Eagles International Forum

I have a 1979 eagle and cant get the parking brakes to release.I have replaced the quick release valve but still will not release. There are no holes in the canisters to cage the brakes, is there another way to release so I can move to a repair shop? I get 120 air back and front on gauges, go thru normal release operations still will not release. Drums are not frozen.

Try running the engine until full air pressure is built up (120 psi), push in the brake release knob, then apply the brake pedal until 100 psi is achieved (you might have a separate brake application pressure gauge). That should do it if everything is working correctly. Since it is cold nowadays, icing might be interfering.

Have tried that numerous times still not releasing.

Well, in that case, particularly since you probably have the DD3 system (and not the spring chambers that can be released with the threaded rod), you are in for a bunch of diagnostic troubles. The Bendix manual at http://www.suspensionspecialists.com/te ... k_2009.pdf, can give you an idea of all the components involved. The DD3 system was constantly changing in the 70's, and is overly complicated. This is why many change from DD3 to spring brakes. Check the archives on this forum and on Bus Conversion Magazine's, this kind of problem has been discussed before. Basically, the DD3 chambers are locked mechanically and are not getting the correct air pressure to release them because of failed relay valves or other mysterious DD3 components. You will probably need a mechanic that understands these systems well, otherwise you are paying for some mechanic's education. Going to Spring Brakes seems to be preferable.

Jackie, With the brake knob pushed down, are any air leaks heard especially near or from the DD3 canisters? Also, when the foot treadle is pushed, does the rod move at the brake adjuster? Do you know if anyone has stood on the brake peddle during full air pressure with the parking/emergency knob pulled?


Jim

Jackie, I see you are in Arkansas. I think it got pretty cold there. As someone mentioned, you could have had an icing problem in the airlines. If that turns out to be the case, you will need to service your air dryer or install a new one.

Now that it is warmer, did you get the brakes to release?

BTW, I always suggest that folks set up a signature in their profile. If your location/model/engine/etc is included, it makes it a bit easier for us to help.

Jim

Jim H wrote:Do you know if anyone has stood on the brake peddle during full air pressure with the parking/emergency knob pulled?

What happens when someone does this? My parking brake won't release on my 88 Model 15. The person who parked it last said they push the brake pedal down while the parking knob was pulled. Now we can't figure out what's going on.

Cirro, first of all welcome to our forum.

This tread discusses both DD3 and Spring breaks. Your 88 will have spring brakes. Folks have discussed how to release them via full break pressure after pushing in the park button. That process was a part of the design of the brake system for Eagle (and other buses). I think that was done to keep passengers from releasing the spring brakes (accidental or on purpose?).

Before I converted mine to a direct connection to the spring chamber (like truck systems) I used to have a ton of problems releasing my brakes. I often had to do the process several times before the brakes released.

A couple of words of caution here. Your profile suggests you split your time between NJ and Florida. That begs the question if it is possible your brake shoes are bonded/rusted to the drums. About the only way you could tell is to crawl under the bus (safely) and observe whether the spring brake are is still applying pressure. If it is then you know that you still have a release problem. If however, you find that the spring brakes are released, you could hit the drums with a hammer and listen to the sound. Bonded/rusted brakes will sound pretty dull as opposed to a ringing sound.

Next caution is to be very careful applying power to break the brakes loose. It is possible to do damage to the drive line.

Now to your question about applying both service brake pressure and spring pressure at the same time. My understanding is that the main issue is concern about the additive forces of both applications doing damage to the brake components. I have never heard of any damage resulting from this practice. If there is a concern about the double force still remaining, I don't think that is an issue. The service brake pressure would bleed off over time and the only remaining force would be from the spring.

Jim

For those of you who are frustrated with issues when trying to release the parking brake with the stock Eagle system (and spring brakes), the following information might help.

First lets look at what Eagle calls the Service Interlock Valve:
This is a combination of an SV-1 "Synchronizing Valve" and a DC-4 "Double Check Valve".

If your parking brakes do not release consistently/properly, likely one of the components in the Service Interlock Valve is not working properly. I think that the components are still available if you want to replace one or both units. I also suspect that they can be disassembled and cleaned/rebuilt

The alternative is to plumb around the service interlock valve so that the PP1 "park control valve" acts directly on the spring brakes to apply pressure to compress the park spring. This modification removes the need to apply the service brake to release the parking brake.

I will post how I did this in a subsequent post.

Jim

Jim, this will be a very useful modification for everybody with the stock system. This interlock arrangement is a source of problems for many people. If anyone is concerned about the parking brake being released, they could install a locking cover over the release button and accomplish the same effect. I look forward to seeing your solution.