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MG Midget and Sprite Technical - Getting clutch hydraulics right the first time

Hi, all.

I just installed a new clutch master cylinder in my 1500 this morning, along with a new hose. The next step will be a new slave cylinder.

SO - I would love for some of you guys to relate the best way to get everything connected, filled, and bled with a minimum of fuss.

My own thought, and one which I tried this morning, was to connect the hose to the master first, fill the reservoir, and then lift the free end of the hose to allow bubbles to rise and vent while the proverbial lovely assistant (actually our son) pumped the pedal to fill the hose... at which time I capped the end with a rubber plug, intending to pass the down to the new slave only after it (the hose) was filled with fluid and free of bubbles.

That worked okay, but only okay... and while trying to remove a few little bubbles, I only made it worse.

So any suggestions are more than welcome - preferably by parties who have actually done the deed.

Thanks!

-:G:-
Gryf Ketcherside

Gryf,

I use the method descibed by 'Colin in Os' it works well for me - realise its written for 1275's but you may find it use full - think its down to moving the fluid fast and unresticted so the air bubbles do not just move about a bit - my therory !

http://www.spriteparts.com.au/tech/bleeding.html

R.
richard boobier

I've had good luck with a bit of a dodgy method- drain the old fluid, fill it back up, connect a long, clean, transparent hose to the bleed nipple and put the other end of the hose in the master cylinder reservoir. Open the bleed nipple about half a turn, then pump the clutch pedal. Fluid should circulate (though in a 3 steps forward, 2 steps back manner), keep going until all the bubbles are gone.

If you pump the pedal too hard tiny air bubbles can be drawn past the threads of the bleed nipple, watch for that.

This method of course only works if the system is clean, otherwise you're just circulating the nasty old fluid.
Growler

I have had good success with the white box and one way valve thing from Halfords - easy bleed or some such. The clear tube allows you to see the bubbles coimg through. Open the nipple about half a turn, slowly depress and release brake peadal, wait 5 seconds and repeat, taking care to re-fill master until no more bubbles come through - can take alot of fluid.

When apparently finished, good tip is to open nipple, depress pedal and leave it depressed overnight with suitable piece of wood jammed in to keep it depressed. Tighten nipple up before releasing.
Mark O

I'd just bin the bleed nipple on the slave and fit another bit of hose in its place. This new hose then has the bleed nipple in the end of it and can be placed where ever is most convenient for you. All of a sudden most of the faff is gone, and you can bleed the clutch on your own too.
S Overy

The big advantage of the easibleed device is that it provides a steady and continuous pressure to push the fluid through. Unlike when using the pedal, when you get a back and forth movement of fluid in the pipes - and therefore any contained air bubbles.
Guy W

Thanks for all the advice. I'll give all suggestions a shot when I get back to the car. BTW, I have a MityVac that I may try as well. I intend to coat the bleeder threads with grease to prevent air ingress while pumping the MityVac.

-:G:-
Gryf Ketcherside

Just wanted to follow up and provide some closure. I finished the fill and bleed last night, and got the system entirely free of air in one attempt. See the pic below... I elevated the clutch master on some 2x4s to make the reservoir the highest part of the system, filled it, and went below to the slave. There was already some fluid in the pipe, so a couple of pulls with the MityVac and I was essentially done. I tightened and capped the bleeder, refilled the reservoir, returned the master to the pedal box, and worked the pedal a few times. This released a few very small bubbles that collected in the "loop" of pipe behind the MC, so I removed it from the pedal box and elevated it again... then tapped the pipe until the bubbles had worked their way up to the MC, which I then remounted. After working the pedal again, no bubbles reappeared. Sweet.

So I buttoned everything back up and took the car for a drive, sans bonnet... I mentioned originally that I'd been dealing with graunchy shifts into first for the last few years, and sometimes second as well. That's entirely corrected now, and the box slips into gear with nary a complaint. What a feeling...

Anyway, that's how I nailed the clutch bleeding. Hope this helps someone down the road.


Gryf Ketcherside

I've always used a method of connecting the easi bleed to the slave cylinder and cracking the union at the master cylinder until fluid comes out. This then gives enough fluid in the line to allow normal bleeding from the master cylinder. This can all be done without removing the master cylinder and works when the pipe between the master and slave is completely empty after a change of parts.
Andrew Dunn

Interesting, Andrew!

Oh, one nice thing about the new MC that Moss sent is that it's quite easy to access its lower mounting nut with the pedal box in situ, using a long socket extension. As seen in the photo above, the reservoir perches atop the cylinder instead of surrounding it, so the nut is unobstructed.

The only downside of the new one (so far, anyway) is that the reservoir cap ends up quite snug against the cap on the brake MC, making either a little more fiddly to undo. Just a minor quibble, but it bears mentioning.

Cheers,

-:G:-
Gryf Ketcherside

This thread was discussed between 25/08/2012 and 30/08/2012

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