Hi all,

I just installed Wilwood’s D8-4 (black) calipers I purchased here from one of our Canadian CF brothers (Thanks!). So, I’m considering getting a matching Wilwood, pn 260-8556-BK, as I’ve seen this pn recommended here on the forum with the suggestion of contacting Wilwood to confirm.

So, I called Wilwood and told the guy I spoke to what I was considering for a C3 Vette with power steering. He asked what the pedal ratio was which I had no idea, so he googled it and said it was 4 to 1 for power steering (vs. manual he said was 5 to 1).

Anyway, his recommendation was model 260-8555-BK but with a 7/8” bore. I countered that C3 Vettes with power steering came with 11/8” in bore. He made some comment about piston sized being different between stock Vette calipers and Wilwood’s which made a difference. He then said I could split the difference and go with a 1” bore but also suggested that I needed a proportioning valve setup. I told him that the C3 didn’t come with p-valves but have a distribution block. He said he understood but still recommended the p-valve.

I know things are not always equal especially with aftermarket products like Wilwood’s bleeder setup on their calipers that has that tiny ¼” nut. What bleeder hose fits that little end and stays one. What a PITA.

I would appreciate advise on this before I go spending more money and once again getting the wrong thing (again!).

Best to all…

 

I called Wilwood a couple of years ago about purchasing the master cylinder for my 73 big block restomod project.
When I told him about the engine going into the car, he advised me to wait until after the engine was dyno’d to see what vacuum it was pulling before he could recommend a m/c bore size.
I thought the guy’s answer was a little off and called back to another tech and got the same answer.
I did a little more research and got the same type of feedback from other people as well.
I would call them back, get as much information about why they are making that suggestion and then do more research.
I think that overall they are trying to supply you with the best possible set up, but because we think it can only be a 1” or 1 1/8” bore, we question their knowledge and experience.
I know my 73 doesn’t have a proportioning valve as well, but they are probably a great device to adjust your braking experience to perfection.

 

OCB,

Yeah, I thought I'd call them back after I got some feedback here (thanks for yours btw). I want to get this right as I've had nothing but trouble getting brake bleed since I changed out my originals with the Lonestar stainless sleeved cast ones. I've got a ton of $'s in this car and hopefully some additional power in my engine swap but I know the brakes have to be right for safety. My wife said she won't ride in the car unless the brakes are working properly!

 

Are you doing manual brakes or power?

JIM

 

Power. Unless someone can convince me to go manual, I can see how that would clean up the engine bay on that side.

 

Love my manual brakes!

 

Did you use a Wilwood MC to convert to manual?

 

I've got manual on mine. Rock solid/high pedal and no big deal to stop at the dragstrip at 160+ MPH or 200 MPH at the TX Mile...or on the street. I ran stock calipers forever, but a few years ago added the Wilwood calipers and kept my old stock M/C.

Have you read up on the effects of master cylinder sizing? Smaller will move less fluid but at higher pressure and cause longer travel. Larger will have higher/harder pedal with less pressure. Higher pressure stops you. But pedal ratio is critical here and can be juggled.

I believe stock manual brakes have a 1" bore and power brakes have 1-1/8" bores.



fl162.pdf (wilwood.com)

 

Thanks for the info Jim. I looked at the chart from the link you provided and it doesn't reference a 4 to 1 brake pedal ratio the Wilwood tech said my car has but if I'm understanding the chart correctly it looks like a smaller MC piston increased the pressure. Which maybe why the Wilwood tech was initially recommending the 7/8" MC vs. what comes with the 11/8" factory MC with power steering. Not sure what he meant about the piston size difference but I believe he was referencing the calipers vs. the MC. I'll call Wilwood back and get some more feedback based on the info I'm getting here.

BTW, what's it like going 160 to 200 MPH!? The fasted I've gone is 140 MPH in my previous 74 Vette with the 454 engine.

 

200 mph in or on anything is a thrilling experience.
I did 200+ on my Ducati, one time.
Everything around you blurs and anything a mile away is behind you before you know it.
I was having a blast until I rolled off the throttle way too fast.
My weight slid forward, which loaded up the front forks and the next thing I knew, my manhood was crushed against the gas tank and I was looking straight down at the pavement.
As soon as I shifted my butt back into the seat everything was good again.
I did it once, had my thrill and said never again.

 

The D8 calipers are sized to be a direct replacement, but lighter and with better seals.
I use them with the OEM 1 1/8" master cylinder (Power Brakes) on our '71 that we autocross, and they work well.

If you're using the stock pedal and the D8 calipers, you should be able to use the Wilwood 1 1/8" MC.
If you're changing to the 13" or 14" big brake kit and using an aftermarket pedal kit, then you may need to go smaller on the MC bore, or if you were going with manual brakes.
Are you sure they understood that it was a power brake application?

I've been considering swapping to the 14" big brake kit and manual brakes on our car. When I did the math, it worked out to a 15/16" MC bore, or 7/8" for higher pressure, but with more pedal travel.

I know some of the folks over here at Wilwood. Who was the rep that told you to go with the 7/8" bore?

-Chris

 

Yes, I used a 1 inch bore Wilwood master. Much prefer manual to power.

 

Thanks! I'm looking to do the same in my 80. I've seen several different bore sizes used.

 

When you do the math on the 6 piston fronts...they aren't larger in area than the stockers...but spread the load out a little better with the various size pistons.

As far as speed....I've been drag racing this car for 25 years....running 142 MPH on all motor and pump gas...and 162 MPH with the turbo's. Prior to hitting the dragstrip with the turbos, I went to a half mile event to get a chance to stuff my foot in it for longer than a dyno pull to make sure it would pull through. It ran 177 MPH using drag radials with the boost and timing turned way down for safety. At the TX mile they didn't allow drag radials so I had to run some slippery speed rated tires. I literally couldn't get my foot in it until 180 MPH and by then you've slipped and slid through a whole lot of that mile. It was pulling like a freight train at the end...lots left in it even with the boost and timing pulled back just like before. To give you an idea it was 9 MPH slower at the half mile mark on the slippery tires.

I was waiting for the point where it was going to go crazy with all those wild aerodynamics stories...but it was really anti-climatic. I was tense waiting for something to happen...but it just drove on through! Felt good!!

JIM

 

CA_WxMan,
Yeah, stock pedal and D8-4's. I called Wilwood back, got a different tech who recommended their MC I have seen some here on the forum getting, 260-8556, which is the 1 1/8" MC and that's what I ended up ordering. And he did confirm I had power steering. He said that the Wilwood MC's are 50-50 between the front and back so he too was recommending a prop valve. I don't know how our factory MC's work in comparison. I told him I didn't want to go with the prop valve for now and he said I could always add it later and also as an alternative to adding the prop valve next to the MC they have a prop valve that you can add in the rear that took some modification of the brake lines.
I don't recall the previous person's name.
Thanks for the reply.

 

On my 79 I bought the 1 1/8" bore diameter Wilwood MC 260-8556 (bought it from someone here on CF).

With the pushrod primary depth being only 1/8" deep on the 77-82 Master Cylinders you also need a spacer from Wilwood, Spacer # 300-13885 https://www.wilwood.com/Search/PartNoSearch?q=300-13885

For the late cars you have to machine that spacer down to fit.

I'm not sure how it works on the earlier C3s.

Adam

 

I went through the same problem on my '57 Chevy Restomod and my '68, power brakes are certainly 1 1/8 bore.