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Post by colin on Jan 20, 2024 21:23:12 GMT
I have a question regarding my servo. It isn't providing any braking assistance, and I assumed the diaphram is leaking. I was about to pull it out and get it rebuilt at a brake shop, but I notice when I suck on the tube there is a solid vacuum....i.e , I can't suck any air. I'm wondering if the problem really is in the servo. The brakes are even, just require lots of pedal pressure. Previous to this the engine idle speed dropped when applying brakes, but since I disconnected the tube from the manifold that problem stopped.
Now I'm confused.
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Post by dave1800 on Jan 20, 2024 23:58:22 GMT
Hi Colin
The manfold vacuum is typically between 9.5 and 10 psi at idle. i doubt very much whether you could suck a fraction of that through the servo vacuum pipe so it may not show up a diaphragm leak. What I do know is that the Mk11 crab brakes only require a light pressure to operate them. Road test reports always decribed them as light and powerful.
It may be a good idea to havethe brakes checked on a rolling road. I assume that this is covered in an equivalent of the UK annual MOT test in NZ?
David
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Post by 1800heap on Jan 21, 2024 0:07:49 GMT
Hi Colin Unfortunately not all servo problems are as easy as that! Some things to help you with diagnosis are as follows. The engine idle will be effected by the servo when you apply the brakes, that is normal. Generally, when the servo has vacuum, there's a slight hiss from the unit as you apply the brakes, but this should stop once the brakes are on. No continuous hiss! That would be a sign of a bad diaphram. Run the engine for a short time, which should put a vacuum in the servo if it is working. Stop the engine and wait for 30 seconds or so. When you apply the brakes after the engine has been stopped, the servo will operate generally twice if it is in good working order. In other words two presses of the brakes with servo assist. At this point the vacuum will be exhausted and the brakes will become unassisted. With my 1800 this means, first press of the brakes they will have assistance and work normally, release them, second press generally still has good assistance, release them, the third press normally will be unassisted and the brakes are not very effective at all. Panic stations if you are going along at any speed! This difference is very obvious in the feel of the brake pedal on my 1800! You can actually test the difference in brake effectiveness with and without servo assistance in this way with gravity. Park on a hill that is steep enough for the car to roll slowly. Obviously great care must be taken with this as the brakes really are rubbish without the help of the servo! Run the engine and turn it back of. Let the car roll engine off. Two presses should stop the car effectively and in general the third press you will need to press hard to stop the car. The greater the difference the better the servo is working. Take care with cars that have a steering lock and remember where the hand brake is!  Edit Any doubt take David's advice and go with the rolling road test! You should also note that the servo needs to be the correct type for the car to work correctly. Nick I have a question regarding my servo. It isn't providing any braking assistance, and I assumed the diaphram is leaking. I was about to pull it out and get it rebuilt at a brake shop, but I notice when I suck on the tube there is a solid vacuum....i.e , I can't suck any air. I'm wondering if the problem really is in the servo. The brakes are even, just require lots of pedal pressure. Previous to this the engine idle speed dropped when applying brakes, but since I disconnected the tube from the manifold that problem stopped. Now I'm confused. |
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Post by 1800heap on Jan 21, 2024 0:49:20 GMT
Hi Again Colin.
It just occurred to me, in case you are unaware Colin, Australian cars are dual circuit, unlike UK cars and only the front circuit has assistance on the dual circuit setup.
I must admit thinking about it, I didn't think my Australian crab had as effective brakes as OKR from the UK. I had not checked they were in good order though and took it off the road after I picked it up!
Nick
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Post by dave1800 on Jan 21, 2024 12:52:36 GMT
Road tests of Australian MkII cars fitted with PBR brakes suggested they were not quite as effective as the UK Girling versions fitted to earlier OZ crabs but I don't recall any criticism of them being heavy. I assume the NZ cars were assembled in Australia?
Nick's MkIII UK car OKR would have heavier brakes than the MKII as less braking is applied to the rear drums.
Worth checking the front caliper pistons are moving freely, but there should be a very noticeable difference with the servo connected.
David
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Post by colin on Jan 25, 2024 5:13:54 GMT
Thanks everyone, for those comments. Lots of good advice to think about there. I'll check the front calipers are moving the pads and the servo is working.
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