Brake question - hard pedal

[chickenofthewoods]

Hey folks,

I've got a '91 7.3 in an E350 econoline, and my brakes went hard last week. Been troubleshooting fuel, so didn't have much time to mess with the brakes until now, as I just replaced my IP yesterday and now she's running proper.

So this is what's happenin. Check for vacuum at the booster, got some. The belt on the vacuum pump is tight, and the pump seems ok. Couldn't find any leaks in the vacuum system, but I'm not confident in my checks. Didn't replace hoses because I can't get to the damn clamp on the main vacuum line coming out of the pump.

So i checked the check valve at the booster - air went both ways, so I replaced that, no change. Hooked a vacuum gauge to the booster, pumped some vacuum and it didn't hold any. Plus I was hearing a whoosh when i hit the pedal. So I bought one at a salvage yard, which I guess could be faulty - but the pedal feels different. It moves better, but is still high and hard. Just put in in this afternoon. No change except the pedal feels different.

I guess my question is, how do I check the vacuum pump for efficiency? Do they just "go out" or do they fail gradually? Also, are there any checks you guys could recommend? Is there anything else that could cause a high, hard pedal besides vacuum issues?

Been out of commission for over two weeks troubleshooting the damn fuel, and I need the vehicle to work, so needless to say I'm gettin broke fast, and still can't rely on the rig.

Help!

[chuckster57]

Vacum test is in CNDSARGUY's photo gallery. there is two parts and they are NOT on the same page. Mine failed without notice last year 2 weeks prior to our road trip.Pedal was rock hard and the ABS light was on.

[waterdude007]

Pete's vacuum test will help you diagnose your problem. You can borrow a vacuum gauge from your auto parts store or buy one.

My pedal went hard a while back, I did Pete's vacuum test and my vacuum pump failed the test, replaced pump...all is good.

Good luck, Hugh

[cdnsarguy]

So I bought one at a salvage yard, which I guess could be faulty

One being a used booster?????? Was it off the exact same vehicle.......

[chickenofthewoods]

cdnsarguy: Yes, it was off of a '91 E350 7.3 - is it hard to find one or what? They charged me $55 for it, and there was one available at another salvage yard nearby as well. I'm not sure I understand why you seem so surprised...?

Chuckster: I downloaded those two pages, and I'll be borrowing/buying a vacuum gauge tomorrow to try and narrow this down. Thanks!

Waterdude: Is the test you're referring to the one in cdnsarguy's pictures? If not, where do I find it?

Thanks for your responses, fellas. I guess there's not much else that could cause a hard pedal, then? Right?

[chickenofthewoods]

Oh yeah, duh...

I forgot to mention, the brake light is coming on intermittently. I heard that the brake light was generally an indication of hydraulic issues, not vacuum stuff. Is this true? I certainly don't see any sensors that would set off a light in the vacuum system.

Also, back in September, I replaced all of my electrical cabling for the batteries and starter - built from bulk stuff, very heavy duty. When I put everything back together, I had the RABS light on. So I went and bought the sensor, but didn't replace it. I still have it, but this current problem just started suddenly last wednesday. I do have to admit that the brakes certainly worked differently after the RABS light came on, and it;s been on ever since - I've just adjusted to the way the brakes work.

So - tomorrow is Big Brake Troubleshooting Day for Chickenofthewoods. Happy Fourth of July!!!!

[cdnsarguy]

The Tuna can item on the front left fender well is the vacuum loss indicator.......

Rabs ....... could be park brake......ensure its off. Low fluid in the M/C or sticking float.

If you want it I can forward the 91 RABs info to you just PM me your email addy.

Please put up a signature with truck info.......

[waterdude007]

Brake light will come on if vacuum is very low or zero. Running the motor with the vacuum hose disconnected should illuminate the brake light.

Part 1: TheDieselStop.Com Photo Hosting - Vacuum test Part 1 of 2

Part 2: TheDieselStop.Com Photo Hosting - Vacuum test Part 2

My guess is that your vacuum pump is toast, but the tests will confirm.

--Hugh

[Snotzalot]

I don't believe the E's have RABS.

[chickenofthewoods]

Hey guys.

I've got no tee to test the vacuum via procedures - but I bought a gauge just now and went directly into the main hose from the pump. What should I see here? What I get is a bouncing gauge - never gets too far from zero, goes back and forth.

This looks grim for the pump. Am I right in assuming I should get a reading this way? Or is my logic faulty... before I thought the pump was at least working, because I could feel suction with my finger. Now I'm afraid the pump is shot, and the place with my pump is closed today.

Also, is my signature visible?

[94_turbo]

vehicle running--it should hold at least 12 in of vac--bouncing needle--means the one way valve inside the vac pump is south--find another pump--or take that one back and ask for another--probably was bad from the day you put it on--

[chickenofthewoods]

94_turbo - this is definitely what I feared. Gonna have to get the pump tomorrow. By the way, I haven't replaced the pump. I just replaced my INJECTION pump on friday, and replaced the brake booster on saturday...

Thanks

[chickenofthewoods]

Done and done! How many more "pumps" can I be expected to replace, dang. In the last two weeks it's been the lift pump, the injection pump and the vacuum pump. Not to mention all the rubber and the brake booster. At least now she runs strong and stops cleanly, what more could I want?

Thanks for everyone's help!

[cdnsarguy]

Normally the vac pump is tested at the plastic manifold where all the lines come too.......this will then give you the vac system reading. If it is lower than it should be then searching out the problem starts with the system isolation.