I need real HELP with my braking issue - Diesel Forum

897.3f350 · 11-25-2012, 08:16 PM

88 f250 4wd auto.
First, here is all that I have bought and installed in the past few days.
Rear brake lines, starting at center hose. Cylinders. Shoes. Front pads. Vacume pump. Master cylinder. Power steering pump. Oil and filter.
I have done many booster test, all but one passes. That's where I hold the pedal, start engine and it should drop a 1/4. Mine fell to the floor. It stays hard when I shut it off. But when the truck is ready to drive, the pedals get stiff at first, then slowly and consistently fall to the floor.
I did a proper bench bleed on the master today after I bought it. Then again, I bleed the brake lines starting farthest away. My pocket is now empty, and I spent my hole holiday week under this truck. If anybody can help me understand what's going on, I'd appreciate every bit of help.
If it helps, after I installed the new vacuum pump, I now hear a small ticking sound. Almost the sound of a air compressor.
I'll check in tommarow afternoon to read any responses. Thanks again.

Early Cuyler · 11-25-2012, 10:17 PM

DISCONNECT THE VACUUM PUMP AND SEE HOW IT FEELS. IT IS A COMPRESSOR RUNNING IN REVERSE.IF YOU HAVE A VACUUM GAUGE IT SHOULD PULL 27-29 HG AFTER A FEW SECONDS,IF NO GAUGE IT SHOULD GIVE A HEALTHY LITTLE SUCK.IF GOOD, TRACE OTHER VACUUM LINES TO THE VACUUM MANIFOLD WHICH IS JUST A 2 OR 3 T PLASTIC SMALL DIVIDER. CHECK FOR DISCONNECTED OR LEAKING VACUUM LINES, CAP OFF OR PLUG ANY NON BRAKE VAC HOSE. SEE IF BRAKES IMPROVE, IF NOT YOUR BOOSTER IS BAD. YOU SHOULD NOT HEAR THE PUMP FROM IN THE CAB WITH ENGINE RUNNING.
THIS IS ALL ASSUMING THE BRAKES WERE TRULY AND THOROUGHLY BLED,THE CALIPERS HOLD A CONSIDERABLE AMOUNT OF FLUID AND IT TAKES TIME TO DO A GOOD JOB OF IT,AND IS A GOOD IDEA TO REPEAT IT PREFERABLY WITH SOME HELP
GOOD LUCK

897.3f350 · 11-30-2012, 09:48 PM

Thanks for the insight. I just got home from being away for a week. I looked under the hood at the vacuum manifold. There is a thin line comming from left side that goes nowhere. I'm getting up early and ill be able to inspect it closely in the daylight. I'll try pluging it first, try the brakes. Hoping it works right. Once the brake pedal keeps pressure, I'll probaly need help putting that hose where it belongs. Once again, thanks. I'll be on here around noon eastern time to post findings.

chuckster57 · 11-30-2012, 10:24 PM

That small hose probably crosses behind the engine and ends at the heater box. There is a vacuum actuator there.

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897.3f350 · 12-01-2012, 08:02 AM

I found the small hose to be broken at the low vacuum switch. The spout is broke inside the hose. Having trouble finding a replacement part. I haven't Tryd closing it off the try the brakes. I need fuel first. She romped once and then shut down last night. I parked sideways on hill. Duh!!
Heading to junk yard to get steering shaft. Hoping one of those trucks are diesel and I can get the low vacuum part.
I'll be back on here shortly.

897.3f350 · 12-01-2012, 03:55 PM

Ok fixed the steering. Used duct tape to fix the coffee can. Still can't find the low vacuum module.
Finally took her for test drive. Brakes are touchy a soft while driving. But when I come to a stop or pump them to stop, the pedal is hard. The truck stops, but not like a safe vehicle should. Vacuum pump is still making a compressor sound. I Tryd plugging the broking hose that is low vacuum, that made the brakes crappy. So I unplugged and let it hang, now the truck will stop. After stoping, the pedal still fades to the floor. I can hear pressure in the cab.
I'm told that I will need a new booster. SO, I will shell out more hard earned money to get this thing on the road safely.
Sorry for the rambling, thanks for any help.

NH2112 · 12-01-2012, 04:56 PM

A bad booster makes a hard pedal. If the pedal fades to the floor you either have a bad master cylinder, a leak, or an air bubble somewhere. I'd suspect the master cylinder first.

897.3f350 · 12-01-2012, 08:00 PM

I've got the booster off. Going to get the new one in the morning. My dad mentioned the new master cylinder could be defective. So, while its hanging loose, I'll swap it for a brand new one and not a reman. Might as well, I'll be at the AZ I bought it at.
Thanks for your help, I really can't wait to get this truck going. Tomarrow is my deadline to be driving it.

NH2112 · 12-01-2012, 08:50 PM

I just recently spent a few days fighting my way through a complete rear brake replacement on an '87 F600, thanks to everything being seized, corroded, or stripped (couldn't use a torch because it's our avgas truck), the holiday screwing up shipping, and not being able to get parts from NAPA till Friday. And just yesterday I had to replace a defective new master cylinder that was just installed on it about 10 days ago, so I feel your pain!

897.3f350 · 12-02-2012, 09:12 AM

Yea I'm kinda wasting good daylight. Can't get my parts until noon. That's if I want a NEW master cylinder. And not a reman. I might be able to get started about 1:30. Leaves me no time to tie loose ends around the house. Gotta go out of town Monday, so yea, I'm still frustrated.
Helpful hint: please take care of your trucks. Even if you don't plan on keeping them. Make it easier on the next owner!!!
I'll post my findings after I'm all done this afternoon.

897.3f350 · 12-02-2012, 07:39 PM

Well, I'm driving.
Still got a little air in the lines I think. But it's able to get me to work, and that's what matters. It stops holds. Never hits the floor. Pedal is still soft. I was told it has air in there. It'll sit at the shop all week until I get back Friday. So I can bleed them then.
Next: I figure out why my head lights suck. Even on high beam they are low yellow. I know I've got a little bit of work still to do. But hey, $1000 find. Can't beat that.
So far this is what I've bought new and installed.
Power steering pump
Center brake line (rubber with brass t box)
Brake lines for both rear
Front brake pads
Rear brake shoes
2 rear wheel cylinders
Vacuum pump
2 master cylinders
Brake Booster
Duct taped my tin can
Rotella 15 40
Antifreeze
Plenty of Brake fluid
And countless hours of frustration. Fix one, next goes out with full pressure.
Feel like I'm leaving out something, but sure you guys will see me in the future. Thanks goes to those that helped me along the way.

NH2112 · 12-02-2012, 09:11 PM

Did you bleed the ABS module, too? It should be done after the rear wheels and before the fronts.

897.3f350 · 12-03-2012, 08:32 PM

No I didn't. I would have never guessed it. Thanks for bringing it up.
Where would I find it? And what's the trick?
88's had the abs?

897.3f350 · 12-03-2012, 09:26 PM

I'm looking at my chiltons manual, and it says to only do this procedure if the HCU ( hydraulic control unit) has been replaced. I don't fully understand. If it means booster or master cylinder, then yes , I did replace it. If not, and it's refurring to another part, then no I haven't replaced it. My new lines started with the rubber center hose that attaches to the rear axle. Kinda lost here. Lol?
Q: my truck does not have hydroboost. Does this procedure still apply to my truck?

chuckster57 · 12-03-2012, 10:22 PM

HCU is probably the RABS unit. If your truck has RABS, the control unit is mounted to the inside of the frame under the D/S seating area: