Remote brake assist servo - how they work

[minorissues135]

Hi, can anyone explain for me the operation of the remote brake servo? I have got mine out, and am about to replace it with a new one. I was hoping the old one would be seized but that doesn't seem to be the case. Can't find anything on youtube about remote servos, only those with the brake pedal as part of the device. If I can better understand how it works, I might be able to tell if it was faulty. As the running of the engine is still less than perfect, something along the lines of an aha (!) moment, such as air leak etc would be great.

I opened it up and the rubber diaphragm looks ok and the remote piston is moving. The odd round plastic piece on the side was missing something that might just be a cover - I think that's the air inlet to allow atmospheric pressure in.

I get the basic principles, that vacuum from the inlet manifold on one side of the diaphragm, is used along with air at atmospheric pressure on the other, to assist the movement of the piston. I'm not clear on where the valve would be that allows the air in to the higher pressure side when the brake pedal is pressed?

Thoughts appreciated.

[Bill_qaz]

https://mgaguru.com/mgtech/brakes/bt201 ... 20pressure.

Follow above li k to how it works

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[minorissues135]

Brilliant thank you!

[geoberni]

https://mgaguru.com/mgtech/brakes/bt201 ... 20pressure.

Follow above li k to how it works
3000118_995.jpg

That site is a great resource, I've learnt loads from that website in recent years, including how to quickly check the Coil polarity is correct if you have any doubt.

[Nickol]

I am never certain whether the servo assist in my Traveller is really working. Is there a way of testing it? I suppose the vacuum is the key element as without it , the thing simply does not function. I did install a repair kit which does not seem to make any difference but perhaps I am expecting too much?

[Bill_qaz]

Remove the vacuum hose from servo end and plug it, brake fluid can still pass through servo but without diaphragm assistance. Compare this brake feel with when the pipe is normally connected.
When working correctly the effect is dependant on what ratio servo is fitted.

[Nickol]

Thankyou for hte tip - following your advice and some UTube videos, the servo assist is definately not working.

I suspect the vacuum and will investigate....somehow...

Ratio servo???

[Bill_qaz]

Thankyou for hte tip - following your advice and some UTube videos, the servo assist is definately not working.

I suspect the vacuum and will investigate....somehow...

Ratio servo???

Yes servos come in different rates of assistance known as the ratio


Typically; a ratio of around 1 to 6 is achieved i.e., 1 kilo of foot pressure on the brake pedal will achieve around 6 kilos of brake pressure at the wheels.
 EG: Lockheed remote brake servo. Made in the UK. Add on kit for single line brake systems. 1.65:1 boost ratio, 7" servo unit, fitted to many cars in the 50's 60's and 70's.


Make sure the air control valve is functioning, its this that let's the air to one side of the diaphragm to activate the assistance. If you take the cover off you can push in the centre pin and get someone to press brake and it should push back against the pin with hydraulic pressure (don't have engine running)

Screenshot_20240510-213201_Samsung Internet.jpg (34.72 KiB) Viewed 187 times

[Nickol]

As a tidy up to the thread.
I did perfom the various tests and it seems the servo is working but perhaps not as expected when comparing to a modern system. So either I am expecting too much or there is something alse not quite right.. In any case the car does stop when asked to and indeed on the downward leg of the rather nasty hills around hier.