I have a 1989 F350 7.5L.

I was having issues with the brakes, I had a slight squeaking coming from the front and a bouncing in the rear. The rear bounce was happening when braking at speeds above 40-45 and was sort of a smooth bounce, not a real bad vibration type bounce. That may sound strange, I'm having trouble describing it, but what I'm getting at is that it wasn't a real harsh shaking or anything, just felt like the drums had gone out of round.

Well I took it to my mechanic thinking it might be minor, well turns out I had some real bad spider cracking on the front rotors, the drums were in fact out of round and I needed shoes.

Well, this time of year money is tight, so I decided to take this job on myself.

I bought new rotors, pads, shoes and drums and got to work.

I installed everything and took the truck for a spin and everything felt great. Stopping well, no more squeak and no more bouncing. I'm stoked...

Well the next day, I drive to work and everything is fine, but when I leave for lunch, the first time I stop I gt this real bad shaking or almost like a vibrating in the back end. It isn't a side to side shaking, more like a real quick bouncing like someone was hitting the brakes very rapidly. I don't feel anything in the pedal or the steering wheel and I further confirmed that it was the rear brakes by coasting at around 40 and depressing the parking brake.

Well, I got home and pulled the rear wheels and drums to look for anything out of the ordinary thinking that perhaps a retention spring popped or something simple had happened. Nothing in the rear brakes looked out of the ordinary. I tore down the shoes and springs again and checked the wheel cylinders and they looked real rough, in fact one piston was locked up. AhHa!
This must be the problem I thought. I pulled the cylinders, removed the pistons and cleaned them real well. I put everything back together and bled the brakes and took it for another loop around the block. Same problem.

I'm stumped at this point. So next day I head back down to the parts department and pick up new wheel cylinders and New calipers for the front. I'm thinking, maybe the front brakes aren't pulling their weight and the rears are overworking, or maybe it's just the crusty old rear wheel cylinders that are just beyond a good cleaning.

I get home, and install everything. I bleed the brakes, taking extra time to make sure I have them bled well and I take it for another test drive. Bouncing is probably 50% better or in other words much less noticeable. It is still there though.

So I am now at the point where I am starting to think it is an issue with the ABS system. I have a basic understanding of how ABS braking systems work and the more I think about it, the more it seems to make sense that this is what it could be. I say this because it almost feels like when I am braking, the Hydraulic unit is pulse dumping the rear brakes.

My problem is, I have no idea how to trouble shoot what component might be causing the issue. I have no light indicating failure in the system but at this point, it is the only part of my braking system that isn't BRAND NEW.
I don't know if the speed sensor is giving the control module false information. I don't know if the control module has just gone bad and I don't know if the Hydraulic control valve is just stuck or gunked up with old brake fluid.

I am leaning toward the hydraulic control valve being gunked up because that would kind of explain why the problem got so much less noticeable after a thorough bleeding of the brakes. However, maybe my bleeding wasn't so thorough, I did it the old fashioned way, and I know rear brakes can often be difficult to fully and completely bleed without a vacuum bleeder or something of the sort.

I am sort of at the end of my expertise and I will probably end up bringing it in to Kenny on Monday when he gets back in town. But I thought I would reach out to a knowledgeable base, such as yourselves for some advice in the meantime, in case this may be something I could try to remedy myself.

I apologize for being long winded, but I know that every bit of information helps when trying to properly diagnose a problem, so I decided being thorough might be worth carrying the stigma of being a blabber mouth...

Thanks in advance to anyone that may actually be reading this final sentence. You are truly patient, my friend.

 

It sounds like your new brake drums may be out of whack. That was a good troubleshooting measure you did with the parking brake. Hopefully you will get more opinions, but it will likely be morning before that happens.

 

Hey 88,
Yeah, I got some more suggestions from other online outlets and everyone seems to be pointing towards the shoes. Someone mentioned, which I should have deduced, that when pulling the parking brake, I was bypassing the ABS system and therefore could rule it out since the shaking existed when the parking brake was applied.

I have since been told by a couple guys that a lot of times the drums can come out of round or have bad surfacing and that it is recommended to resurface before even installing brand new.

It was also mentioned that since I had the rear wheel cylinders sticking, that I may have warped the drum then.

I think what I am going to do at this point is re-install the old drums, which bounced a little, but no where near what I am experiencing now, and see if the problem persists.

I will update thread when I have some results.

Thanks for the advice.