Master cylinder and booster part numbers

petek · #1 (**permalink**) 05-03-2005, 04:48 PM

OK, I've had it!

The brakes on my Cobra have never been anything to write home about. Fair amount of pedal travel and little braking until the far end of the travel. I'm a big guy and I can just get the brakes to lock up.

So I decided to convert to 11" rotors up front (thanks Clois). While I was at it I checked the linkage between the brake booster and master cylinder to make sure it was the correct length (it was). I also drained the system and put new fluid in. Bled the system, waited a couple of weeks and then bled again.

Result: no difference.

Don, here is where I need your help. The only parts that I am not 100% confident of is the master cylinder and the booster. Both of these were from the old CR and, well, I figure what the heck, I'll replace them and see if anything is better.

Picture below... what should I tell the guy at the parts counter?

thanks!

Curt C. · #2 (**permalink**) 05-03-2005, 05:33 PM

Looks like a Corvette MC from a 72 model with disc brakes. Outlets to the outside? I have this MC. Good MC assuming it works correctly>

byron w · #3 (**permalink**) 05-03-2005, 06:30 PM

PETEK, ARE YOU SURE YOU DO NOT HAVE A VACCUUM LEAK? IF NOT ,HOW BIG IS YOUR CAM AND HOW MUCH VAC ARE YOU PULLING AT IDLE? IF YOU HAVE ANSWERED ALL OF THIS BEFORE, SORRY. JUST A THOUGHT. ALSO, WHAT IS YOUR PEDAL RATIO?
GOOD LUCK,
BYRON W.

dscott · #4 (**permalink**) 05-04-2005, 08:22 AM

petek, the booster is a stock Mustang II, 1974 to 1978. The master is 1975 Corvette. The holes on the master need to be elongated to fit on the master.
Don

petek · #5 (**permalink**) 05-04-2005, 10:46 AM

Thanks Don (and everyone).

The brakes are one of two things I want to fix on my Cobra this Spring (darn, it's almost summer)!

Next on the list: high speed (70+ mph) handling...

petek · #6 (**permalink**) 05-04-2005, 03:41 PM

Don,

The master cylinder, 1" bore or 1 1/8" bore? I'm thinking with the booster to go ahead with the larger bore (to move more fluid).

thanks again

dscott · #7 (**permalink**) 05-05-2005, 08:57 AM

petek, I use the 1" bore. I don't think there is a problem with volume. The 1" should increase the pressure.
Don

petek · #8 (**permalink**) 05-05-2005, 09:17 AM

Hmmm... good point. It is pressure not volume that is needed.

Thanks again Don.

J. T. Toad · #9 (**permalink**) 05-05-2005, 03:50 PM

pete
maybe this will help, maybe it won't but what the heck

please bear in mind I do not have hardly any time on my car, but in the 3 miles I have 'tested' I have found the breaks to be quite excellent with the same master and boost you have, BUT... two things

1) I am running Wilwood 13" - (the master/boost seem to have plenty to run them) http://www.wilwood.com/BrakeKits/Pages/01/index.asp

2) After first install try, the supplied 'plunger' in the boost was too long. (this was a real head scratcher) It did not allow the master to move through full rage of motion. I machined it down and seem to have plenty of brakes. I can't imagine needing more, unless I were racing (ie abusing them, but yet maybe I presently have enough).

petek · #10 (**permalink**) 05-06-2005, 09:17 AM

Thanks for the pointers JT. I'm 99.9% sure the new booster and master will fix the problem (heck, I'm 90% sure it's the booster). My experience with brake systems up until now have been sans booster. Heck, most of the brakes I've ever worked on had separate masters for the front and back brakes.

One of these days I'm going to get myself a high pressure gauge so that I can just connect the gauge to the brake lines and see what sort of pressure can be developed.

Jack21 · #11 (**permalink**) 05-13-2005, 02:40 PM

Pete, here's what I'm using and the brakes work great.

Stock MII booster direct from CR. Master cylinder is from the Ford M-2300-C late Mustang rear disk brake conversion kit. I'll get the PN for you if you want to go this route. It's from the '87 - '89 T-bird Turbo coupe, as are the rear disks. Brake lines come out the MC on the engine side, so installation is easier.

Front brakes are Stainless Steel Brakes Force 10 (A148 kit for MII). They use Grenada 11" rotors, and 4 piston calipers.

This 11" front, 10" rear disk setup fits 15" wheels, and works extremely well.

CobraEd · #12 (**permalink**) 05-13-2005, 02:48 PM

Pete,

I had exactly the same problem as you in my CR for years. Turned out that the power booster was bad. Suck on the hose going into the booster. If the air flow never stops, there is a tear in the diaphram. It the air stops, then it is ok.

Once I replaced the booster the brakes worked great and I only have drums in the back and the pitiful little MII 9.25" disks in the front.

I drove with bad brakes for years before I realized that the problem was not just some inherent problem with kit cars but a bad power booster.

Good luck!

Ed

petek · #13 (**permalink**) 05-27-2005, 07:52 PM

Thanks to Don I've finally got my brakes working great. Problem turned out to be that I had swapped the front and rear lines on the master cylinder. The only reason the brakes worked at all (prior to installing the larger front brakes) is that I've got discs both front and rear.

Swapping the lines fixed the problem. I can lock up all four wheels in a "panic stop" situation.

Thanks again Don (and I wish Jack21 was still around to hear that I finally like my brakes ... )

Next on the list: alignment so I can drive this thing at 80+ mph without freakin' out!