Master Cylinder Questions

Border Dave · 07-23-2023, 08:49 PM

Hi Everyone. I'm new here, so please forgive me if I ask dumb questions that have already been answered in previous posts. I did a search and couldn't come up with very much that would help me.

My son has a Pitster Pro 125. We took it on some trails and the front master cylinder went out. I think something internally is bad, but I'm not sure. There is a little fluid around the master cylinder and the lever has no resistance. I tried taking out the phillips screws that hold the lid on, but they are so tight that I ended up rounding them out a bit.

A friend suggested that I don't even try to repair it, but instead buy a new master cylinder from one of the Japanese companies. Any opinions on this?

Also, I noticed that the handlebars on the Pitster Pro are not 7/8" like my other bikes. They appear to be 13/16". Are there master cylinders that will fit on these smaller-than-usual handlebars?

TIA

TominMO · 07-23-2023, 09:11 PM

You can make up the slack on the handlebar with a winding or two of electrical tape, if needed.

Bruces · 07-23-2023, 09:45 PM

Please buy a set of JIS screwdrivers before you ruin every screw on that bike ,they are not Phillips screws .Pitbike specific parts will fit the pitster pro ,they are based on smaller children’s bikes so they use parts from z50-crf110 sized bikes .

Border Dave · 07-23-2023, 10:54 PM

Quote:

Originally Posted by Bruces

Please buy a set of JIS screwdrivers before you ruin every screw on that bike ,they are not Phillips screws .Pitbike specific parts will fit the pitster pro ,they are based on smaller children’s bikes so they use parts from z50-crf110 sized bikes .

I was under the impression that those smaller bikes have front drum brakes. Is the master cyclinder on those the same as the one on my son’s bike that has a front disc brake?

Border Dave · 07-26-2023, 02:31 AM

My son and I were finally able to solve the problem. We ended up using a propane torch to heat up the heads of the screws. We then used a hammer and screwdriver and then we were able to loosen them.

It didn’t appear that any damage was done inside the MC, so we cycled out the old fluid, bled the brake, and put the cap back on. The brake seems to work as usual. My older son thinks he might have squeezed the brake lever too hard when he was helping his younger brother move the bike out on the trail, thereby causing too much pressure in the MC and a lot of the fluid was forced out of the vent in the gasket.

We’ll see how it works when we take the bikes out next week…

EDIT as of 4/20/2024: Just an update on this. The front brake still works fine and the problem hasn't happened again.

07-23-2023, 08:49 PM	#1
Border Dave Join Date: Jul 2023 Posts: 4	Master Cylinder Questions Hi Everyone. I'm new here, so please forgive me if I ask dumb questions that have already been answered in previous posts. I did a search and couldn't come up with very much that would help me. My son has a Pitster Pro 125. We took it on some trails and the front master cylinder went out. I think something internally is bad, but I'm not sure. There is a little fluid around the master cylinder and the lever has no resistance. I tried taking out the phillips screws that hold the lid on, but they are so tight that I ended up rounding them out a bit. A friend suggested that I don't even try to repair it, but instead buy a new master cylinder from one of the Japanese companies. Any opinions on this? Also, I noticed that the handlebars on the Pitster Pro are not 7/8" like my other bikes. They appear to be 13/16". Are there master cylinders that will fit on these smaller-than-usual handlebars? TIA
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07-23-2023, 09:11 PM	#2
TominMO Join Date: Sep 2021 Location: De Soto, MO Posts: 1,869	You can make up the slack on the handlebar with a winding or two of electrical tape, if needed. __________________ 2021 Lifan Xpect--sold 2022 Lifan KPX 1972 Honda CT90--The Carrot 1969 Honda CT90--The Tomahto Cheesy is the WDK (workplace drama king). Now retired. Nope, back in the saddle. Climate: The Movie https://www.youtube.com/watch?v=A24fWmNA6lM How our government really works https://www.youtube.com/watch?v=QjadCd0VRBw Question all authority.....think for yourself
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07-26-2023, 02:31 AM	#5
Border Dave Join Date: Jul 2023 Posts: 4	My son and I were finally able to solve the problem. We ended up using a propane torch to heat up the heads of the screws. We then used a hammer and screwdriver and then we were able to loosen them. It didn’t appear that any damage was done inside the MC, so we cycled out the old fluid, bled the brake, and put the cap back on. The brake seems to work as usual. My older son thinks he might have squeezed the brake lever too hard when he was helping his younger brother move the bike out on the trail, thereby causing too much pressure in the MC and a lot of the fluid was forced out of the vent in the gasket. We’ll see how it works when we take the bikes out next week… EDIT as of 4/20/2024: Just an update on this. The front brake still works fine and the problem hasn't happened again. Last edited by Border Dave; 04-20-2024 at 01:38 PM.
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07-23-2023, 09:45 PM	#3
Bruces Join Date: May 2018 Posts: 1,577	Please buy a set of JIS screwdrivers before you ruin every screw on that bike ,they are not Phillips screws .Pitbike specific parts will fit the pitster pro ,they are based on smaller children’s bikes so they use parts from z50-crf110 sized bikes .
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