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In 25 years of Triumph ownership I've never had a car with a Brake Servo, until last year when I finished the restoration of a MKIV Spitfire as I decided to fit one of the usual remote kits available from the usual suppliers. The brakes on the Spitfire work great, but they don't feel servo-assisted but as I haven't got any previous knowledge of how they should feel with a servo maybe I'm just expecting too much. 

Can anyone recommend a series of test to determine whether the servo is actually working.

Thanks

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cant you disconnect the vacuum line to the servo and see if it make a difference?
Or get you friendly MOT man to do a brake test with the engine running or not running  to get more accurate data.

Its shouldn't make any difference to the brake effectiveness but you should feel a difference in the effort required on the pedal.

BTW Do they do modern MOT brake tests with the engine running or not?

mike

Edited by mpbarrett
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7 minutes ago, Nick Jones said:

The usual test is to put your foot firmly on the brake with the engine off, then start the engine. You should feel the pedal sink slightly as the engine builds vacuum.

I had tried this and there is no difference in the pedal feel when the engine starts. 

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1 hour ago, mpbarrett said:

BTW Do they do modern MOT brake tests with the engine running or not?

Running. They tend to leave the engine running for the whole time regardless of whether there is power anything or not. Because they are “keeping cat warm for the emissions test”. Then they moan about the fumes….. Turn it off then F-wit, there is no cat!!!

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Not had much time to look at this, but I did disconnect the vacuum hose from the servo and it made no difference to the brakes, so that confirms the servo is doing nothing. 

From the disconnected end of the vacuum hose, should I be able to feel any suction? Because I don't, regardless of revs. 

A couple of photos before just for reference. 

20220615_161338.jpg

20220615_161344.jpg

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8 hours ago, Nick Jones said:

One of those end connections (or maybe even both) should have a one-way valve in it. This will need to be fitted the correct way around for the suck to reach the servo….

The one way valve is at the manifold end, there was only one way it could be fitted. I'll take it off to see if it's working OK. 

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6 hours ago, Darren Groves said:

The one way valve is at the manifold end, there was only one way it could be fitted. I'll take it off to see if it's working OK. 

That's unusual, unless it is an additional NRV. I have had a number of these in my posession over the years and there was always a non-return valve at the servo end. They can get gummed up.

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19 hours ago, Escadrille Ecosse said:

I have had a number of these in my posession over the years and there was always a non-return valve at the servo end

This. And will be pointing the wrong way if fitted at the manifold….

You say in the first post that the brakes work great (without any help from the servo apparently), so I’d be tempted to bin it….

Tempted to bin the one on my GT6 as I don’t like the jerky action it has.

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21 hours ago, Escadrille Ecosse said:

That's unusual, unless it is an additional NRV. I have had a number of these in my posession over the years and there was always a non-return valve at the servo end. They can get gummed up.

You are correct, the NRV is at the servo end. 

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1 hour ago, Nick Jones said:

This. And will be pointing the wrong way if fitted at the manifold….

I have to admit to being a total numpty and fitting the, what I now know was an alternative NRV, at the manifold end, which of course was pointing the wrong way. 

In my defence the kit come without instructions, so taking the 'I don't need instructions' attitude assumed it was for fitment at the manifold. 

So..... I have now removed the innards of the incorrectly mounted NRV so it is now just operating as a barb. This was done late last night, so I've not had an opportunity to test yet. 

I'll hang my head in shame... :blush:

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4 minutes ago, Escadrille Ecosse said:

Good.

With the hose disconnected are you getting a vacuum at the mnifold end?

We've just posted at the same time....  not had time to test, but I'm guessing it will be ok now... :confused:

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Just now, Darren Groves said:

I have to admit to being a total numpty and fitting the, what I now know was an alternative NRV, at the manifold end, which of course was pointing the wrong way. 

In my defence the kit come without instructions, so taking the 'I don't need instructions' attitude assumed it was for fitment at the manifold. 

So..... I have now removed the innards of the incorrectly mounted NRV so it is now just operating as a barb. This was done late last night, so I've not had an opportunity to test yet. 

I'll hang my head in shame... :blush:

Darren, we have all been there at some point (at least once or twice...or...) :blush:

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We have progress, there is plenty of suck from the hose attached to the manifold, so as expected not having a NRV pointing the wrong way has fixed that. However......as soon as the car is running and the servo has pressurised the brakes are locking on and the only way to release them is pull out the NRV on the servo.

Again I didn't have time to investigate further, though as I adjusted the rear brakes recently could it just be they need backing off a little?  

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1 hour ago, Darren Groves said:

though as I adjusted the rear brakes recently could it just be they need backing off a little?  

Wouldn't have thought so.

I suspect that it's either the master cylinder or one of the pistons in the servo (the brake piston or the air valve piston) that are sticking. Probably one of the servo pistons. If the brakes work and don't stick on when the engine is stopped then I would suspect the air valve piston - or the air valve diaphragm or air valve. If they do stick on with the engine stopped then it's either the master cylinder or servo piston that's sticking.

servo1.jpg.00d9707ed8abbcf7b57bc7c039c253fe.jpg

This gives a decent description about how the contrary object is supposed to function. When it can be bothered.

http://www.mgb-stuff.org.uk/servo.htm

One last question, what type of brake fluid are you using? Reason I ask is that whilst otherwise excellent silicone fluid is less lubricating and is definitely something that will cause a slightly reluctant remote servo to mis-behave. Seen problems with brand new ones as well.

Do tend to come back to what we say which is that with decent Mintex or Ferodo pads, Sptifire brakes are very good without a servo

Edited by Escadrille Ecosse
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The air valve is what sticks  be on my GT6, though it’s slow (then sudden) to come in rather than reluctant to release.

I’d try coming on and off the brakes a few times with the engine running to (hopefully) exercise things and remind them of their purpose. If the brakes release a few pumps after the engine is switched off (ie vacuum all gone) then it’s definitely caused by the servo.

I also recall something about these servos being fussy about mounting orientation and sticking-on being one of the manifestations of this being incorrect. Though having had mine apart I don’t really see why.

It might just be crappy manufacture. Mine did not impress me.

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I don't think it's MC related as it's never stuck on previously when the servo wasn't working. It's mounted on the bracket provided so orientation should be spot on. 

I'll hopefully have an opportunity to look in more detail over the weekend... 

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6 minutes ago, Darren Groves said:

It's mounted on the bracket provided so orientation should be spot on. 

That's just how the PO (who got rid of the thing) had it mounted. Doesn't mean it's correct :blush:

It can be rotated round the bolts on the bracket (the cylinder can also be turned on the vacuum pot).

Nick is right. I would suggest you try fitting it with the air valve on top rather than underneath. That way its self weight is helping open it rather than hold it on. Most installations I have seen have the air valve uppermost. That is how it is shown in the Triumph manual for the GT6/Vitesse.

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10 hours ago, Nick Jones said:

Destructions here…..

https://www.psautoparts.co.uk/userfiles-psak/RLE72696 Fitting.pdf

Though mounting angles etc seem mainly to ease bleeding, which makes more sense.

 

Thanks for sharing this link, I had seen that a couple of days ago and it confirms that I have installed as per the instructions, so angle is correct and the air valve pointing downward is also correct.

The brakes lock on pretty much immediately after starting even without touching the brakes, pumping the pedal doesn't help. I have checked the MC operation and that all seems fine.

 

 

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