Need advice on a 7/8 M/C

[mnm99]

I'm looking to convert my brake system for various reasons from power to manual. It's a 68 Camaro. Currently I have a 1 1/8" master with a dual diaphram booster. The engine Idles at 12" of vac. I ended up moving the pedal rod to the upper hole on the pedal. The upper ratio is 6-1 and the normal power is 4-1. The brakes work well as of now. I'm wondering how it will be going manual.

I called Wilwood and they said I could use either a 1" bore or the 7/8" bore. With a pedal ratio of 6-1 and front calipers with single piston of 2 15/16" size and drum rear brakes with a 10lb residual valve what master should I use? Wilwood said 7/8 would work. Some others say it wont. Many people say a 1" master would be too hard to stop.

Thanks

[indebt69]

Talk to Tobin at Kore3. He really knows his stuff. I think he will recommend a 7/8.

[Apogee]

Talk to Tobin at Kore3. He really knows his stuff. I think he will recommend a 7/8.

Darren, I would normally recommend the 7/8" bore unit if he were running C5/C6 components, however with his OE 2-15/16" piston front calipers having significantly more piston area than a C5/C6 front caliper (6.78 square inches versus 4.00) and stock rear drum brakes, that may not necessarily be the best choice. Due to the inverse relationship between pressure and volume, it's all about striking a balance such that pressures are adequate for good modulation and feel and volume is sufficient such that pedal travel doesn't become excessive.

Most factory manual disc/drum applications from the 60's came with a 1" bore MC, which would certainly be a decent option here. However after chatting a bit, I suggested that he may want to try the 15/16" bore manual MC from a '76-'77 Malibu. It's inexpensive and a good compromise between pressure versus pedal travel IMHO at the 6:1 pedal ratio. Stepping from the 1" to the 15/16" should yield ~14% additional pressure given the same input along with the associated increase in pedal travel.

Tobin
KORE3

[mnm99]

Thanks for you help. Nice talking to you. They did have the master. I should have it in a couple days. It cost $37. I'll let you know how I make out.

[Apogee]

Sweet. Something we didn't talk about on the phone was what you were running for brake hoses. If you haven't already upgraded to braided stainless, you may want to consider it. Smaller bore MC's are more sensitive to the overall compliance of the system, so you tend to notice it more at the pedal. It doesn't take much hose swell to make you question your brakes at what could be an inopportune time.

Tobin
KORE3

[indebt69]

Thanks for the reply Tobin. I definitely like how you always recommend a cheaper option and help the customer get what's right instead of just selling the most and best system out there. I'll definitely be calling you soon to get setup on a brake system once my ATS spindles come in

[mnm99]

Sweet. Something we didn't talk about on the phone was what you were running for brake hoses. If you haven't already upgraded to braided stainless, you may want to consider it. Smaller bore MC's are more sensitive to the overall compliance of the system, so you tend to notice it more at the pedal. It doesn't take much hose swell to make you question your brakes at what could be an inopportune time.

Tobin
KORE3

No, I don't have braided. When I rebuilt the whole front end I went with factory style hoses. When I get the master I'll just give that a try. If I'm not 100% happy I'll replace the lines and get the pads we talked about.
Question about the master...Does the rear brakes connect to the front of the master? Mine has the front in 1/2 fitting thats in the front of the master and the rear in the 9/16 fitting thats in the rear..
I'll look into the braided. Thanks.

[Apogee]

Yes, the '76-'77 Malibu master cylinder has opposite ports, so the front port goes to the rear brakes and the rear port goes to the fronts. Easy way to tell with most disc/drum master cylinders is that the small reservoir goes to the drums and the large one goes to the discs...this is so that you have more fluid available to compensate for pad wear and the associated piston travel.

Tobin
KORE3

[mnm99]

Thanks.

[mnm99]

Yes, the '76-'77 Malibu master cylinder has opposite ports, so the front port goes to the rear brakes and the rear port goes to the fronts. Easy way to tell with most disc/drum master cylinders is that the small reservoir goes to the drums and the large one goes to the discs...this is so that you have more fluid available to compensate for pad wear and the associated piston travel.

Tobin
KORE3

Tobin.
Did you get my PM? CPP won't have a 15/16 master for like 6-8 weeks. Do you or anyone know where I could find one, new.?

[Apogee]

You have a PM.

Tobin
KORE3