Master Brake Cylinder Repair


(Lou) #1

List:

I have a leaking master brake cylinder on my 71 XJ6. After reviewing the cost of a new one, a rebuilt one and a new parts only, my plan is as follows.

I purchased a rebuild kit from XK Unlimited and will go through that process. If that is not successful, I will have it rebuilt including sleeving. I assume that will work, but if not, new units are available.

I am a complete novice when it comes to brake cylinders. Although the instructions in the factory manual are clear, I would appreciate any comments from Listers who have done this before. I have hopefully attached a photo of the repair parts provided in the repair kit and the manual exploded diagram. The numbers in red on the photo of the repair parts coincide with the numbered parts in the factory manual. One odd item is the two machine screws which are different diameters and different threads. I assume the reason for that will be clear once I disassemble the unit.

Regards
Lou


(Frank Andersen) #2

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Being a complete novice, Lou; note/picture/write down each step during dismantling - reassembly is the reverse process. Pay special attention, and note, to the relative position and orientation of parts/seals - bare memory will fail…:slight_smile:

While the usual fault is with the seals, to be changed - but another possibility is the pitting/corrosion in the bore. Inspect carefully; if the bore is not perfect it may be the cause of the leak - and a resleeving is required…

Use plenty of brake fluid to clean and lubricate all internal parts - specs of ‘grit’ is enough to cause leaks.

Assembling will tell if you have the right kit…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
**


(tony) #3

you need a 1/2" (I think) allen key to take it apart

photograph or draw the orientation of the seal lips as they come out


(Rob Reilly) #4

Its been a long time since I did mine but I thought they should be identical. Maybe somebody at the factory packed a wrong part?


(tony) #5

I am of the same opinion. Re-use the old screws if needed


(Lou) #6

List:
With regard to the repair parts for the master cylinder from XK Unlimted, the two machine of different size and thread are correct.

The screws hold the cap on the top of the master cylinder, and are inserted from the underside of the housing. On my unit, they are not long enough to take up all the thread; some is visible from the top. Without disturbing the existing screws, I was able to thread both screws supplied and in fact, the two different sizes fit perfectly. So two different size and thread machine screws are correct for the master cylinder for a series 1 XJ6.

Regards
Lou


(Carl Hutchins, Jr. ) #7

Two points:

  1. One method I’ve used on various components, begining with a Corvair engine is to lay out the parts on a board in the exact order that I removed them or the order in which they need to be reassembled in.
  2. Have a good luck, in the absence of a means to measure, the bore of the cylinder. Too many pits and you are doomed, one way or another.
    Leave and the rough surface will destroy the rubber. Hone til clean and the bore will be too big! Each not good.

Hence:

!. Sleeve.
2. Get a better casting.
3. Abandon the project and get a rebuilt unit from a respected source.

Unreliable brakes not acceptable…

Carl


(Lou) #8

Carl:

Your comments are appreciated. Based on your remarks, I have two questions.

Looking at the master cylinder, I don’t see how to get into the bottom of the unit. There is a cap on top held by two machine screws. If I remove them, does that give me access to the parts in the bottom of the unit? I cannot see how. There appears to be access from the back of the unit, (the end attached to the brake booster) but that does not appear to be removable. Tony suggested that a 1/2" (maybe) allen wrench is needed. Maybe it will become clear once I remove the cap. Sorry for all the questions, but I prefer to have all my ducks in order in advance so I don’t lay an egg.

And as important, if I do disassemble the unit and find it is internally corroded, will the fact that I disassembledI it make the reassembly, after sleeving, difficult or impossible for the rebuilder, to assemble it correctly?

Frankly, at this point, I am getting strong vibes that I should sent it to a professional.

Regards
Lou


(tony) #9

you are going ok so far…the brake master cyl seals go bad after about 20-30yrs, and should be changed as a maintenance item, as the pedal goes to the floor!

from your pic, item 3 is the allen key plug, under the cap…then is a little tipping valve, then it all springs apart. You will probably need to place the MC in a vice to get that allen plug out, it may be tight

with a bare master cyl, you can hone it yourself with a drill driven hone, very inexpensive tool, examine the bore under a bright light…any brake place could probably hone it for you for a few $

I recently stripped down a spare unit that came in the boot of a wreck i bought for $300.
Found it had already been sleeved in brass


(Rob Reilly) #10

This is how you get it apart; after you get the allen hex plug out you push the main piston into the bore, you remove the tipping valve on top, and then all that stuff inside comes out. You may need compressed air in the front end to get everything out.

