Which M/C to use LS1 front LT1 rear brakes

[BIGKO]

Hi, everyone. My first post here. I'm sure this has been answered hundreds of times but what size m/c should I use. I have 72 Skylark with the GTA/GNX style 16" rims, all 4 "fronts". Yeah I know there are bigger rims out there and honestly, probably for less than I have invested in these, but I love the look. I test fit my wheels on both a 01 Trans Am and 95 Camaro, and the rims seemed to fit too close for me on the rear LS1 calipers, therefore I have gathered all the parts to install LS1 front brakes and LT1 rear brakes. So... the question is which M/C is recommended on my stock vac booster which is only a few years old. The "F" body M/C would be my obvious choice, but the ports exit on the right. Have I seen somewhere the use of a M/C from an "export' model S-10 which has LH ports? Thanks

[GregWeld]

Wilwood has a master cylinder which will exit out either side. It's a nice aftermarket piece and works great. Watch out for pressure and brake pedal ratio... if you're using MANUAL brakes you want the pedal ratio to be 6 to 1 --- and use a 1" or 7/8" master... the 1 1/8" M/C are for DRUM brake applications. Disc brakes need PRESSURE -- the smaller the dia M/C - the MORE pressure they make. Weird - but it is what it is.

[Apogee]

Actually, the 1-1/8" master cylinder was used extensively on the GM power disc/drum applications due to the overall piston area of the calipers. The drum/drum applications typically used a 1" bore MC.

As for your application, the LS1 calipers have twin-43mm pistons and the rear LT1 calipers have single 45mm pistons. With a standard '72 Skylark vacuum booster, a 1" bore master cylinder should work well for your application assuming you have sufficient vacuum to run the booster. The LS1 MC would be an excellent choice, but if you're not interested in bending a couple of hard lines to match the MC, then there are other options...but they'll probably require some bending as well. The early 2000 S-trucks MC you mentioned is a good 1" option and has SAE ports instead of metric ISO bubble flares.

The S-truck MC's are available in both left and right hand drive versions, with the only difference being the side of the ports. The RH drive application has ports on the driver's side whereas the LH drive application has them on the passenger's side.

Tobin
KORE3

[BIGKO]

Thanks for the input guys. I guess it goes without saying that I'll have to ditch the factory prop. valve and go with one of the adjustable brake bias valves for the rear. I'll have to do some plumbing anyhow.My car is factory disc/drum right now so am i correct assuming that either the LS1 or the S10 m/c has the rear ports for the rear disc and the front ports for front just like my factory is now.

thanks, Keith

[Apogee]

Originally Posted by BIGKO

Thanks for the input guys. I guess it goes without saying that I'll have to ditch the factory prop. valve and go with one of the adjustable brake bias valves for the rear. I'll have to do some plumbing anyhow.My car is factory disc/drum right now so am i correct assuming that either the LS1 or the S10 m/c has the rear ports for the rear disc and the front ports for front just like my factory is now.

thanks, Keith

Both the LS1 and S10 MC's are opposite with the forward port being for the rear brakes and the rearward port nearest the firewall being for the front brakes. An adjustable prop valve is a good idea since you're replumbing everything anyway...it should allow you to optimize your rear brake performance given your setup.

Tobin
KORE3

[GregWeld]

Funny --- I was just going to post that the ports and resevoirs are NOT always front for front and back for back! Don't EVER get caught up in that trap! AND some M/C have internal proportioning valve so adding an external unit would be a serious degradation in pressure (reducing pressure that has already been reduced!).

A quick revue of how the M/C is set up is to WATCH the fluid in the reservoirs as you slowly apply brake pressure - the FRONT brakes should be applied FIRST so if you see fluid movement in one reservoir before the other - then that tells you which one should go to the front.

Another arguable point to check on is that everything I have ever read - and every brake manufacturer I've talked to (Brembo - Baer - Wilwood) will tell you to run 3/16" brake lines when using disc brakes. Disc brakes work on pressure (volume is critical as well but we're talking about your average street car here...). Smaller diameter M/C make higher pressure. A 7/8" bore M/C is making about DOUBLE the pressure of a 1 1/8" version with the same amount of effort applied.

Personally I have a motor that makes almost NO vacuum due to having 8 stack EFI -- so I save the vacuum for the MAP sensor... when I changed to this manifold - I eliminated the power brakes and went with a 7/8" Wilwood M/C -- I have big azz Baer discs all around -- and I can tell you that my braking improved by 500% !! It takes little effort to brake effectively and I swear the brakes work so much better! I had the "Corvette" M/C (disc disc) before with a dual booster... but with low vacuum so the pedal was always 'hard' but without the resultant braking power. Now, I'll throw you out the front window if I stomp the brakes.

[BIGKO]

Thanks all for the input. So are there advantages with going with one of the newer alum. m/c with the plastic reservoirs, like the LS1 or the S10 which appear to have 1" bore. Or, would one of the older "classic" read oem style m/c be a good choice. See this link for one that states it's a 15/16" bore and designed for disc/disc apps. I think i would be more inclined to go with one of the more period correct cast iron m/c only for looks. But please if the alum. newer style m/c is better i'll choose that. Even though i have a booster in good shape and a mild engine producing plenty of vacuum it seems like the 15/16 bore will give me more braking power over the LS1 or S10 which are 1" bore.

here's the link to the m/c I'm speaking of : http://cgi.ebay.com/ebaymotors/ws/eB...3AIT&viewitem=

thanks, Keith

[GregWeld]

Keith --- this is a good choice... for your application.

If you are running power brakes - then your pedal ratio is 4 to 1 --- if you're going with manual brakes - then it's 6 to 1

This ratio calculation can been seen here:

http://www.hotrodheaven.com/tech/brakes/brakes6.htm