# 25.4 MM master cylinder upgrade



## Slytle (Apr 28, 2002)

I have the Girling 60 dual piston calipers on my Mk2 GTI and the 22mm master cylinder wasnt getting the job done. I heard a few rumors about an 25.4mm master cylinder form an audi, but no definitive answers. So I went to the junkyard and searched for one. The one I found came off a 1990 Audi 200 Quattro. It is dimensionally identical to the Mk1/Mk2/Mk3 master cylinders. 
Installed it last night and it works great. No modifications necessary. Pedal feel is much more solid and brakes feel much more powerful, also pedal travel is reduced a great deal, which is great because with the 22mm master, the pedal was almost hitting the floor.
I recommend this upgrade to anyone running larger displacement calipers than was originally intended for the 22mm master cylinder.


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## billzcat1 (Sep 10, 2001)

*Re: 25.4 MM master cylinder upgrade (Slytle)*

I definetly agree - there are only a few cars that have the correct 25.4 MC - if anyone can't live without one I've got two extras. These things work great especially if you go with the larger brake kits like Girling 60s or any number of aftermarket kits.


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## yellowslc (Aug 29, 2000)

the newer eurovan's with vr6's have the 25.4mm MC for use with ABS..


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## PRJCT GTI (Sep 4, 2002)

*Re: 25.4 MM master cylinder upgrade (Slytle)*

would this be a good upgrade if I was just using the calipers from a 98 vr6 on my MK2. I am doing a 5lug swap on all corners and I was just going to go with the 22mm but I wondering if I should go eith this idea.


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## Racer_X (Jul 14, 2002)

*Re: 25.4 MM master cylinder upgrade (PRJCT GTI)*


_Quote, originally posted by *PRJCT GTI* »_would this be a good upgrade if I was just using the calipers from a 98 vr6 on my MK2. I am doing a 5lug swap on all corners and I was just going to go with the 22mm but I wondering if I should go eith this idea.

If the donor for the calipers had a 22mm master cylinder, go with the 22mm master cylinder.
A bigger master cylinder is technically a downgrade, not an upgrade. Larger master cylinders reduce your hydraulic advantage on the calipers, meaning that you have to press the pedal harder to get the same braking force. The only reason to go to a larger master cylinder is if you are installing larger calipers that require more fluid flow to operate. Then, the downgrade at the master cylinder is generally more than offset by the upgrade to the calipers, and the overall system performs better.


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## Slytle (Apr 28, 2002)

Agreed. General rule of thumb: Use the same size master cylinder as the car you took the front calipers from.


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## baupfhor (Apr 10, 2002)

*Re: (Slytle)*

never had problems with my 20mm and girling 60s. http://****************.com/smile/emthup.gif


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## Slytle (Apr 28, 2002)

*Re: (baupfhor)*

Youre kidding right? With my 22mm, the pedal almost touched the floor.


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## IntakeManifold (Jul 3, 2002)

*Re: (Slytle)*

From my experiance, a larger master will allow you to push more fluid which in turn provides more force on the the calipers. 
Pedal feel might be a small bit firmer, but thats what i prefer.


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## Racer_X (Jul 14, 2002)

*Re: (IntakeManifold)*


_Quote, originally posted by *IntakeManifold* »_From my experiance, a larger master will allow you to push more fluid

Good so far.

_Quote, originally posted by *IntakeManifold* »_ which in turn provides more force on the the calipers. 

Actually, no. Not unless the calipers have larger pistons. Force at the calipers is based on pressure, not volume. And that force is multiplied by the ratio of the caliper piston (wheel cylinder) area divided by the area of the master cylinder piston. Increasing the master cylinder size reduces the force multiplier.
A larger master cylinder is the hydraulic equivalent of a shorter lever. You don't have to push as far, but you have to push harder. 
Imagine a 20mm "slave cylinder" positioned vertically with a 100 pound weight on top. Hook that up to a hydraulic line and then hook up a 20mm master cylinder. Now, push on the pushrod on the master cylinder. Since the master and slave cylinders are the same size, you'll have to push with 100 pounds of force to lift the weight on the slave cylincer. And since they are the same size, for every 1mm you push in on the master cylinder pushrod, the slave cylinder will push the weight up 1mm. 
Now, change to a 22mm master cylinder. That will have about 20% more area on the piston, so it will push 20% more volume. When you push the master cylinder in 1mm, the weight on the slave cylinder will move up 1.2mm. The price for this is that you have to push with 120 pounds of force to move the 100 pound weight. 
If you think of it like the classic "teeter totter" lever, a larger master cylinder is exactly like moving the fulcrum point toward the end you push on. It reduces the distance you have to push, but increases the force you must use to push. A smaller master cylinder is exactly like moving the fulcrum point toward the load. You have more "leverage" and don't have to push as hard to lift the weight, but you have to move the end of the lever further to move the weight the same distance.

