Anyone running 4 wheel discs + 79 master cylinder have a FIRM pedal?

[jt1]

I took 1.38 superlites off to put on the 1.75 superlites. I now have more braking force but a longer and less firm pedal. I don't think going to 1.38s will help with braking force, that's going to give less clamping force at the rotor/caliper interface, and generate less brake torque.

 

John

[TimZ]

I took 1.38 superlites off to put on the 1.75 superlites. I now have more braking force but a longer and less firm pedal. I don't think going to 1.38s will help with braking force' date=' that's going to give less clamping force at the rotor/caliper interface, and generate less brake torque.

 

John[/quote']

 

If you can easily lock the wheels, how much more do you need?

[A. G. Olphart]

Yes' date=' I am running disc brakes on all 4 corners and have a firm pedal. 15/16 master cylinder, 8 inch power booster (stock 1978Z), wilwood NDL 1.75 calipers front and 240sx single piston calipers rear, wilwood proprotiong valve in rear line to balance system.

 

My issue is brake performance, my Integra and Taraus out brake the Z. I swapped out the wilwood Q compound street pads for hawk hp pads and finally had a much harder bite I was looking for, but the squeal was so bad I replaced them with hawk hps pads to get rid of the squeal , now the car stops only slightly better that with the wilwood Q compound pads. In short if I tried to slam on the brakes and lock the wheels it will not happen. This is what I am needing to fix before I need to make a hard stop in a short distance that ends badly.

 

I contacted hawk and was told there was no quiet pad for the street. I contacted wilwood tech and was told that with an 8 in power booster and 15/16 master cylinder I should be using 1.38 piston calipers. I am not generating enough clamping force with the 1.75 pistons. To use the 1.75's I would need a 1 1/4 master cylinder with a 8 in power booster or 1 1/16 master with non assisted brakes.

 

I plan on ordering the NDL 1.38 piston calipers and will report back after I make the change.

 

Rusty[/quote']

 

 

JT1 is correct on the clamping force... hydraulic pressure is measured in pounds per square inch, so if one drops the size of the pistons (1.75 to 1.38) , the clamping pressure drops. As an example-

 

1.75 pistons = 2.4 square inches; assuming 500 psi, that's 1200 pounds of clamping force

 

1.375 pistons = 1.48 square inches; at 500 psi that's only 740 pounds of clamping force.

 

500 psi is just a convenient number for the example.

 

The issue with master cylinder size (besides the ratio of the area of the master to the area of the wheel cylinders, which determines force multiplication-- think gear ratios) is the volume of fluid available in the amount of pedal travel available. That may have been the tech's concern (giving him the benefit of a doubt). There is no worry there though, unless your current setup runs out of pedal travel... at which time I'd consider a larger master for more volume. Might be cheaper than 2 new calipers. Are street pads available for the smaller calipers?

 

You need new street pads that bite well when cold, or live with the noisy Hawks..

 

 

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[GAZRNR]

Thanks for the input. Has anyone found a bigger master cylinder that will work with the datsun brake booster? May an 1 1/16 bore?

[JMortensen]

Datsun truck uses 1" I think. I believe Dan Baldwin is runing one. Might search or PM him for more info.

[J__]

OK!! i think i got the cure for all you guys with the spongy brake, no brake pedal feel symptom! well this seems to be the problem for ppl with rear disk conversion... but those rear calipers BLEED nipple is not 100% at 12 o'clock position... so no matter how much u bleed it like mad, theres still air inside. after spending 2 weeks and 24/7 pulling my hair out and 2 mechanics later after i couldnt figure it out, finally figured out to loosen the bottom bolt and tilt up the rear caliper so the bleed nipple is at 12 o clock... then a couple of pedal presses and burps of air later, voila.. we have brakes. well at least this was my case. try it, if it works, then we'll finally knw wtf was causing all this headache, time and $$$$$ gluck

[Phantom]

I have the forged Willwood Superlites on the front on 12.2" vented rotors along with the 240SX/300ZX disk brake converion on the rear and the the 15/16" 280ZX master cylinder. My first experience with the brakes was locking them up at about 60 mph and almost putting a flat spot on my tires. Since then they have degraded due to other problems but I can still lock the fronts up.

Also - at this point my car does NOT have an adjustable propotioning valve and it is very front brake dominant.

[tonycharger72]

I have 298mm Vented Rotors with R32 4spots on the front, for the rears its 287mm with 45mm single piston floating calipers, I am using a 1" bore MS from a 1979 Patrol,

 

My pedal is really spongy - Brakes work really well, put your head through the windscreen, but the pedal dosent bite untill about half way down the pedal stroke,

 

I am using rubber hoses - but i did away with the solid mounts that were on the struts - so i have a hardline from a basis adjuster in the engine bay all the way to the chassis rails - then a rubber hose straight to the calipers (front and rear) - i no longer have that little solid line that ran from the strut to the calipers,

 

Was thinking that if i got rid of the rubber and installed braided steel lines that might firm up my pedal a bit? any ideas?

[rudypoochris]

This might be kind of off topic, but I am stumped. The 240z MC's had external proportioning (at the rear right before the T) right? The later cars, inlcuding the 280zx's that we source the MC's from happen to be internally proportioned... correct? So how does adding a proportioning valve on the rear brake line help the bias? I thought we wanted more to the rear then stock? Or is it that since the 1.75" front 4 pistons consume so much more then the rear 240sx's that the rears will lock up prematurely any way? Just trying to figure this one out, sorry for the hijack.

[JMortensen]

None of the masters have the prop valve built in. I believe on the 280Z and ZX there was a dual metering/prop valve on the right side frame rail towards the back of the engine compartment, so you'd want to get rid of that just the same as you do the 240Z prop valve before installing an adjustable one.

[rudypoochris]

None of the masters have the prop valve built in. I believe on the 280Z and ZX there was a dual metering/prop valve on the right side frame rail towards the back of the engine compartment, so you'd want to get rid of that just the same as you do the 240Z prop valve before installing an adjustable one.

 

Thanks! Was my piston size theory way off? Just wondering haha.

[TimZ]

I have 298mm Vented Rotors with R32 4spots on the front' date=' for the rears its 287mm with 45mm single piston floating calipers, I am using a 1" bore MS from a 1979 Patrol,

 

My pedal is really spongy - Brakes work really well, put your head through the windscreen, but the pedal dosent bite untill about half way down the pedal stroke,

 

I am using rubber hoses - but i did away with the solid mounts that were on the struts - so i have a hardline from a basis adjuster in the engine bay all the way to the chassis rails - then a rubber hose straight to the calipers (front and rear) - i no longer have that little solid line that ran from the strut to the calipers,

 

Was thinking that if i got rid of the rubber and installed braided steel lines that might firm up my pedal a bit? any ideas?[/quote']

 

Braided steel lines will help a bit, but I doubt that they will make a "half pedal stroke" kind of difference. Could be you need a still larger MC, could still be some small amout of air trapped somewhere.

 

Could also be that these calipers have a large amount of piston seal rollback (the deformation of the seals pulls the piston away from the pad when pressure is released - oems sometimes do this on purpose for fuel economy). You could try the Wilwood residual pressure valves and see if that makes a difference.

 

What was the reasoning behind taking out the short solid line at the caliper? That's there to stress relieve the caliper inlet. I see no advantage to doing this.