So I have been diagnosing brakes that the peddle slowly goes to the floor when the truck is shut off. Well I finely traced it after all these new shoes,pads, wheel cylinders, master cylinder down to the vacuum pump facing down on my 90 it seems to be leaking oil n makes a sucking sound when I press the brakes without it running. With the truck running that one pump is making 4 inches of vacuum now the other one is making 16 inches.

What should it be making overall?

 

about 20 the one making 4 is done get a new set

 

I removed the lower vacuum pump on mine (made a block-off plate out of aluminum and used RTV under it) and still saw about 20 in. Hg. with the side pump only.



For a pump diagnosis, put the vacuum gauge somewhere you can see it and push the brake pedal with the engine running. The vacuum will drop momentarily but should pick back up if you hold the pedal down. You only need to have above 8" to keep the warning/parking brake light off.

 

I upgraded to the IC style vacuum/power steering set-up and see 25" no problem. The old Non-IC style unit used to push out about 21" of vacuum.

 

I plan on doing the same. Not to mention, the i/c style vacuum pump can be resealed for far cheaper than the non i/c vacuum pumps cost to replace. A $160 replacement, by the way.

 

I tried just the one good one to see if it would tell me if that was the problem brakes still felt weird but not as bad so.

I was thinking of the ic style pump but whats all involved in the swap just unbolt old bolt on new n hook up the lines?

 

A single non-I/C diaphragm-pod vacuum pump in working order will provide more than sufficient vacuum for the truck's brakes alone.

The reason Dodge/Chrysler saw fit to include TWO diaphragms (and something rare for a manufacturer to foresee anymore) was to provide not only enough vacuum for the trucks functions, but also to support a vacuum-over-hydraulic trailer-brake system, which were common when these trucks first came into being.

The later I/C inline rotary-style vacuum-pump barely provides enough vacuum VOLUME to handle the needs of the truck, let alone keeping the big tank on a trailer under constant vacuum.

Where vacuum is concerned, you not only need a strong enough vacuum, but many functions also require a certain VOLUME of vacuum to acheive whatever work that is being performed.

Many functions will work under rather low vacuum "pull", so long as there is sufficient vacuum volume to finish the chore.

29"HG is a perfect vacuum.

Once 29"HG is acheived, no matter how strong the pump, that is as far as she goes; after that, things start to collapsing, if they haven't already done so.

Most decent vacuum-pumps IN A LEAK-FREE SYSTEM will acheive and hold between 20- and 25"HG, with a shiny new diaphragm holding probably 27"HG.

The warning stickers on vacuum-over-hydraulic trailer systems say not to move the truck/trailer when under 15"HG is showing.

 

When you install a double-pod vacuum-pump engine in a Ford truck, alas, you must do as jimbo has shown and eliminate that bottom pod, as it interferes with the massive engine cross-member on the Ford.

Although I lament the sacrifice of that bottom pod, I fabricated brackets and run the trailer's system off of a belt-driven unit.


The single engine-mounted pod holds about 22"HG for the truck system and the belt-driven pump holds about 25"HG for the trailer system.

 

Okay if I ran one pump that's making about 16-17in of vacuum and put a vacuum canister on it would that work over the two pumps my brake peddle still sinks with only one pump hooked up.

 

Rockauto carries remans...Mark

 

I have to retract my previous statement about the cost of the non i/c vacuum pumps. Mark mentioning Rock Auto helped me recall when I was looking around on their site the other day, I noticed that the non i/c vacuum pumps only run about $80-$90.

 

Yeah try local $150 through my account at the parts store. and $450 for i/c one

 

Here they are for around 95 bucks plus shipping...Mark

 

I looked at em a few days ago I just don't wanna wait till they come in to drive my truck I'm addicted to that torque n dads 96 215hp model ain't quit cutting it.

 

Rock auto is pretty fast shipping, even internationally. I had a part shipped to a small town in Mexico and it got there in like 4 or 5 days. ...Mark