I recently did all the wheel cylinders for my Mark V with one of these brake hones with maroon Scotchbrite then white Scotchbrite wrapped around the hone shoes, and they all came out with a mirror finish.

BTW my parts catalogue shows two screws the same size but does not give a part number for them as they are part of the rebuilding kit.


(Lou) #11

List:

I removed the “Cover” of the Master Cylinder, #1 in the diagram attached to this post. After removing the Tipping Valve Cover Seal, the next item is #3, the Tipping Valve Securing Nut. This holds the Tipping Valve #2, in place. However, the nut on my Cylinder is not what is pictured in the attached diagram. It is the reverse off a bolt. Instead of having six faces above the threaded area that can be turned using a socket, this has six faces recessed inside a hollow tube. I assume the threaded portion is below that.

I assume there is a tool to remove such a fitting but I don’t have one. However, I found a bolt with a head that fits perfectly. Using a vice grips on the thread, I cannot budge it. I left Liquid Wrench in it over night, but to no avail. Should I apply heat from a blow torch? I am a little concerned about the flammables that may be underneath.

Regards

Lou


(tony) #12

That is where the 1/2" allen key is needed, its the same size as the crankshaft plugs

Considerable leverage is needed, some heat may help

if you have welding gear, weld a stout lever on the 1/2" bolt head, otherwise carefully file the bolt thread, such that Stilsons will grab, or a long 12 point ring spanner can be hammered over the end

or buy or borrow the correct tool


(Lou) #13

Tony:

Sorry for the empty email.

Used the 1/2” Allen key you mentioned. And some PB Baster, I was then able to remove the nut with a few taps back and forth on the allen key. I depressed the plunger and the tipping valve came out along with some brake fluid.

The next step in the shop manual is “The remaining parts may now be “blown” out of the cylinder with compressed air.”

Where should I apply the compressed air and where will the parts fly from? After all, are under some pressure from the two springs in the lower channel and the pathways are sealed except for the one containing the nut.

I also remember Frank’s advise………

Being a complete novice, Lou; note/picture/write down each step during dismantling - reassembly is the reverse process. Pay special attention, and note, to the relative position and orientation of parts/seals - bare memory will fail…:slight_smile:

While the usual fault is with the seals, to be changed - but another possibility is the pitting/corrosion in the bore. Inspect carefully; if the bore is not perfect it may be the cause of the leak - and a resleeving is required…

Use plenty of brake fluid to clean and lubricate all internal parts - specs of ‘grit’ is enough to cause leaks.

Assembling will tell if you have the right kit…:slight_smile:

Thanks

Lou


(tony) #14

To the best of my memory Lou, just tap the body of the MC face down on a block of wood, and the springs will push the pistons right out.

I dont think their is any circlips or other obstructions with these, rather the tipping valve is the retainer.

just tap, tap and should see the main cyl working out, it will all pop out as one unit, so be careful

take digipics of seal orientation

there is a mongrel white plastic piece that fits in the small spring that is hard to get back together, avoid taking it apart if u can

I never used compressed air, it would need a fitting to be made up from old or new brake line & fittings


(Frank Andersen) #15

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You blow at the brake line connections, Lou - pushing the piston assembly out…

But as Tony says; it is not usually necessary…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)
**


(Lou) #16

Frank:

Thanks for your reply.

I notice that the rubber gland seal at the open end of the cylinder holds the ten other parts in place. Rather than blowing the pieces out, would it I be wise to depress the primary plunger, and then cut the gland seal. And then slowly release the primary plunger, allowing the remaining parts to be pushed out by the intermediate spring (#14 in the diagram in the manual) and secondary spring. Maybe the secondary spring, valve spacer, spring washer, valve stem and valve seal might need compressed air to get them out .

Lou


(Frank Andersen) #17

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Not during operation in-car, Lou - the mechanical connection between the pedal through the booster and master cylinder holds everything in place inside the cylinder…

The gland seal is just a dust cover, to be removed - and the bits extracted as you describe. Normally, as the parts run in brake fluid, and as the seals faces forward - everything should just slide out. Notice that it is the seals that seals, not the fit of the metal parts…

Frank
xj6 85 Sov Europe (UK/NZ)
**


(Lou) #18

Frank:

Thank you for the explanation. However, the confusion is my fault because I did not mention that the master cylinder is out of the car.

Regards

Lou