Clutch Master Cylinder Piston "Stuck" Inside Bore

[ea6driver]

I recently found an old used Nabco 5/8" clutch master cylinder stowed away in a box in my garage. It had been stored there for many years...like over 20 years...I decided that I'd try and restore/rebuild it. The first problem I encountered is that the piston is "stuck" inside the cylinder bore.  After reading the inter web and watching Youtube videos about how to solve this problem, I squirted AeroKroil into both sides of the cylinder bore and let it sit overnight. I then went to Harbor Freight and bought a grease gun with the intent of pumping grease into the cylinder bore behind the piston to force it out. However, as I was pumping grease into the cylinder, the grease began coming out of the hole in the bottom of the reservoir before the piston started moving.

So my question is...how do I effectively plug the hole in the bottom of the reservoir so I can pressurize the cylinder bore enough to push out the piston with the grease? Or, alternatively, is there a better way of attacking/solving this problem?

[jonbill]

Tap the reservoir hole and put a little bolt in there.

The better approach to this problem is buy a new MC.

[Captain Obvious]

@Patcon, Didn't you tap a hole in a master cyl for some reason? Don't remember if it was brakes or clutch, but I do remember you doing something like that.

[Diseazd]

5 hours ago, jonbill said:

Tap the reservoir hole and put a little bolt in there.

The better approach to this problem is buy a new MC.

 

5 hours ago, jonbill said:

Tap the reservoir hole and put a little bolt in there.

The better approach to this problem is buy a new MC.

Why would you ever do anything else….break for a new MC….they are “dirt cheap!”

[ea6driver]

Captain....I'm not sure what you're refering to...could have possibly been something to do with a brake cylinder, but I honestly don't remember. This is the first time I've had this sort of problem with a clutch master cylinder.

Edit:....Never mind Captain O...I see now that comment about tapping a hole was directed to Patcon, not me...thank you for mentioning that.

As far as simply discarding it and buying a new one as suggested...first, I'm retired...I don't mind tinkering with things...to either fix them or just gain a better understanding as to how things work...second, while replacement cylinders are cheap and easy to come by, as far as I can tell, the original equipment NABCO clutch (and brake) cylinders are much harder to find...especially in "as new" condition. I'm not gonna loose any sleep over this problem...I just thought the group might have some good suggestions.

Edited April 1, 2023 by ea6driver

[Patcon]

Start at post #597 p24

The bottom screw/pin retains the cylinder in the bore. You will need a sacrificial pin or a bolt for that hole. I had a corroded one that I cut off so I could plug the bottom. Tapped the reservoir.

I agree, I have several Nabco clutch master cylinders and I like the idea of having the original Nabco part. The finished rebuilt part is shown in the following pages

 

[ea6driver]

29 minutes ago, Patcon said:

Start at post #597 p24

The bottom screw/pin retains the cylinder in the bore. You will need a sacrificial pin or a bolt for that hole. I had a corroded one that I cut off so I could plug the bottom. Tapped the reservoir.

I agree, I have several Nabco clutch master cylinders and I like the idea of having the original Nabco part. The finished rebuilt part is shown in the following pages

 

Holy cow Patcon! That is EXACTLY what I was hoping to find. Thank you so much. Now I am on a mission to find those screws I'll need to complete this job.

[ea6driver]

Thought I'd post a quick update on my progress rebuilding the Nabco clutch master cylinder. I removed the piston/spring out of the bore today. Tapped the hole in the reservoir as recommended above. I didn't have a sacrificial screw to cut off for the hole in the bottom, so I had to order a plug for it. The threads are very fine (M5 X 0.5). Screwed it in and forced the piston out using my grease gun. Next step is to locate/purchase a Nabco rebuild kit.