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MG MGB GT V8 Factory Originals Technical - How to determine proper brake MC bore

I have upgraded suspensions both front and rear of my supercharged 79 MGB with Wilwood disk brakes on the front and Ford Sierra disk on the rear. Despite a new MC, rebuilt brake booster and multiple bleeds(manual, power and vacuum) I still have a softer pedal than I would like. The car will stop but I just don't feel it is where it should be. I believe it may be the MC is not adequate for the brake upgrades. Can someone walk me thourgh how to determine the proper bore, travel, etc I need for an alternate MC. I already have the brake booster recommended by Bill Guzman from MP that fits my pedal box and now need to deterime the proper MC to get.
Frank

The smaller the bore, the longer the pedal travel to move X amount of fluid, and the lower the effort.

Larger bore = harder pedal, lower travel, more effort.

I wouldn't have bothered with a servo myself, but then half my MGs have non-servo 4 wheel discs - the effort isn't all that high.

Three of my other cars with 4 wheel discs do have servos but then they are larger heavier vehicles.
Bill Spohn

Bill,
It is my understanding that the disk brakes need a greater volume of fluid than a drum set-up. Is this true?
Frank

The stock MC does not have sufficent volume to feed front and rear disc brakes.

Also what size calipers are you using at front and rear.
A 1" BORE MC with and equalizer is needed to properly feed the correct bias between the front and rear.
Your MC and stock valve that controls the bias between the front and the stock drums will not work with the rear disc and front disc.

When installing rear disc brakes, everything changes, the rear calipers need diferent pressure and volume than wheel cylenders.
Bill Guzman

Bill,
Thanks so much for responding. If I lived in your neck of the woods I would just bring her to you and know this would be sorted out properly. Unfortunatley I disovered your website after purchasing my suspension upgrades and not before. My car has a Fastcars front coil over set-up and a Hoyle rear IRS. I have just recently gotten her on the road and she handles wonderfully however I am unwillng to push her to the limits with the brakes where they are right now. I am unsure how to calculate the volume the front and rear calipers I have and don't know the formula to use to determine the correct bore size to order. Do I just need to measure the diameter of the pistons in the calipers and then is there a formula to plug this into to determine the MC bore size? Again I very much appreciate any help you can offer. Also since I have already purchased the booster from MP I guess for now I will stay with the stock pedal ratio and keep it a power assisted system.
Frank

Frank, e-mail me. I have a spreadsheet for that.

Gary
http://www.rc-tech.net/MGB
gw mr

Thanks Gary,
I keep forgetting you are also my disk/disk specialist from the MGB experience. I will e-mail you off line.
Thanks!
Frank

Frank I will be glad to help you over the phone with any questions you may have.
It's not a big deal, it's a simple thing to do, brakes are important.

You can get my # on the web
Bill Guzman

Bill G.
Thanks...I will try and get all my questions together...educate myself as much as possible and give you a call. Your previous posts on this thread and in the archive have always been very helpful in assisting my understanding of this topic.
Frank
Frank

Hi Frank,
I've delt with this issue on a few other cars. I'm in Marion NC if you need a hand.

Kelly
Kelly Combes

Hey Kelly...it is truly a small world. I am just up the road in Rutherforddton. The designer of my front end, Ted Lathrop of FastCars has suggested I try some residual pressure valves first, prior to any MC changes..so that is next in line. Will report back my results.
Frank

This thread was discussed between 01/06/2006 and 10/06/2006

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