Soft brake pedal

[jakriz]

G'day guys

I've just installed Nissan R32 4 pot calipers to the front of my Superbug (1302).
I have Ford Falcon single pot calipers on the rear & had late type 3 calipers on the front before swapping them for the Nissan setup.

I have driven it a few times now since finishing them yesterday, I have bled them 3 times now, not getting anymore air out of them, they stop perfectly, even from 110kph (62mph) , But, I have a very soft pedal. I'm used to having a high hard pedal, so this feels very weird.
I am using the standard master cylinder which is only a few years old.

Should I just give them more time? or is there something u may think that I'm missing. Should I keep trying to get air out of them?

regards
Jak

[evilC]

Are you running the same discs (rotors)? If so then the cross section shape of the disc will have been determined by the VW twin pots causing too much stand off on the new front pads in the new calipers. The only way to over come that is to increase the stroke on the m/c - hence the soft pedal feel.
For a better understanding of what you've got can you describe more fully the brake spec - disc size, caliper type and piston size, both for front and rear.

[ricola]

I'm assuming monoblocs with them being 4 pot so they should require only small amounts of travel. Have you given the pads time to bed in fully? Have you tried braided hoses? What are the pedal forces like for comparable amounts of braking? The other thing to try is possibly vacuum bleeding the system rather than pressure bleed, are skylines traditionally tricky to bleed? Are the bleed nipples at the top of your calipers? Might get a better bleed by taking the calipers off the spindles...

I'm sure you have probably thought about most of these, just trying to eliminate possible causes...

Rich

[jakriz]

Thanks for the reply guys, & thanks Rich, I lost your email.

I already have braided lines all round. The new front rotors are 280x28mm ventilated & slottted. The rear single piston is 40mm I think (quick google search) they have been on the car since 1999. The front Nisssan calipers are 4 pots, & according to the internet they have 4 x 40mm pistons? Does that sound too big? Yes the bleed nipples are on top Rich, & I had thought that maybe the traditional way that we bleed our brakes at home may not suffice & they have to be pressure bled.
regards
Jak

[ricola]

Off the top of my head I can't remember what my 996 piston sizes are but I think they are about as big as I would want to go with a stock master cylinder, 4x40 does sound pretty big. I think it's time to go up a size master cylinder for you... Do you have VW Golfs over there as they are 20.64mm so a nice middle ground without increasing pedal forces too much?

[jakriz]

is the golf mc a bolt on? what mods are needed. Also, is a kombi mc an option, are they 23mm?

regards
Jak

[Steve C]

Hi Jak

I forgot to mention the other day, I have a vacuum bleeder if you want to borrow it.

Steve

[jakriz]

Thanks Stevie, unfortunantly we don't live next door to each other (good thing for u, I'd be over all the time) I just posted on AVD as I just picked up a kombi m/c, it's 24mm
regards
Jak

[ricola]

The golf is a bolt on, you may have to use the golf reservoir too as the reservoir ports are a different size and also shorten the pushrod a bit from memory. I'd be very wary about going as big as a 24mm, pedal forces will go up a LOT, remember it's fluid pressure that gives you braking and the area increase going from 19 to 24 is 60% so you will need that much more pedal force for the same braking. It is also harder to modulate the brakes when you have much reduced travel. I'd go for the smallest you can get away with..

[evilC]

Hi jakriz,

Those front calipers are way too big for the rears. You will need to up the size on the rear quite considerably to balance it out. The fronts are 4x larger than the rears but for a bug they ought to be about the same. What discs have you got on the rear - Porsche 944? If that is the case then I would swap in a set of 928S4 calipers that will balance out much better.
At the moment I think you are running out of stroke on the rear circuit before the fronts have come into play properly giving that spongey pedal feel. Even with the 944 stepped m/c (24/19) that only provides a 160% upgrade to the front if you use the 24mm bore whereas you actually need a 400% upgrade that is equivalent to 38/19 m/c - they don't make those!
An alternative solution would be to use a balance bar set up with say a 25mm (1") front m/c and a 16mm (5/8") rear m/c that would give 240% variation and then accept 2/3x1/3 pivot arrangement.
At the moment you are/will not be getting the fronts working hard enough and there is a great danger that the pads will glaze regularly.
One last thought. Which way round did you plumb the front brakes - front m/c piston to the rear?

[Steve C]

Hi Jak

So how are your brakes now?

Steve

[jakriz]

The brakes are amazing, I didn't get time to swap the master cylinder for the nationals supersprint, but I needn't have worried. They are incredible! I've never had such good brakes on the track, no fade, no lockups. Will be even better when I change the MC. Was well worth all the trouble
Jak

[Flintstones]

So what MC will you be changing to then Jak?