Hi everyone, new here so i'll give a short intro and I could use some assistance in diagnosing an issue. First off I just bought my first 7.3 idi the last week of may. I've always loved the OBS fords and I had the opportunity and the need to move up from my 2005 Nissan Titan so I did.

Truck stats
1994 F-350 CCLB 7.3 IDI turbo with 214k (had 213k when i bought it)
4X4 Automatic trans.

So far I have put 1000 miles on it and the truck has been fantastic for the most part. Runs great, starts up quick and doesn't blow any smoke other than a little white for about 30 seconds on a cold start.

As I mentioned I came from a Titan and upgraded because my family was outgrowing the small cab and my trailer was outgrowing the tow rating. I did about a months worth of research and looking for a powerstroke. Unfortunately the only ones in my area were in pretty rough shape and commanded a premium price. Finally I stumbled across this 94 idi and it was a perfect fit.

Now for my issue. I'm trying to pin down the problem and I am hoping you guys can help me out.

Symptoms
-The truck brakes very well but normally the pedal goes about 3/4 of its travel and only feels like the rear drums are braking. Then when it hits 3/4 you can feel the front brakes kick in hard.

-truck stops nice and straight even if you stomp on the brake, doesn't dart to either side.

-2 days ago I was test towing a trailer. Weighed about (3500-4000lbs). I used a hill in my area with a very steep grade about 1 mile long and has a round about at the bottom so you start the climb at about 20 mph. I took o/d off and went full throttle up the hill. It climbed easily to 45 mph and held there all the way up. Now the problem I had was about halfway up was this high pitched squealing noise just like a loose belt on car when you cold start one. It sounded like it was distinctly coming from the drivers side of the engine.

-When i got to the top of the hill and hit the red light the brake pedal was extremely stiff (still braked ok but not as well) there was also a burning rubber smell.

-Then when i let off the pedal the brakes were still clamped onto the rotors and had to give it some gas to get the truck moving again.

Note: The next day i did this test again without a trailer and got the same result although to a lesser extent.

Additional note, my brake light and abs lights come on intermittenly, always off when I first start the truck but will come on at some point while driving. usually after I hit the brakes pretty hard.

The squealing noise:
I hear it generally when the truck is under high load, towing uphill, accelerating hard, but always goes away if I let off the gas a little.

Sorry for the ridiculously long post just trying to give as much info as possible. Also I replaced the front pads a week after i bought it with motorcraft pads, and inspected the rear which looked good. They were done last year by PO with receipts.

I appreciate any help in advance, thanks guys.

 

Check the rubber lines to the calipers they deteriorate from the inside a piece of rubber can actact like a check valve and not let the pressure release

 

I'll double check them, they should be good one of the receipts from last year is new front brake lines, but I'll make sure. Any other ideas?

 

Check the belts. The vacuum pump is belt driven off the alternator sits below it.

 

abs and brake light could be the rear abs unit malfunctioning. I went through the same scenario in mine. replaced all rubber hoses, calipers, wheel cylinders and bypassed the rear ABS unit. brakes like a new truck now. I would check the vacuum pump as mentioned, could be trying to seize causing the belt to burn

 

Belt looked ok. Though it's only happened a couple times, may be too early to tell. Tomorrow I'll test the vacuum pump and check out the rear abs, thanks.

 

If you are loosing vacuum check the coffee can on lt fender well

 

Ok so I tested the vacuum pump and it went to 21 right from the start and held there. We turned the truck off and now the glow plugs won't come on. No wait to start light no audible click. Truck cranks strong.

 

Well crisis averted for now. We let it it for about 15 min went back and everything was normal. Anyway the vacuum pump tested fine as did the can by the fender. Last night I pulled the fuse for the abs system and now the truck brakes normally and evenly. I got up to speed and tried to lock up the brakes on dry pavement and it didn't happen so I'll leave it disconnected for now. So the only issue left is the noise it makes under high load, possibly the turbo going out? I did forget to mention I never heard this noise before last week when I built my own I take (3" pipe with 6637 filter) now I hear it.

 

You may have leak in the air intake pipe that you built thay would put the noise on the drivetr side

 

Ok I'll check out the intake pipe see if I can find a leak.

Further update I took the truck unloaded up the same test hill. If you recall the brakes locking up occurred unloaded as well when I tested it earlier but not as bad as with the trailer. So today I ran the same hill and nothing, no burning smell and the brakes were perfectly normal. Looks like the abs system was the culprit there as well.

I appreciate your guys help looks like I've solved all my problems, just got to track down this noise think it might just be the turbo I'm hearing. Thanks again!

 

Squealing noise under load, esp. if followed by a hard brake pedal, is the belt slipping. Check the tensioner.

 

Ok looking at the tensioner the gap looks uniform as far as I can tell. I did notice however the belt on the bottom pulley is sitting just off the front edge and not in the middle. Belt has good tension, I think I'll just replace the tensioner and belt as soon as funds allow. Better safe than sorry.

 

ok guys wanted to update this now that i've done a little more testing. I waited to get my guages before I hooked up the trailer again so i could better test some theories without accidently reforging my pistons.

I got everything installed yesterday, (the usual tranny temp, pyro and boost). So i hooked up the trailer and went to run the hill again. Just to recap i'm still driving with the abs fuse pulled and running the hill unloaded I didn't have the previous brake issue. (still had the noise though).

Ok so I went up the same hill started at 50 and made it to about the last 100 yards when my pyro got to 1200 so i slowed to about 40 mph and crested the hill. No hard brake pedal at all this time, felt the same as when I started at the bottom. Looks like ill bypass the rabs valve and then reinstall the abs fuse.

As for the noise and burning smell they were still there so as soon as I got to the top i pulled off, popped the hood and smelled all 4 brakes to make sure it wasn't a bad caliper or drum, they were fine. I popped the hood and it was pretty aparant that the smell was coming from the belt.

New tensioner and belt will be purchased as soon as funds are available and I will update this at that time if it fixes the issue that way anyone having the same problem in the future can find it.

 

And since you were all so helpful here are some pictures of the truck and trailer I've been talking about. Hopefully these work.