Brake Pedal Very Stiff - Brakes Still Working

[No Crust Racing]

This is a copy paste from my build thread so I'll add details up top for those who don't know the car.

CA18, 4 piston fronts, slotted/vented front rotors, slotted solid rears, QFM A1RM pads, BM50 Master, new fluid, standard lines, non ABS, all calipers recently rebuilt and system fully bled with 2 people, brake duct vents.

Only the caliper rebuild , master rod adjustment, fluid, and brake duct vents are new, everything else I already had before the caliper rebuild and worked fine.

I can't figure out why the pedal feels stiff.

I noticed on the last track day that the pedal felt quite firm (runs were only 45 or so secs so not enough time to warm brakes) The car would still stop and I could lock up the brakes if I pushed hard enough but it felt like I had to push fairly hard and that there wasn't a lot of progression in the pedal, as in only a small amount of travel (but lots of force) was required.

I've pulled the front wheels and there's plenty of meat on the pads and no obvious issues with calipers/rotors.

I've test the booster by pumping the pedal a few times and holding it then starting the car and the pedal dropped down a bit as vacuum builds so I "think" it's fine. I also adjusted the brake master rod to the pedal after rebuilding all the calipers.

I'm thinking one of two things.

1) It's stiff because they are such hard pads and need a lot of heat in them, though I don't remember it being "this" stiff when I did this brake upgrade originally.

2) During the bleed process I've pushed too hard and the master is shagged, though I'd of thought it'd leak? (It's a BM50).

Thoughts? I can just wing it at the next track day which is a proper circuit day so will be able to get the pads hot, but don't want to risk damaging something or having brake issues at speed.

[GTSBoy]

I'd put money on the booster having a hole in the diaphragm or something wrong with the vacuum supply (like a leaky 1 way valve).

[No Crust Racing]

Even after my comments about testing it?

[GTSBoy]

Yuh. Inadequate vacuum <> no vacuum.

[macaroni646]

I'd get it sorted before going to a track day man. Don't want brake failure when you're at full speed.

[No Crust Racing]

Removed 1 way valve, tested, can't fault it but I doubt my mouth can pull the same vacuum as the engine. (Even after all my years working the corner).

I've pulled the booster out (shit job) and cannot "see" anything wrong with it, but I have not disassembled it yet (need to review my Nissan manual).

What am I looking for once I pull it apart?

[No Crust Racing]

I'm also thinking seized caliper or non returning sliding rear but you'd think the car wouldn't drive evenly and wouldn't brake evenly.

[89CAL]

Its in your brake booster. If the brakes still work fine then it's a booster problem.

[GTSBoy]

And you can't disassemble a booster. That needs special tools. I got the one on my car rebuilt....actually that may have been on my ALFA, about 15 years ago. I just took it to ABS (I think, although it might have been Power Brakes in Norwood). I'm sure there's an equivalent in Melbourne....not so much up at the river though

[No Crust Racing]

Bummer, I enjoy a good DIY rebuild.

Anyone know what other boosters will fit as I also read that an undersized booster can be an issue with larger front calipers and a larger BMC.

[niZmO_Man]

I doubt my mouth can pull the same vacuum as the engine. (Even after all my years working the corner)

[No Crust Racing]

Spoke to brake guy and he said he's almost certain it will be that those pads have hardened/are too hard but gave me some more booster tests to do, connect to vac on the car and then I should be able to move the rod by hand, if not it's dead, if so it's fine.

If it tests fine I'll put it all back together and see what happens when I get the pads fully hot at Winton in a few weeks.

Annoying because removing the booster was a shit job and putting it back will be worse. Probably shouldn't have jumped the gun in removing it...

[warps]

Just rip the lot out and put in an adjustable pedal box.

"Hmm where can I get one of those?" you say

I'm glad you asked

http://www.skylinesaustralia.com/forums/topic/443943-brand-new-obp-adjustable-pedal-box-assembly/

[No Crust Racing]

Don't believe what they say about you mate, you're alright

[Bushy]

Doubt it's the pads. I have the same on my 32, they were used for a few months then sat for 2 years and still work fine (have been used at track a number of times since).

Also they don't require much heat in them to work to their full potential either, I have never noticed any difference between first and last hot lap.

On a side note, I have noticed they aren't a very 'progressive' pad, they bite reasonably hard with little pedal effort.

As others suggested I'd look elsewhere. Good luck with it, interested to know the outcome.

[No Crust Racing]

I have another set I can try but the car isn't registered and it's too wet to get it out.

I've done some more booster testing and it seems fine so what else does that leave?

If it had a seized caliper you'd think it would pull to one side or brake unevenly and it didn't.

I think his point was that I'd cooked the pads and that they're cactus.

I did get to a point a few times at the last Winton day where I'd over heated the brakes and had to back off, which is why I added the brake ducts.

I had to machine the rotors back so much that there's no slots in the fronts anymore. Just above minimum thickness.

[Bushy]

If you can post some photos of the pads someone might be able to tell you if they're cooked.

But also when you overheated the brakes it could have been that you burnt the fluid, did you bleed them in between sessions and check the colour? This doesn't explain why you've got the stiff pedal all the time but just making the point that it may still not be the pads.

However if you've got a spare set of pads you may as well try them.

[No Crust Racing]

I can try to get some pics.

Fluid is all new from when I rebuilt all calipers.

[Bushy]

It's up to you.

Those pads are rated to 780 deg. so it's likely you would burn or boil brake fluid, even if new, before you cook the pads.

[No Crust Racing]

What would you suggest then? As I said I'd expect the car to drive poorly if a caliper was seized so that leaves me with the master being stuffed, and though it's not leaking internally that's not to say the diaphragm isn't stuffed from being pumped during bleeding.

I'd really love to avoid having to bleed the bloody thing again.