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Old 10-16-2021, 07:32 PM   #1
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How to adjust transmission mounted parking brake (air over hydraulic)

I posted a while ago about my parking brake. I am concerned because when the parking brake is engaged, if I give it some throttle it will start to charge away and I do want it a bit stronger.

Here are the pictures I took. It's hard to tell but I did my best. The drum is circled and there is an arm/spring which moves when the brake is engaged/disengaged. The spring seems a bit stuck together when it moves but whatever for now. I can see the shoes moving when engaged.

Is there an easy way to tighten this up, or is this something better left for a mechanic? I'm pretty handy myself and I do know someone who is a heavy duty mechanic, the issue is not so much the ability it's more being able to get under the rig and do the work.

How is this brake adjusted? Thank you

1993 Gulf Stream Scenic Cruiser, 5.9 Cummins, MD3060 Allison.
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Old 10-16-2021, 07:46 PM   #2
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Please tell us what coach you have.


That will make it more likely that someone has worked on exactly what you have.
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Old 10-16-2021, 08:37 PM   #3
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Done, see original post. Not sure why my signature doesn't show up on mobile.
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1993 Gulf Stream Scenic Cruiser diesel pusher, 5.9 Cummins, 6 speed Allison. I tend to act before I think. It gets me into trouble, and so I end up here in the forums asking for help. I learn the hard way. Thank you all for your help.
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Old 10-17-2021, 12:59 AM   #4
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To me it looks like a clevis attached to a threaded rod with a nut. But it seems there isn't much rod left to adjust does this mean I need new shoes? Should I just max out the threaded rod on the clevis and see? Just turn with a wrench with the parking brake disengaged?
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Old 10-17-2021, 05:41 AM   #5
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Be sure not to over tighten/adjust the brakes. You don't want the parking brake "dragging" when it is released as the shoes could overheat going down the road and maybe start a fire.
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Old 10-17-2021, 05:59 AM   #6
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Does this have a ‘foot brake’ or a ‘hand brake’ in the drivers compartment?
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Old 10-17-2021, 01:54 PM   #7
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This is an air parking brake. Yellow knob is pulled to presumably release air which holds that spring. When the spring is pulled back to its resting state, the shoes make contact with the drum. When I push the knob, air is forced into the system and the spring is put under tension, which then removes the shoes from the drum.

I'm wondering if anyone knows if I'm supposed to adjust it using that clevis and bolt/nut in the picture I posted. I'm worried because the bolt is almost gone, I'm guessing because previous owners have tightened it already.
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Old 10-18-2021, 08:05 AM   #8
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Yes, that linkage would be the means to adjust it.
Whether you shorten or length the rod depends on if the linkage pulls the brake On or if it pushes/extends to apply the brake.

If the linkage pulls when brake is applied, then you would shorten the rod to make the brake apply harder. And vise-versa. I cant tell from the photo how the linkage is setup.

When you make adjustments you need to have the Coach jacked up in the back (and block the front tires so it can't roll away), or disconnect the driveshaft, so you can turn the brake drum and make sure it is not dragging when in the released position (adjusted too tight).
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Old 10-18-2021, 07:52 PM   #9
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Quote:
Originally Posted by CountryB View Post
Yes, that linkage would be the means to adjust it.
Whether you shorten or length the rod depends on if the linkage pulls the brake On or if it pushes/extends to apply the brake.

If the linkage pulls when brake is applied, then you would shorten the rod to make the brake apply harder. And vise-versa. I cant tell from the photo how the linkage is setup.

When you make adjustments you need to have the Coach jacked up in the back (and block the front tires so it can't roll away), or disconnect the driveshaft, so you can turn the brake drum and make sure it is not dragging when in the released position (adjusted too tight).
Because the arm moves up to release the brake, and down to engage, I think I need to make the arm shorter. To me though it looks like there isn't much left, if anything, to shorten. If that's the case, is it time for new shoes?
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Old 10-19-2021, 11:53 AM   #10
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Before adjusting the rod length , look very carefully at the drum or backing plate for an oval rubber plug 1/2" x 1 1/2", that would be access to a star wheel adjuster for the brake shoes .
If someone has adjusted the rod length , without adjusting the shoes using the star wheel , undoing the rod adjustment will probably be required before the shoes can be properly adjusted.
Proper adjustment of these systems is a balancing act; it would be great to figure out a brand name of the park brake system, to get instructions.

The plug , if in the drum ( blue oval ) may require the drum be turned to line up with the star wheel for the shoe adjustment .
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Old 10-19-2021, 01:26 PM   #11
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Quote:
Originally Posted by Skip426 View Post
Before adjusting the rod length , look very carefully at the drum or backing plate for an oval rubber plug 1/2" x 1 1/2", that would be access to a star wheel adjuster for the brake shoes .
If someone has adjusted the rod length , without adjusting the shoes using the star wheel , undoing the rod adjustment will probably be required before the shoes can be properly adjusted.
Proper adjustment of these systems is a balancing act; it would be great to figure out a brand name of the park brake system, to get instructions.

The plug , if in the drum ( blue oval ) may require the drum be turned to line up with the star wheel for the shoe adjustment .
Thanks for the information, I know some drums are adjusted using a star wheel on the drum itself. I'll look to see if there is one, once I get back to my motorhome. Otherwise is there any way to determine the brand? Here's another picture, albeit not the best.
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Old 10-19-2021, 02:16 PM   #12
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I'll see if a Google search will turn up anything on manufacturer of the brake .

When using a mobile app to post in the forums , signature lines don't appear , not sure if site administrators are looking for a fix .
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