I have been appending this issue to my other thread about the 4000 mile trip I have coming up, so here is a more direct thread.

I replaced the front brakes because I was getting squealing when I came to a stop. Shortly thereafter, I started having problems with a mushy or hard brake pedal. It has done both and some times it starts normal and half way down becomes hard.

I then replaced my passenger side caliper and bled the system. The fluid ran all out at the reservoir while I was messing with the line to the caliper.

After some bleeding and more bleeding, I still need to bleed the rear brakes. I guess air could have gotten to those lines some how.

I bought a vac gauge and hooked it directly up to the vac pump. It pulled a consistent 20inHG. The needle didn't wobble, either. I attached the gauge to a spare port on the vacuum splitter and the best I saw was 15Hg and after two pumps of the brake pedal it went down to 1Hg and took 30 seconds or so to come back to 15Hg. The needle shook like crazy after being hooked into the splitter. My next test is to hook the brakes up directly to the pump.

After I shut the engine off, the vacuum dissipates at about 5inHG per 90 seconds or more.

 

Cruise control or heater vac lines could be leaking. ALso the diaphragm in the low vac switch could be bad.
the system doesnt hold vacuum with engine off.

 

This was what i did when i suspected vac pump.
here is my thread about my vac problems on OB.net
Brake Light possibly caused by dieing vacumm pump - Oilburners.net

 

Where is my low vac switch? I'm going to Home Depot tonight to pickup some hose barbs for testing. I'll tee the vac gauge in with the vac pump and brake booster only.

How much if any, should the system leak down?

 

Low vac switch should be near the voltage regulator on the passenger side fender. If I remember its roundish in shape. You should be able to find it by following the vac lines from the splitter.

Ideally, it shouldn't leak down any when off. Realistically, probably slowly, but thats a guess on my part.

 

Oh, OK. I remember seeing that now. So, are you guys saying that the sensor may be bad and causing a vac leak or bad and not turning on the dash light?

 

Have you replaced all your vacuum lines and the check valve at the booster? I did that to my truck when I got it just for the hell of it, allot of them were dry rotted.

Need to make sure you are sound and then take some more readings. Do you ever see the brake light go off?

If you still get those same numbers and the connections are good I wonder about the pump only because mine reads like 23 when hooked up to the manifold. I don't see the brake light during normal operation and I can get atleast a handfull of pumps at the brake pedal before it comes on so hard pedal hasn't been an issue thus far.

 

OK, here are my test results from today.

I disconnected and capped everything on the vacuum splitter except the brake booster, vac pump, and gauge. After doing this, I got a maximum of 15in Hg. After two pumps of the brakes, they got stiff and my vac went down to less than 5in Hg. I hooked the brake booster directly into the main vac line with a 3/8" nipple and the brakes seemed a lot better but not perfect during the test drive.

I am trying to narrow this down as much as possible because I am running low on money and I need this truck to be reliable before the trip. Brakes are about the most important thing I can think of to have working properly.

Thanks for all of y'all's help and suggestions. Keep 'em coming.

Edit: The gauge bounces the needle until it settles at 15in Hg. I have also never seen the brake light come on.

 

Kinda sounds like your pump is going south.

 

It kinda seems that way to me, too. It can keep up with the CC and heater controls but I have noticed that after getting off the highway with CC on, my brakes are stiff as I get off the exit ramp.

I plumbed the gauge into the splitter and I have it in the cab. I'll be able to monitor the pressures during normal stopping and highway driving. I am leaning towards the pump, too.

 

On the way to work today, I had the gauge attached and on the highway with just the brake booster, gauge and heater controls, it read 9-10in Hg. When I hit the brakes it goes down to about 6-7. If I hit the brakes again quickly, it goes down more. If I idle at a stop light it goes up to about 13in Hg.

Looks like I need a vac pump.

I hope the parts store has a P/S pulley tool I can rent.

 

You are overdue for a vac pump. it is living on barrowed time.

 

I'm looking for one right now. O'Reilly's doesn't have one in stock. Maybe Autozone does.

 

i got mine from rock auto, but from the sounds of it you need one ASAP.

 

Yeah, I'm supposed to be leaving for my trip Saturday morning. I spent two hours tonight finding a place that actually had a vac pump in stock. I got a reman pump and I just need to swap the pulley and install it. I rented a P/S pulley tool. It seems pretty simple to do. Lock the tool around the inner lip of the pulley, turn the screw in and the pulley comes off. To reinstall, lube the shaft (on the vac pump, you sickos) and use the tool to push the pulley on the new pump. The only hard part I foresee is getting the pulley on straight.

Any tips would be greatly appreciated!