Home » Public Forums » GMCnet » Sanity check on rear brakes
| Sanity check on rear brakes [message #307296] |
Sat, 17 September 2016 17:57  |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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So, I did a brake/bearing service on the rear four wheels...
1) New 1-1/16" wheel cylinders on the middle bogies, one new 15/16" cylinder on the rears (the other one was fine)
2) New "Thermo quiet" brake shoes on all four wheels
3) Cleaned and re-packed all four wheel bearings
4) Cleaned and lubed (as much as possible) the parking brake cables - they were pretty sticky before, all seem to move OK now
5) Adjust the brakes by turning the adjusters to "really dang tight", then backing them off to where they're easy to spin by hand, and are obviously "free" at at least one point in the rotation (they pass the "ring test").
6) Gravity bled the brakes - I'm sure I still need to do a good old-fashioned "real bleed", as the pedal is a little soft, but gets really stiff before it hits the floor.
Took it out for a spin, and stopped after a couple miles of stop and go driving, and all the drums were warm, but none were really hot. Ran the coach up and down the freeway a few miles, and did a few "both feet panic stops" from speed (~50mph, down to probably 30mph), and one or two 35-0 full stops. All this was in the last 1/2 mile of driving.
Got it backed into the warehouse, and checked the temperatures of the drums. The two on the left side were nice and warm, but I could touch either of them with my finger, lightly (no way I could leave my finger there though).
The two drums on the right were well over 212° based on the "spit sizzle test" (no fingers involved). The middle wheel drum was obviously hotter than the rear wheel drum.
I jacked up the right side, and with a stiff push with my foot, the rear (cooler drum) wheel would rotate about 3 revolutions before stopping. The front (hotter drum) went around 15 times. The bearings both feel good with just the tiniest bit of discernible play when you push/pull on the wheels.
My guess is that the middle right drum is hotter because it's working better than the others, which I'm guessing might have something to do with less contamination on the pads and drum during reassembly (it was the least fiddly of the bunch), and that the others will "come around" as they're used and bed in. Or possibly, there is air in the lines on the other "cooler drum wheels"?
Anyone out there agree / disagree with my SWAG?
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Sanity check on rear brakes [message #307299 is a reply to message #307296] |
Sat, 17 September 2016 18:25  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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habbyguy wrote on Sat, 17 September 2016 18:57So, I did a brake/bearing service on the rear four wheels...
<snip>
5) Adjust the brakes by turning the adjusters to "really dang tight", then backing them off to where they're easy to spin by hand, and are obviously "free" at at least one point in the rotation (they pass the "ring test").
6) Gravity bled the brakes - I'm sure I still need to do a good old-fashioned "real bleed", as the pedal is a little soft, but gets really stiff before it hits the floor.
<snip>
Mark,
Gravity Bleed is as good as anything else.
Pressure bleed is faster, but can blow past trapped air.
Vacuum bleed needs the screws sealed with pipe dope or teflon tape, but it is still faster than gravity bleeding.
If you left the self adjusters in, wait a few trips, then get rolling backwards in a big lot and jam the brakes a few times. They will then be adjusted as well as they can ever be. Self adjusters do work if you keep them free and use them.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: Sanity check on rear brakes [message #307300 is a reply to message #307296] |
Sat, 17 September 2016 18:30 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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It just occurred to me that I should mention that the one wheel that's getting the hottest is the only one that "acted right" when I adjusted it - that is, I snugged it up, then backed off the adjuster, and it spun free 360°.
All the others were dragging at least a little by the time the adjuster was backed off enough for them to "ring" at one point in a rotation (meaning that the shoes were no longer contacting the drum). None were dragging enough to concern me, based on me being able to easily spin the wheels by hand and get at least a couple rotations (that's not gonna be enough drag to generate any serious heat, IMHO). But would that also indicate that the shoes / drums have to "bed in" to get a perfect match between the surfaces, and that the braking might be compromised until that happens?
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Sanity check on rear brakes [message #307301 is a reply to message #307299] |
Sat, 17 September 2016 18:34 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Quote:If you left the self adjusters in, wait a few trips, then get rolling backwards in a big lot and jam the brakes a few times. They will then be adjusted as well as they can ever be. Self adjusters do work if you keep them free and use them.
Matt
Yep, I left them in, and they seemed to be free and able to do their job. They all "ratcheted" when I was tightening the self-adjusters to center to brakes, and had to be released to loosen them again. I did a few "full brake reverse stops", but only from 5mph or so. I'll do a few more of those (in a MUCH bigger parking lot than I was using) and see if things get better.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Sanity check on rear brakes [message #307335 is a reply to message #307296] |
Sun, 18 September 2016 13:38 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Yes, things got better. After every few reverse stops, the brakes got better. Soon enough, I was leaving skid marks (from the rear wheels, no doubt), and the coach was stopping better than it ever did. Hooray.
