Honing clutch/brake cylinders

[Mark]

I recently replaced the clutch master cylinder seals on the Vitesse as it started to grate going into reverse. Checked under the rubber boot and could see fluid. Bought new seals for both master and slave, but having moved the engine back it's impossible to get to the slave without removing tunnel etc. Clutch master seals replaced, and all seemed good for a few weeks, then gradually sensed I wasn't getting as much travel on the peddle, and over a few days the biting point became a nats off the carpet. 

I had to leave everything for few weeks whilst having a hernia op, but last week removed the interior and found the slave was leaking. This was s new County version, probably 10 years old, and around 1000 miles, disapointing. Stripped it down and the seal appeared in good condition, but there was wear on the top half of one side of the bore, where I assume the piston had been rocking on its travel creating the wear, which could be felt. 

I found a couple of old Girling slave cylinders, which I sand blasted. The bores in both felt a bit rough so thought about honing. I have numerous brake and clutch masters, most 3/8 and a couple 0.7. I could only find one Honing tool small enough to fit the 3/8 bore and also expand enough to hone the larger slave bores.

Never used one before but easy to use, and to get a consistent light cross hatch. 

Then I started to think!

I know this method works well on engine bores to get a good seal with the rings, but what about with rubber seals? Isn't it better to have a silky smooth bore, otherwise it's going to wear the rubber. The hone is very fine.

I re-fitted the slave cylinder and have got good pressure with no leaks coming past the piston seal in the bore. However I found another leak from the clutch pipe, (copper), the female end has been squashed and not seating right.

What's your thoughts on honing brake / clutch cylinders. I know it's been done for years, so assume it's effective, despite my thoughts of if acting like a cheese grater on the new rubber seals.

Here's the honing tool and finished bore.

Edited November 5 by Mark

[Ade]

For something of that size I would err towards a flex hone tool https://pacehigh.co.uk/index.php?route=product/category&path=6767  and lots of light oil to flush as you hone.

 

The issue with honing using the flex hone tools is that they tend to follow the surface profile, so if you have a deep gouge you will end up polishing it. 

[Mark]

I did look at that type of honing tool but couldn't find one of the correct diameter. The one I purchased (pictured) goes from 13mm to 64mm, I think overpriced at £21, but appears to work ok.

[Escadrille Ecosse]

Recovered a few m/c's over the years with a tool just like that and plently of light oil to lubricate and flush.

Does the job for me.

[Nick Jones]

I think you used the right tool Mark. Hope it works!

Some of the current seal kits are not that great. Fluid going black (with shed rubber/carbon from rubber) in the m/c is an early indicator that there’s trouble coming.

 

[rogerguzzi]

Hello All 

              Try these people for seal etc used them 10+ years ago on front brakes seals and S/S pistons and still good!

 

Home - Bigg Red

roger

 

 

 

 

[Nick Jones]

+1 for anything caliper related. Not sure if they do M/C seals or wheel cylinder seals as well?

[Mark]

Honed both clutch slave and master cylinders and fitted new rubber kits. Good pedal pressure took it for a quick drive everything good. Left the interior out over night. Next morning tried the clutch, couple of inches of pedal movement before slave push rod moved. Bu**get. Next press there wss full movement of slave. Found a Girling bleed nipple as the one fitted was from the crap county slave cylinder. Bled the clutch again. I am using Automec silicon fluid, so pricey, and pissed off I've use nearly half a litre, although, most recovered,and once filtered and left to sit I'll re-use it.

Good clutch pressure again. Wedged the clutch pedel down, and left the system pressurised for half an hour after making a mark on the push rod. Nothing had moved, took the car for a drive. All good. Refitted the interior went for a long drive. It was good to give the car a long drive after a month off due to clutch issues and hernia op.

Got in the car this morning, no clutch. Couple of pumps, good clutch again and went for a drive. Air must be getting in the system somewhere. Tried two masters and two slaves, honing and swapping in the new rubber seals.

So reluctantly just ordered new clutch slave and master cylinders. Could only find county master cylinder, but found a Bastuck made slave cylinder.

So interior out again and have another go when the new cylinders arrive. 

Can't remember ever having this problem in the past. Go to the local car spares shop, buy a Girling rebuild kit and good to go for the next ten years. 

