Brakes Servo Vacuum

Hi All Looking for wisdom again
My 2200TC has a brake/Vacuum issue.
I have the warning coming on light sometimes also when braking first press of pedal seems to give a ok stopping force press the brakes again and I could stop on a dime the pedal seams to get harder and little force required to stop. the brakes then tend to stick on give the engine a rev and back to normal.
The PO has had new brakes all round and a new servo however this looks like an after market as it has been relocated by 2 inches back, I cannot find any leaks and have taken the hose off from servo and the engine speed starts to increase
Any advise before I attack with my spanners


Well-Known Member
I had this issue on my TC. Always suspected the rear calipers, but after rebuilding them it felt the same. The problem went away when I rebuilt the front calipers, the pistons were hanging very slightly giving the same feel you describe. I rebuilt them with new stainless pistons and rubber seals and they feel great now.


Active Member
On a P4 ,I had the brakes staying on , when I had the servo sticking, revving up and releasing the throttle will produce more vacuum which may be freeing it again.


Active Member
Right it’s the air admittance valve. The white flying saucer looking thing prize off small cap catching spring as it pops out. Wd40 on plastic sliding bit make sure it slides in and out. Stretch spring a bit put it back and try brakes.
Checked the air admittance valve cleaned and stretched the spring still the same I have a brake warning light on now and the brakes seem to be locking on and not releasing its like driving off with handbrake on.


Active Member
If it has changed the braking I would still suspect it. Might be worth taking it apart and checking the diaphragm. The light could be a sodden cork float in reservoir cap, a duff handbrake light switch or a short somewhere.
Thanks for the replies I have now taken the servo apart and I now know it is a power tune type all looked new inside diaphragms were good the air valve piston took a lot of pressure to release.
Now silly question before I put it all back on the car should the air valve assembly be on the top? mine was on the bottom
When the manual says 7inch is that the size of the drum or the slave cylinder?


Well-Known Member
Hi, Air valve top or bottom? If you read round the internet there's divided opinion about that. One thing I did discover, and this is from memory now, is that on one of the Lotus forums they were having the same problem, they have it on the bottom, and the manufacturer was saying to take one of the 'O' rings on the air valve piston out if there were two. Apparently brake fluid can get between them and the brake pressure can lock it up. So take from that what you will. However I would say mount it at the top because it's easier to maintain or change.

The size refers to the vacuum chamber.

Good day Gents.

looking to buy a servo. MGBD have recon units at £135. see picture .
Does anyone have any experience, good or bad , from them with regards to this unit ? I see others on offer in e bay but don't know any
provenance etc. Could someone steer me to a reputable company at good costs ? Thanks. Rgds, Stuart


Not all applications have the air valve at the lower position, but if you buy a new Lockheed remote servo that fitting guide is included. Or it was in the one I bought a few years ago. I think some installations have a problem with air locks in the hydraulic side.
Hi Cobraboy.

Checked PastParts but they can only do the work on my existing unit. They do look good however.
Due to various issues, of which I wont go into, I cannot do this. I have to have a recond. unit ready to fit and then send the old one back as service exchange. I am waiting for MGBD to get back to see if they have any off the shelf, so really my question still holds
Does anyone have any experience, good or bad , from them with regards to overhauled unit from MGBD ? I see others on offer in e bay but don't know any provenance etc. Could someone steer me to another reputable company at good costs ?
Sorry to be a pain.
Thanks. Rgds, Stuart