e brake release

mikke60 · December 30, 2019, 03:26:24 AM

bought a 77 scenic cruiser. having trouble getting the e brake to release? thoughts?

richard5933 · December 30, 2019, 03:39:40 AM

1977 Scenic Cruiser??

mikke60 · December 30, 2019, 03:46:27 AM

okay, 77 gmc
sorry for the mis info

richard5933 · December 30, 2019, 05:27:38 AM

Are the shoes rusted to the drums, or are they not even trying to release when you push the button?

Full air pressure at 120?

Have you tried making a full service brake application while pushing the button?

Utahclaimjumper · December 30, 2019, 06:23:54 AM

In 77,, GMC made a class C mtorhome that was not a bus,,,it had hydraulic brakes..>>>Dan

richard5933 · December 30, 2019, 06:42:26 AM

Quote from: Utahclaimjumper on December 30, 2019, 06:23:54 AM
In 77,, GMC made a class C mtorhome that was not a bus,,,it had hydraulic brakes..>>>Dan

Then I guess that begs the question... Are we discussing a bus or motorhome?

My bus says GMC on the nose, and assumed we were talking about a GMC bus badged like that.

luvrbus · December 30, 2019, 06:54:43 AM

You guys

just help the guy

mikke60 · December 30, 2019, 09:54:04 AM

Sounds like they release, but don't. Sometimes they even lock back up a few times before I can actually keep going.

luvrbus · December 30, 2019, 09:58:29 AM

The latches on the D-3 chambers rust and build up with crap they may need cleaning,they also have a grease fitting too do you grease the chambers ?

richard5933 · December 30, 2019, 10:49:05 AM

Quote from: luvrbus on December 30, 2019, 09:58:29 AM
The latches on the D-3 chambers rust and build up with crap they may need cleaning,they also have a grease fitting too do you grease the chambers ?

I see in the manual mention made of greasing parts when reassembling, but cannot find mention of a grease fitting. Is this something that all GM DD3 brakes have? Or is it something that was added later and will only be found on replacement chambers?

luvrbus · December 30, 2019, 10:52:27 AM

Quote from: richard5933 on December 30, 2019, 10:49:05 AM
I see in the manual mention made of greasing parts when reassembling, but cannot find mention of a grease fitting. Is this something that all GM DD3 brakes have? Or is it something that was added later and will only be found on replacement chambers?

I never saw the D-3 chambers without a grease fitting for the latches on any bus ,could be the early models didn.t have a fitting I don't know but Eagle and MCI calls out Lubriplate the white stuff to grease those with Bendix calls for Aero or Lubriplate

richard5933 · December 30, 2019, 12:46:34 PM

Thanks luvrbus. I was looking at the diagram and missed the last paragraph of the text. I assume that the fitting they're talking about is the grease fittings. Still can't find it on the diagram - assume I'll see it on the chambers though. Not sure where the relief holes are that they mention though.

Here's the info from the manual in case it helps mikke60.

Utahclaimjumper · December 30, 2019, 02:15:06 PM

My point was that a 77 GMC came in many forms.>>>Dan

chessie4905 · December 30, 2019, 02:39:43 PM

One of the Bendix manuals calls for Never seize.

Dave5Cs · December 30, 2019, 03:22:15 PM

Park brakes will not release.

Usually having too much air pressure applying the park brakes causes this. In the air supply line for the park brakes is a pressure regulator which is set to 85 pounds. This is the amount of air pressure used to apply the park brakes, not the 120-pound system pressure. If this regulator is set too high, or the regulator has been removed, the brakes will be applied too firmly to be released by the service brake application. Setting this regulator too low will affect the stopping/holding capabilities of the park brake. 85# is the magic number to remember.

Air is leaking out of the R-14 relay valve located above the drive axle (On ABS equipped coaches, air leaks out of the modulator valve.)

In the DD3 brake chamber, the park brake diaphragm separates the park brake section and the service brake section. If this diaphragm develops a hole in it, air will leak into the service brake section. When the service brakes are not applied, this section is vented to the exhaust port on the relay valve (With ABS, the exhaust port on the modulator valve.) Any air entering the service brake chamber will be exhausted out immediately thus causing the illusion of a faulty relay valve (With ABS, the modulator valve.)
To troubleshoot this situation, remove the service brake airline from one of the DD3 brake chambers. (This is the middle hose on the chamber) If air is leaking out of the service brake port, that is the chamber with the leaking park brake diaphragm. If air is still leaking out of the relay valve and the hose in your hand, then it is the chamber on the opposite side of the axle (On coaches with ABS, air leaking out of the RH modulator valve would mean the leaking park brake diaphragm will be in the RH DD3 brake chamber, LH modulator valve would point to a leak in the LH side.)