Brake servo test.

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boguing

boguing

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How much pedal drop should I expect on starting the engine folks? I've been overthinking stuff again have convinced myself that it's not really working.

It's a petrol engine, vac is good at the top of the hose when disconnected, there's a bit of a chuff noise as the pedal goes down, but the travel on start up is maybe a millimetre. I'm also convinced that the brakes have been better.
 
Press the pedal a bunch of times until there's no vacuum left and the pedal feels hard with not much movement.
With firm/normal pressure on the pedal, start the engine and you should feel it drop significantly.
 
kermit_rr said:
Press the pedal a bunch of times until there's no vacuum left and the pedal feels hard with not much movement.
With firm/normal pressure on the pedal, start the engine and you should feel it drop significantly.
Click to expand...
'Tis wot ah have bin doing, and the drop is tiny, damn it.

I've also found out why the brakes are worse than they were. Wheel cylinder's blown a seal. I've got an order of cylinders and shoes coming and will fit them and pray not to be splashing £150 on a servo once they're in. Faint hope though I fear.

This will teach me. This is the one that I rebuilt every inch of - except the brakes because they were working fine.
 
If the servo is leaking, you should hear it.
Do the brakes actually work? Ie work just no servo? I recall there's adjustment on how much pedal movement is required 'free play' before the vacuum side opens. If it's out of adjustment and not letting the valve open.. could be worth a check.
I can't really remember though, not messed with one in a long time
 
Discovering the leaking cylinder has stopped play. Parts may get here on Friday and I'll resume then.

Very good thought on the adjustment, I'll dive in to the books and have a look. This is why I was puzzled - there is a slight movement when the engine starts, the servo makes the hiss noise when you press the pedal (engine off) it's just not effective in either the pedal drop, or. I'm convinced. in the actual braking. I think that it must have got worse so slowly that I haven't really noticed until now.
 
If you have the std series servo now is a good time to fit the early 90/110. Its 1" bigger, I fitted one a few months ago and its noticably better. If you get the aftermarket one it has a M10x1.25 thread on the clevis so you can unscrew it and fit one (you'll have to tap it) to fit the series pedal and you need to make an adaptor plate. Servo was about £70, clevis £5, M10x1.25 tap £5 and the plate was a few hours work. There's some more info on TerriAnne's pages.
I've still got the old servo kicking about in the shed if you're interested.
 
I fitted a new servo to mine a few years ago, (Britpart) the improvement to braking was significant but when I did the test I couldn't detect any pedal drop at all. However, the better braking was undeniable. I reckon Rob is right, an upgrade to a bigger servo is the way to go if you can afford the time and expense.
 
Does the petrol still have the vacuum reservoir as diesel , when mot man concerned about servo I connected direct from servo to intake manifold he liked that better as movement more pronounced
 
The servo is the same, petrol or diesel.
On proper engines, vacuum comes from manifold, on diesels it comes from a vacuum pump i believe
 
kermit_rr said:
The servo is the same, petrol or diesel.
On proper engines, vacuum comes from manifold, on diesels it comes from a vacuum pump i believe
Click to expand...
My series had the proper 2286 Diesel engine in with vacuum from manifold including a steel bottle as reservoir near washer bottle
D0388C34-878A-46EB-9F98-B5169C31DBE6.jpeg

Now I have the 200di in just from the standard pump
 
Petrols don't need or have a vacuum reservoir, the vac pipe goes direct to the inlet manifold just below the carb. 2.25 diesels have the vac pipe to the far end of the inlet manifold just behind a butterfly valve which is closed when the engine is idling, this causes vacuum in the manifold. When the throttle is opened the vacuum butterfly opens too and the vacuum would be lost, so the reservoir tank is provided to store the vacuum already made. More modern diesel engines such as the 200 engine have a mechanical vacuum pump to provide for the servo. A much better arrangement.
 
Extreedoc said:
Petrols don't need or have a vacuum reservoir, the vac pipe goes direct to the inlet manifold just below the carb. 2.25 diesels have the vac pipe to the far end of the inlet manifold just behind a butterfly valve which is closed when the engine is idling, this causes vacuum in the manifold. When the throttle is opened the vacuum butterfly opens too and the vacuum would be lost, so the reservoir tank is provided to store the vacuum already made. More modern diesel engines such as the 200 engine have a mechanical vacuum pump to provide for the servo. A much better arrangement.
Click to expand...
there is little vacuum at idle hence the butterfly on the diesel ,to mimic a petrol, at higher revs there is,
 
Well. That turned into a bit of a game. All I wanted to do was get the brakes adjusted.

As I mentioned, new cylinders, shoes and springs up front, then got doubts about the servo. Bought a new one and thought I might as well give the m/cylinder a refresh, so bought a kit. (New m/c being £350....). Get home, wrong kit, back to the lovely chaps at Dunsfold to eventually discover that I have the 1" bore 109 m/cyl on my bench. Rebuilt that yesterday and got it all back in this morning.

Now when I was bleeding the fronts the flipping shuttle valve triggered and no fluid would come out, but because the light isn't on and the test circuit works I'm kind of hoping that it's reset itself. Mindful of that I decided to do what you're meant to and bleed front and back simultaneously (to avoid tripping it again). Now I've got awkward steps in the workshop right where the car is parked, so decided it would be easier just to take the wheels off to get to the adjusters and bleeders. And am met with a very damp looking drum. Take it off. Just like the right front.

IMG_20201013_152018795.jpg


Back to Dunsfold for more cylinders and shoes. Why didn't I do these on the rebuild? I suppose because the brakes were working fine, and when I had the drums off all looked well. Passed its post build MoT with flying colours too. Losing two cylinders (maybe three, haven't looked in the other side yet) in a couple of thousand miles I guess points to old seals and lack of use.
 
That looks like a hub seal, I would certainly change those, are the seal lands removeable, if so do those at the same time.
What does it taste of? EP90 and brake fluid are very different.
 
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