it with a  Wilwood Brake Booster Delete Kit (PN 260-10375) - I looked up the stock specs on a r32 GTR (non SpecV) and found that it is a 25.4 mm (1 ") bore size. I sourced a STAINLESS STEEL 4 WAY BRAKE UNION and STAINLESS STEEL 4 WAY BRAKE UNION to put it all together. There we some fittings that were needed as well but overall it is installed and front and rear have been bled.

No matter how many times I bleed it and make sure there is no air in the system. The brake pedal is soft, if I pump the brakes it'll get firm but then go soft again. Definitely not able to drive around at all at regular speeds. The guy at the shop that installed it and has my car (I been really busy with school and work and decided to have someone take a go at it) cant get it to work.

He suggest to find the stock brake booster new or have my old one rebuilt. At this point I agree. I don't know what else it could be. You all have any info or insight? 

Pending your advice and help. 

[Duncan]

I don't see how an issue with a variable pedal could possibly be due to not having a brake booster.

Basically the booster adds assistance to make the pedal lighter (when the engine is running and making vacuum). Without a booster it should either be just right, too hard or too soft at all times depending on the master cylinder bore size and where the pivot is on the brake pedal (pedal ratio)

What you are describing sounds like there is still air in the system somewhere; when you first press the pedal the air compresses which is why the pedal is soft and on subsequent presses because the air is already compressed you get the proper hard pedal feel as the wheel cylinders move.  Do you have a pic of the changes you made around the master cylinder (or elsewhere like abs?) and how are you doing the bleeding?

[Jjtxaz24]

Duncan,

Here are a few pictures of the current changes and set up. I never had an ABS module on it when I got it. 

Let me know if this helps. 

Break down (hope it's not too confusing)

They are color coded to the description. 

Edited September 29, 2021 by Jjtxaz24

[Duncan]

I think that does help; there is a high point in the "to 4 way" line which is above the master cylinder fluid level; it is possible you have air trapped there no matter how well you bleed it.  Can you re-bend/re-route so that no brake line is higher than the master cylinder fluid level?

Also, how are you bleeding; manual with a person pumping a pedal and another opening a bleeder into a (hopefully clear) hose, or vacuum bleeding at each nipple, or pressure bleeding from the master cylinder.  At least having no ABS removes that issue as you can get air trapped there too because valves cycle when the ABS actuates.

[Jjtxaz24]

Dam that is a good catch. I wasn't sure if that mattered or not but I feel that you are right. I can see if I can rework it. The guy at the shop built the lines and that's how he set em up i just gave him a diagram of how everything should be routed.

He said he would bleed the brakes manual. So I'm assuming 2 people. One pumps the brakes and holds pedal down, the other cracks the line, fluid pushes out then bleeder is closed. Rinse and repeat.  

[Duncan]

Yep, so the reason I asked that is vacuum and pressure bleed can be more reliable, manual bleed you can make errors (eg allowing pedal to retract before bleeder is closed, or not using hose to ensure only fluid gets pulled back in, or simply not flushing enough fluid through to clear out all bubbles because it is such a painful process......)

[Jjtxaz24]

On 9/29/2021 at 7:51 PM, Duncan said:

Yep, so the reason I asked that is vacuum and pressure bleed can be more reliable, manual bleed you can make errors (eg allowing pedal to retract before bleeder is closed, or not using hose to ensure only fluid gets pulled back in, or simply not flushing enough fluid through to clear out all bubbles because it is such a painful process......)

Maybe I can try and vacuum/pressure bleed them before I redo the line to make sure there is no. I ordered a brake line kit to rework that main line so it is lower than the master cylinder fluid but it wont be here till next week. I wasn't able to source one locally.  

The front Brembo's have speed bleeders on them so theoretically it should allow air out and not let anything back in. I will rebleed the system and when the kit shows up I will redo that line. **fingers crossed** hopefully it works. 

[Jjtxaz24]

Good news is I was able to bleed the system, used a vacuum bleeder and took about 10-12 minutes on both rear calipers,  There was lots of air. Fronts were good to go. I had speed bleeders on the brembos so took like 3 pumps and they were good. 

