Home » Public Forums » GMCnet » Rear Brakes Dragging
| Rear Brakes Dragging [message #300008] |
Mon, 02 May 2016 04:00  |
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thainglo
Messages: 132
Registered: March 2015
Location: Iowa
Karma: 2
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Senior Member |
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In preparation for the GMC Midwest June rally, I want to dig back into my rear brakes to try and improve performance. I'd replaced shoes and springs last summer and have less than 50 miles on them. It seems to take a lot of effort on the brake pedal to come to a stop. I decided to put in all new wheel cylinders with 1 1/16" on middle bogey and 15/16" on rear. Jacked up the rear yesterday just to get a look and was surprised to find that each wheel takes a significant effort to turn by hand.
Are the brake drums supposed to be that difficult to turn when properly adjusted? I'm certain I set the adjustment last year according to the FSM, which states to back off 30 clicks once the shoes drag on the drum.
The rear brake lines were replaced roughly 10-15 years ago with units from Cinnabar. Could those have failed?
I had adjusted the parking break at that time as well, need to check it is properly releasing.
Any help much appreciated!
Matt
Matt Sladek
1976 Eleganza II
Coralville, IA
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| Re: Rear Brakes Dragging [message #300011 is a reply to message #300008] |
Mon, 02 May 2016 07:38  |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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Matt,
You are over 50% of the way to a completely renewed brake system. Buy and install a new master cylinder(they are cheap), then Give Jim Bounds a call and get a proportioning valve. You will sleep better at night. As for the rear hoses, you have to use your judgement.. I would believe them to be good, if only 12 years old, and I don't think your brake drag has anything to do with a bad hose. I would think you would have ALOT more drag, or you would have one brake alot hotter then the rest. That is my guide as to if the brakes are dragging, is by measuring the temps and comparing.
As for the holes for the adjusters, when i did my rear brakes last year, one side popped right out with a hammer, chisel, and pliers.
The other side, as you said, I hit it with air chisel, hammers, and then I ended up doing like Wally stated... Drilled them out and filed them to size with a rotary file in a die grinder. What a PAIN!.
My personal opinion on what you are describing, is not all a rear brake problem?? It sounds more Master/booster, or proportioning valve problem. I like Wally's idea of testing the brake pressure to see what is going on.
Now if you do decide to dive into more Brake parts and open up the system, send me an email.... I could send down my Hupy bleeder with my crew if you want to use that.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: [GMCnet] Rear Brakes Dragging [message #300015 is a reply to message #300009] |
Mon, 02 May 2016 08:57 |
powerjon
Messages: 2446
Registered: January 2004
Karma: 5
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Senior Member |
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Matt,
The rear brake lines are beyond the 10 year limit. I would suggest that you replace the rear rubber brake lines a they present one of the symptoms that you have written about. The lines tend to swell up inside and severely restrict the brake fluid and sometime block the brakes from totally releasing. If you replaced the fronts when you installed the 80MM in the fronts you should be OK there as you had to go to a banjo type connection line to the caliper.
The rear the wheels should move or have a very slight drag with the brake peddle released. The adjustment is to back off 3 or 4+ clicks until the wheels turn, not 30 clicks, you may have had a mistype. If the rear rubber “T” brake lines have never been replaced then do so. http://www.appliedgmc.com/prod.itml/icOid/786 As for removing rubber plugs for adjusting the brakes take a knife and cut them out and replace with new, the old ones are hard and way pass use. Parking brake could be an issue but it should be slightly loose.
or
http://tinyurl.com/jo5n2z2
If you determine that you need to replace the Master Cylinder then this is the part number that is recommended. The mounting ears will need to be cut down to .500 thickness as the thickness varies. This is the part# that Dave L uses.
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=MC39075
or
http://tinyurl.com/zrcc9vg
As for your booster if it is stock then a sensitize unit would be a next step. I run the same braking system on my Buskirk Stretch that Dave Lenzi makes and uses. That includes the MC39075 master cylinder, DL built Sensitized booster, DL aluminum check spacer with pressure ports, Ford Astair Vacuum pump set at 21”Hg, 80MM front calipers, Leigh Harrison 12 1/2 in Ford rotors with 80MM calipers on the middle bogey, GMC drum brake system featuring John Evans carbon metallic shoes, all new interior parts, 15/16 inch slave cylinder, still using the stock combination valve and this was installed in Oct 2015. This is the best brakes bar none that I have had in the past 19 years in all the coaches that I have owned. You have to determine how far you need to go for brake that you feel that are acceptable.
