10 replies to this topic

[djsmith74]

Hello,

 

Does anyone have any experience with, or can point me towards a rebuild guide, for the later model brake servo (the one with the master cylinder bolted onto it)?

 

My master cylinder blew a seal and has been leaking fluid into the brake servo itself. I've rebuilt the master cylinder, but find that any information regarding stripping and building the servo is almost non-existent (even in the Haynes manual) despite the availability of rebuild kits. Looking at the servo itself, it would appear that the back plate is secured by 'tabs' from the housing itself, so I assume it's a case of loosening these tabs and it should come apart?

 

Thanks.

[rally1380]

Hello,

 

Does anyone have any experience with, or can point me towards a rebuild guide, for the later model brake servo (the one with the master cylinder bolted onto it)?

 

My master cylinder blew a seal and has been leaking fluid into the brake servo itself. I've rebuilt the master cylinder, but find that any information regarding stripping and building the servo is almost non-existent (even in the Haynes manual) despite the availability of rebuild kits. Looking at the servo itself, it would appear that the back plate is secured by 'tabs' from the housing itself, so I assume it's a case of loosening these tabs and it should come apart?

 

Thanks.

 

No. It twists apart. 

 

Those tabs are left in place and the two halves of the servo unscrew from each other.  Takes a bit of effort and isn't the easiest thing in the world but that is how they come apart.  I've actually got one split apart at the moment, if you don't have any joy with images off internet land then drop me a PM and i'll take some shots for you.

 

When I say 'unscrew', they don't take much to 'unscrew' them.  

[Steve220]

They're an absolute f£&@ to get back together too when you put the new seal in.

[Swift_General]

Internals are fairly basic, and the rebuild job should be fairly straightforward. I've had 3 apart now and have found the trick with splitting the halves is to firmly clamp the front of the servo (via the 2 studs that hold the master cylinder). Make sure they are clamped (and prorected) all the way to their base as they have to resist quite a large torque and could otherwise bend. Then use 2 prices of stout angle or box tubing secured to the 4 studs on the rear (i.e. 2 studs to secure each peice). They should be positioned 180 degrees apart and need to be at least 2 feet, better still 3 feet long and used these to twist anticlockwise idea to release. Reassembly is the reverse of disassembly as they say but I use a little grease on the diaphragm where it's clamped by the 2 halves on reassembly (red rubber grease of course) although I think the rebuild kits include some rubber grease from memory.

[slidehammer]

When I did mine I used this guide as a guide it is for a Triumph Servo but they work the same way.

http://www.buckeyetr...Servo/Servo.htm

They are indeed a bugger to get apart, rust gets on the flanges and they grip the rubber diaphragm, stopping the two halves from twisting apart. Once apart and the rust cleaned up I used red rubber grease on the areas where the flanges meet the rubber diaphragm and then reassemble was pretty straight forward and could almost be locked back together by hand. Good luck.

[djsmith74]

Many thanks for the excellent & helpful responses. I will give it a go this weekend. The servo doesn't look too bad but my only concern was the effect of the brake fluid to the internal seals of the servo, hence the reason for stripping it down and wanting to clean it up properly.

 

Thanks & much appreciated.

[Narrowwater]

My servo has stopped working but the brakes work fine you just need to press harder.  How easy is it to replace the brake servo on my 1992 City E?

Edited by Narrowwater, 10 March 2017 - 04:21 PM.

[Steve220]

Quite straight forward, there's enough flex in the brake pipes for you to move the master cylinder away when you undo everything. Get yourself a Haynes manual if you haven't done already.

[tiger99]

Brake fluid will not have damaged the servo seals.

[Narrowwater]

Yes I have a manual and was trying to work out if the brake master cyclinder had to be disconnected or not from the brake pipes, sounds like it might be a good idea and then bleed the brakes after putting it back together.

[Deeppockets]

I have just rebuilt my servo after having replaced a sheared master cylinder stud.  Without a dedicated tool I improvised using the servo mounting bracket.

 

• Screwed serval nuts onto the master cylinder studs for gripping the servo half-case in the bench vice
• Assembled the parts (twice after initially forgetting the spring). I found the unit had a good dose of talc inside when I split it (to help protect the rubber diaphram?) so re-dosed with a fresh layer of talc - which should also help dry lubricate the close rotation. Not completely convinced but surely can't harm.
• Using the servo mount bracket on the top of the assembled parts I was able to compress down and turn with the help of a breaker bar through the bracket. With the rubber seal friction the rotation was slow and steady.

 

On the subject of the master cyliner/servo stud torque setting and over-torquing, the MPI manual (RCL0163 v5 p244) states reassembly torque to 14Nm but lists the setting as 25Nm (Brake master cylinder nuts) in the Torque Wrench Settings table p46.  Guess which one I used...