Lockheed Servo

Cammsjb · Post by **Cammsjb** » Sat Apr 23, 2022 5:59 pm

BCB24B66-2EA9-42F4-A65E-8AE118BA1627.jpeg

6A5C4777-47B5-4244-9921-A54A26C86B14.jpeg

Advice please,

I have stripped down my 5 1/2” standard Lockheed servo today and discovered a spring approx. 1 1/2” x 1” within the air valve cover next to the diaphram.
I have looked at the BMC workshop manual diagram showing the breakdown of parts for the servo but a spring doesn’t appear to be shown, has anyone any thoughts on why this spring has been fitted?

Two photos attached.

Cammsjb · Post by **Cammsjb** » Sat Apr 23, 2022 6:00 pm

Cammsjb wrote: ↑Sat Apr 23, 2022 5:59 pm BCB24B66-2EA9-42F4-A65E-8AE118BA1627.jpeg6A5C4777-47B5-4244-9921-A54A26C86B14.jpeg

Advice please,

I have stripped down my 5 1/2” standard Lockheed servo today and discovered a spring approx. 1 1/2” x 1” within the air valve cover next to the diaphram.
I have looked at the BMC workshop manual diagram showing the breakdown of parts for the servo but a spring doesn’t appear to be shown, has anyone any thoughts on why this spring has been fitted?

Two photos attached.

Cammsjb · Post by **Cammsjb** » Sat Apr 23, 2022 6:02 pm

Cammsjb wrote: ↑Sat Apr 23, 2022 5:59 pm BCB24B66-2EA9-42F4-A65E-8AE118BA1627.jpeg6A5C4777-47B5-4244-9921-A54A26C86B14.jpeg

Advice please,

I have stripped down my 5 1/2” standard Lockheed servo today and discovered a spring approx. 1 1/2” x 1” within the air valve cover next to the diaphragm.
I have looked at the BMC workshop manual diagram showing the breakdown of parts for the servo but a spring doesn’t appear to be shown, has anyone any thoughts on why this spring has been fitted?

Two photos attached.

Post by **Peter Laidler** » Sun Apr 24, 2022 7:43 pm

I thought that I was going to ride to the rescue on horseback with the answer Cammbs....... Just been through the Lockheed technical manual and there's absolutely no mention the spring at all. The plot thickens...... Sorry

Anyone.......

Oneball · Post by **Oneball** » Sun Apr 24, 2022 8:18 pm

There is a spring in there on the bigger servos used on Jags. Maybe someone got muddled up. They diagrams probably look very similar.

winabbey · Post by **winabbey** » Mon Apr 25, 2022 3:38 am

In case it helps here is a page from the Lockheed Service Manual.

Lockheed Servo Service Manual p09.jpg

Kiwi Craig · Post by **Kiwi Craig** » Mon Apr 25, 2022 4:27 am

I am by no means an expert, but....there seems to be an issue with these servos where they can lock on with a hard application.
I have an issue with one on my Cooper S, that is why it is disconnected.
Could that spring be an assist to the diaphragm # 4 ??
I wonder if the problem is with rubber cup #9 on piston #8.
There was a discussion, maybe on this forum, maybe another, where the brake lock issue seemed to be caused by the cup #9 not being free.
Turned out there were 2 different shaped cups, 1 worked fine, the other caused problems.
The spring may have been retro fitted to solve a problem, but the real issue was as outlined above.

winabbey · Post by **winabbey** » Mon Apr 25, 2022 5:59 am

Kiwi Craig wrote: ↑Mon Apr 25, 2022 4:27 am I am by no means an expert, but....there seems to be an issue with these servos where they can lock on with a hard application.
I have an issue with one on my Cooper S, that is why it is disconnected.
Could that spring be an assist to the diaphragm # 4 ??
I wonder if the problem is with rubber cup #9 on piston #8.
There was a discussion, maybe on this forum, maybe another, where the brake lock issue seemed to be caused by the cup #9 not being free.
Turned out there were 2 different shaped cups, 1 worked fine, the other caused problems.
The spring may have been retro fitted to solve a problem, but the real issue was as outlined above.

I'm also not an expert, just have some possibly relevant documentation.

The exploded parts diagram below shows two different parts for that cup - 3862-439 and 87143. Could they be the different shaped cups referred to?

Lockheed Servo Parts a.jpg

Lockheed Servo Parts b.jpg

Minicooper1964 · Post by **Minicooper1964** » Mon Apr 25, 2022 1:48 pm

Had my Lockheed servo renovated by Past Parts. Suggest you give them a call and ask about the spring

Cammsjb · Post by **Cammsjb** » Wed Apr 27, 2022 8:34 pm

Thanks for all the comments on this subject.

I've spoken to an engineer who overalls period servos, he said the 'retro' fitting of a lightweight spring inside the air valve is fairly common practice as it improves the function of the air valve diaphragm.

TECH396 · Post by **TECH396** » Wed Apr 27, 2022 10:19 pm

As has been said, That spring doesn't belong there, but my guess is someone installed it to resolve a leaky vent valve( atmospheric port) issue.

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