_Quote, originally posted by *IntakeManifold* »_Pedal feel might be a small bit firmer, but thats what i prefer. 

"Firm pedal" usually means less pedal travel. But when it comes with less force generated at the brakes for the same force at the pedal, it's not such a good thing. A little doesn't necessarily hurt, but you don't want to go to the biggest master cylinder you can find. Really, VW did well with matching the master cylinders to the brake systems on our cars. If you change front calipers, using the stock master cylinder from the donor vehicle for the calipers is almost always the best choice.


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## DubPhreek (Apr 17, 2003)

*Re: (Racer_X)*


_Quote, originally posted by *Racer_X* »_
Good so far.
Actually, no. Not unless the calipers have larger pistons. Force at the calipers is based on pressure, not volume. And that force is multiplied by the ratio of the caliper piston (wheel cylinder) area divided by the area of the master cylinder piston. Increasing the master cylinder size reduces the force multiplier.
A larger master cylinder is the hydraulic equivalent of a shorter lever. You don't have to push as far, but you have to push harder. 
Imagine a 20mm "slave cylinder" positioned vertically with a 100 pound weight on top. Hook that up to a hydraulic line and then hook up a 20mm master cylinder. Now, push on the pushrod on the master cylinder. Since the master and slave cylinders are the same size, you'll have to push with 100 pounds of force to lift the weight on the slave cylincer. And since they are the same size, for every 1mm you push in on the master cylinder pushrod, the slave cylinder will push the weight up 1mm. 
Now, change to a 22mm master cylinder. That will have about 20% more area on the piston, so it will push 20% more volume. When you push the master cylinder in 1mm, the weight on the slave cylinder will move up 1.2mm. The price for this is that you have to push with 120 pounds of force to move the 100 pound weight. 
If you think of it like the classic "teeter totter" lever, a larger master cylinder is exactly like moving the fulcrum point toward the end you push on. It reduces the distance you have to push, but increases the force you must use to push. A smaller master cylinder is exactly like moving the fulcrum point toward the load. You have more "leverage" and don't have to push as hard to lift the weight, but you have to move the end of the lever further to move the weight the same distance.

"Firm pedal" usually means less pedal travel. But when it comes with less force generated at the brakes for the same force at the pedal, it's not such a good thing. A little doesn't necessarily hurt, but you don't want to go to the biggest master cylinder you can find. Really, VW did well with matching the master cylinders to the brake systems on our cars. If you change front calipers, using the stock master cylinder from the donor vehicle for the calipers is almost always the best choice. 

what he said. 
I think there are many upgrades to be had with the braking systems, I am a proponent of the steel braided lines, upgraded master, and bigger vented drilled brakes, nicer pads.
however I always tend to ask myself - where oh where did all the rubber go??















nuts. Perhaps I need a scooter.


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## Slytle (Apr 28, 2002)

Yep. My pedal is much firmer and the travel is reduced to where it should be. The 22mm master made pedal travel too long and felt mushy. 
So, in a sense, the larger master cylinder IS an upgrade, because it allows me to properly operate the larger volume calipers.


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## IntakeManifold (Jul 3, 2002)

*Re: (Slytle)*


_Quote, originally posted by *Slytle* »_Yep. My pedal is much firmer and the travel is reduced to where it should be. The 22mm master made pedal travel too long and felt mushy. 
So, in a sense, the larger master cylinder IS an upgrade, because it allows me to properly operate the larger volume calipers.

Are you using audi dual pistons?
what car did you get the master off of.


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## billzcat1 (Sep 10, 2001)

*Re: (IntakeManifold)*

The only good cars to get the master cyl from are 90-91 Coupe quattros and 89-91 200 10v (not 20v) as far as I know. These are the ones I have direct experience with. Some others might work such as 93-95 90 or 94-98 Audi cabriolet. I know for a fact that the Audi 5000 25.4mm master does NOT work with stock VW line locations. 
Also, FWIW, these ones I have listed as working duplicate the stock line locations for Mk1, Mk2, and I think Mk3. In Audis, it doesn't matter if there is ABS, the lines still go to the same location. Is this true for VWs?


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## Slytle (Apr 28, 2002)

*Re: (IntakeManifold)*

Yes, I am using the dual pistons. The 25.4mm master would be a BAD idea with stock calipers.


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## bengone1 (Jun 17, 2003)

*Re: (Slytle)*

i have the audi DPs on my rocco with 11 raddo rotors and 22mm MC. the brake pedal travel is almost none existant. my problem is now getting more pressure to the rears to even it out.


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