Regards,
JR Wright
GMC Great Laker MHC
GMC Eastern States Charter Member
GMCGL Tech Editor
GMCMI
78 GMC Buskirk 30’ Stretch
1975 GMC Avion (Under Reconstruction)
Michigan
> On May 2, 2016, at 5:14 AM, Matt Sladek wrote:
>
> I should describe symptoms better. Brake pedal is firm the whole way, not spongy like air is trapped in the lines. It just seems to require a lot of
> effort to get the coach to come to a complete stop. Earlier this week I confirmed good vacuum to brake booster and a good check valve at booster. I
> have the OEM (could be original) master cylinder. Looks like original proportioning valve. Upgraded to 80mm front calipers when I did rear shoes last
> year.
>
> Related question, does anyone have a trick to remove the inspection plugs on the backing plates? I got after one yesterday with a cold chisel like
> the manual shows and made absolutely zero progress. Couldn't get a very good angle on it, but still think I got a few good raps in with the hammer.
> --
> Matt Sladek
> 1976 Eleganza II
> Coralville, IA
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J.R. Wright
GMC GreatLaker
GMC Eastern States
GMCMI
78 30' Buskirk Stretch
75 Avion Under Reconstruction
Michigan
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| Re: [GMCnet] Rear Brakes Dragging [message #300016 is a reply to message #300011] |
Mon, 02 May 2016 08:50 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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If those slots are still intact, how are you adjusting the shoes? When I
repair drum brakes, I use the following procedure on adjustment. Adjust the
star wheel until you have no remaining movement. Then, while holding the
self adjuster pawl retracted, back off 5 clicks and try to turn the wheel.
If you can't, back off 5 more and repeat. Do this until a light resistance
is felt. This process will completely center the shoes in the drums.
REMEMBER DRUMS EXPAND WHEN WARMED UP, AND SOME DRAG WILL GO AWAY. Test
drive the coach and shoot the rear brakes with an infrared thermometer. If
you have big and little wheel cylinders, each pair will be slightly
different temps, but should be close side to side.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On May 2, 2016 5:59 AM, "Jon Roche" wrote:
> Matt,
>
> You are over 50% of the way to a completely renewed brake system. Buy
> and install a new master cylinder(they are cheap), then Give Jim Bounds a
> call and get a proportioning valve. You will sleep better at night. As
> for the rear hoses, you have to use your judgement.. I would believe them
> to
> be good, if only 12 years old, and I don't think your brake drag has
> anything to do with a bad hose. I would think you would have ALOT more
> drag, or
> you would have one brake alot hotter then the rest. That is my guide as
> to if the brakes are dragging, is by measuring the temps and comparing.
>
>
> As for the holes for the adjusters, when i did my rear brakes last year,
> one side popped right out with a hammer, chisel, and pliers.
>
> The other side, as you said, I hit it with air chisel, hammers, and then I
> ended up doing like Wally stated... Drilled them out and filed them to size
> with a rotary file in a die grinder. What a PAIN!.
>
>
> My personal opinion on what you are describing, is not all a rear brake
> problem?? It sounds more Master/booster, or proportioning valve problem.
> I
> like Wally's idea of testing the brake pressure to see what is going on.
>
> Now if you do decide to dive into more Brake parts and open up the
> system, send me an email.... I could send down my Hupy bleeder with my
> crew if
> you want to use that.
>
>
>
>
> --
> Jon Roche
> 75 palm beach
> St. Cloud, MN
> http://lqqkatjon.blogspot.com/
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: Rear Brakes Dragging [message #300019 is a reply to message #300008] |
Mon, 02 May 2016 09:38 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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All good advise but if you are pretty sure a shoe is dragging pry each shoe away from the top pin with a large screwdriver an inch or so and see if it returns when you remove the screwdriver if it doesn't return ,the return springs have lost there tension and will need to be replaced. The parking brake cables can also add to the problem if they don't move freely.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Rear Brakes Dragging [message #300042 is a reply to message #300040] |
Mon, 02 May 2016 14:09 |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
Karma: 5
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Senior Member |
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yes. I have his plate for the OEM master cylinder.
mine is actually a Motive bleeder, and I have the Motive Plate as well:
https://www.motiveproducts.com/collections/domestic-bleeder-kits/products/power-bleeders-multiple-adapter-kits
I bought that because I wanted to use it for lots of other cars(and have), but I found the plate that came with the Motive Bleeder a little large to get a good seal without some rigging.
So when I was in Oregon, I picked up the plate from Jim, and his plate is alot thicker, stronger then the motive plate, and works great! So I even have used his plate on some other vehicles.(a few different jeeps).
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: Rear Brakes Dragging [message #300085 is a reply to message #300008] |
Tue, 03 May 2016 08:39 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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'I'm leaning towards a parking brake adjustment issue as the drum still dragged with the drum adjustment screw all the way in. '
Did you center the shoes after you replaced the drum? If they are offset a bit they may drag even though they're proper;y adjusted. If you didn't, when you put the drum back on, get in the coach and stomp the brakes HARD a time or two, to make the shoes center on the backing plate and touch the drum equally all around. Than see if there's a drag.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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