master cylinder brake vs mc clutch

[Hawkscoach]

I tried to find this answer with no luck, 59 AH 100/6 bn4. I am planning on honing the MC's (have one rebuild kit from Moss). I removed them a few years ago and now ask myself, "which one is brake and which is clutch?" they both appear to be the same, with the exception of one having a "slightly" different "end" internally...........I know this is probably a dumb question. thanks again in advance and I am always asking questions of you guys..............Doug - Also, please note that the front brakes are disc and it is a very late 59

 

[bob hughes]

Doug

I.M.O. honing of the MCs is not an option that I would like to take up, tolerances for the rubber seem tight in my experience when re- building them. I have had some failures (and that is without honing) and had to replace the units completely.
Get them re-sleeved by an engineering firm or replace with new.



Bob

 

[Superwrench]

They both should be the same. Bob is right, re-sleeve them or replace them. :eagerness:

 

[Keoke]

They both should be the same. Bob is right, re-sleeve them or replace them

 

[Hawkscoach]

Bob, Keoke, & Super..........many thanks. Will replace. Regards, Doug

 

[Patrick67BJ8]

They both should be the same. Bob is right, re-sleeve them or replace them

I'm sure this question is in the back of everyone's mind that's been around a while..."what are honing tools for"? (if we're buying new cylinders)

 

[57_BN4]

"what are honing tools for"?

Cast iron wheel/master cylinders- only. And only in a bygone era where resleeving wasn't available and new parts were only available from OEM at OEM prices, if at all. They are a desperation-fix tool that has no place in a modern workshop.

 

[Hawkscoach]

wow. guess I should have asked this before spending time cleaning and $ ordering trying to save original parts.......................it is/was a good question Patrick.

 

[Patrick67BJ8]

wow. guess I should have asked this before spending time cleaning and $ ordering trying to save original parts.......................it is/was a good question Patrick.

I have been told that there's a coating on the inside bore of the aluminum cylinders and you could remove it with a honing tool and that's the reason not to use the tools, but on the other hand a friend who repairs cars today told me that if the bore is "smooth" just install a kit in it. How much material can you remove due to honing that would make the bore no longer useable? I used to repair big Healeys for extra back in the '70's and did brake jobs and never had a Healey come back with a leaky brake/master cylinder and "I honed them all".

 

[57_BN4]

Eventually the gap between the piston and cup seal becomes big enough to allow the (highly compressed) rubber to be squashed into the gap and get 'nibbled'. Sometimes you see cups that look like a mouse has had a chew at the outer edge- this is the cause. The cups can wear on the rough surface too- black chunky brake fluid is a sign of honed cylinders.

You can hone and reuse ali cylinders but their useful life will be much shorter than new/resleeved. Stainless steel sleeved bores will last indefinitely, even if they are neglected and for about the same price as a low quality replacements you can have the originals in better than new condition. Andy.

 

[Hawkscoach]

Does that mean I should replace the slave cylinder as well??? I assume, however, thought I would ask first. thanks again, Doug

 

[bob hughes]

Doug

If the master cylinders and the slave cylinder do not work then some thing has to be done, have you tried them? do you know that they are no good? if they are duff then you could try just cleaning them up on the outside, clean out the inside with a small artist's brush and brake fluid and re rubber them. If they are sound then just clean them up on the outside and refit them. I have had varied success with re rubbering - the slave cylinder was fine, but the clutch MC failed after about a year, so I eventually bought a new one and then swapped the MC's over on the engine rebuild so the newer one is now on the brake.



Bob

 

[Hawkscoach]

Thanks Bob! All the MC and the slaves were seized. I carefully pushed the piston in and with some penetrating fluid and pressure, they broke free. From where the piston was to the "outside" it is rough. Inside, where the piston travels, the bore is smooth and not pitted. I like to use as many original parts as possible, however, anytime there is a safety issue, I replace. It just seems that I am replacing so much..............this is a total restoration and I am putting components back on the car now after several years of work.................I cleaned the outsides and used the air hose and parts cleaner so they look good. I only purchased one rebuild kit from Moss, then decided to ask the honing question. Doug

 

[Patrick67BJ8]

Thanks Bob! All the MC and the slaves were seized. I carefully pushed the piston in and with some penetrating fluid and pressure, they broke free. From where the piston was to the "outside" it is rough. Inside, where the piston travels, the bore is smooth and not pitted. I like to use as many original parts as possible, however, anytime there is a safety issue, I replace. It just seems that I am replacing so much..............this is a total restoration and I am putting components back on the car now after several years of work.................I cleaned the outsides and used the air hose and parts cleaner so they look good. I only purchased one rebuild kit from Moss, then decided to ask the honing question. Doug

Since rebuilt kits are being sold I wonder what MOSS is giving for instructions? To hone or not to hone?

 

[steveg]

You don't hone aluminum master cylinders. If you clean it up and the coating on the bore is uniform and has no scratches or streaks, rebuild it like that. Or sleeve. Or buy new.
You can see if there is any problem with the coating.

Reference: see page 5 of this auto shop class textbook pdf:
https://tinyurl.com/lojd986
or
https://www.sanjuan.edu/webpages/ja...nder, Caliper & Wheel cylinder Service TB.pdf

Note: earlier in the pdf they say shiny areas on the anodizing are "not a defect" as they're just caused by rubber polishing the anodizing.

They also say seizing is caused by petroleum product contamination of the fluid, causing the rubber parts to swell.