Master cylinder size

[firehawk408]

Don't mean to beat a dead horse here in regards to choosing the right master cylinder for a c5 brake swap but...... I am putting c5 brakes up front and already have the WS6 disc brakes in the rear from an 81 turbo trans am. This is on my 73 firebird. My question is I have a master cylinder form the 81 turbo trans am with 4 wheel disc, is this the same as a early (67-74) vette manual M/C (1" bore) which everyone reccomends? I guess my main question is, does anyone know the M/C bore size of a 81 Turbo Trans am with 4-wheel disc brakes? Thanks

[Skip Fix]

1 1/8" aluminum/plastic tank is the spec on the 81. 79-80 4WD used 1 1/8" cast iron and a different dual diaphragm booster as the regiser on the MC is larger on the aluminum.

[firehawk408]

Okay then I have the 79-80 M/C because it is cast iron and I did get the dual diaphragm booster. However it sounds like this is not going to work because you are saying it is a 1 1/8 inch bore. That is too big. Need a 1 inch bore from what I have been reading.

Also if anyone has any expierence with it, is it necessary to get the quick take up style master cylinders with these C5 calipers.

Thanks for the help

[BRIAN]

Call MP Brakes they stock evey size master you can think of. I do not know the size of the C5 pistons but if you are using the stock large booster you can probably use either. The 1" will give you a harder pedal and the 1 1/8 will be a little softer but should rid a volume issues.


Do you self a favor and call the above as F'ng around with brake fluid and mismatched brake parts is a disaster and worth the $90 they charge for a new master.


By the way those rear calipers are a bitch and for the extra $2-300 I would ditch them also. If not pressure bleed them and make sure your e-brake is adjusted properly or you will never get a hard pedal with those calipers.

[firehawk408]

Spoke with someone at MP Brakes and he recommended starting with a 1 1/8 MC and go from there. I will try using the M/C I have and see what happens

[Skip Fix]

The disc/drums also used the 1 1/8 also from the factory on second gens. My guess would be the factory new a little about what size to move the volume of fluid for the disc pistons. Drums use smaller volume to move the wheel cylinders.

Be sure you use the 4WD pedal with the dual booster. It has LESS leverage. I didn't when I first made the swap and had no "feel" but it stopped great.

The calipers do need to have the parking brake used regularly to make that ratchet work. Best thing I did was get lifetime warranty calipers from O Reiley!