Brake Servo Rebuild

[shirelets]

I'm rebuilding the Mk2 servo following failure with brake fluid entering the inlet manifold - which gives lovely clouds of white smoke and makes you think the engine has blown! I've sourced a hydraulic cylinder seal kit (readily available around £30) and luckily having the air cannister seal etc in a box of redundant parts bought from a pal in Solway Jag. OK, I could spend £250 on a new servo, but I'm technical and rather like a challenge! At least I thought so ...

Workshop manual (proper Mk2, not Haynes) fully describes sequence, but most difficult thing is to measure and set clearance between hydraulic piston and air piston push rod - needs depth gauge and compounded by fact that can't insert it via hydraulic cylinder with innards in place as return spring has solid cap rather than hollow as shown on exploded diagram. Then there's the new air cannister seal which is rubber, unlike the manual which describes the original leather one (and the rope expander that goes inside it) which should be soaked in oil - not a good idea with rubber!

I can take a punt at all this with a bit of engineering guessork, but if anyone out there DIY or 'trade' has ever done a rebuild and can provide some helpful advice, especially as regards setting that pesky clearance, it would be much appreciated!

Phone number is 01768 881894 if anybody prefers to chat rather than tippy tappy!

[Martec]

Hi,
When I first rebuilt my MkII about 12 years ago I replaced the hydraulic seals and set the push rod position using a vernier caliper down the barrel of the hydraulic cylinder , first with it hard up against the seat and then by trial and error kept dismantling and adjusting the rod position.

It was just a punt as there was corrosion in the big vacuum drum. Last year in France we also started using brake fluid, 2 litres later got home.

As the drum was now past its best I sent it to J & L Spares of Rochdale 01706 44210 (recommended by Ken Jenkins) who rebuilt it with a new drum and air valve. I found them very helpful, maybe worth a call.

Brian

[shirelets]

Thanks Brian. I had already called J&L who said they basically bin the old air piston / seal / rod assembly and replace with their own more modern version. They also said to ignore the servo rod clearance specified in the manual which is too small, but instead they set 'by eye' so that the rear of the air piston is between 5 and 10mm below the rear flange of the air cannister. Seems quite a range compared to the +/- about 0.5mm servo rod clearance specified in the manual so a bit surprising, though their own innards may be more tolerant of course. So really not a lot of useful information, but I would get a replacement from J&L if mine fails to work when reassembled in a few hours time .....