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MG MGB Technical - Brake servo fitting

I am fitting a genuine Lockheed servo to my 72 BGT, exactly as per the optional item that wasn't fitted as an option to mine new.
The instructions say point the valve downwards but pictures of B's in the varuious books, including Original MGB, show the valve pointing up.
It won't fit down anyway because there seems to be no enough room to clear the valve.
Are my fitting instructions wrong and the pictures show how it actually should be fitted?

Your instructions, technically, are not wrong. Air valve at 4 or 5 o'clock is accepted as better for bleeding purposes. Originally, as you rightly observed, the valve was fitted at approx 2 o'clock. Fitted at this angle many find bleeding the servo slave an issue. Both my V8's are fitted with servo's as per factory installation, chichis the only way they physically fit due to the windscreen washer bottle. I have got round the bleeding issue by installing a bleed nipple on the end of the slave, and used a double banjo, as per picture.

Allan Reeling

Lockheed after-market instructions how the valve in the lower position, and the cylinder angled upwards as it leaves the vacuum chamber, whereas the factory fitted the air-valve uppermost and the cylinder horizontal. The former possibly reduces the likelihood of the air-valve sticking (a known problem that can cause the brakes to stick on to a varying degrees), the latter possibly aids bleeding.

Factory fitted in my roadster I do get the brakes sticking on slightly in hot weather, although only when travelling slowly such as touring lanes on club runs. Never had it in my V8. The only 'problem' I have to deal with in bleeding is that it needs a two-stage process. First low-pressure such as from a gunsons EeziBleed to fill the system, which always leaves a long and spongy pedal i.e. air in the system, then high-pressure bleeding where someone presses down on the pedal as hard as they can while I rapidly open and shut each caliper nipple in turn, which always blasts more air out. The nose of the car has to be higher than the rear. After that they are fine.

However be aware that the factory servo (the remote one on single-circuit brakes) only adds very light assistance. I've driven a V8 with it disabled, and couldn't tell the difference even though I was looking for it. I've also driven a pal's car and had no idea it didn't have a servo until he told me.

There are various Lockeed Type 6 servos which fit our cars. The usual ones supplied these days are the lowest boost ratio, 1.65 : 1. These were the ones usually fitted to 1800 B's. and I've had both assisted and non assisted 1800's and I have to agree with Paul, it's hard to tell the difference It would seem however, having had this discussion with Paul previously, that Leyland didn't seem all that consistent on which Lockheed Servo they fitted to V8's. The one fitted to my V8 from new, and one or two others I have worked on, is a 2.3 : 1 and you do notice it's absence. If you have the choice get a higher ratio unit.
See chart for varieties.

Allan Reeling

Interesting topic, and the comments from Allan and Paul lead me to hesitate, as I was about to order a servo for the '73 BGT which does not have one. As a point of order, just how good should my front brakes feel? - I don't remember our roadsters in the '80s being hard to arrest, but honestly after putting in new master cylinder,expensive new pistons and having the calipers overhauled, I can feel little effect from the front brakes. What's the best way to test the front brakes (apart from the obvious!), as a preliminary to deciding whether servo assistance would be worth it?
Thanks for raising the topic Mr Neckieman. Regards, John.
J P Hall


Fitting a servo won't improve your brakes, it will mean that you don't need to press the pedal quite so hard to achieve the same effect.

You should still be able to lock the brakes without a servo.
Dave O'Neill 2

Exactly Dave, but having a higher boost ratio, besides requiring less effort on the pedal with standard pads, allows the use of harder more fade resistant pads, which do require more of a push.
John, the front brakes do 65-70% of the braking. If they weren't doing their job you really would notice, in a big way!
Allan Reeling

I want the factory version, my brakes are very good and the only reason I wanted the servo was to even out the difference from the modern cars by reducing pedal pressure slightly.
I can't get the servo to fit at the angle the lockheed instructions say, hence the question when comparing factory fitted versions fitted upwards.

Allan, I've had problems in the past with bleeding my remote servo and think your solution of fitting a double banjo and a bleed nipple a really good idea. I assume that the standard banjo bolt for the servo (C5192A)would not be long enough - what bolt and bleed nipple did you use?


Andy Robinson

Got it off the internet from Trevor Howell,, it is a Harley Davidson item I seem to remember, item 14187881728, Venhill dome head banjo bolt. It is 3/8" UNF.
Allan Reeling

Personally I wouldn't fit a remote servo to an MGB. As others have said it makes very little difference to the pressure you have to apply to the brake pedal (unless you get a high ratio one as Allan described). The brake pedal will also feel "softer" with the servo, with a longer travel. I drove a 1971 MGB without servo as my everyday car for 12 years and never had a problem swapping from that into our modern family car. The MGB's brakes, while they won't stand the car on its nose like some over-servoed moderns, are perfectly adequate for the roads today. They are actually large brakes for a car of that weight.

The remote servo adds unnecessary complication, makes the brakes harder to bleed, and when the servo gets old it can let you down in spectacular fashion. A failing remote servo can suck the brake fluid and hold it in its case without you noticing until suddenly you have no fluid left, and no brakes at all. This has happened to a number of MGB owners.

Still, lots of MGBs have them and seem to get along OK, but I wouldn't bother.
Mike Howlett

Very well put, Mike - you've summarized my understanding of this issue better than I could have done myself. So for me, it's leave well alone, but try to find out whether my front brakes can be made more effective. Maybe new and better discs ... Yours, John.
J P Hall

"You should still be able to lock the brakes without a servo."

Exactly, on an MGB at any rate, and with progressive pressure from high speed. Of course grippy tarmac and sticky tyres will make locking that much less likely, but you should still be able to lock them by banging them on.

If you can't, then maybe your pads are too hard i.e. intended for competition. I can't really see that discs will make a difference unless it is fading after heavy use that is the problem. You may also need to consider whether you have incorrect brake components giving the wrong ratio of master to calipers.

There is also the possibility that, for whatever reason, you are not able to apply the pressure to the pedal that MG expected. In that case a servo, and one of the higher ratio ones, should make life easier.

I don't know about a servo making the pedal longer and spongy as some say, as it doesn't change the ratio of master to calipers. All the servo does is make it easier to move the pedal a given distance. The pressure between master and servo will be less with the servo, but after the servo will be exactly the same.

Allan, thank you, I have ordered a Venhill dome head bleed nipple double banjo bolt 3/8 unf thread, so I can modify my own remote servo.

Mike is correct that the remote servo can if faulty drain the brake master cylinder and cause catastrophic brake failure. To overcome this possibility, I have fitted a brake fluid level alarm made by Bob Owen at TE Electronics - see web site below.

Andy Robinson

Andy, Just mount the servo slave cylinder as far "nose up" as you can get it.
Allan Reeling

I prefer to mount the servo on the inner wing rather than the L/H side of the baulk head, more room, less pipe run and better to secure the pipes, as they don't have to go right across to the other side of the car.


This thread was discussed between 17/01/2017 and 20/01/2017

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