23mm Master Cylinder?

[AudiVWguy]

Rumor has it that a 23mm MC off a Audi 5000 (84-87) would work on VW's looking a brake upgrade. Anybody tried this? I thought that the 22mm was the way to go.......
--J.B.

[jtanguay]

Rumor has it that a 23mm MC off a Audi 5000 (84-87) would work on VW's looking a brake upgrade. Anybody tried this? I thought that the 22mm was the way to go.......
--J.B.

apparently some dude off ebay is selling them as direct replacements... i want to get a 23mm MC when I do my rear disc conversion

[dogday]

OK - dumb question...

Presumably we are talking about the interior bore of the Master Cylinder - what advantage does going larger - upto 23 mm - give? :?

DD

[zukgod1]

I think in theory having a larger piston/ bore would move more fluid with less peddle travel.

[jtanguay]

more fluid = more braking power... then again you better hope that you don't have any rusted lines that are weak... because they will be under more pressure with the larger mc.

i might need a new mc anyways due to it running low on fluid, and if so i'm upgrading to a 23mm one.  would be nice to have a good stiff pedal

[cyrus #1]

more fluid = more braking power... then again you better hope that you don't have any rusted lines that are weak... because they will be under more pressure with the larger mc.

With a larger master cylinder you actually get less brake line pressure for the same amount of pedal force.  As mentioned the advantage is the ability to move more fluid so you're not hitting the floor with your brake pedal.

[jtanguay]

more fluid = more braking power... then again you better hope that you don't have any rusted lines that are weak... because they will be under more pressure with the larger mc.

With a larger master cylinder you actually get less brake line pressure for the same amount of pedal force.  As mentioned the advantage is the ability to move more fluid so you're not hitting the floor with your brake pedal.

well let me see here.  you're moving more fluid, into the same size of calipers/cylinders/lines.  wouldn't that mean that there is more pressure on the smaller parts?  i would imagine the pressure to be the same if you upgraded calipers/cylinders to offset the larger size of the mc.  

maybe i'm wrong, but i picture it this way.  you put a bigger pump (water pump or a hydraulic pump of some sort, not IP) in place of a smaller pump, and the bigger pump should naturally create more pressure no?  but increase the size of the lines and it should be the same pressure but with more flow?

[cyrus #1]

It all has to do with the area differential between the master cylinder and the caliper.  Since we know pressure = force / area we can easily figure out the difference.

for example:  P=(100lbs.) / (1 sq. in)        P=100psi

The 100 lbs is the force being applied to the master cylinder through the brake pedal and the 1 sq. in is the area of the master cylinder.  Now lets substitute the 1 sq. in area with a larger 10 sq. in area master cylinder.

P=(100lbs.) / (10sq. in)        P=10psi

Obviously this is an exaggerated example but the concepts still apply.  You are correct that a larger pump, etc. will create more pressure if its flow is greater than the flow of the lines.  However, the pressure and forces in a brake system that concern us are static so flow doesn't really flow factor in.

[AudiVWguy]

OK, I bought the 23mm MC from the guy on E-bay, put it in today. Let me say first that I have a 10.1 setup off a Passat wagon, rear discs, Hawk HPS pads, 22.2mm master cylinder on my Caddy (2200 lbs). The Passat weights in the neighborhood of 3200 lbs. so you can see it was very good to stert with before the 23mm MC. The larger MC made a very small if any difference. The reason is that the your leg is having to push slightly harder to move the larger piston. Its a little hard to explain. The bottom line is that the 22 mm MC is the best compromise and probably the most cost effective. The only improvement might be finding the biggest vaccuum booster that would fit. Mine is off an 89 convertible. Hope this info helps.

[jtanguay]

OK, I bought the 23mm MC from the guy on E-bay, put it in today. Let me say first that I have a 10.1 setup off a Passat wagon, rear discs, Hawk HPS pads, 22.2mm master cylinder on my Caddy (2200 lbs). The Passat weights in the neighborhood of 3200 lbs. so you can see it was very good to stert with before the 23mm MC. The larger MC made a very small if any difference. The reason is that the your leg is having to push slightly harder to move the larger piston. Its a little hard to explain. The bottom line is that the 22 mm MC is the best compromise and probably the most cost effective. The only improvement might be finding the biggest vaccuum booster that would fit. Mine is off an 89 convertible. Hope this info helps.

yea i think you need to get a bigger vacuum booster

[VWralley]

there is absolutly no need for that large of a master cylinder on that car. i'd even say you are almost going into the "overkill" category by running the 10.1's.

you are going to add effort to pushing in the pedal and it will not substantially increase your braking performance. these cars are very light, so unless you are adding a ton of weight, huge brakes and MC's are not neccesary

[AudiVWguy]

Yes, thats what I came around to thinking. I did notice the pedal effort was harder during extreme braking, but for the past couple of months this setup has been in a daily driver situation and the 23 feels amazing. Very little pedal effort to produce very quick stops. If I was racing the truck, I think the 22 would be a better choice due to the increased piston pressure from the smaller 22mm size. There is also the outside chance the overall brake set-up is stressed less due to the larger size and hopefully last longer.