Geneqco

This is how we had to do mine... only we used a bit more pressure in the pressure bleeder.

I have mentioned this before Patrick but is the "Power Bleeder" you mention a "pressure" or "suction" bleeder. Most workshops here use the suction type as the pressure bleeders are not so readily available here.

JET951

hi Scott, its a pressure bleeder.

333pg333

The Suction bleeder is permanently attached to my wallet!!!

333pg333

Stock m/c for reference. See the measurements on the m/c itself 23 & 20.
More precisely they're 23.81mm front and 20.64mm rears.

Geneqco

G'day Sean,

Difficult one to sort out...

Do you have any ideas re ABS wrt what Andy said? He said he's seen a number of Nissans with ABS end up with "no brakes" on the track due to ABS - I think he said it's something to do with the pump not refilling quickly enough (I could have misunderstood him on that part though), not something I've personally experienced in the BMWs or Audis.

I'll be seeing him week after next so I'll try to get more information. Meanwhile I thought I'd see if you had any ideas.

JET951

im not to sure why ABS can play up. i know autohaus hamilton/ or maybe Chris stannards mechanic had a 968 CS that had the abs fail at wakefield. 20 or so laps into a race, came into turn 2 at 130km/h. the pedal was as hard as a rock and nothing was happening. the car ended up rolling 3+ times after in hit the sandtrap sideways. the locked pedal made me think, possible its the abs pump locking up? there is fluid being supplied, its just not getting through.

Geneqco

OUCH! Sounds really nasty. Just confirms to me that it's not worth risking using ABS for the track. I'll see what more I can find out - thanks for the input.

pete95zhn

That's basic physics...or actually it goes something like this: pressure = force / area ( N/m2 = N / m2 ). From this formula you can see how changing of area changes the force when the pressure stays the same ( as it is with non-compressibles, ie fluids ) or contrary. So when you have two connected cylinders, you apply 0,1N force to 0,1m2 cylinder it provides 2N of force to 2m2 cylinder when the pressure is 1N/m2.


EDIT: BTW, the condition of brake pads and discs affect on pedal travel. There's more than 10mm of piston movement between new discs and pads vs. totally worn out. And that's a lot of brake fluid!

333pg333

So my desire of a shorter, firmer pedal will be solved with a bigger MC?
This is what I've based my search on and that's my bottom line.

Papamurphdog

Another idea for you; check the play in your wheel bearings! My '86 was giving me a soft pedal on the track off the straights at the Glen (un-nerving to say the least) after hard conering in the twisty bits...so, no one could figure it out, good bleed, fluid pads etc., then a buddy suggested we pull a wheel and check the hub, sure enough it was a bit too loose allowing the rotor to tilt side-to-side under load. Idea was it was pushing the pistons away from the rotor, so on first hitting the pedal it is soft till you give it a pump (really screwing up my heel/toe). Slightly tightened the hub (not too tight mind you) and the problem dissapeared. now the bearings looked fine but I replaced them anyway and now I always check the hub with a quick tug on the tire (wheel on) to see if it moving side to side, jsut to be sure, before I hit the track. might help you.

Fishey

If your pedal is soft its likely a bad MC so just test it. I have never seen a soft pedal from a properly operating stock brake setup.

Go buy a short brake line with the right ends on it and pull off your current lines form the MC. Loop the short line and just keep pumping and if it doesn't get hard as a rock then your MC is bad.

Geneqco

If your issue is cause by a problem somewhere in the system, the bigger MC might not help you.

JET951

this is a brand new mastercylinder. the old one had the same problem. Patrick also has new calipers on the front. unless there is something wrong with the original ABS pump.

333pg333

Yes just about everything has been replaced by new components that are correctly installed. Can we check the ABS pump Sean?

APKhaos

So, the pedal in my 89 has always felt softer than other turbos I've driven while instructing. In fact, I;ve come away from a couple of nice earlier turbos with pedal envy.

What's the definitive word on bleeding the ABS pump itself?
- Is it required?
- If so, what is the correct procedure?

I've alway suspected that there could be a stagnant pool of old and bubbly fluid sitting in the ABS pump bladder and causing the slightly soft pedal. Am I dreaming?