Anybody using a GT3 master cylinder - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Quadcammer · 12-05-2017, 10:22 AM

Anybody running one of these?

Would like to firm up the brake pedal a bit (for reference, brakes are bled and they don't sink as the session goes on, the pedal has just a bit too much travel to make heel/toe seamless.

part number is 99735591030 , made by TRW

Any reviews would be great, as well as any install tips.

thanks!

Topless · 12-05-2017, 12:38 PM

Nope, but a bunch of 987 drivers did at some point for the reasons you suggest. A lot of them reported: "awesome!", "totally transformed my brake pedal" "solid as a rock now".

My impression after driving hot laps in several of their cars vs mine with stock master cyl? It did not do what they wanted it to do. I noticed no significant difference between the two. I chalked-up the comments to confirmation bias. YMMV

rastta · 12-05-2017, 01:52 PM

Quote:

Originally Posted by Topless

Nope, but a bunch of 987 drivers did at some point for the reasons you suggest. A lot of them reported: "awesome!", "totally transformed my brake pedal" "solid as a rock now".

My impression after driving hot laps in several of their cars vs mine with stock master cyl? It did not do what they wanted it to do. I noticed no significant difference between the two. I chalked-up the comments to confirmation bias. YMMV

Since I have a 987 Cayman S as well as the Boxster - I had been following the forums and I never quite understood the whole GT3 Master Cylinder thing. My Cayman's pedal is very firm. Same with my 986 Boxster S. Pedal location on both is fine for heel/toe as well.

Lemming · 12-06-2017, 05:44 AM

I think this is more about personal preference. My spb brakes feel over boosted, making it very easy to over brake. My last race car had a dual-master cylinder setup with no boost, which, when set up properly, made it very easy to modulate the brake, but you had to push HARD. I believe the GT3 master and vacuum setup do the same (you must increase foot pressure to get the same brake pressure) for the spb, but I'm finding it hard to justify the cost when I have other items still on my list.

Larger MC = equals shorter throw, but more foot pressure to build brake pressure.

Quadcammer · 12-06-2017, 08:04 AM

Tim, the part can be had for $180, so really not too bad.

Its made by TRW, part number is the same (99735591030), and arizonaautohouse (use abrreviation for arizona and german word for house) has it for $181.

I think i'll give it a shot.

Lemming · 12-06-2017, 12:02 PM

Quote:

Originally Posted by Quadcammer

Tim, the part can be had for $180, so really not too bad.

Its made by TRW, part number is the same (99735591030), and arizonaautohouse (use abrreviation for arizona and german word for house) has it for $181.

I think i'll give it a shot.

Priorities, right now I need a two post lift and tire mounting and balance machines first.

Quadcammer · 12-06-2017, 12:31 PM

haha, I know how that is and I want a tire mounter/balancer in the worst way, but no place to put them.

Quadcammer · 12-19-2017, 07:50 AM

ok, pulled the trigger on this. will report back my findings.

jimk04 · 01-21-2018, 12:35 AM

I fitted one to my 986... although I also had larger calipers so it needed the extra push. Made a great difference.

We also did it on my brother's Cayman R. That had a really long pedal as stock but the GT3 cylinder made it how it should have been IMHO.

TRW PMN 166 if you are doing a search.

Quadcammer · 03-01-2018, 01:01 PM

GT3 MC is in. Pedal feel is superb. Travel is reduced.

Excellent mod in my book.

steved0x · 03-01-2018, 01:41 PM

Quote:

Originally Posted by Quadcammer

GT3 MC is in. Pedal feel is superb. Travel is reduced.

Excellent mod in my book.

DIY thread!! How easy was it, any tricky gotchas?

The Radium King · 03-01-2018, 01:51 PM

does it mess w your heel/toe?

Quadcammer · 03-01-2018, 04:56 PM

Quote:

Originally Posted by steved0x

DIY thread!! How easy was it, any tricky gotchas?

Not even necessary. Its dead simple. suck or drain the fluid from the MC, remove the two hard lines and the push in clutch line. pull off reservoir (friction fit), and then two bolts. reverse to install, then bleed. piece of cake

Quote:

Originally Posted by The Radium King

does it mess w your heel/toe?

Its much better actually as I felt the pedal travel was too long for me to heel and toe well (i use the ball of my foot on the brake and side of my foot on the gas), which makes it harder with a pedal height mismatch. less useful if you actually use your heel and toe.

bkovac · 04-06-2018, 04:44 AM

i have the GT3 master cylinder upgrade on my spec boxster, definite plus. Firm hard pedal, I found myself needing to bleed brakes often trying to firm up brake pedal. Very confident braking.

Quadcammer · 04-06-2018, 05:20 AM

after the track at lime rock dried up on thursday, I really got to get a feel for this mod and really believe it was helpful in my situation. While the pedal requires a firm push to really get on the brakes hard, the reduction in travel means the pedals are more evenly aligned for me to heel/toe, which is hard for me with a height mismatch since I use the ball of my foot and the side.

Pretty happy overall.

steved0x · 04-06-2018, 10:52 AM

Quote:

Originally Posted by Quadcammer

after the track at lime rock dried up on thursday, I really got to get a feel for this mod and really believe it was helpful in my situation. While the pedal requires a firm push to really get on the brakes hard, the reduction in travel means the pedals are more evenly aligned for me to heel/toe, which is hard for me with a height mismatch since I use the ball of my foot and the side.

Pretty happy overall.

Any videos!!!!

Quadcammer · 04-06-2018, 11:01 AM

unfortunately I haven't gotten to the video stage....add go pros to the list

FirePowered · 04-16-2018, 01:47 PM

I testing and fully switched to this the minute it was announced. The shorter braking travel helped my speed to apex as I can apply it the millisecond I wanted to and create the shortest distance possible to brake. It's also more consistent throughout the lifespan of the race. I don't want my pedal travel to modulate throughout a race and feel this upgrade helped considerably.

--
#750 SPB / Drake

longhorn986 · 06-22-2018, 11:44 AM

Just to confirm, the part number 99735591030 (which is the 997 GT3 master cylinder, not the older 996 version) fits on the 986 Boxster without any modifications required? I saw a reference to this unit in another forum that implied the poster may have had to use a thread adapter?

harnishclan · 06-23-2018, 05:06 AM

So where in the rule book does it say that using a GT3 master cylinder is a legal SPB modification?

5. Brake System
A. Brake pads are free.
B. Steel braided brake lines are allowed.
C. Emergency brake, lever, cables and associated parts may be removed.
D. Brake cooling systems are allowed if they use only air. Air may be vented through the front air dam. Dust shield may be removed.
E. One piece stock size steel rotors are required. Rotors may be cross‐drilled or slotted.

SPB Class Rules and SPB Eligible Models
All parts must be factory stock from one of the eligible years, except where modifications are specifically allowed below. Modifications not specifically listed are prohibited.