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Fixing the old truck

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Joined: Nov 2001
Posts: 128
F
Wrench Fetcher
Wrench Fetcher
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Joined: Nov 2001
Posts: 128
I just took my 46 gmc 1/2 ton out for it maiden voyage, which was about 1 mile around the block. I noticed at about 1/2 mile, there was some drag. When I got in the driveway, there was a noticable drag almost like the emergency brake was left on.
I jacked up the front end, and both front wheels were very difficult to turn. I thought I left enought wheel bearing play, but now I am asking for help. I will check the bearing once things cool down, but any other suggestions??

Joined: Nov 2001
Posts: 128
F
Wrench Fetcher
Wrench Fetcher
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Joined: Nov 2001
Posts: 128
Ok, bearing is fine, and not tight. I loosened it and it did not change the tightness. So I loosened the bleed screw, and out came fluid. About a table spoon amount. I tightened back up on the screw, and the disk is now free. Any help??

BY the way, I have a mustang duel master cyylinder for a drum/disc setup which is recommended by many others who have done it in the past.

Joined: Oct 2003
Posts: 5,152
O
Cruising in the Passing Lane
Cruising in the Passing Lane
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Joined: Oct 2003
Posts: 5,152
Did you use residual valves?

It sounds like you have a drum brake residual valve on the disk brakes.


1955 1st GMC Suburban | 1954 GMC 250 trailer puller project | 1954 GMC 250 Hydra-Matic | 1954 Chevy 3100 . 1947 Chevy COE | and more...
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Joined: Nov 2005
Posts: 238
S
Shop Shark
Shop Shark
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Joined: Nov 2005
Posts: 238
You don't say if you have an inline vacuum servo (booster) on your setup, but it sounds like you may have a problem caused by having no free play in the brake operating rod that goes into the master. If you have a booster that will need to be adjusted to allow some free play onto the master piston.

If you have a plain dual circuit master there needs to be a minimum 1/16" free play in the rod from your pedal when the pedal is in the released position; if you don't have this, the brake fluid jams the brakes on when it expands with heat when you drive your truck.

Stuart.

Joined: Feb 2004
Posts: 28,674
H
Kettle Custodian (pot stirrer)
Kettle Custodian (pot stirrer)
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Joined: Feb 2004
Posts: 28,674
+1 on the residual valve suggestion. If the master cylinder does not match the caliper, it's probably holding pressure on the piston. Drum brake M/C's have a check valve that holds a few pounds of pressure against the shoe return springs. Since disc brake calipers have no return springs, the residual pressure valves aren't required, and they can cause major brake drag problems if they're used. Disc brake M/C's also have a larger fluid reservoir for the calipers than for the rear wheel cylinders.
Jerry


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