[Escadrille Ecosse]

Bugger

[Nick Jones]

That’s really frustrating.
 

Perhaps worth noting that none of the brake/clutch part reconditioners will warranty parts used with silicone fluid. It’s not considered lubricating enough.

It’s also my observation that aftermarket cylinders and seal kits are no match for Girling originals. Even the ones claiming to be the originals are not as good as once were.

[Mark]

Tempted to empty the silicon and use DOT 4 to see if it makes any difference.

I think the problem with the 1" clutch slave is the county version had an obvious 1/2" long wear mark on one side of the bore, push rod end, around 1000 miles use, which could easily be felt. 

So the piston is tipping and wearing the bore, and presume when the wear is bad enough the piston tips and oil passes the seal. The seal looks and feels like new, and apart from wear on one side, the bore is good.

Two of the four old Girling slave cylinders have the same wear mark.

If I had a lathe and the skill I would consider cutting a grove around the piston, and fitting a self lubricating plastic split ring so the piston couldn't  tip in the bore.

[JohnD]

Mark,

"Silicone" brake fluid is DoT 5.    DoT 5.1 is glycol-based fluid of exactly the same spec, while DoT4 has a lesser boiling point.

DOT 4	230 °C (446 °F)	155 °C (311 °F)	≤ 1800 mm2/s	≥ 1.5 mm2/s	glycol ether/borate ester
DOT 4+	230 °C (446 °F)	155 °C (311 °F)	≤ 750 mm2/s	≥ 1.5 mm2/s	glycol ether/borate ester
LHM+	249 °C (480 °F)	249 °C (480 °F)	≤ 1200 mm2/s[15]	≥ 6.5 mm2/s	mineral oil
DOT 5	260 °C (500 °F)	180 °C (356 °F)	≤ 900 mm2/s	≥ 1.5 mm2/s	silicone
DOT 5.1	260 °C (500 °F)	180 °C (356 °F)	≤ 900 mm2/s	≥ 1.5 mm2/s	glycol ether/borate ester
DOT 5.1 ESP	260 °C (500 °F)	180 °C (356 °F)	≤ 750 mm2/s	≥ 1.5 mm2/s

From the Wiki, https://en.m.wikipedia.org/wiki/Brake_fluid

If you're going to change, 5.1 is a better bet.

John

[Escadrille Ecosse]

Hopefully the clutch fluid isn't going to get anywhere near the boiling point of water, let alone lowly DOT 4

Edited November 12 by Escadrille Ecosse

[Mark]

I replaced the clutch master and slave cylinders with new items and now have a clutch. It takes disconcertingly little effort to press and the bite point is just off the floor. My gt6 mk2 takes more effort, both have 5/8 masters, but probably down to the relative age of the pressure plates. 

I examined both refurbished master and clutch cylinders, honed and new seals, and definately no evidencd of any leaks.

I then re-examined the clutch pipes I made. The first was the original one I made years ago with no issues. When I reused it to fit the refurbed cylinders it leaked at the slave end. I made a new one using the same cheapish flaring tool I bought years ago. When looking closely the flared ends look more mushroomed in shape, and wondered if this was not sealing properly. I found an old original clutch pipe, the last of the three pictured, and it has a smaller rounder profile, and felt like it went in deeper in both cylinders. I was going to retry the refurbed cylinders with the original pipe, but as the new cylinders had turned up, and I was getting fed up of crawling around on my knees, just fitted the new ones. 

I really suspect the problem was the clutch pipe not sealing properly, but I couldn't see any evidence of leaks and the reservoir level stayed the same. I assume a tiny leak could cause the loss of pressure. 

I'll use the master cylinder on the Spitfire at some point, to try it out.

[Escadrille Ecosse]

4 minutes ago, Mark said:

but as the new cylinders had turned up, and I was getting fed up of crawling around on my knees, just fitted the new ones. 

A perfectly reasonable response . Glad it is now functioning.

4 minutes ago, Mark said:

I found an old original clutch pipe, the last of the three pictured, and it has a smaller rounder profile, and felt like it went in deeper in both cylinders.

I have noticed similar with my ancient cheapo QH flaring tool, there is a bit of finessing needed to get the flare just right. And I actually think the steel and copper/kunifer pipes behave slightly differently too.

[RedRooster]

I never could get kunifer pipes to bend where I wanted them, gave up went with copper.