Brake servo goosed?

[Shoddy]

Hi All

My 71 bay has front discs and servo, although you seem to have to put quite a bit of force on the brake pedal. I've pumped the brake pedal then started her up and the pedal never moved at all.

I have a new non return valve and ordering a fresh length of servo hose. But is there anything I can do to check if the servo is dead?

Cheers
Craig

 

[Trikky2]

Rest you foot on the brake pedal and start the engine. You should feel the pedal go down a little as the engine starts running. If not then your servo isn't working.

 

[Shoddy]

Cheers, did that and no movement. So that's defo a dead servo then? Can't be anything else..?

 

[Bluesnailman]

got your new one way valve in the right way around? also, check/replace the hose if it could be suspect...

 

[Trikky2]

Cheers, did that and no movement. So that's defo a dead servo then? Can't be anything else..?

Well, provided your new non return valve is fitted the right way round, your only other possibility is a blocked or collapsed vac hose - because if the hose were leaking or disconnected, the the engine would not idle (because of the vacuum leak).

 

[kreemoweet]

My brake pedal does nothing at all when I start the engine, and my servo and brakes are working hunky-dory.
So methinks that is not a reliable test of servo function.
Here's a test that would seem to give incontrovertible results: disconnect the vacuum line to the servo (plugging the engine end of course) and compare brake
function to when the hose is connected as normal.

 

[Trikky2]

My brake pedal does nothing at all when I start the engine, and my servo and brakes are working hunky-dory.
So methinks that is not a reliable test of servo function.
Here's a test that would seem to give incontrovertible results: disconnect the vacuum line to the servo (plugging the engine end of course) and compare brake
function to when the hose is connected as normal.

You have to apply the brakes several times with the engine not running to use up the residual vacuum in the system first before doing the test :lol:

 

[Middleton]

I have the same issue.

I have checked for vacuum leaks with a smoke machine but I couldn't find any.

I don't think my servo is broken because the brakes do work better with it connected. I also did the other test where you have your foot on the brake pedal with the engine running, then turn the engine off and keep the pressure on the brake for 30 seconds to see if the pedal stays in position. Mine does and apparently that means the servo is OK.

Does your idle speed increase when you press the brake? Mine does but I'm not sure if that's really supposed to happen or not.

I have an 1800cc Type 4 engine with dual Weber 34ICT carbs, with a balance tube connecting them but also teeing off for the brake servo.

 

[Trikky2]

I have the same issue.

I have checked for vacuum leaks with a smoke machine but I couldn't find any.

I don't think my servo is broken because the brakes do work better with it connected. I also did the other test where you have your foot on the brake pedal with the engine running, then turn the engine off and keep the pressure on the brake for 30 seconds to see if the pedal stays in position. Mine does and apparently that means the servo is OK.

Does your idle speed increase when you press the brake? Mine does but I'm not sure if that's really supposed to happen or not.

I have an 1800cc Type 4 engine with dual Weber 34ICT carbs, with a balance tube connecting them but also teeing off for the brake servo.

If your idle speed increases and stays faster when you apply the brakes, then it's a sign the vac is leaking after the main vac valve in the servo. Such a leak will be either the shaft seal or the diaphragm or, in rare cases, the servo casing rusted through.

The leak, not being very large, will still allow the servo to function but at reduced efficiency, due to loss of vacuum.

If on the other hand the idle speed rises but only briefly and then settles back to normal, then it's not leaking.

 

[Middleton]

Thanks for that info Trikky. Just to confirm, my idle rises when I press the brake pedal and stays up until I take my foot off the brake pedal, when it returns to normal. From your description, it sounds like I need to make some repairs to my brake servo!

 

[Trikky2]

Thanks for that info Trikky. Just to confirm, my idle rises when I press the brake pedal and stays up until I take my foot off the brake pedal, when it returns to normal. From your description, it sounds like I need to make some repairs to my brake servo!

Yes I agree, it needs fixing. Let me know how you get on.