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10-14-2020, 11:08 PM | #1 |
Registered User
Join Date: Apr 2019
Location: Fort Lauderdale, Florida 33311
Posts: 101
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All new brake system: rears lock up and drag with weight in bed?
I'm not really sure where to look, at this point, but I'm beyond frustrated.
About 3 months ago I picked up a 71 LWB (350/350 auto) and on the test drive quickly realized the brakes went to the floor and there was almost no stopping power at all. So, I YOLO'd it home 2 hours (all back roads or long, open highways across the middle of Florida) with the expectation of making it my daily driver. In the process of getting her to DD status, it took about a month to finally give up on the brakes and replace everything with new. So, now it's got a Wilwood 4poston disc front, Wilwood 2.5" Drop spindles with a 1" CPP spring, Belltech shocks, Wilwood master cylinder, Wilwood proportioning valve, chrome double hump booster, stainless front lines, etc... And out back, I replaced the stock drums, wheel cylinders, soft lines, shoes, 5 inch springs, and matching shocks. The only thing left from the original system is the hard lines. So, with all that, the truck stops great, but ONLY if there's no weight in the bed. The SECOND I throw even a few hundred pounds back there, and as soon as you hit the brakes, the rears lock up and eventually drag until they decide to release. (discovered this with a friend's 5.3 LS long block in the bed) I'm not sure what to do after spending several thousand dollars on brakes, but the real concern here is it definitely can't tow even a small trailer, so I'm super frustrated. If anyone has some tips as to where to look, I'm all ears and entirely appreciative. Thanks!!! �� |
10-14-2020, 11:37 PM | #2 |
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Join Date: Aug 2009
Location: Bowser
Posts: 13,671
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Re: All new brake system: rears lock up and drag with weight in bed?
Pics of your master and prop valve might help.
You might need an additional adjustable prop valve in the rear line. |
10-15-2020, 08:08 AM | #3 |
Registered User
Join Date: Mar 2020
Location: NJ
Posts: 12
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Re: All new brake system: rears lock up and drag with weight in bed?
I agree with the above. I have heard of many disk/drum conversions where the rears lock up, and as mentioned the solution is usually an additional adjustable prop valve in the rear brake line. As far as them dragging, that sounds like some kind of residual pressure valve that is wrong for a drum application, but I'm not really sure there.
I am in the process of converting to 4 whl disk and hope it isn't an issue. Wilwood should also be able to tell you what going on with their system and their prop valve.
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1969 C-10 Supercharged 355 12.20@104 1968 Firebird Nat.Asp. 355 12.50@106 2002 GMC 2500HD Duramax 13.0@104 |
10-15-2020, 09:43 AM | #4 |
Moderator
Join Date: Dec 2012
Location: ON, Canada
Posts: 2,162
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Re: All new brake system: rears lock up and drag with weight in bed?
My bet is on "four wheel disc brake master cylinder" when it should be a disc/drum master.
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10-15-2020, 10:17 AM | #5 |
Registered User
Join Date: Jul 2018
Location: Catskill Mountains,NY
Posts: 8,588
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Re: All new brake system: rears lock up and drag with weight in bed?
Seems weird the rears would lock up when loaded only . If it was the portioning valve giving to much pressure they would lock all the time more so when empty. Same with the master. Could it be the parking brake is engaging when the rear drops a little? Could be causing the cable to tighten .
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Mark 72 c20 custom camper Husky edition, 66 SS396 Chevelle 1964 Hawk, 63 Avanti,62 lark 1969 AMX , 1968 c20 stepside ,85 K20 1977 Suburban sold 68 anniversary. |
10-15-2020, 11:53 AM | #6 | |
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Join Date: Jul 2015
Location: Sedalia Mo.
Posts: 1,131
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Re: All new brake system: rears lock up and drag with weight in bed?
Quote:
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He who is without oil shall throw the first rod. Compressions 8.7:1 1972 C10 1976 C10 (parts truck) 1985 K20 |
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10-15-2020, 11:55 AM | #7 |
Registered User
Join Date: Jul 2012
Location: Whitehorse yukon
Posts: 1,218
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Re: All new brake system: rears lock up and drag with weight in bed?
Could the back brakes be dragging slightly at all times just more noticeable while carring extra weight
My question have you talked to wildwood about your setup ? |
10-15-2020, 12:05 PM | #8 |
Senior Member
Join Date: Dec 1999
Location: Southern California
Posts: 2,839
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Re: All new brake system: rears lock up and drag with weight in bed?
Saw you replaced the "soft lines" Any chance the rear is being kinked because of the drop?
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Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 |
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