rebuilding brake wheel cylinders

I honed and polished my brake slave cylinders for a John Deere 4420. They looked very good. Bought the correct kit and installed properly. Now they seem very stiff. I have put some brake fluid in both ends for lubrication. Takes a pretty good push to get the cup and piston to go to the bottom. I mean like leaning in to it against a pole in the machine shed. Then to get the cup and piston to move outward to the snap ring on top it takes a lot of compressed air forced in the bleeder hole while holding your finger over the brake line hole. Are they subpose to be this tight???? Any ideas??? Thank you.

I"d make sure I had the right cup size. You may have different wheel cylinders that the tractor came from the factory with

Dang near $200 each for little cast brake slave cylinders for a combine. YIKES!


The honed surface is too rough, and I would suspect it will be tough on the cups. I am NOT recommending YOU do this, since brakes are involved, but I have often polished up the honed finish with crocus cloth.

I always put the individual parts in for a test fit before assembly.Found wrong parts in right box more times than enough.

I use Silicone brake fluid on anything I intend to use and keep.
It IS a lubricant and does not attract moisture like standard brake fluid..
Ron..

You can only hold maybe 25-30 PSI with your finger over the brake line hole. The system will operate at up to 2500 PSI. So if you can move them with compressed air they will easily move with the brake pressure applied.

Some things to do:

1) Remove the bleed screw and liberally cover it with anti-seize. I have had much better lucky with the copper high temperature product over the silver zinc base kind.

2) Install the brake cylinder on the mounting plate. Install the return spring and make sure it will pull the piston back down. If it does than you have no worries. If it does not then something is not correct. Take it apart and see if the cup is the correct one for the bore. Measure the small part of the cup. It should match the bore. If it does then maybe the bore is not smooth enought. Hone it some more and see what happens. Also use silicone lube rather than the brake fluid when putting it together. The brake fluid is not a very good lubricant. Put some between your fingers and rub and you will see what I mean. It is actually close to a solvent.

Try this and let us know.

(quoted from post at 02:08:07 03/29/13) I honed and polished my brake slave cylinders for a John Deere 4420. They looked very good. Bought the correct kit and installed properly. Now they seem very stiff. I have put some brake fluid in both ends for lubrication. Takes a pretty good push to get the cup and piston to go to the bottom. I mean like leaning in to it against a pole in the machine shed. Then to get the cup and piston to move outward to the snap ring on top it takes a lot of compressed air forced in the bleeder hole while holding your finger over the brake line hole. Are they subpose to be this tight???? Any ideas??? Thank you.

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DOT5 is all i can say! I use it in everything! Allways have brakes

What kind of oil did you use to hone your cylinders with? If your system uses brake fluid you have to hone the cylinders with brake fluid. Any other minute amount of oil or solvent in a conventional hydraulic brakes system will cause all the rubbers in the system to swell and cause the problem your are describing.

Spent decades in a tire and brake specialty shop. Rebuilding brake cylinders was SOP. I always honed with brake klean. Lubricants don't let the hone do it's job well enough and can leave contaminants. As others have said, check to see if the cups are the correct size as mismarked or mispackaging is not that uncommon. The brake pistons also need to be buffed off as they commonly get built up corrosion that will (most commonly) bind the cylinder. Brake assembly fluid is the only correct lubricant to reassemble the cylinders with (hard to come by these days I've found). Regular brake fluid (dot 4) is meant to be hydroscopic to hold moisture in suspension and will promote corrosion on the pistons. Silicon fluid (dot 5) will not hold moisture but withstand more heat. The silicon downside theory is that water droplets will settle in spots and rust through a line (I think that is nonsense myself). It is also not compatible with dot 4, (which is why it does not make a great assembly fluid), and requires complete system flushing to change over to do it correctly. The silicon upside is that if you spill it on your paint it won't hurt it. If the cylinder is aluminum you can't hone it. Of course "farm repairs" don't count.

Jim

As long as the bores were properly honed all nice n smooth n polished and concentric and the right size cups were used Id say there's no problem if you consider the PSI exerted by the master cylinder versus your finger or 100 PSI air compressor. If the brake return springs force the cylinders back you can rest assured the PSI generated by the master cylinder will force it out. Id give her a try.

PS for no more then the cost I quit rebuilding cylinders and just buy new ones

Let us all know

John T

>PS for no more then the cost I quit rebuilding cylinders and just buy new ones<

That's why 'brake assembly' fluid is rarely seen these days.

Fer sure, while I used to hone n hone n polish n polish etc they just never seemed to work/last as well as new ones but hey if a guy likes to rebuild them more power to him but I bet they wont be as precise and as fine smooth polished as the factory bore???

John T

so what kind of finish should the wheel cylinder have when done? im fixing to do them on a old truck where they are no longer available new i have to rebuild

Surprisingly you don't need a mirror finish at all. The honing was just to get the crud and lumps of corrosion out. With new rubber a cylinder with even heavy pitting would work fine, leak free, for half a dozen years or far longer. But like you said, over the years the cost of a new cylinder is now so close to a rebuild kit (if anyone still carries them) then why bother to rebuild.

New ones for a John Deere 4420 combine were $170 + each. That is why I decided to rebuild them.