Binding brakes this time.

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Post by Tinker man » Wed Jun 27, 2018 12:59 pm

hi,

you could just take the hose off the servo to eliminate the servo operation perhaps (probably have to blank the end of the pipe when you remove it)

or would that not work? easier tan removal and dismantling.

regards, Ian


If it is made of nuts and bolts I WILL take it apart..... going back together is a whole different ball game

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Post by scimjim » Wed Jun 27, 2018 1:16 pm

Rev Light wrote:
Wed Jun 27, 2018 12:27 pm
Have you changed your servo to an after market one - Lockheed?
SE6, so not a remote servo like yours Steve.


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Post by scimjim » Wed Jun 27, 2018 1:17 pm

Bikergonebald wrote:
Wed Jun 27, 2018 12:41 pm
.... the previous owner has replaced the master cylinder, he said something about it being off a "rover" but was bought ready machined to fit.
That would be my first suspicion then.


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Post by Bikergonebald » Thu Jun 28, 2018 12:33 pm

I checked things last night but with everything cold and it jacked up with no wheels on.
The pushrod coming out of the servo protruded by 24.7mm but the recess to the master cylinder rod was only 21.6 so I thought this could be the problem, I made up a 3mm shim which was as much as I had material for. Pressing the pedal hard and releasing they didn't bind, doing this with the engine running they did bind until I turned the engine off. So a good indicator that it could be the servo. The servo rod is adjustable but I can't hold the shaft to adjust it without stripping the servo.
Looking at parts manuals the servo on my car is more like the 6B than the 6A (look at the position of the vacuum connection), I called QRG but they can't get rebuild kits for these servos but they didn't think it would be a servo fault and wondered whether it could be a servo from a different car given the problem with the pushrod length.

Can anyone help me by checking the pushrod length on another servo and the recess in to the master cylinder. The photos should give you an idea of how I measured them.

Thanks.
Kevin
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Kevin

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Post by Bikergonebald » Fri Jun 29, 2018 5:37 pm

I just went for a test drive with a 5mm shim fitted, brakes worked fine and no dragging but the pedal was low. 3mm shim fitted instead and the pedal was near to where it should be and no dragging.
However with the radio off I noticed a continuous hissing when I touch the brake and sometimes even after I release the pedal. I know this will be the air being drawn in to the servo but I think it should only be while pedal is going down and not continuous, right?

If I push the brake down with the engine running then turn it off the brake pedal pushes back up instantly, I think this means I’ve got a leaking diaphragm, right?

With rebuild kits not available and servos costing £300 I need to be sure I get the right one and I don’t know if mine is standard. Can anyone send me a photo of a standard Se6a Lockheed servo and master cylinder?

Thanks.


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Post by AndyKing » Fri Jun 29, 2018 8:18 pm

It's worth checking that the brake servo is able to fully release on the pedal side and isn't being held slightly pressed in. There is a valve in the servo that opens when the pedal is pressed to allow air in, which is what provides the assistance.

This may not be the cause of course but you never know.

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Post by Bikergonebald » Sat Jul 07, 2018 8:05 pm

Well I stripped the servo and after some searching got hold of a rebuild kit. Today I put it back together, quite a simple job and I had all my photos and a servo parts manual diagram. Without instructions to guide me I put a smear of red rubber grease on all of the seals as it went together.
While it was apart I adjusted the output rod to suit my master cylinder.
Now that’s it’s back in I don’t get any servo assistance at all. Should I have put grease on the seals?

Any other ideas?


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Post by rebel alliance » Sat Jul 07, 2018 9:16 pm

Non return valve faulty...maybe stuck shut ?



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Post by Corky » Sat Jul 07, 2018 10:41 pm

If this was a change that occurred with use, ie not immediately after the new MC was fitted by the PO. It’s unlikey to be anything to do with MC. They either work properly when fitted or bind the brakes due to incorrect adjustment of the servo locating pin. On failure of an MC you need to pump the pedal to make them work, they don’t lock up or bind the brakes.

If I’ve followed this thread correctly, I think by spacing the MC you are masking another problem.


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Post by Bikergonebald » Sun Jul 08, 2018 8:34 am

Hi Steve,
Since studying how the servo operates I’ve been thinking that could have been part of the problem. A significant air leak on the input shaft could cause the servo to pull the brakes on but it can’t have been the only problem because the brakes would stay locked on even after the engine was stopped. It might have been enough though to make the brakes over heat and lock up leaving me stuck at the side of the road.


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Post by Corky » Sun Jul 08, 2018 9:23 am

The small difference in the length of the servo locating pin and depth of the primary piston recess is enough to hold the brakes on. But if this was OK when the new MC was fitted, it suggests that the locating pin extended outwards during use. In my mind this would point towards a servo problem.

I have a couple of primary pistons on the bench taken from genuine Reliant supplied MCs and will measure the depth of the recess for you. If yours isn’t deep enough, they are easy enough to drill out a touch with a 6 or 7mm bit (IIRC). At least if you get it to factory spec’ you can discount the MC.

I’ve not heard of a Rover MC being used before, but I believe it’s a 22.2mm bore, which should be fine. But you may have an MC from a Sherpa Van, which could have a bore of anything from 19mm to 24mm. This would alter the distance that the pedal needs to travel.


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Post by Bikergonebald » Mon Jul 09, 2018 8:27 am

I found the problem with the servo not working, when I put the key in that holds the input shaft I'd missed the retaining slot in the shaft so it was in the wrong place and didn't press on the rubber seal. With that corrected the servo is working fine (although I did use a thinner silicone based grease rather than the thick red rubber grease) and holds vacuum for an at least an hour. With the back brakes carefully adjusted and the brake pedal sits at the right height and I can lock the front wheels under braking. So as long as nothing starts to bind on a long journey then all is good.

My conclusion is that there were two faults, the leaking servo was holding the piston slightly forward and the servo output shaft was too long.

I know that the output shaft adjuster hadn't moved by itself as I had to get it really hot to be able to loosen it off to adjust it.


Kevin

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Post by Corky » Mon Jul 09, 2018 7:40 pm

Great news, I hope that’s your problem solved.


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