V8 brake servo shambles

dmblbit

dmblbit

Active Member
Cleverly saving money by purchasing replacement servo unit on ebay. How frugal - well done me. However, upon dismantlement (new word!) it appears the piston is seized solid inside the cylinder. Pin that holds arm to piston bent in half on first attempt to remove. All attempts at twisting, tapping and thumping have failed. Have left for over a week soaking in WD40 - still won't budge. have tried heating the outside with blowtorch while trying to twist the piston with a chisel jammed up its percolator. Still no joy. Its too far down to get an ezyout onto it.

I know what I'd like to do with it now - but does anyone have any constructive suggestions?

Steve
 
Hello Steve,

I assume that you removed the back off the vacuum chamber and then detached the push rod from the vacuum diaphram assembly. It fits on a keyway and there is a proper tool and method to use in order to detach it. The push rod then will withdraw the piston from the slave cylinder to which it is attached. That is what is supposed to happen.

Ron.
 
When I pushed down on the diaphragm the key came out very easily with a pair of long nosed pliers. It was the bit where you use the push rod to "withdraw the piston from the slave cylinder . . . . " where I came unstuck. The push rod and piston were inside the cylinder as far as they would go. When I tried to pull the whole thing out, the pin that retains the push rod inside the piston bent double (ahem - some force was involved in this part), and the pushrod came out leaving the piston firmly stuck at the bottom end of the cylinder.

To be honest I think it's done for, but I thought I'd ask anyway.

Steve
 
Hmmm, doesn't sound too crash hot. Try this for size...grab a bleed screw and screw it nice and snuggly into the fitting along the side of the cylinder. Feed a length of plastic hose that is a good tight fit into the threaded end of the cylinder. Attach a bicycle pump to the end of the plastic hose. Have an enthusiastic assistant hold the cylinder with a thumb firmly over the hole where the air contol piston resides and then pump away. I use this method for blowing pistons out of the front calipers, works a treat, they fly out very quickly indeed so keep your fingers clear and watch where it lands.

Ron.
 
That was something I enquired about some time back now. A new MGB cylinder fixed to the P6 vacuum chamber as a cost-saving exercise. I don't recall getting any concrete answers or opinions.
 
If I recall correctly the servo power output is dictated by the diameter of the diaphragm and vacuum chamber and the inside diameter of the reaction cylinder. If you can get those for the MGB servo and your existing servo you should be golden. Just a thought.

Steven
 
I did try Ron's bicycle pump trick, but couldn't generate any air pressure behind the piston - not exactly sure why, but I suspect you need the push rod to be in place to complete the seal. So I reluctantly gave up. I may have another shot at it when I have stopped hating it quite so much.

However, all is not lost. When collecting a new interior mirror purchased via ebay from Gino, I asked if he had a servo and hey presto, he did, and sold it to me for a tenner. He wasn't sure if it was working or not, but as far as I can tell, after a clean up and new seals it will be perfect, so I am considering myself very lucky indeed.

He has a stunning red 3500S with a five speed SD1 gearbox and SD1 wheels. He is very modest about it, but to me it looks fantastic. So, although I am very happy with my new servo, I'm the tiniest bit jealous - it would be nice to have a car I could actually drive . . . on the road, but that seems a very long way of at present.
 
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