7/8 master cylinder with Hilux and vented s13 rotors

Hi,

my car in undergoing this conversion. 4x4 hilux calipers with vented S13 rotors. standard rear drums.

My question is my 7/8 M/C is functioning well, and i didnt really want to change it but will if it wont work very well.

15/16 seems like overkill to me. plenty of people run 7/8 on silvia with a GTR brake conversion all round (4 front and 2 rear) and it reportedly works very well.

opinions please. I am a bit 2 ways about it. A 15/16 new is about $175 but i wonder if its worth it if my 7/8 is going strong.

cheers,

Peter

Work out the individual square cm area of the four original pistons, then compare to the square cm area of the eight new ones, any increase in sq cm area difference will mean that ypur master cylinder will need to displace more fluid for same given amount of pad movement.

Try your system as it is, there may be more pedal travel, ina race/sprint situation with possibility of brake fade, the pedal will get closer to the floor behind much quicker.

The slight diffetence 14/16 to 15/16 will mean more fluid is pushed through the master, equating to less pedal travel, but slightly more effort

Nice to have a technical answer. at this stage i was hoping to hear from anyone who has run that setup on both 7/8, 15/16.

The concept i understand, and the application is more street than track.

cheers,

Peter

I think Dat2kman’s point was that if you do the piston area calculations, and they come up very similar then you shouldn’t have any issues retaining the 7/8” master cylinder and therefore no need to listen to opinions on which is better.  The reason is, some drivers prefer a harder pedal feel than others and not all custom setups are exactly the same (any slight misalignment between the calliper to disc will result in more fluid needing to be pushed and therefore a bigger master cylinder required), so you'll get differing opinions.

Hopefully, someone who has a set of the standard callipers lying around and a set of the Hilux callipers can use some Verniers on the pistons to get the diameters, and put the results up here…

According to this post click here, most of the S13W Hilux callipers have a 45mm piston diameter.

I did the write up on the rear R31 disc conversion that Lurch and i did but previous to that i ran the 7/8 with the hilux conversion and it was faultless. With the rear disc conversion i ended up going to 1 inch because i had a low pedal but the larger master cylinder didn't solve that. I went through the entire braking system and found the it was only an adjustment to the pedal at the box that solved the problem. Perhaps if i had of done this with the new 7/8th i had on there it would have had a similar result but i'll never know now.

I'll be fitting a 15/16th some time soon to another Zed with the Hilux calipers but i also fitted the hilux calipers to another club members ride and it to has no issues. I must admit that with mine i do like the harder pedal and the more you push the quicker it stops, was good value at $154 too.

Yet another conversion i performed was on a 200B with Hilux calipers and and a H165 diff from a TRX which has rear disc. With the stock 7/8th master cylinder it too has pleanty of stopping power but has a larger reservoir.

I think Dat2kman’s point was that if you do the piston area calculations, and they come up very similar then you shouldn’t have any issues retaining the 7/8” master cylinder and therefore no need to listen to opinions on which is better.  The reason is, some drivers prefer a harder pedal feel than others and not all custom setups are exactly the same (any slight misalignment between the calliper to disc will result in more fluid needing to be pushed and therefore a bigger master cylinder required), so you'll get differing opinions.

 

Hopefully, someone who has a set of the standard callipers lying around and a set of the Hilux callipers can use some Verniers on the pistons to get the diameters, and put the results up here…

 

According to this post click here, most of the S13W Hilux callipers have a 45mm piston diameter.

+1

On the race car I had a Wilwood 4 spot set up on the front, Saab 2 spot on the rear with 15/16unboosted cylinder. I did some work on the fronts, full tear down and check of calipers and reassembled with new slotted rotors. For some reason could not get any pedal pressure, had the car in a brake workshop for a week and they were scratching their heads as to what had happened as the rod in the MC was now at full travel and the fluid wasn't coming through the front calipers with any force to push the pistons out. Upgraded to 1" MC and the pedal was nice and firm as it was before. The only thing we could come up with was that the volumer required for the system was marginal on the 15/16 MC and putting the calipers back on was enough to upset the system. The extra volume in the 1" MC cured the problems.

But back to topic, work out the total piston areas of the old and new systems. As said above, if they are similar you should be good. Try it with your existing MC and if you don'tl like the pedal, ie too low, then you can go up to the 15/16" MC.

When done properly, upgrading your brakes isn't just a matter of slapping on the biggest rotor and caliper combination you can, there is a lot of thinking that needs to be done to make sure that everything matches, from the balance front to back, the size of the MC and the amount of work done by your foot to make the brakes work and how the pedal feels.

My experience with Hilux calipers and R31 rear was that the 7/8 wasn't that great.  Once I installed the 15/16th, I was much happier with the feel. 

Good to see ideas on mc ill most likely go the willwood 1" just because there eady to get what I want to know is if you or any other 260 owners had clearence issues between the silvia vented disk and the caliper ears mine seems to rub