Engine not giving break servo enough power?

[cjhillman]

A few months ago when I took my Capri to a garage for a once over they mentioned the reason the Brake servo might not be working is that the engine wasn't giving it enough power (I cant remember the exact term they said) although the engine seemed healthy enough. They mentioned I could test the servo valve if I could get it out by blowing into it... they didnt want to incase they broke it and couldnt find another one.

If the valve is working fine and it is the engine not giving it enough waft... is there anything I can do? I only thought about this again as they other day when I was doing a bit more spirited driving, I'm sure the pedal felt servo assisted for a couple of presses until back to the non assisted feel.

[bmw2101]

has it got cams in it or anything liek that? I had the same problem with my volvo engine, due to the cam over lap, after 2 presses on the pedal and it was hard.

I solved this with a electric vac, but id imagine you have another problem?

[colnerov]

Hi, How old is the servo pipe fitted on the car? Is it proper servo pipe? You could start with leaving the existing valve in place as the connection to the manifold and fitting new servo pipe and in-line servo valve. The old servo pipe could be porous or collapsing in side so losing the vacuum.

Colin

[truckdoctor]

Nov 17, 2022 18:22:40 GMT colnerov said:

Hi, How old is the servo pipe fitted on the car? Is it proper servo pipe? You could start with leaving the existing valve in place as the connection to the manifold and fitting new servo pipe and in-line servo valve. The old servo pipe could be porous or collapsing in side so losing the vacuum.

Colin

I had that very defect, and a new hose fixed it.

[cjhillman]

I guess there is a lot more tubing than I thought of. It seems to run from the manifold to the valve on the servo.



Its an over head cam engine on the Capri. Seems a bit over kill for this engine but what was the electric vac you used on the Volvo.

[nickwheeler]

The valve they're talking about is the white plastic part on the servo body. It is easy enough to pry out to test that it only flows from the engine into the brakes. New hose and generic valves are cheap and readily available, although you might need to make a new fitting into the servo if you go that route.

Has the car has a failed brake master cylinder at any time? Those tend to leak into the servo, which could have rotted the body.

Having looked at your photo again, that's the master cylinder off a 2.8i which is different sizes to the four cylinder cars and could be the problem.

This is a simple and boringly reliable system, so changing it rather than fixing fault will be lots more work and expense than is justified.

The question about the cam was asking if a performance cam has been fitted, which can reduce the engine vacuum at low speeds. None of the milder Pinto cams do this, and the stronger ones don't run well with the stock carb.

[cjhillman]

No performance cams here. I wish it did have something a bit hotter under there.

I will check the piping again first and try pry the valve out. I did think of finding some old (clean) hose pipe to try and test the valve in situ.

I know the previous owner did a landrover master cylinder which is apparently an upgrade, although I've heard the opposite to that. I guess thats why its got that fitting on the end.

Not sure if its ever had a master cylinder leak before me.

[nickwheeler]

Nov 18, 2022 12:00:13 GMT cjhillman said:

I know the previous owner did a landrover master cylinder which is apparently an upgrade, although I've heard the opposite to that. I guess thats why its got that fitting on the end.

It's a needed upgrade if you fit the Sierra sliding calipers and 260mm discs. It's utterly unnecessary with stock M16s.

[cjhillman]

Yeah, as you know I'm just on standard M16s with solid discs. Maybe I should change the master cylinder after checking the hoses and valve.

Not sure if its a job I should undertake myself though... I hate brake fluid.

[kevins]

I would try some decent pads something like greenstuff, a lot of the modern pads sold through the usual motor factors are way harder than was available back in the good old days when you could pack them with nasties like asbestos, on modern cars with boost ratios of 5 or 6 they are fine, on a classic with no servo or if they have one only a ratio of 2 they don't work.

Going to greenstuff on my Elan was like night and day.

[cjhillman]

Good to know. I've got Borg & Beck ones on at the moment. Its not so much the stopping just using it regular around town is killing my leg. I only noticed it a few weeks ago when i'd been out in the Car ever day. Jumping in my Escort mk3 is completely different, it nice and easy to use around town and I don't even think of stopping. I'm sure it should be something similar to that.

[madmog]

I can't see a non-return valve on your piping. Perhaps hidden near carb?

There should be a valve that holds the vacuum in the servo once created so it remains available rather than leaking away. Once apart you can test by sucking each end. Only one end should allow you to suck. Also it needs to be fitted the correct way so low pressure from manifold can suck air out of the servo.

[nickwheeler]

Nov 19, 2022 16:48:19 GMT madmog said:

I can't see a non-return valve on your piping. Perhaps hidden near carb?

There should be a valve that holds the vacuum in the servo once created so it remains available rather than leaking away. Once apart you can test by sucking each end. Only one end should allow you to suck. Also it needs to be fitted the correct way so low pressure from manifold can suck air out of the servo.

It's a Ford, so to save parts and money they combined a one way valve with the hose to servo adapter - it's the white plastic fitting on the body of the servo. The whole vacuum system is so boringly reliable, that a visual inspection is almost certainly enough to start looking other things. Like the 'upgraded' master cylinder.