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rgwar
United Kingdom
4 Posts |
 Posted - 03 Nov 2018 : 19:07:31
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I have a Sunbeam Rapier H120 which when I obtained it was supplied with the original bulkhead mounted servo but not fitted to the car.
I have overhauled the servo and fitted it but now when I apply the brakes with the engine running the brakes lock on and will not release until I switch the engine off and pump the pedal a few times.
My problem might be that I have not assembled it correctly as the piston was not connected to the operating rod when I dismantled it.
when putting the rod into the new piston I have put the retaining pin in so that the internal spring draws the rod into the piston rather than pushing it out. Is this correct? I cannot find any information on how this should be assembled.
Any other suggestions as to what the problem might be would be greatly appreciated.
Many Thanks
Richard |
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hillman
France
107 Posts |
Posted - 04 Nov 2018 : 07:22:18
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Hi ,
I do not know if this will help but this is an exploded view of the unit
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hillman
France
107 Posts |
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rgwar
United Kingdom
4 Posts |
Posted - 04 Nov 2018 : 09:38:35
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Thank you for that. An excellent diagram showing all the spring locations very clearly. Unfortunately this is not the same as my servo which is a Lockheed remote servo Type 6.
Since my original post I have now found a diagram of my servo which shows I have assembled it correctly but this does not solve my problem of the brakes sticking on.
I now suspect either the air valve piston or the main piston are sticking in their bores.
Any comments would be welcome.
Thanks
Richard |
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pruyter
Netherlands
320 Posts |
Posted - 04 Nov 2018 : 10:31:13
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Hi Richard,
I have experienced several times with Lockheed servo's on Sunbeam Tigers that indeed the air valve was sticking with the result that the brakes were hanging on. Fixing this problem needed less than half an hour, it is nothing more than taking out the piston (no need to take the servo of the car) and then do some brake grease (the blue one) on the piston and placing it back again.
Regards,
Peter |
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rgwar
United Kingdom
4 Posts |
Posted - 04 Nov 2018 : 14:28:26
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Hi Peter,
Thanks for that. I agree I think it is the air valve piston. I will have to take the whole servo ff unfortunately as the air valve is underneath the servo on the H120 and too difficult to get at.
I note you recommend the blue lubricant. Is there a reason for that as I would have thought any brake piston assembly grease would have been ok.
I will have a go at this tomorrow and let you know how I get on.
Thanks again.
Richard |
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pruyter
Netherlands
320 Posts |
Posted - 04 Nov 2018 : 14:43:28
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Hi Richard,
I am only aware of blue brake grease from AT, so if other brands have other colours it should be no problem.
Regards,
Peter |
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JPSH120
United Kingdom
1168 Posts |
Posted - 05 Nov 2018 : 08:57:18
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I'm interested to read this, as I have a similar issue with my brakes. When I lift off the pedal, there is a very brief delay before the brakes release. I'll have a go at this and see if it cures the problem.
I don't have any of the blue grease, can I use white PTFE grease for this (which I have got)? |
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pruyter
Netherlands
320 Posts |
Posted - 05 Nov 2018 : 13:27:06
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I mentioned the blue grease because I am used to this grease from ATE, but grease from any other brand will do. So forget about the colour.
Your experience with the very brief delay before the brakes release is typical for a sticking air valve. I guess that the air valve in the servo of Richard's car is sticking much more than usual if the cause is the air valve of course.
Regards,
Peter |
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JPSH120
United Kingdom
1168 Posts |
Posted - 05 Nov 2018 : 13:59:57
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And just to be sure, when we say air valve, it's this bit;
And the bit that is sticking, is the small plunger in the middle. |
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pruyter
Netherlands
320 Posts |
Posted - 05 Nov 2018 : 14:12:52
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No, the piston is below this and with pointed pliers you take the piston out. There is no need for more dismantling than you obviously have done so far.
By the way there should be a spring under the white plastic cover, if this spring is missing than you also get the effect of the brakes hanging on.
If you possess WSM 149 than all the details of the servo are exposed in the K section (brakes) on page 23 in figure 14 (first issue of WSM 149).
Regards,
Peter |
Edited by - pruyter on 05 Nov 2018 14:41:33 |
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JPSH120
United Kingdom
1168 Posts |
Posted - 05 Nov 2018 : 16:53:50
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That's just a library photo, not removed the one from the car yet.
I do have the WSM, so hopefully all will be crystal clear!
Thanks. |
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Sunbeam-mike
United Kingdom
164 Posts |
Posted - 05 Nov 2018 : 17:51:46
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Hey thanks for this. very good timing.
I too have brakes that lock on.
I was just about to spend £135!
Mike
Mike Hooper |
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pruyter
Netherlands
320 Posts |
Posted - 06 Nov 2018 : 07:19:39
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Be aware of the fact that a sticking aire valve piston is only one of the possible causes of brakes that are hanging on.It surely is one of te causes that is often not detected.
Regards,
Peter |
Edited by - pruyter on 06 Nov 2018 07:20:51 |
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rgwar
United Kingdom
4 Posts |
Posted - 09 Nov 2018 : 17:20:41
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Hi Everyone,
I can confirm that the problem with my brakes was caused by the air valve piston sticking in its bore.
It was very difficult to get out and I had to use an airline to push it out as unable to get a proper grip with point nosed pliers. I cleaned the bore with 2000 grip emery and used red rubber grease to lubricate it. (important to make sure the rubber grease is compatible to use with hydraulic systems - such as for installing brake caliper pistons etc.).
It all went back together fine and the brakes now work ok.
In my case when I took it apart the air valve piston was in the out position as if it had been pushed by the hydraulic fluid but the spring in the air valve was not strong enough to push it back in because the valve was sticking.
This results in the back of the diaphram being open to atmospheric pressure and hence with the engine running and creating a vacuum on the piston side the brakes stay applied until the engine is switched off and the vacuum is lost.
Hope this makes sense and helps others who may experience similar problems.
Thank you everyone for your help.
Regards
Richard |
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Topic |
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Remote brake servo problem H120
