Upgraded master cylinder?

[PITT40]

OK, so I did my brake conversion using a Datsun master that matches the Girling pattern and used 4 piston calipers in front and 2 piston in rear. I bought a Wilwood adjustable proportioning valve for the rear circuit.

I'm not thrilled with the stopping power up front. I called Wilwood tech support and they told me that the pedal ratio is not great enough to make those front caliper pistons moved enough. I explained that it's stock pedal geometry.

Has anyone had similar issues when they changed from the stock master? My calipers are 4 piston with 1.5" pistons. My master has 3/4" bore. Funny thing is that I called Wilwood tech support and gave them all the info and they blessed it before I bought everything. From my measurements, the pedal ratio of the Tiger is 4.8

Any thoughts?

 

[66TigerMK1A]

..."Any thoughts? "...

My non engineer carpenter brain tells me that for a given stroke, a bigger bore should move more fluid for those bigger caliper pistons... ( ya, I know there's a whole lot more to consider )

When I bought my car, it had 4 piston ( 1 3/4" ) Wilwoods on the front and Porsche 914 2 piston calipers on the back ( no booster ) . The P.O. said it had a 3/4" Datsun tandem master which it sorta did... the front and rear outlets were joined with a 't' about 4" from the master and the car was plumbed with a single ( original ) line!

I called Dale A. after looking at his brake kits online and he was most helpful... He thought I would need about a 15/16" so I bought an OEM 15/16" tandem master for a '79 Nissan 280ZX ( matched the mounting holes and I made my own rod and clevis ). I also added a Wilwood proportioning valve. The pedal is 'firm' but not overly...I need somewhere around half travel to stop the car and I find the braking good to excellent!

Your results may.. ( and probably will ) vary... but that's what works for me...

 

[PITT40]

How much leg effort do you need with 15/16"? I asked Wilwood about going to a larger bore size and the guy told me that was a band aid but not a true fix.

My problem is that they don't lock up. It stops pretty decently but takes lots of pedal leg. Even with damp roads after a rain I could not get it to lock up the brakes. So it just needs something more.

 

[at the beach]

Have you looked at Tom Hall's kit to improve the mechanical advantage of the pedal?

bt
at the beach

 

[PITT40]

Where do I find it?

Have you looked at Tom Hall's kit to improve the mechanical advantage of the pedal?

bt
at the beach

 

[Warren]

In

The White pages .

 

[0neoffive]

Air ??

How much leg effort do you need with 15/16"? I asked Wilwood about going to a larger bore size and the guy told me that was a band aid but not a true fix.

My problem is that they don't lock up. It stops pretty decently but takes lots of pedal leg. Even with damp roads after a rain I could not get it to lock up the brakes. So it just needs something more.

FYI: Every time (no exceptions) that happens to us at the shop, we find air hiding in the lines somewhere. It compresses but does not allow enough psi to close tightly on the callipers. 3-cents

 

[michael-king]

Agree with randy,

what's the pedal feel like at the top of the pedal? Is it firm at first touch or has slight movement before you feel resistance... Could be air hiding in the high spots in the lines