Seized Front Brake Master Cylinder

I have two front brake master cylinders for my '85 XJ700X and BOTH have the same problem. The piston is literally seized inside of the housing and I cannot, for the life of me, figure out how to remove them so I can clean them up and rebuild them. I let them soak in PB blaster for almost a week, but that had no affect on getting them out. I'm able to grab on to the end of the piston assembly with a pair of needle-nose vice grips, but the thing just will not budge.

Anyone have any other suggestions for me before I clamp this into my drill press and go to town?

 

i know this sounds odd, but take a bolt thats about the same size as the piston, set it on the piston and give it a tap with a hammer a few times to try and dislodge any debris that is siezing it up?

 

An idea, but I run the risk of jamming it in even farther!

 

If you have a rebuild kit it all gets replaced anyway. I used the PB as well on one from the output side. Tapped it in, used some PB on the back side, tapped it back and forth until it free'd up enough to get it out.

 

1) Grind up some ice cubes into shavings and stick them in the piston bore, or, freeze the master cylinder overnight int he freezer.

2) Heat up the outside of the master cylinder housing, all around the bottom where the piston bore is, with a heavy-duty heat gun (you can use a small propane torch, but you run the risk of burning off the paint).

You're going to have to get it REALLY HOT since the piston bore inside the alumimum m/c body is a stainless steel sleeve.....and that is what you are trying to heat up.

3) Keep putting more ice chips JUST ON THE PISTON.

4) Then try to extract with the driven blt or other method.

5) Be prepared for the relaity that the piston bore may be gouged and not in real good shape when you finally do get the piston removed. You may have to polish it using a flex-hone, and even that may not help if there are deep scratches or rust in there......in which case the m/c is pretty much junk.


it23) Aftermarket 1100-F degree FLAMELESS HEAT GUN. This good quality, inexpensive heat gun is useful in a variety of situations. Great for helping to remove frozen carb and engine fasteners (it quickly heats up the metal surrounding the stuck gastener, helping to un-seize the fastener threads), applying electrical shrink tubing, and other uses. Two-speed/heat settings, 750-F and 1100-F. 120V. Can be used stand-alone with supporting clip or hand-held. Includes a air concentrator nozzle. For light-duty use only!

HCP9809 Aftermarket flameless HEAT GUN.
$ 39.95


HCP1743 Aftermarket master cylinder piston bore FLEXHONE, for use with all XJ650RJ Seca and XJ650 Turbo master cylinders, all XJ750 Maxim and Midnight Maxim master cylinders, all XJ700 model master cylinders, and XJ900RK front master cylinder. Each:
$ 38.00



Once you start adding up the prices of the tools and rebuild kits to fix a m/c such as the ones you are working on, it may be much simplet (though not necessarily cheaper) to just buy an entire new m/c unit:

HCP3015 OEM complete MASTER CYLINDER ASSEMBLY, brand new unit perfectly replaces your original. Comes with cover, diaphram, low fluid sensor, clamp, and piston assembly, ready to install. Hand lever, brake light switch, and mounting hardware is not included. Fits all XJ650 Seca models, all XJ700 models, and the XJ900RK Seca model. Mounting clamp is included. 16mm piston bore, horizontally level reservoir orientation, forward-facing fluid outlet port.
$ 249.00

 

If I can get your stuck piston out, can I have the other master cylinder???

 

Well, using a combination of jswag5 and chacal's methods, I got the pistons out of both master cylinders! What I did was heat the underside of master cylinder up until it was nice and hot and then I gently tapped the piston downward until it freed up in that direction, then I took a pair of needle nose pliers and yanked them out.

The "guts" of both master cylinders were covered in solidified brake fluid and the bore housings were no better. Looks like I have some cleanup to do!

 

Here's what I'd do.

Remove seized Brake Master Cylinder.
Place in trash.
Install new or refurbished Master Cylinder.
Done.

A seized Brake Master Cylinder is ruined.
Don't spend a dime or waste a moment fooling around with it.
Your LIFE depends on that part!

 

Why do I think this Thread was about Calipers?

 

HEAT GUNS......

"they are so hot that they're cool."

 

glad it worked, when i rebuilt my mc i ran into the same problem with the solidified fluid, anyone know what causes this, ive never seen it happen before.

 

You're 60.

[grinning, ducking and running]

 

Alrighty Wombat good job!
How long did you heat it up for? I'm in the same boat with my front brake piston. It's STUCK like Chuck!

'82 XJ650J Maxim

 

Left the heat gun on there for a good 10-15 minutes. The housing was hot to the touch, so be careful! Just tap it downward and that should loosen it up enough to pry the thing right out.

I installed a master cylinder rebuild kit and it seems to be working well so far.

Good luck!