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Discussion Starter · #1 ·
Hey all, I didn't want my first post to be a question but I cant seem to find enough info on my issue to make an executive decision.

I am driving an 02 SER Auto without ABS. Recently I discovered a vacuum leak on my brake booster inside the car at the wall when the pedal was pressed. Even with the small vacuum leak the brakes, albeit a little soft, engaged right at the top.

I have what feels like excessive play in my brake pedal after replacing my brake booster. With the vehicle off and brake pedal pressure pumped up as much as it will pressurize I can press the pedal roughly half way down before encountering any significant resistance. Even when the pedal seems to encounter resistance there seems to be a little too much give, there is almost a "step" in the pedal travel. My initial thoughts were the clearance for the push rod on the booster is too short so the first half of pedal travel isnt even contacting the master cylinder until half way down.( with the old booster first sign of pedal resistance felt higher on the stroke but there was still a little give as there is now) With the vehicle on the first half of pedal stroke has NO brake effect until roughtly the half way point, after that the brakes will grab and stop the car. A small detail I did noticed during road testing is that when I got on the brakes hard enough to lock the front wheels one locked before the other or only one locked at all. Even before I replaced the booster I know this was happening due to a scenario where I was full on panic braking a month ago, on inspection of the skid marks I left only one from the front right.

While I did not bench bleed the master cylinder during the re-install I did make sure to bleed all 4 corners according to the FSM, I even went as far as to cycle enough fluid through the system to get out all the old and only have new DOT4. Even after I was sure all the old fluid was cycled out I made another pass to ensure I got whatever air could be hiding in the system. Over 1.5 big bottles were consumed during the bleeding, not to mention all the old fluid removed. Me not being an expert I feel this is enough but if the more educated could please weigh in. During the removal and bleed no leaks were present at the master cylinder and no leaks or damage were observed at the brake lines or calipers.

A little background on some of the components and work done in the past. The currently installed master cylinder and front calipers were installed 05/17 and have about 100K miles on them, I am also running 2J's stainless brake lines with the same mileage, brakes were bled and the system was swapped to DOT 4 at that time as well. The rear calipers were replaced about 7/15. Within the past 10K miles I have replaced the front wheel bearings and spindles, Pads with hawk street performance, rotors with 2J's slotted and drilled, brakes were also bled during the pad and rotor replacement. The booster I just installed doesn't have more than 10 miles as of posting this.

My general feeling and assumption knowing what I know is that one of the master cylinder pistons is leaking internally. With the way non abs systems put one front and rear on each half of the master and the fact that one of the front wheels is locking before the other, this makes sense to me. But again I am no expert and have limited experience troubleshooting hydraulic systems.

Am I on the right track thinking I have a bad master cylinder piston seal? Did I miss something critical or did I leave out a crucial step in the reassembly? Im open to any suggestions as this is my daily driver and I really want to get her back in spec.

Thank You.
 

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Not entirely related, but my '03 SER had its ABS system fail and the mechanic simply reverted it to a non-ABS braking system. TBH, the damn thing was better at braking. Now, I have to give the caveat that I started driving in 1972 and never much liked ABS better than pumping brakes "old school," and when I moved from Texas to Iowa was thrown for a loop with ABS, finding it far less effective in snow and ice -- which I thought is what it was supposed to excel in. After the car was returned to plain old braking, I had MUCH, MUCH better control in hard pumping stops in such conditions. I even had a chance to test this in a near-identical before and after situation on a snowy road. As I said, no real answer, but "I'm just sayin'."
 

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Discussion Starter · #3 ·
Update

Dug out the OE master cylinder, disassembled, visually inspected seals, cylinder walls and thoroughly cleaned everything. Bench bled, swapped the current master with OE and bled the system down again. The rear brakes were able to clear all air in the system but both front brakes seem to have a leak. No matter how much fluid I put through the system air just kept coming. However, brake feel is better, brakes engage a little higher on the stroke and overall pedal feel is more consistent. So now im considering brake lines and/or calipers even though there are absolutely zero visual leaks anywhere between where the brake line connects and the calipers themselves.

As for the master cylinder that was removed it too was disassembled and inspected. Nothing glaringly obvious. Though I did notice fine black particles in the crevices/cylinder bore and a small amount of buildup on the piston seals. Makes me think the aftermarket rubber may have started to break down earlier than expected.

I have removed the calipers plenty of times and safety wired them out of the way, I can safely say the lines have never experienced excess force or handling. Before I go throwing money at a set of calipers AND brake lines, does anyone have a suggestion as to what is the most likely culprit here?
 

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There is a special tool designed to measure the measure the travel of the piston that protrudes from the brake booster and the tip of it presses against the piston of the master cylinder.

these two have to be almost touching for this to be PERFECT then you use another tool to flush air out from master cylinder down brb for links and video…

It is a sold for Corvette only tool but applicable to all application under this premise brb…
 

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IIRC Nissan is either 7mm or 8mm on the adjuster, on the vehicle. Unlike the video YOU DO THIS WORK on the car.

ise a broom stick or have a helper press and hold the brake pedal down to extend and keep extended the shaft so you can grip it with vice grips and bolt it from rotating while you use the 7mm or 8mm around the bullet shaped tip and either screw it in or out BASED ON YOUR MEASUREMENTS WITH THE SPECIAL TOOL FIRST…

Once your clearances are set you’re solid and then flush it all out with the Motive Brother brb…
 

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Discussion Starter · #8 ·
Dude, thank you so much for the info! It did not occur to me the output rod on the booster might be way out of spec! Booster is from autozone so I should have known better than to blindly trust their adjustments.

Considering my brake pedal sits higher since the booster replacement, if adjusting the output rod forward affects pedal height, this would explain alot.

I have a reman master on hand and I'm already looking at ordering a booster rod measuring tool and vacuum bleeder. I will report back once I get the new master installed and booster rod adjusted properly.
 

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Discussion Starter · #9 ·
The tools arrived and the reman master cylinder has been installed. Final verdict : brake pedal feels like brand new. Brakes engage at the very tippy top of pedal travel and are nice and firm throughout the stroke.

Thanks to @Big Lettuce for the tool suggestions, they were exactly what I needed to sort this out!

Tools used :
Brake Booster Pushrod Adjustment Tool : Power Brake Booster Pushrod Pin Adjustment Gauge Tool | eBay
Brake Bleeder tool : Motive Products 0107 Power Brake Bleeder Fits Ford 3 Tab for sale online | eBay

In the event these links break, it would seem most booster pushrod tools will do the job. More importantly the Motive 0107 kit is the exact kit needed to fit the b15 mater cylinder. Do not order the 1107 kit unless you already have the motive pressure vessel, this part number is an adapter ONLY.

Hand Purple Fluid Finger Nail
Purple Fluid Finger Nail Material property


On top of having to adjust the booster the reman master cylinder (also autozone) did not have its proportioning valves properly torqued. Nothing more fun than taking the extra time to bench bleed and carefully thread and wiggle everything into place only to find one of the proportioning valves slowly leaking under pressure...just something to watch out for.

Some final thoughts : obviously my booster output rod was not adjusted to spec and with the discovery of my reman master cylinder valves not being torqued I strongly suspect I could have reused one of my old masters. The leaks were only present with the system under 15+ psi, something I could not test until I received the motive bleeder. I didn't realize pressure testing the brake system was so critical, had I not been able to pressurize the brake system I believe I would still have mushy brakes. I cant say enough good things about the motive 0107 kit, if you are a home gamer this will make your life so much easier when dealing with your brakes, overhaul or otherwise.
 
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