Current new issue is my stock and aftermarket boost gauges aren't reading anything. They stay at 0 at all times. 

[joshuaho96]

On 10/2/2021 at 3:19 PM, Jjtxaz24 said:

Good news is I was able to bleed the system, used a vacuum bleeder and took about 10-12 minutes on both rear calipers,  There was lots of air. Fronts were good to go. I had speed bleeders on the brembos so took like 3 pumps and they were good. 

Current new issue is my stock and aftermarket boost gauges aren't reading anything. They stay at 0 at all times. 

Are they pinned at the minimum level or are you saying they read atmospheric? If it's the first then I would trace the power and ground. If it's the latter make sure the vacuum line is hooked up properly.

[Jjtxaz24]

On 10/2/2021 at 6:59 PM, joshuaho96 said:

Are they pinned at the minimum level or are you saying they read atmospheric? If it's the first then I would trace the power and ground. If it's the latter make sure the vacuum line is hooked up properly.

Gauges just read 0/neutral spot where they land if the car is off. They don't move at all. I found a torn vacuum line leading to my aftermarket greddy analog gauge. And just replaced it ziptied and made sure all lines were tight and good to go. Still nothing. 

[Jjtxaz24]

This one stays at 0

this one goes to zero when I start it. 

Here's the stock boost sensor and an aftermarket one. The aftermarket one isn't hooked up so I'm not worried about that. The blue line goes to the balance tube where the boost signal is grabbed from. 

Edited October 2, 2021 by Jjtxaz24

[Duncan]

Where does the black line from the bottom of the 2nd t piece go?

[Jjtxaz24]

On 10/2/2021 at 7:55 PM, Duncan said:

Where does the black line from the bottom of the 2nd t piece go?

That runs into the back of my greddy gauge on my A pillar. 

Edited October 2, 2021 by Jjtxaz24

[GTSBoy]

Diagnostics 1 0 1.

Unplug all those lines.

Run one line from the plenum source to ONE of the sensors.

See what happens.

Rinse, repeat.

[Jjtxaz24]

 

On 10/2/2021 at 9:54 PM, GTSBoy said:

Diagnostics 1 0 1.

Unplug all those lines.

Run one line from the plenum source to ONE of the sensors.

See what happens.

Rinse, repeat.

Check. Will do tomorrow. It's pretty late here and I called it a night. 

[Jjtxaz24]

I removed all the vacuum lines (to the stock and aftermarket boost gauge) and left the one from the back of the balance tube (blue line) and plugged that in directly to the stock sensor. Nothing. Stock gauge stayed in the middle. I unplugged the pig tail from the stock sensor and in doing so it let the stock gauge turn off as if the car was off and the needle dropped. So there is a signal going to it.

It has been sitting for a little while, and before it went down I was able to get a signal/read out on both gauges. Issue was I forgot to plug in the vacuum line in back of the balance tube and couldn't figure out why i was hitting a wall (oversight on my end.)

 

[Duncan]

Not plugging it in ......there's your problem!

[Jjtxaz24]

On 10/4/2021 at 4:31 PM, Duncan said:

Not plugging it in ......there's your problem!

The vacuum hoses is plugged in. Car runs great now. Only issue I have is the no boost gauge. 

Not sure which one you're referring to when you said not plugged in. 

I followed GTSboys advice and unplugged all the vacuum lines that I showed in the picture and only left the blue one (from the balance tube) to the stock boost gauge sensor. Didn't get any feedback on the gauges when I was in boost on a drive. 

[Jjtxaz24]

Any other advice? Still haven't figured this out. 

[Jjtxaz24]

Ok so I will be the first to admit that I made an ass of myself for assuming someone else knew what they were doing. 

Issue is fixed. Guy never plugged the vacuum line to the balance tube nipple. It was in the general area (on the throttle body rod assembly, in his defense it does look like a nipple lol) unplugged everything in frustration and realized it was never plugged in. 

Issue is resolved. GTR is good to go. Thanks for your help guys. Sincerely mean that.