I've replaced the complete braking system, other than the antilock valve in the rear of the truck, on my 93.

This includes
Calipers, hoses, steel lines, wheel cylinders, brake shoes & pads, hardware kits and adjuster kits, master cylinder (new not rebuilt) and power brake booster.

Long story short is that no matter how well the rear brakes are adjusted (tight as possible against rear drums without causing overheating) the brake pedal is still low.

Having spent several hours bleeding, then rebleeding, I'm confident that there is NO AIR in the hydraulic system. THere are no air pockets or bubbles in the fluid when bled. Clean solid fluid streams when purged, then locked off.

When the truck is not running, the pedal is high, as where you would expect it to be, but when the truck is running, the pedal travels to where its just a few inches off the floor.... much too low for my comfort level. I've checked the freeplay between the booster rod and the MC, and it's within spec. I've thought that this may be a vacuum issue, but I guess I'll have to do a little testing to find out.

Any thoughts on how to correct this.....? or is this considered "normal" in these trucks.


Thanks.

 

Bypass the RWAL, I'm betting that's your problem. If your pedal comes back after bypassing and bleeding, replace the abs modulator.

 

Sounds like the modulator (dump) valve is stuck open. One thing that is routinely done is to force the wheel cylinders in without the bleeder open. This is not good for our abs system because it forces crud into the valve. Another cause of this is the garbage in, garbage out syndrome, If your sensor in the rear end is sending garbage data to the ecm, it will send garbage out and open the valve. Could be crud on sensor, bad sensor or bad wires. The ecm can also be bad, but is less likely. Good luck, because been there done that (a few times)...Mark

 

Quick way to tell is to unplug the RWAL control box. If you loose rear wheel anti-lock, but the peddle is still mushy its the valve. If the peddle gets hard its the box.

 

How, by running a new steel line directly from the tubing that leads to the valve to rear brake hose, which goes to the rear axle ?


Ok, it's behind the glove box, so I've read here. I'll give that a shot first.

Muchos Thanks.

 

Vac reading is good & High.. so I don't have to replace the vac pump anytime soon.

 

Excellent sticky thread, BTW

https://www.dieseltruckresource.com/...ad.php?t=59092


For anyone who is experiencing the same issue.

 

Nice thought, and good hunch although........someone long ago beat me to it..... I disconnected the box, when I realized the two wire was missing, so I poked around in there, and someone had shoved the two wire lead up and to the left behind the box on the left. They taped the wires together / separated in a sticky tape mess, and forgot about it.





and



and....

 

Has the master cylinder been replaced? If it has, the rod from master cylinder and brake booster may not adjusted correctly.

 

Answer in post #1

 

UPDATE:

In the construction trades, we here have a common thought that 95 percent of construction failures, which are anything from a simple faucet leak to a major failure of any system that gets installed in a residential home, are due to the contractor, or his employees that didn't follow proper procedure for either installation of the said particular product. This can be attributed to attitude, incompetence or cutting corners. For the most part, the product itself, isn't to blame for the results, but the person who installed it, is at fault.


I am no different.


Although I do my best to read, research and re-educate myself, when it comes down to my trade, and how I perform my daily routines, I guess I was just too lazy to think that I was the one at fault for my dodge brake problems.

After reading this post, https://www.dieseltruckresource.com/...68&postcount=2 something clicked in my head that I needed to again, review the FSM to find out why my brakes were as low as they were. Thrashingcows simple little homemade device opened my eyes to the 30 years of incompetence that I've been performing when it comes down to bleeding brakes properly, on all of my vehicles, I've owned since the early 80's. I cannot tell you why this truck didn't work "the old fashioned way" but for some reason the rear brakes on these dodges must be different, by design or engineering, and require the fluid in a bottle reservoir routine that TCows showed us. None of the other vehicles I've ever bled have had this issue. Ever.

The other day, I purchased the Mityvac system for my vehicle annual brake bleeding chores, and I attempted to use it on my Dodge. Unfortunately, my air compressor isn't large enough to properly use the vac. I don't have a large enough compressor reserve to fully bleed my dodge system, and it loses sucking power too early, which caused air to enter my brake system again @ the rear wheels.

So.... after my "Eureka" moment with Tcows pic, I re-read the FSM, and made my own reserve bottle out of a clean dry peanut butter container. I cut the hose off of my mighty vac, drilled a hole slightly smaller than the tube, and forced it into the jar. This gave a super tight fit so that while bleeding the tube wouldn't pull out of the jar. It worked like a charm.

I will say that after all of this time, of dealing with these Dodges for the last year, that my brakes NOW work as designed. The pedal is up high where it should be, the truck stops on a dime, and I'm amazed at how well the system really works.

Turns out that my rear brakes were the culprit for the low pedal, and it was simply that there was air in the rear brake lines. Bleeding the RWABS, then the Right drum, then the left, gave me a high firm pedal that didn't fade at all. This time I used my own version of TCows reservoir, but it worked flawlessly.

Any of you guys having a "mushy or low" pedal, need to do this...

I'm telling you that these brake systems work fantastic when the person working on them, actually does the correct bleeding procedure.

T.

 

Dang when did you put the mudders on?

 

And I think i am gonna leave my buddies out of the equation and make up one of those bottle bleeders and try it myself next time......did you bleed the proportioning valve on the front driver side frame of truck?

 

That is great for you, but I bled my brakes at least 50 times exactly as written in the FSM and every other way. I used the mighty vac, I held the valve open on the proportioning valve, I did everything. I would have good brakes for a while, but something always caused them to fail again. That said, I agree that the problem is in the rear drum system because since I converted the rears to discs, I have had perfectly functioning brakes, with the modulator valve still in the system. I always suspected the rears because I always got air out of the left rear cylinder. In the end, it was way worth it to dump the drums...Mark

 

No,

there's no bleeder valve on it, so I'd have to crack a line,


Mark,



The issue was with the rears.... 100% positive on this.

Rears had air, which gave it the low pedal. The minute I got the air out, all was fixed

If the brakes feel good, then they fade away to low pedal again, a few days later, there is absolutely (in my mind) that the process of air infiltration into the system has occurred again.

My brakes are fantastic. Not bragging, but just making a statement.

The Mighty Vac I purchased didn't do a thing for me. $150 I'll have to use on some other vehicle.....

This was the MOST DIFFICULT vehicle I've ever worked on in the last 30 years, with diagnosing what was going on with the brakes.

By far...

T.