1988 E350 7.3 ide.
I seem to have lost power boost on the brakes, what should I look at first as I have never had this problem before on any of my trucks.
I'm not familiar with this system.
Yes, all new brakes recently, fluid is up, belts are good.
Started as intermittent, now no power assist.

 

I had this problem on a truck I had. really ticked me off. Have you checked the master cylender? is it leaking at the firewall? could also be in the master cylndr. somthing about the diaphrams. now that was a slightly newer truck but the first thing I would check is that.

 

vacuum pump

 

Is there a way to test the vacuum pump?

 

Pull the vac hose off the brake booster. Put your finger over the end and see if the hose sucks to your finger.

There's more formal specs if you do a search. I'd check the vacuum tubes first and see if there is a leaky hose or connection somewhere before replacing the pump. Also check to see if the belt is in good shape. I'm not sure if its the same as in a truck, but on my 88 the vac pump is directly below the alternator. A short belt runs between the two.

If the vac pump tests out ok, the booster may be at fault.

 

I will check it tomorrow and post my findings, thanks!

 

I pulled the vacuum hose off the booster and not having a vacuum gauge or knowing how much vacuum it should have I put my thumb over the hose and I can feel the pump pulse, but I kind of feel that it really doesn't have a lot of suction to it.
It pulls on my thumb but not really a good strong suction that snaps to it.
Any ideas or specs on how to do a more refined test than using my thumb as a gauge would be appreciated since it's $189.00 here locally for a pump and a miserable job to change so I don't want to start throwing parts at it.
By the way, I checked some old posts on this subject and noticed that some guys had been having trouble with their cruise as well.
I did notice surging on my cruise control at the same time this problem started.

 

If you can connect a vacuum gauge then a new pump will pull 22in and a decent old one around 18in.
If you put the palm of your hand against the end of the pipe with engine at idle it should feel like it is going to suck the skin off of your hand.

 

For a more accurate test of the pump itself, trace the hose coming off of it, and disconnect that at the first connection. Comparing that to a test at the booster will tell you in there is a leak someplace in the system.

 

Good point, this thing doesn't feel like it would suck the skin off anything ya know?
Guess the doghouse comes off.

 

Just courious of your findings....I started having an issue on my 92 E350 yesterday. Seemed to be only when it was raining but I had a hard pedal and no stopping. I'm planning on switching over to a semi-metalic pad tomorrow (someone thought the organic pads had issues with wet/humid weather)....Let me know

Thanks,

Joel

 

My truck has stiff brakes but I think that is normal. I do have to put some leg into it if I want to stop quickly. I would say vacuum pump if the brake system looks good. Check the hoses and connections. I second testing the pump with a vacuum gauge.

 

I took it up to the IH truck repair in town and had them replace the power steering pump because I'm to busy and it's a crappy job to do on this van anyway.
They checked out the vacuum pump and although for what ever reason they don't have a vacuum gauge, they are pretty certain it's the pump.
Auto parts want's $189.00 for it here but there are some on eBay for around $90.
So if the shipping isn't too high I may try that, I'm just worried about part compatibility. When I get it changed I'll post my findings.
I have ALL the services records for this van because it belonged to a fire department, seems it's had issues with brakes for awhile, and the ambulance service center just kept putting new drums, rotors, lines, and calipers over and over.
Missed the problem entirely.
BUT, I won't have to worry about brakes for a good while!

 

You didn't post the hard pedal in the other thread. Just that it wasn't stopping right. Thats two totally different symptoms there!! If the pedal is hard to push, the booster system isn't working right, and it makes no difference what kind of pads you have. Check your vacuum system!!

The wet or humid might be causing to belt to slip, is this a V-belt or serpentine system?

Save your money, don't change the pads yet.

 

If you have a hard pedal and no stopping power your vacuum pump has taken a dump. You guys should look into switching to hydroboost.