r33 gtst brake upgrade on r33 gts HELP

[timothy]

After doing a 5 stud conversion + brake upgrade (r33 gtst brakes) onto my r33 gts I cant get my brake pedal to feel firm. 

The car used to have ABS but everything has been removed including the sensors on the calipers. I have compared my brake setup to another non abs r33 and its exactly the same so theres no reason it shouldn't work. 

Ive already had a mechanic look at it, tried to bleed it, but still no improvement on the brakes. Besides that I have also tried to bleed the brakes and master cylinder using the brake pedal and a hand pump vacuum bleeder. With the car not running, the first 20% of the brake pedal has play, and the last 80% of the brake pedal feeling solid as.

With the car running, is literally the opposite, 80% of the brake pedal is useless and the last 20% is when the brakes stop the car although i haven't tested it at speed higher than 30km/h. 
Theres no leaks, every connection is tight, fresh brake fluid etc. The brake booster is also from a turbo r33 to match the turbo gtst brakes. 

Could the master cylinder be broken? is there a way to test if it is? the brake booster and master cylinder both worked before installing them. 

I read on a forum from someone who did the same brake upgrade, same car, and had to upgrade to brake booster and master cylinder cause the brake pedal always felt soft/spongy. But there was no information on the upgrades he made? 
Any help would be appreciated! 

[ossy]

Tbh I was told this is a normal and that stock brakes are crappy??? As you said, there's no feel at the start and all of a sudden everything happens in last bit. Mines a non turbo with 5 stud conversion also.

 

A few people recommended getting a brake stopper which I'm considering trying and plus they're quite cheap. It fits in the engine bay and say it stops the flex in the firewall when braking. Makes the brakes feel stronger (more bite) and has better feel in pedal.

Edited October 6, 2018 by ossy

[timothy]

My last 33 brakes felt a lot more firmer tho but that was with stock non turbo brakes, I just can’t understand that upgrading to gtst brakes would leave my pedal feeling so soft? Surely it can’t be normal? Having brakes that don’t work until the last 20% just doesn’t feel safe or reliable aha. 

And yea the master cylinder brace I seen that the other day they’re only like $50. But like you said it will only help with stopping the fire wall from Flexing. It won’t improve the 80% of the pedal that doesn’t do anything :(

[GTSBoy]

Have you considered the bore size of the GTS's master versus the GTST's master?  With respect to the  caliper piston area difference, that is?

[timothy]

The gtst master looks pretty identical to the gts master. But I couldn’t use it because it only uses two brakes lines, and I need three.

No experience with brakes so I’m not too sure what you mean, although I read something saying that since the gtst brakes are bigger it requires more brake fluid to work resulting in a softer pedal. If that’s what you mean by the calipers piston area difference? I thought brakes just relied on pressure which means having bigger brakes really shouldnt affect it But I’m not really sure so yeah..

[KiwiRS4T]

Bore size is like gearing. Small bore means more pedal travel with less resistance. A bigger bore will mean less travel but harder pedal. The biggest stocker is the GTR BM57 but something close to that will help. Also steel braided brake lines will help.

[GTSBoy]

Here's the lesson for the day.  If you don't know what you are doing (with brakes), don't f**k with brakes until you do know what you are doing.  It's only the most important safety function on the car, ferchrissake!

[timothy]

Here’s a another lesson for the day, you won’t learn anything if you don’t try  I ain’t gonna apologise for giving something a go. Like I said, I even got a mechanic (someone who knows what they’re doing) to try and sort it out. So chill bro 

[GTSBoy]

Hahha.