The Stovebolt Site Forums The Shop Area General Truck Talk Honing/boring/reaming of master and wheel cylinder

I am wondering how much material you can safely remove from a wheel or master cylinder to get rid of pits and still have the cups not leak fluid past them? I have adjustable reamers and some fairly well pitted cylinders. For instance, a 1 1/8" cylinder comes in at 1.125. Can you take it out to 1.140 and still be safe?

My rule is just hone enough to have a smooth surface for the new seals.If they are pitted so bad you have to hone a lot of material replace them or sleeve them.To me if it's worn replace it correctly and be safe.
Check here for parts I had very good luck with them in the past.
http://www.brakeplace.com/

I'd agree with Webster, if you need to take more than a few thousands out of the bore to clean up the pits then just replace them. If the rust pits are isolated to the center of the bore and not in the outer bore where the cups ride then you should be ok. Don't try to get the pits out of the center or you will for sure be oversize and asking for a blown out cup one day during a hard stop.

Denny Graham
Sandwich, IL

I have honed a lot of cylinders that were pitted pretty badly and had good success. I have an old Ammco hone that puts pressure on the stones. I used to buy honing oil, but I now use a mixture of vegetable oil and bioDiesel for honing oil. They have to be honed deep enough to remove every trace of pitting. The rubber cups are pretty forgiving about oversize, but any small imperfection will cause a leak. That includes honing without honing oil which leaves metal filings in the bore. Some cylinders are easier to replace than to hone. However the cylinders on some larger trucks are almost impossible to find and honing or sleeving is the only option. The hydrovacs put a lot of pressure on the wheel cylinders, but I have never had a sudden failure.

Ron, another alternative is to find cylinders with a smaller bore for the same vehicle family and bore them to the size you need. For example, a 1 1/8" cylinder can be bored to 1 3/16" just like an engine block can be bored. I have found Chevy cylinders that can be bored 1/16" to yield the 1 1/4" front size and 1 3/16" rear size that my '36 pickup uses.

Denny is right on about the pits in the center of the bore. As far as how much you can take off I'd refer to a shop manual. You may want to try the online manuals if you do not have one for your particular truck. I think most of them is around .005 You stick the piston in the cylinder and then slide a guage down in there. It took very little to clean up my cylinders but, as Denny mentioned, I did not hone the ones out in the very center. I've bled my brakes ect and so far no problems.

For what its worth. If you do some shopping around you may find new cylinders for not much more than the wheel kits.....You can't just find the rubber cups...."maybe" at some old parts houses. Find out how late a model wheel cylinder is like yours and ask for that year model. You may get lucky.

I have bored the huck type wheel cylinders with good success. I did all four on a 46 1.5 ton 6 years 15,000 miles ago and have had not one problem. The cylinders were done on a Bridgeport with a simple home made jig to hold them. I turned the new bigger pistons out of t6 aluminum. This was done with a total outlay of about 8 bucks for cups and a fun afternoon in the shop.

Ttodd, how did you decide to do the job on a milling machine rather than a lathe? Did you bolt the wheel cylinders to an angle plate then use a boring head?

Can you think of a reason why doing the same job in a lathe using a boring tool held in the tool post would not work?

Thanks for your input.

Ray

My opinion, Ron:

You're going from (nom.) 1.125 to 1.140, taking off 0.015 on the diameter, which (ideally) is 0.0075 from each wall. Those cups in my kit didn't appear to be any "precision" injection molding. It isn't like they are rings in an engine cylinder- these are just plastic cups that have quite a bit of conformance.

I did my hone job with a spring-loaded hone and an electric hand-drill. I made sure to run it well past the working length of the cylinder, with (IIRC) brake fluid as the lube. I didn't measure before or after so I have no idea what kind of concentricity/perpendicularity I have. I figure that is the job of the cups.

No leakage 2 years afterward.

...just watch: I'll come home to a pool of brake fluid tonight.

Bill

The set up is more difficult in a lathe Ray. Lacking a mill, I suppose you could mount a fixture up on the cross slide and use a boring head in the chuck, or mount a fixture up in the chuck and a boring tool up in the compound.
But as you guessed it's a simple setup in a Bridgeport. I bored and re-sleeved my rear wheel cylinders in my Bridgeport a couple of years ago to keep the same diameter bore in the cylinders. Here they are before the rebuild: http://rides.webshots.com/photo/2213841560098611668BwvTtz and here they are after they were bored with the sleeves: http://rides.webshots.com/photo/2623085370098611668ETUIML and here’s the simple fixture that I used in the Mill with the boring head: http://rides.webshots.com/photo/2288635180098611668HkoLar

You can pass out all the “this is what worked for me” advice you want guys, but as Chip pointed out, the piston clearance is just as important to proper cylinder performance as the cups are. The factory specs are .001” to .005” for the piston to cylinder clearance. That’s what I would recommend you shoot for unless your going to make new pistons and try to find oversize cups, which by the way I’ve never seen.
Denny Graham
Sandwich, IL

Any reason you can't chuck them in a 4 jaw and bore them in the lathe?
If I only had a couple to do that's what I'd do, no need to make fixtures unless you want to or expect to do lots of them.

Grigg

There are several ways you could do it on a lathe. If you have milling attachment for your lathe it would be a snap with a angle plate. I made a angle plate from a heavy 4'' peace of angle iron useing the bolts that hold the cylinder to the backing plate to hold them to the home made angle plate. The machine work from the factory was not real accurate so each cylinder had to be dialed in to get the bore right. Each pass with the boring bar was real light so as not to stress my home made plate and also not get chatter in the bore. I bored them .002" small and honed to the right size and then lapped them in with really really fine clover polishing compound. The new pistons were made to have around .002" clearence.

I did mine on the mill so I could do the boring honing and lapping for each on one set up.