Slave Cylinder

[mark westbrookwhite]

On My return from Donington last weekend (Great turn out Guys ) I got home and tried to reverse on to my drive no chance. On inspection I found that the Slave cylinder was leaking. I was working in Wisbech so i dropped into MGB Hive for a new set of rubbers but found that I could have a new cylinder for £15 so i went with that. I fitted it and eventually got all the air out of it but it won't actuat the clutch. if i remove it the cylinder it is moving it just doesn't have enough power.
At the moment I have an MGB slave with a Marina Master which I am sure isn't helping but it was working with the old MGB slave.
Any ideas?

[stevejgreen]

Re: Slave Cylinder

I don't know without a lot of checking, whether there were different bore MGB clutch slave cylinders.
I do wonder though whether you might have reached the limit of clutch plate wear with your combination of master and slave, but I'm trying to work out the logic.
Anyone else?

[cameronfurnival]

Re: Slave Cylinder

My old MGBGT only used to have about 1/2" or so of movement. It was also one that had the nipple on teh bottom and the hose on the top so bleeding it was a bleeding nightmare. I swapped them over. My guess is there is still air in it, they are renowned for not bleeding well. A tip worth trying is to open the bleed nipple and force the piston back by hand

[b_caswell]

Re: Slave Cylinder

Bore Sizes
MGB and V8 master and slave bore sizes differ as follows: MGB M/C: 19mm
MGB slave: 32mm
i.e. a ratio of 0.594:1.
V8 M/C: 17.8mm
V8 slave: 25.4mm
i.e. a ratio of 0.701:1, i.e. more slave movement for a given pedal movement, which seems a little odd as the V8 clutch should be heavier than the 4-cylinder. Ironically the V8 uses the same master and slave as some Midgets. There is also a 22.2mm slave as well so it may pay to try and measure the bore of the new one against the old one. Apparently they quite often come with the nipple in the wrong hole so that it will fit in the box !!............... If the clutch plate is worn then the release point would be earlier in the stroke.

[mark westbrookwhite]

Re: Slave Cylinder

Yes it was a pig to bleed but I did try that trick and got some air out that way I also swapped the bleed nipple and pipe over to no avail. I have an MGB Master cylinder but was reluctant to fit it as the MG is actuated at the top of the foot pedal and the Marina is part the way down.

[stevejgreen]

Re: Slave Cylinder

For reference and more calculations.
Standard Marina clutch master cylinder bore is 1/2"
there are two slave cylinders
Mk1 1.3 saloons - 1"
all other models, vans, mk2, ital etc 7/8" bore

My personal favourite is to use a vacuum bleeder, sucking air out of the slave cylinder. One advantage is only needing to top up the master cylinder, no need for an assistant to press the clutch pedal up and down and then hold it. On the ital cars that had an extended bleed pipe that came from the slave to the rear of the cylinder head, this truly makes bleeding a one man job.

[mark westbrookwhite]

Re: Slave Cylinder

I like the sound of the suction bleeder i will look for one on ebay thanks.

[b_caswell]

Re: Slave Cylinder

Make your own http://www.youtube.com/watch?v=kgpY_oGINU8

[mark westbrookwhite]

Re: Slave Cylinder

Thanks guys as the consensus was that it was very likely to be air in the system i spent another hour on bleeding last night using all the tricks I had been told and hay presto! so it was off into the countryside for a test drive.

PS.Ben I fitted a new set of plugs running much smoother. It still needs the carbs sorting out though.

[stevejgreen]

Re: Slave Cylinder

Pleased you got it sorted. It's not an uncommon problem.
Persistence is a wonderful thing.

I think the suction/vacuum bleeder is more effective because air is more likely to be trapped at the slave end, and it provides constant suction not just a master cylinder quantity at a time.
I don't like the pressure devices that replace the master cylinder cap as whilst you are under the car, there is the potential for brake fluid to escape under pressure over nice paintwork, when you are not looking, something that cannot happen with a vacuum.

Top Tip. A cap from a large sized jar of Marmite makes an ideal replacement for the original Brake master cylinder cap. I have not tried smaller Marmite caps on the Clutch master cylinder. Anyone?

[Mike]

Re: Slave Cylinder

Make your own http://www.youtube.com/watch?v=kgpY_oGINU8

Cracking good tip, Ben! So simple, that we could all do it.

My BMW slave cylinder has the bleed nipple at the bottom, which strikes me as a very poor design as it makes it very difficult to remove the air which will be at the top of the cylinder! The solution is to take the slave cylinder off and bleed it before re-fitting. But this is very difficult to perform from the brake pedal, as its too easy to over stroke the slave piston, either damaging it, or forcing it all the way out.

Using a vacuum bleed jar is such a simple idea - brilliant.

[b_caswell]

Re: Slave Cylinder

Not really roadster subject(wish you could get a BM six in a roadster). The recommended method for BMW is to first bleed the clutch as normal and then dismount the slave and turn it so the bleed nipple is upper most, open the bleed nipple again and push the pushrod back as far as it will go to expel any remaining air. Then refit the slave and press the clutch pedal one more time.

[stevejgreen]

Re: Slave Cylinder

Lets stick with a specific Roadster problem (that's where the thread is located) that frequently occurs not just with Marlin's but with original Marinas and other Marina based cars.
All too often there is a simple commercially available, economic and efficient solution to a problem, rather than resort to a Heath Robinson solution that may well work in a crisis.

[b_caswell]

Re: Slave Cylinder

MMMM Marmite you either love it or hate it!!

[Mike]

Re: Slave Cylinder

Lets stick with a specific Roadster problem (that's where the thread is located) that frequently occurs not just with Marlin's but with original Marinas and other Marina based cars.
All too often there is a simple commercially available, economic and efficient solution to a problem, rather than resort to a Heath Robinson solution that may well work in a crisis.

It is a great idea, and certainly not Heath Robinson at all.

As an engineer, I can recognise it is performing all the functions required of it, cost next to nothing, and applies to whatever car you have, Marlin or beyond.

It was this type of intelligent thinking that got the Apollo 13 astronauts back home safely, so don't be too precious about your Roadster and what is, and is not, good enough for it!