Land Rover Repair/Vacuum Pump

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Question
QUESTION: Hi,
I am trying to fix the cruise control on my Land Rover Discovery1 1995 and started with checking out the vacuum system, Pump, Diaphragm and Hoses. First the hoses and the Diaphragm, simply just tested per mouth and everything holds the vacuum also the diaphragm works and is not leaking. Then the Pump, I pulled the plug off and hooked up 12.7 Volt direct from the battery. The pump was working and the Diaphragm tightened up to the linkage. While the pump was running I pulled the throttle linkage a bit and simulated accelerating, the Diaphragm again was able to close the cap. But now if I let go the throttle linkage, the vacuum is not able to hold the the linkage in place, in fact it slowly went back to the idling position.
At this point I thought the pump is to old and produces not enough vacuum anymore and I decided to buy an other used pump of a Year 2000 Disco. This new pump looks great and is 5 years newer, so I hook it up and the the result was the same, also this pump was not able to hold the linkage in place.
Now, for me the pumps are looking good, but I have the feeling I miss something. Is there an other source of support to hold that linkage.
Any tips are welcome and appreciated.
Thanks
Andy

ANSWER: Did you check where the vacuum hose goes through the dash, and down to the dump valve above the brake pedal?

---------- FOLLOW-UP ----------

QUESTION: yes, it's a new hose and holds the vacuum.

ANSWER: If that's the case what I would do is clamp off the pump and see if it still leaks.  The pump may have residual leakage when its not on the car and running.  You may be chasing a problem that isn't really there

If so you'd want to trace the electronics next.

---------- FOLLOW-UP ----------

QUESTION: If the pump is off and I suck on the hose, everything is holding the vacuum perfect.
So if I interpret you right, the pump has to be able to hold the vacuum, without any other source of help?
Both pumps I have are creating the same weak vacuum, have those vacuum pumps a second stage, in which they produce a stronger vacuum?

Answer
Andy, I cannot remember when we last changed a cruise pump.  It's been years.  They hardly ever fail.  I can't believe you would have two bad ones in your hand out there.  If the vacuum is tight downstream of the pump I think that points you to an electrical problem.  Here in New England the things we see most often are bad brake switches, and bad contacts where the steering wheel signals come down the steering column.  And - of course - dry rotted hoses under the hood

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John Elder Robison

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I own J E Robison Service in Springfield, MA. We are Bosch Car Service for Land Rover, BMW, Mercedes, and other European lines. I can answer most questions about Land Rover service or repair. I'm known as a car enthusiast, machine aficianado, photographer, writer, and speaker. I've been around Land Rovers and British cars most of my life. Visit me at my car business, www.robisonservice.com or my author website, www.johnrobison.com. Check out my autism and writing blog at jerobison.blogspot.com or my photos on www.pbase.com/robisonphoto John Elder Robison

Experience

I have been a Land Rover service manager since Land Rover returned to North America in 1987. My company is a four-star Bosch Car Service facility, known nationwide for Land Rover service, overhaul, customization, and restoration. In addition to Land Rover our company services BMW, Jaguar, Mercedes-Benz, Rolls_Royce, and Bentley motorcars. We have factory-plus-level service capability for all makes. Visit my company online at www.robisonservice.com > service > land rover Also visit my blog at robisonservice.blogspot.com

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In the Land Rover world, my writing can be found in various print magazines and online at robisonservice.blogspot,com. In the wider publishing world, my work is published by 20 publishers in over 50 countries. Mt books Look Me in the Eye, Be Different and Raising Cubby have made US and international bestseller lists.

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I am ASE certified, Bosch Trained, and trained by Omnitec/T4 and Autologic on their Land Rover test systems.

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