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Old 06-01-2013, 10:41 PM   #1
Jimbo0076
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"Load Sensing" Brake Valve on '85 K2500

Got a good question for yall fine fellers here. I own a '85 GMC K2500 that I've had for a good while. It has a valve in-line of the rear brake lines that has a rod hooked to the rear semi float 14 bolt. This valve(if its like the ones on late 80s Toyota 4WD trucks) should allow more or less brake fluid pressure to the rear drums depending on how much of a load the truck has in the bed(if Im thinking right) Problem is this little valve has started leaking around one of the lines so I need to replace or get rid of all together. It is very simple and has a brake line in and out and is mounted on a frame bracket right close to the rear axle. I found a Wilwood brake portioning valve I thought about replacing it with but didnt know if that would be a good idea or what would be my best bet. Even thought about tossing it and put a union on the brake lines but didnt know if that would cause me to have rear brake lock up problems.
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Old 06-01-2013, 10:57 PM   #2
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Re: "Load Sensing" Brake Valve on '85 K2500

That thing is commonly tossed. A friend of mine removed his and the brakes worked fine.
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Old 06-01-2013, 11:48 PM   #3
meatwagon83
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Re: "Load Sensing" Brake Valve on '85 K2500

mine is bypassed, my truck stops fine!
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Old 06-02-2013, 08:44 AM   #4
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Re: "Load Sensing" Brake Valve on '85 K2500

lots here seem to bypass those without issues
they are used on lots of other makes /vans etc now too,
hard braking can lift the rear when empty,puts more braking to the front,keeps the back from skidding
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Old 10-29-2013, 09:13 PM   #5
Jsfucttruck
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Re: "Load Sensing" Brake Valve on '85 K2500

Does anyone know what size those fittings are going in/out of that valve? I got a buddy that doesn't want to crack his lines loose until he has the right fittings/hose to replace his.
Thanks.
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Old 10-30-2013, 07:02 PM   #6
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Re: "Load Sensing" Brake Valve on '85 K2500

1/4" tubing in and out - so the fittings would be 7/16" - 20.
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Old 10-30-2013, 07:24 PM   #7
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Re: "Load Sensing" Brake Valve on '85 K2500

Bypassed a 3500 that was lowered.
We just turned the T of the flex towards the front.
Best peddle the trucks ever had.
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Old 10-30-2013, 07:24 PM   #8
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Re: "Load Sensing" Brake Valve on '85 K2500

Delete double posted.
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Old 10-30-2013, 08:02 PM   #9
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Re: "Load Sensing" Brake Valve on '85 K2500

I'm in the process of deleting mine right now. In my case, the way its oriented allows me to slightly tweak the line coming into it to line up with the brake hose that comes out of it.

Unbolt and toss, tweak line, screw line into hose, install little clamp to hold it in place.
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Old 10-30-2013, 09:04 PM   #10
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Re: "Load Sensing" Brake Valve on '85 K2500

I just zip tied it on the wide open position.
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Old 10-30-2013, 10:43 PM   #11
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Re: "Load Sensing" Brake Valve on '85 K2500

Good thread. I want to remove the valve on my 1 ton. I was also thinking of just replacing all the lines sometime and elliminating the valve then.
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Old 10-31-2013, 03:58 AM   #12
chengny
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Re: "Load Sensing" Brake Valve on '85 K2500

FWIW - The TSB recommending removal and the approved GM removal procedure:

GMC NUMBER: 88-T-151

GROUP: 5 - Brakes

DATE: August, 1988

CORPORATE NUMBER: 865010R
SUBJECT: REAR BRAKE SENSITIVITY - HEIGHT SENSING VALVE REMOVAL

MODELS: 1984-86 C/K 3500 AND 1987-88 R/V 3500

THIS BULLETIN IS A REVISION OF TRUCK SERVICE BULLETIN 85-B-79, DATED MAY, 1985, UPDATING FOR MODEL YEARS 1984-1988.
1984-1986 C/K 3500 and 1987-1988 R/V 3500 series trucks are equipped with a rear suspension height sensing device that optimizes the brake proportioning valve setting for the load the vehicle is carrying. The height sensing system adjusts the brake balance in vehicles subjected to a range of loading conditions. Occasionally, vehicle modifications by body builders or owners influence the height sensing device. If a vehicle has had rear suspension modifications that affect its trim height or the spring rate, and the driver comments about the brake modulation characteristics of the vehicle, it is recommended that the height sensing system be removed and the brake system be revised as described below:









Parts listed below are currently available from GMSPO.

1. Detach rear brake hose from lever and bracket assembly. Reference Figure No. 1.

2. Remove lever assembly and bracket from axle.










3. Install rear brake hose bracket (P/N 348978) and spacer (P/N 2355099) with a 3/8-16 x 1.38 bolt (P/N 358000 - shorter bolt removed in Step No. 2) in the upper cover hole. Reference Figure No. 2. Use Loctite 75 or equivalent on the bolt threads.

4. Attach brake hose to bracket with bolt from original installation.

5. Install a 3/8-16 x 1-3/4 bolt (P/N 9439637 - longer bolt removed in Step No. 2) through spacer P/N 14055556 (removed in Step No. 2) in remaining axle cover attaching hole. Use Loctite 75 on bolt threads or equivalent.

6. Disconnect brake pipes from height sensing valve and brake hose, and discard short brake pipe. Reference Figure No. 1.

7. Remove and discard height sensing valve, bracket, and bolts.

8. Carefully reposition the rear brake pipe, and connect it to the rear brake hose.

9. Bleed and test brake system per Section 5 of the appropriate Light Duty Service Manual.
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Old 10-31-2013, 07:02 AM   #13
Keith Seymore
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Re: "Load Sensing" Brake Valve on '85 K2500

Quote:
Originally Posted by chengny View Post
FWIW - The TSB recommending removal and the approved GM removal procedure:...
Very nice.

By way of background it was placed there specifically as a "test beater" to pass the unladen portion of FMVSS 105 and FMVSS 208 brake tests.

We also used specially trained brake test drivers who we knew could achieve the best stopping distances, to help ensure passing the test.

Lastly, there was no limit to how many attempts we could make so we could also keep testing until we got the truck/configuration to pass.

I say all this to say: removing the valve should not be a problem. It was released to address this one (very specific) test situation and not for general use or customer pleasability.

K
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Old 10-31-2013, 09:58 AM   #14
dieseldawg142
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Re: "Load Sensing" Brake Valve on '85 K2500

my valve must have been closed a bit 'cause my brakes firmed up some after i removed it
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