Bare with me as I'm new to the forums and it might take a minute to get the hang of this.
I have been having issues with power brakes in my 95 F250 for the last couple years now. Problem started off with losing pressure in the brakes after stop and go, and the BRAKE light would come on. Stupidly started with the booster due to lack of research, and of course I get a bad booster from the parts store. Long story short it ended up being the vacuum pump and I got a new one in, after two tries with those. After replacing booster and vacuum pump, everything was well. But, a couple months later, the brake light comes on again and start having the same stop and go, losing vacuum pressure situation. And being busy and it not being too bad I left it alone for a couple months but now its gotten to the point of having to deal with it.

Today I checked vacuum pressure, at idle, from the hose into the booster, Im making 5 in Hg of vacuum pressure, at 2,000, its at 10-11 ish. It does slowly drop off. Could this again be the bad vacuum pump? If so, what causes them to go bad so fast? I have heard a couple times that diesel gets in there but I'm not sure how that's possible? Leak in a hose somewhere?

But, its brought me to the point of joining this website to ask my fellow Ford people what the hell is going on.

Any tests that I can do? Places I should look? Etc. Etc.

thanks in advance!

 

EdTom7.3 Welcome to the best forum on these old OBS trucks! When I have had problems with the vacuum pump, the peddle was HARD. You could get the truck stopped, but it took a lot of effort. Have you inspected the hose from the pump to the booster for cracks, worn spots? Is the belt in good condition? It runs in my mind that you should get 9 in. of HG at idle, but I'm not positive on that. With a lot of parts made in China these days, it seems to be a crap shoot on the quality you get. The good news the brake light is working like it is supposed to, indicating you have a problem in the brake circuit.

 

I had to check and see if memory served me right. You should have 21 to 22 in. at the pump. Sounds like just a bad pump,which is not uncommon with parts house vacuum pumps. I have never heard of diesel getting into the vacuum pump.

 

Thanks for the warm welcome! The issue I have been having is the hard brake pedal, which gets especially hard after 1 or 2 depressions. I have checked the hoses but it might be worth another look over to save some $ on a vacuum pump. Is there any way for the plastic manifold to go bad? That idea has been sitting in my mind. I guess I could check that by testing pressure before the manifold in the hose directly from the pump. And from what I've heard it should be making 20 in to the booster. So really it should either be a leak or a bad pump.

Really the reason for starting this thread, though, is because I've been through 3 vacuum pumps, and I'm wondering if something is causing them to fail or if I am just getting bad parts. Any recommendations out there on which pumps to get a hold of?

 

Hook your gauge direct to pump and see what kind of reading you get.

 

You could also have vacuum leaks elsewhere; the pump also drives some HVAC controls. Some tests to figure out where the low vacuum is originating should avoid throwing part at the wrong "problem".

I see no way for diesel to get into the vacuum system, unless it's spraying onto a leak in a vacuum line and getting sucked in there.

If pumps are repeatedly failing, might it be a pulley alignment issue? Did you check vacuum at the pump outlet to confirm the pump actually was bad?

A high-dollar option to get rid of the vacuum brake booster is to go to a hydraboost system. That basically replaces the vacuum system with a hydraulic booster operating off the high-pressure side of the power steering pump. However, hydraboost is likely to expose every weakness in your existing brake system. After installation, while testing in my driveway, I blew a hard brake line, and then had problems with sticking front calipers. Ended up replacing all hard and soft brake lines (some I think were still original), master cylinder, rear wheel cylinders and small parts, and front calipers. After much work, the brake system is entirely new and works better than stock. But it was a lot of time and effort. I did the hydraboost about a year ago. Many years ago, when my vacuum pump failed, it was obvious. Casing cracked at the neck, and pump head was laying loose on the engine. I had no problems with the new pump, but now it has an easy retirement and only has to operate the HVAC controls.