Failing master cylinder? Possible excuse to upgrade!

AhMuhFace · Oct 19, 2018

Hey fam, I just noticed today that my weak brakes have become even more underwhelming. Furthermore, when stopped at a red light or in heavy traffic, the pedal is no longer firm and hisses while dropping well below the usual firm point.
First, does it seem like the master cylinder is my issue?
And second, will a PP gti master cylinder be a good choice to swap in if my stock master is on its way out?
Might be worth noting... I loved the firmer pedal in my mk2 Jetta after swapping the stock 19mm master for a 21 or 22 mm master from a Passat g60.
Last, would a PP gti master cylinder work with a NQSBBK if I choose to go that route?
Car is a Stage1 golf 1.8 with southbend stage 2 endurance clutch, 119000kms.

Elwood · Oct 19, 2018

Well, the hissing doesn't sound good, but if the pedal continues to move, it probably is the master cylinder.

Leave the master cylinder alone (for upgrade) and put the GTI rotor and caliper carrier on the car (non-PP). The GTI has the same calipers and pads. It's a comparatively cheap upgrade and it makes a huge difference. You need 16" wheels to clear the brakes.

DAS_STIG · Oct 19, 2018

Nqsbbk should work with stock golf master cylinder since it works well with non-pp brake system and the 312mm brakes work well on golf setup.

AhMuhFace · Oct 19, 2018

I called the dealer with my vin# while inquiring about the calipers.
Turns out I have the smaller piston calipers equipped, so I’d need calipers from the non pp gti, which is why I was thinking of slowly acquiring parts for the NQSBBK. Was thinking of starting out with a master cylinder that could support the NQS, but using it with stock calipers for now.

AhMuhFace · Oct 19, 2018

Sorry Dybz, didn’t see your post.
I have a feeling I might have a smaller master cylinder since I have the smaller calipers equipped. My pedal has always felt soft compared to my two friends 2015 1.8 golfs.
I have the trendline model, one friend has the exact same spec with a different build date, and the other has the comfort line 5 door.

Wrath And Tears · Oct 19, 2018

AhMuhFace said:
Hey fam, I just noticed today that my weak brakes have become even more underwhelming. Furthermore, when stopped at a red light or in heavy traffic, the pedal is no longer firm and hisses while dropping well below the usual firm point.
First, does it seem like the master cylinder is my issue?
And second, will a PP gti master cylinder be a good choice to swap in if my stock master is on its way out?
Might be worth noting... I loved the firmer pedal in my mk2 Jetta after swapping the stock 19mm master for a 21 or 22 mm master from a Passat g60.
Last, would a PP gti master cylinder work with a NQSBBK if I choose to go that route?
Car is a Stage1 golf 1.8 with southbend stage 2 endurance clutch, 119000kms.

The brake booster can hiss when there is an issue with it. The hissing is the loss of vacuum. The low soft pedal could be caused by air in the system, or the master cylinder failing.

Bäsemödel · Oct 19, 2018

I too was looking at the NQSBBK for my 1.8. I’ve come to understand that, since I’m not tracking the car, there is no reason besides vanity to go with that setup. I’ll be doing 312mm blank faced rotors, a good ceramic pad, high temp fluid and (maybe) ss lines. Going to 312mm requires the GTI non PP calipers so I’ll do that as well.

Best of luck!

DAS_STIG · Oct 20, 2018

The NQSBBK is supposed to provide a very nice pedal feel and better brake modulation than the single piston setups. If that is needed on the street is up to you.

AhMuhFace · Oct 20, 2018

I appreciate the input. I’ve had some near misses with this setup and it doesn’t inspire confidence. It sounds like it’s really worth it for the pedal feel, modulation and other benefits with the only downside seeming to be cost.
Eventually this will be more of a track car. I have this to look forward to!http://rockymotorsports.com

The Fed · Oct 20, 2018

I've never had a master cylinder partially fail. Unless something's different now, it either works or it doesn't. Did you bleed the brakes? You're supposed to change the fluid at the 3-year mark which would necessitate bleeding the brakes. A brake booster rarely fails. If it wasn't holding vacuum you would know it. Shut off the engine and see if you have a couple of pumps left.

Tooly · Oct 20, 2018

I had a hissing issue on my old mk5 when I was pressing the brake pedal, say while waiting at a red light. Had the brake booster replaced and the issue went away.

The Fed · Oct 20, 2018

Tooly said:
I had a hissing issue on my old mk5 when I was pressing the brake pedal, say while waiting at a red light. Had the brake booster replaced and the issue went away.

I guess I'm just lucky. I never had a brake booster fail and only one or two masters. I stopped hard to avoid an animal about a mile from home. The next morning most of the fluid was gone from the front brakes reservoir. Had a new one installed and a front caliper blew. Now i needed two new calipers. Should have traded the car the day before.

bdelaney4000 · Oct 20, 2018

I had a similar issue on my mk5 Rabbit with the hissing I talked to the VW shop manager and he basically said exactly what other are saying its the brake booster. To get it to stop hissing he recommended going to and open road and doing a couple hard stops. Sure enough the hissing went away it would come back about 6 months later but I'd do a couple hard stops again and it was gone. Kind of a weird issue, but that was my experience with the MK5. Should be pointed out my brakes still functioned fine other than the occasional hissing.

WhyNotZoidberg? · Oct 20, 2018

AhMuhFace said:
I appreciate the input. I’ve had some near misses with this setup and it doesn’t inspire confidence.

When you push the pedal once and it is softer and/or travels further than before, here's the Master Cylinder test: pump the pedal more than once, if it gets stiffer after a few pumps and stops higher, then the master cyl is going (the seals are worn, you can rebuild it w/ new seals or replace it)

The hissing sound seems more like a booster problem/vacuum leak.

AhMuhFace · Oct 21, 2018

I performed a couple of tests as suggested. It seems like the booster is doing it’s job but doing WhyNotZoidberg?s master cylinder test, my pedal stiffens and stops higher than before, while lightly hissing/huffing out air.
Brake fluid was changed out at the 2 year mark while removing clutch delay valve.
About 10 months ago I had a local shop change out my clutch, haven’t had issues or any odd noises until now.
Owned the car for almost 4 years.
I couldn’t hear any obvious vacuum leaks but these engines are pretty noisy...
I guess I’ll try a new MC first.

Failing master cylinder? Possible excuse to upgrade!

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