Well, I've searched as much as possible trying to validate my concerns on my truck. Here are the symptoms:

-in dash brake light comes on occassionally
-Heater controls sometimes stick in the same position (won't go from defrost to vent)
-A/C just stopped working (haven't verified this problem yet).

Before all of the above started happening, I had just swapped out the stock dp for a dpp dp and deleted the cat. I haven't heard any ugly noises coming from the pump, or any grease/oil coming from it. Could I possibly just have a vacuum leak somewhere? Can I verify the vacuum coming from the pump to see if it's going bad? Or does this not sound like a vacuum problem?

Also, any suggestions for the A/C? Was ice cold just a week ago....doesn't seem like it's something related to the other problems I listed.

Don't want my brake assist to go out on my sister with her horses in tow, so I'm looking for help guys. Thanks in advance!!
Ken

 

you can test the vacum pump by hooking a vac gauge up to the single hose coming from the pump. it should have 18 in. hg., it also possible that during your downpipe install you disturbed the vacum reservior on the heater box under the foild insulation, or the tube going to it.

 

Sounds like it to me. I could get my brake light to come on while in park at an idle hit the brake 3 times quick then the brake goes hard. Put a new pump on and it solved the problem.

 

Sounds like you hit or bumped loose the vac lines on the canister above the passenger valve cover. Also there is another vac line that runs an accuator right next to the passenger fender. Normally it's a white vac line. It get's brittle and breaks often. Check that too. Hope that helps.

 

I have a 96 PSD and had to replace the vp twice, sounds like thats your problem.... I had the same symptoms you were talking about both times... but I also agree with rubberduck too.....

 

Thanks for the replies....so there should be definate signs that the vac pump is going out? I think you guys are right about the vacuum lines....I will go over them closely tonight and see if I might have yanked one loose or cut it in the process of swapping my DP.

Love this site!!!

 

I started to have problems with my brakes and saw some oil or grease on the underside of my hood and on the air filter housing. I wasn't sure where the oil was coming from until yeserday. I was on my way home from work and the front of the vaccum pump broke and the pulley wedged itself against the pump and smoked the belt. I shut the truck off and pulled over to the side, lifted my hood and saw the broken pump. I thought it was some type of vaccum pump but I wasn't sure, so I took it off and my wife carried me to advance auto. I told the folks at advance I needed the vaccum pump and they looked for a couple minutes and told me they sell that part. As usual I had to show the dumb a_ _es how to use their own computer to look up the part. I found the part for $98 but they didn't have one in stock, they said it would be the next morning before they could have one, the closest store that had on was an hour away. I didn't want to leave my truck on the side of the road over night so before I drove to pick up the pump I decided to call around to see if I could find one closer. After 30 mins of calling I found one about 20 mins away at auto zone, the pump there was $150. I installed the new part and had the new belt on in about 15 minutes, it was easier to install because there was no pulley on the new pump, and was on my way. I noticed the difference in the brake as soon as I started the truck. I'm not sure if the pump has anything to do with it but the turbo is making boost right off idle now and it didn't do that before.

If the vaccum pump is giving you problems I would definitly change it before you run into similar problem that I had.

Jason

 

Changed mine a few weeks back, nice to have brakes again! Had to get used to driving it with brakes, the first few times I almost put myself against the windshield. I also know that the cruise control must need vacuum to operate because it works now also. Just glad I didn't go to the dealership for the sensor before replacing the pump.

 

The vaccume lines on these trucks are nearing the end of their lives. I'd check those real good before replacing a pump. Mine were so brittle I could just touch them and they'd crumble. And it's been garage kept all it's life.

The brake light only comes on for low fluid right? I'm not sure about 97 models. On my 91 the abs and red brake light came on for low fluid. I think the red light only was just the park brake switch. I'm pretty sure the 97 is the same.
With as many abs repairs and brake jobs as I did at ford I should know this.

Feel the accumulator when the AC is on and engine running. If it's good and cold then it's vaccume related.

I just had to recharge my AC yesterday. It's the first time ever on this truck. It was starting to short cycle and I knew it was low but I put it off. We had to drive to Amarillo yesterday and boy was it a hot ride. I fixed it as soon as we got home. It was just a cheap Oring on the high side.

 

My new '96 f350 is having the same symptoms with and intermittent brake light coming on in the dash. The book glove box manual said it might be fluid, vacuum or something else I forgot. I will be looking over my vacuum system this weekend. Thanks! What does the vacuum pump do for the brakes. Does it run the brake boost pressure?

 

the vacum is used for power brakes. just like most cars but diesel engines don't create vacum so they just use a vacum pump to create it

 

Again, thanks for all the comments. I did a quick inspection with the little time I had over the weekend and found a few vacuum lines to be in pretty rough shape. I agree with the post above that it appears the lines have pretty well shot. I'm going to pick up a spool of it this week and go through it all next weekend....hope it will fix the problem. Didn't get a chance to look at my AC though....hoping this might have something to do with it....because that AC is COLD and very welcome here in TX!!

I am curious about the brake light coming on. The first thing I checked was the fluid because I did my brakes about two months ago...fluid was fine. The few times I've seen it come on is often when I just start the truck and have the brake depressed. Seems in line with a vacuum problem???????

 

if you have a larger enought vacum leak yes the brake light will come on. it comes on when there is not enough vacum for brake assist.

 

How does it come on for a vacuum when the switch is on the master cylinder?

Just wondering if there is another switch for vacuum somewhere that I was unaware of.

 

yes there is a vacum switch on the vacum manifold on the driverside inner fender directly under the master cylinder. that is where the vacum pump line connects and splits out to a varius other places. I believe there is a vacum switch there that lights the brake warning light also.