I do want to take it out after the drums (finally!) cool down - the middle drums were near 300 degrees, and the rears about 220 degrees. That's after quite a few hard stops, but with five miles or so of "normal driving" before taking the temperatures.
I believe this might be partly because of the parking brake. After the "self-adjusting session" in the parking lot, I could only pull the lever up a couple inches. I had to unscrew the cap a LOT to get it adjusted properly (or as close to properly as these things get), but I did that after I got back to the warehouse and measured the drum temperatures.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] Sanity check on rear brakes [message #307339 is a reply to message #307335] |
Sun, 18 September 2016 14:20 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Remember that drums expand quite a bit as they warm up. So, adjusting them
when hot might result in some dragging of the rear brakes when they are
completely cold. The idea is to have them right when at normal operating
temperature. The extremes just have to take care of themselves. What you
don't want, is to have the drums expand so much that you sacrifice some
braking effort. (Fade)
Many coach owners, myself included, never apply the parking brakes for
the reasons that you described. They don't always release completely and
the result is dragging brakes. Be careful locking up the rear tires, they
are easily flat spotted. The different sized wheel cylinders should help
some in that regard. The final solution would be the reaction arms. That
system really does work well.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Sep 18, 2016 11:39 AM, "Mark" wrote:
> Yes, things got better. After every few reverse stops, the brakes got
> better. Soon enough, I was leaving skid marks (from the rear wheels, no
> doubt), and the coach was stopping better than it ever did. Hooray.
>
> I do want to take it out after the drums (finally!) cool down - the middle
> drums were near 300 degrees, and the rears about 220 degrees. That's after
> quite a few hard stops, but with five miles or so of "normal driving"
> before taking the temperatures.
>
> I believe this might be partly because of the parking brake. After the
> "self-adjusting session" in the parking lot, I could only pull the lever up
> a
> couple inches. I had to unscrew the cap a LOT to get it adjusted properly
> (or as close to properly as these things get), but I did that after I got
> back to the warehouse and measured the drum temperatures.
>
>
> --
> Mark Hickey
> Mesa, AZ
> 1978 Royale Center Kitchen
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: Sanity check on rear brakes [message #307349 is a reply to message #307296] |
Sun, 18 September 2016 15:53 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Started the test drive with all the drums right around 100°. Did a few miles of (careful, slow) stop and go, and stopped to check them again. The rear drums were around 115° and the middle drums 125° (I should mention it's in the high 90's outside today).
Also, the brake pedal seems good and stiff, so I'm going to forego any additional bleeding.
Seems good to me, so I'm going to call this one fixed and done.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
[Updated on: Sun, 18 September 2016 18:45] Report message to a moderator |
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| Re: [GMCnet] Sanity check on rear brakes [message #307357 is a reply to message #307349] |
Sun, 18 September 2016 18:55 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Mark,
make sure you have replaced the rubber hose, as they collapse and will not
let the fluid back out of the cylinders.
On Sun, Sep 18, 2016 at 1:53 PM, Mark wrote:
> Started the test drive with all the drums right around 100°. Did a few
> miles of (careful, slow) stop and go, and stopped to check them again. The
> rear drums were around 115° and the rears 125° (I should mention it's in
> the high 90's outside today).
>
> Also, the brake pedal seems good and stiff, so I'm going to forego any
> additional bleeding.
>
> Seems good to me, so I'm going to call this one fixed and done.
> --
> Mark Hickey
> Mesa, AZ
> 1978 Royale Center Kitchen
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: Sanity check on rear brakes [message #307396 is a reply to message #307296] |
Mon, 19 September 2016 10:38 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Thanks, Jim... I'll be replacing those soon - they look "OK" but I know they can age out and cause problems. It seems that the brakes are (finally) dialed in and working better than they ever have for now, so I'll be replacing those lines a little later.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] Sanity check on rear brakes [message #307399 is a reply to message #307396] |
Mon, 19 September 2016 11:01 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Great, the springs will look good, but the trick of dropping it on concrete
does work.
On Mon, Sep 19, 2016 at 8:38 AM, Mark wrote:
> Thanks, Jim... I'll be replacing those soon - they look "OK" but I know
> they can age out and cause problems. It seems that the brakes are (finally)
> dialed in and working better than they ever have for now, so I'll be
> replacing those lines a little later.
> --
> Mark Hickey
> Mesa, AZ
> 1978 Royale Center Kitchen
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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