Brake Servo Piston Removal

[rogerotto66s]

1966 Austin Cooper S

I am attempting to rebuild my brake servo.
At this point I am trying to remove the two pistons which are quite snug!
In the image below they are #8 and #35.

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What options do I have to remove them without damaging anything?

[cmiller]

Have done many servos and you will have a hell of a time getting them out if they are corroded in place. I just did one that had been sitting for over 40 years and was able to get the upper one out but the lower one #35 was hopelessy frozen in place rendering the body junk. Try your favorite penetrant oil and a lot of patience. Heat can help some times but remember that there are a few plastic parts at the bottom of #35 that could be damaged this way. The biggest problem is there is no easy way to grab these parts and pull them out. Good luck.

Chris Miller

[InnoCooperExport]

Just to agree with Chris above, number 8 is real pain in the proverbial to get out if it doesn't want to. I can second soaking it in penetrating oil. I can't now remember if I got it out with air pressure or heat... I think heat, but IIRC there is a seal kit that includes the seal that goes on that piston. In the end I didn't rebuild mine as it needed honing and the specialist I asked to do it said they often need sleeving as well by which time it cost more than a new one...

[Peter Laidler]

Thinking of it as a mechanical problem on my feet and without the benefit of having one in front of me - except in my car - I'd ask whether you have a repair kit. If you have, and the servo is stripped except from the piston rearwards I'm minded to suggest that: I'd do all that the others have suggested with oil and a bit of heat for several days. Note; a BIT of heat because uneven heat can play tricks on uneven tubular items such as this.

Then I'd make a brass bush that fitted down to the stuck piston. Bore a hole centre hole down through the centre of the bush
Mount the body in a lathe OR carefully on a drilling table and drill through the stuck piston through the centring hole in the bush.

Time taken 45 minutes

Remove the brass guide bush and tap a suitable coarse-ish(?) thread into the stuck piston and wind the piston out. NOT with the thread in the stuck piston but by using a length of threaded rod threaded into the new piston thread..

Alternatively you could use the threaded rod as a slide-hammer shaft.

A new piston is simplicity itself to machine-up afterwards.

Would welcome comments but like I said, I've just got the workshop manual and Lockheed manual to work from. But if everyone comes up with an answer, you'll solve it! Good luck

[TECH396]

I can't remember if the seal is solid behind that piston, but years ago, we installed a grease "zerk/nipple in the end of calipers, then used a grease gun to push out the seized pistons.
You can create a LOT of pressure this way...... It might work for you here if that cup seal is solid.

[cmiller]

Paul's idea will work great on a caliper piston. The pistons in the brake servo both have holes through them so you probably will not build up any pressure to pop them out.

Chris Miller

[cmiller]

Just reread Paul's idea. Yes there is a solid rubber seal in front of the lower piston that blocks the hole in it. Grease pressure from the front of the servo just might work. Now to find a zirk fitting to screw into the front hole of the servo body.

Chris Miller

[Peter Laidler]

Easily made Chris. It's a standard UNF thread too. But I think that once the pressure gets up it'll cause the rubber seal to pop and shear at/through the hole. Depending on how hard the piston is stuck of course. Comments?

[rogerotto66s]

Another member recommended Power Brake Exchange (California) that rebuilds servos.
I told them about my stuck pistons and sent pictures of my disassembled servo.
They fe l confident they can rebuild. The estimate is $380-450. The high side comes into play if they need to re-sleeve the cylinder.

I have not been able to locate a “new” servo. All major suppliers indicate unavailable.

Someone also recommended a “penetrate oil” and being patient. Their favorite was “Kroil”. I will begin with this approach for now.

I will also try to locate a “zirk” fitting and try this “non-destruction” approach.

Thanks for all the suggestions.

[rogerotto66s]

Well .... I got lucky!

I sprayed WD40 into the piston cylinders and let sit overnight.
Then used a small socket to hammer one of the pistons (#35) and it did move slightly.
More soaking with WD40.
Then compressed air loosened and shot the entrapped pieces across the room.
Took us more time to find the missing pieces then it did to remove the pistons!

For the second piston (#8) we were able to use a tap to grab onto the piston and it turned in place.
We did this for a while and then used compressed air and the piston came out.
This time we were sure to cover the hole so as not to have another hunting expedition.

Then cleaned the entire slave cylinder body and removed some crude from within the cylinder.
Still a bit pitted but much better than it had been!

Then sand blasted the end cover and valve housing. Looks pretty good.

Next step is to send to Power Brake Exchange for the rebuild.
Not sure I can avoid a re-sleeve.

I will post pictures shortly.

[InnoCooperExport]

I was very lucky that my preferred brake rebuilding company had a Benditalia servo in new condition on the shelf they were willing to let me have for less than the cost of rebuilding my original Bonaldi (Benditalia bought Bonaldi in the 70s, so odds are most Inno's are built with either, they built the Lockheed Mk1 Servos with their own name on the body), which they then applied a club discount on top for me too.

The quoted rebuild cost was around 400 euros, so not much different from your price given in the States there Roger.

[rogerotto66s]

Ready to send off for a rebuild.

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[cmiller]

Glad you got it to work. Patience and creativity are needed skills when restoring a Mini. I would suggest finding an electroplating shop that still does bright CAD plating. The plated parts look so much better than painted.

Chris Miller