Well I was not going to do this until later this summer but the vacuum leaks had gotten worse so I did change the system. I removed the rear vacuum venturi and associated parts:


I then mounted the vacuum canister and a electric vacuum pump from a Volvo 740:

I added a vacuum cut off switch that switches off the pump at 23 in.hg and back on at 20 in.hg.

For a more complete write-up and pictures in .PDF format go here:
vacuum system redesign

After I return from this next trip, I will run a long plastic line from this system to the front and remove the venturi generator up there, the Volvo vacuum pump will handle both front and rear easily, I will leave the vacuum canister up front for a reserve volume of vacuum.

I forgot to mention, the venturi vacuum generator, Prt # D7HT-19C747-AB is NLA at Ford or Freightliner, I checked around the Western States to try to find one but--
Discontinued part:

I too notice irregular cruise control operation and like your fix. Did Volvo vacuum units come from certain models in the wrecking yard? How about the regulator, was that a new or wrecking yard part? thanks

I got those vacuum pumps at a wrecking yard. I think they all came from the 740 model and it located on the driver's side inner fender.
It doesn't have a regulator and I added a vacuum switch to stop the pump after 23 in.hg vacuum has been built up. In the Volvo application I don't think the pump ever shut down when the cruise control was engaged, I could not find a vacuum reservoir anywhere in the Volvos that that I scrounged the parts from. That vacuum canister that is shown was originally in the Barth, just relocated.

When we head to Nevada this trip, I am going to engage the pump continuously as an experiment, can't hear it. The pump only draws 0.6amps while running under the worse case load. I ran it on the bench for 5 hours and it was just barely warm to the touch. I think I paid US$30 for each pump. I believe I can get more but it will be after I get back from Nevada on May 22.


It has the following numbers:

003 572

Under the name Volvo:
1273226

Pump is made by Hella.

It is a very common pump on Euro cars (Volvo, SAAB, BMW, MB...)for the cruise control and also used by Ford. You can get one on ebay here
http://cgi.ebay.com/ebaymotors/NEW-FORD-HELLA-12V-ELECT...Z33626QQcmdZViewItem
I have replaced a few over the years but they seem to be very reliable when use with cruise control. Not sure how it will hold up to constant use though. On Volvo's the pump is turned on and off by the controler. The pump also has a dump valve that the controler uses to regulate the road speed.
Neil.

Just "googled" the vacuum generator part number and they now seem to be available again for $45.



http://www.ebay.com/itm/Ford-D...enturi-/230788368204

Is this a part that one should pick up before they go extinct again??

MWrench:
Might this pump work for your design?
https://www.summitracing.com/p...=GSAPI+5ba283b27cfaf
(noting the pump has an internal activation switch set at 11 in.hg and deactivation at 15 in.hg)
Or do you possibly have a link to an external switch similar to what you used? Thanks.

A response to a posted question about this pump states:

"I'm sure that it will work for you. It controls the heater controls and the cruise control on my 98 Dodge Cummins. It only runs when you first turn it on for about 4 seconds and then only when you call for vacuum. The main thing is making sure you have no leaks in the system."

The pump/switch i am using works well but it does not shut off when I reach 5K-6K feet. The pump can not pull enough vacuum at those altitudes and is noisy. My switch is set to deactivate at 17 in.hg probably to low for the pump to work well in certain circumstances. It is on one of my "things to do list". later