How to improve brake feel, Modified 914/6 (conversion) Options

[tornik550]

I have seen a lot of posts regarding brake feel however my setup is a bit different than the articles I have seen. My car is mainly used for spirited street driving and occasional auto-x. Here is my current setup (all components are close to new):
-“wide-A” 911 front calipers
-vented front and rear rotors
-“vintage brakes” 914/6GT rear calipers
-19mm master cylinder
-ss brake lines
-adjustable proportioning valve

I realize my brakes are overkill for my needs. I have bled the brakes many times.

My main question is- would a different master cylinder be of benefit? If so- larger or smaller?

[DickSteinkamp]

What is it about the present "feel" that you don't like?

[mepstein]

Larger MC = harder brake pedal, less pedal travel & less force at the caliper.
Smaller MC = softer brake pedal, more pedal travel & more force at the caliper.

I’ve always liked the brakes on my bicycles to have that light soft spongy feel but to be powerful at the wheel. I found it easer to modulate and easer at the end of a long ride or race. We did the opposite at the shop for new bikes that people wanted to test ride in the parking lot. They wanted stiff quick moving brakes.

[tornik550]

I don’t really like how the pedal is somewhat soft and I have to press the brake quite far to get the desired effect.

I did just find one other thing that I forgot to mention. The PO installed a lever type proportioning valve. I’m not exactly sure how to adjust it. It’s similar to the one pictured. Unfortunately, the handle is not original and there are no markings.

[tornik550]

What exactly does the lever type proportioning valve do? In the picture, the red handle has arrows and says “more pressure”. I thought that a proportioning valve simply controlled the percent of braking force going to the front and rear calipers?

[roblav1]

A lot of brake feel has to do with the pads too.

[tornik550]

Also- forgot to mention that I have porterfield r4-s pads all round.

[yeahmag]

Have you set the rear venting clearance correctly? A 19mm should be about right with that setup.

[914Sixer]

Put the brake regulator back on and ditch the valve.

[roblav1]

1) 19mm master cylinder is right, as already stated.

2) Your description would tell me air is in the system somewhere. I used to pressure bleed my brakes on my formula cars, about 5 psi to the reservoir is plenty. And I continued that practice on PCars. Drill a hole through an old reservoir cap and epoxy in an air fitting.

3) Dump that proportional valve and use the original, as already stated.

4) Brake "feel" is always a personal thing. On the track, I absolutely hated super hard pads that had no feel (felt like pressing on wood) even though everyone else used them (like Porterfield). I always exclusively used the old Hawk Blue.

5) I would maintain that there's not a good compromise between a street pad and an autocross pad. Much different heat dissipation requirements. Personally, I'd use a street pad (lower heat range) and see how it works at the autocross. Replacing pads more often would be par for the course... but what? Every couple years? So what!

[mepstein]

Also replace your ss soft lines if they are old. They will swell internally. Standard rubber lines are fine.

[GregAmy]

Do these rear braskes require manual adjustment? I don't know those specifically, but many 914 owners are unaware that stock rear brakes require regular adjustment.

What fluid are you using? If you got talked into DOT 5 silicon then dump that crap. Take a cheap DOT 3 and flush the s**t out of it (like at least a pint through each corner), then replace with a good DOT 4.

The lever-type adjusters are generally OK, but overkill for a street car. They consiste of spring-loaded valves that "tip" over when a certain pressure is reached to reduce rear brake pressure; the lever changes that tip-over point. AT least with the stock 914/4 brakes on my race car, I can run almost full-rear brakes in the dry and not worry about rear lockup too much. Haven't payed around with it much in the rain but I'd suggest being very conservative with rear bias when wet.

[roblav1]

Do these rear braskes require manual adjustment? I don't know those specifically, but many 914 owners are unaware that stock rear brakes require regular adjustment.

What fluid are you using? If you got talked into DOT 5 silicon then dump that crap. Take a cheap DOT 3 and flush the s**t out of it (like at least a pint through each corner), then replace with a good DOT 4.

The lever-type adjusters are generally OK, but overkill for a street car. They consiste of spring-loaded valves that "tip" over when a certain pressure is reached to reduce rear brake pressure; the lever changes that tip-over point. AT least with the stock 914/4 brakes on my race car, I can run almost full-rear brakes in the dry and not worry about rear lockup too much. Haven't payed around with it much in the rain but I'd suggest being very conservative with rear bias when wet.

Did you race with NER SCCA? If so, I probably know you! I used to be Assistant RE of NER and did the track layout for PMP.

[GregAmy]

Did you race with NER SCCA? If so, I probably know you! I used to be Assistant RE of NER and did the track layout for PMP.

Aye-yup! Still do. Also Steward and Tech. Lately mostly in Improved Touring (red Nissan NX2000 and black Integra GSR), Super Touring Light (black Integra Type R), E Production (black '08 Civic Si). The orange 914 has done primarily historics events (Lime Rock, NJMP, Thompson) but I've had it out at Regionals at Palmer a couple times...love that place buty I keep telling Fred he's gotta find a way to cut some spectator trails/areas somewhere... I also manage the Track Night in America events at Palmer and Thompson. I'm sure we've met, we'd probably recognize each other face-to-face (if we ever get to do that any time soon..) - GA

[roblav1]

When you see Fred again, tell him for me to dump that kink at the last corner before the last straight! He'll know what you mean.

I still need to run PMP and Thompson at speed. Maybe wife and I will get up there this summer with my GT build.

Take Care, and back to your regularly scheduled programming.

Rob Laverty

Did you race with NER SCCA? If so, I probably know you! I used to be Assistant RE of NER and did the track layout for PMP.

Aye-yup! Still do. Also Steward and Tech. Lately mostly in Improved Touring (red Nissan NX2000 and black Integra GSR), Super Touring Light (black Integra Type R), E Production (black '08 Civic Si). The orange 914 has done primarily historics events (Lime Rock, NJMP, Thompson) but I've had it out at Regionals at Palmer a couple times...love that place buty I keep telling Fred he's gotta find a way to cut some spectator trails/areas somewhere... I also manage the Track Night in America events at Palmer and Thompson. I'm sure we've met, we'd probably recognize each other face-to-face (if we ever get to do that any time soon..) - GA

[sixnotfour]

Check floor board flex..see tanegerine racings brace kit