anyone out there have experience with manual 4 wheel disc brakes? I have a 68SS with manual drum brakes that I am converting to 4 wheel discs. I only have 13-14 inches of vacuum, well below the recommended 18" of vacuum recommended for power brakes.I don't really want a vacuum pump or to have to re cam the motor so I need to know if the manual disc/disc system will work? Thanks for the help

Cheers
Steve

4 wheel discs work great if you size your caliper piston area and MC bore size / pedal ratio accordingly.

For a reasonable pedal effort, you will want calipers with a good amount of piston area so you don't need to develop a ton of line pressure to have good clamping force.

I speak from experience that Vette 2-piston PBR's up front and 1 piston PBR's out back are NOT a good choice for a manual setup. I ran mine like that for a while with a 15/16" bore MC, and pedal travel was not only on the long side but it was REALLY hard, so hard you couldn't stop the car fast. You just couldn't press down hard enough. You could have eased up on the pedal effort by going to a smaller bore MC but then the pedal stroke would be even longer-- likely on the floor. The PBR calipers simply didn't have enough piston area to work well as manuals.

Now, going with something like Wilwood 6-pistons on the front and Wilwood 4-pistons on the back would work out just fine, as the greater piston area means less hydraulic pressure is needed to generate adequate clamping pressure, so it would work just dandy as a manual brake setup.

For a while I ran my car with stock single piston calipers up front and the PBR calipers out back with a 15/16" bore MC (manual), and that was actually quite pleasant. I had to bias a lot of pressure to the rear brakes to get them to work, but everything worked just fine, reasonable pedal effort and good feel.

The other option is to run a hydroboost (runs off the power steering.) That's what I eventually went to to solve my hard pedal problem, and I'm very, very happy with it.

Troy

Steve,
If you go back in time and search thru the archives, this has been discussed at great length! I did a lot of experimenting of brakes and actually did run 4-wheel MANUAL disks brakes for my '71 SS and they worked great! The trick as Gokou already said is to match the components wisely or you will have nothing but frustration. I'm glad he mentioned the PBR type calipers because many people think they are the greatest thing, but truth is, they don't work as good as the old single piston do IMO!! You do shave some weight off with them, but they are designed to be run with a power booster AND a smaller bore MC to create lots of pressure!

Do a search and decide on some parts and let us know and we will try to help further.

One more thing... 13-14 inches of vacuum SHOULD be enough to power a stock-type, large single-diaphram booster if you wanted to go that route. Most of those will work down to about 11 or 12 inches...

Good luck,
Bill C.

Thanks guys for the input. I based the vacuum minimum on what mp brakes quoted on their website but it makes sense that a large booster with 12-13" vac should work as well as a smaller one with more vac. What I'm looking at is the Baer serious street disc setup. It has two pistons up front and one in the back.
Cheers
Steve

The Baer systems use the PBR calipers I am speaking of. My advice is don't even try to run them manual; been there, done that. I don't want to see someone else waste the same effort I did. PBR calipers needs lots of line pressure to work (read: a booster of some sort and a smaller master cylinder.) If you "feed" them right, they are quite good though. I'm very happy with mine now that I have a booster.

I would consider going to the larger Suburban calipers that some of the guys use (they have LARGE pistons and will work very well in a manual system) and then probably go with the single piston PBRs on the rear with no proportioning valve, or a proportioning valve dialed down just a little bit. My car stopped very well with stock discs up front and the 12" PBR setup out back with a manual 15/16" bore MC. Pedal effort would be even lighter with the larger bore suburban calipers up front.

Troy

Troy
I'm not familiar with the term PBR. What is a PBR type caliper? Also, do you think 13-14" vac would be enough for a power booster? I want to go power but am concerned about the vacuum. Eventually I want to change from the solid cam to a more conservative roller hydraulic setup with more available vacuum.
Steve

My wagon will have stock-style front discs with late model F-body rear discs. I was planning to run manual brakes. Can anyone recommend a specific master cylinder? Will this combination of stock a-body front and stock late model f-body rear calipers be compatible with a manual system assuming I use the correct master cylinder?

TIA

Steve-- 13 to 14" should be just *barely* enough for a large diameter single diaphragm (original style) booster. Don't even try a late model smaller diameter dual diaphgram booster with that little vacuum. Also, PBR calipers are the late model Vette and F-body aluminum caliipers, typically 2-piston front and 1-piston rear. The calipers are guided by the pads. They are good lightweight calipers but need a fair amount of line pressure to work because of the small piston area, which is why they don't work well in a manual brake setup.

Originally posted by Rich-L79:
My wagon will have stock-style front discs with late model F-body rear discs. I was planning to run manual brakes. Can anyone recommend a specific master cylinder? Will this combination of stock a-body front and stock late model f-body rear calipers be compatible with a manual system assuming I use the correct master cylinder?

TIA That's exactly what I ran for a while Rich, stock front discs with single piston PBR (late model F-body and Vette) rear calipers. Worked great! Very reasonable pedal effort and good feel. I used a 15/16" bore MC, application was for a 77 Malibu with manual brakes. The one thing to keep in mind is the ports on the 77 MC are opposite the original MC's for our car-- front port is for rear brakes, rear port is for front brakes. I think you'll be happy with that setup.

Troy

I'll have to print this out and save it since it will be quite a while yet before the body kisses the frame again and a MC would even be needed.

I almost went with the Baer street system but for the money, I think my stock-style set ups will likely have almost as much braking power and reliability for much, much less cost especially since I already have the stock front spindles, calipers and rotors.

I'm going to be installing the rear set up soon. My kit did not include dust shields but I see they are available. Any advantage or disadvantage to using them or not?