QuestionQUESTION: 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?
AnswerAndy, 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
