Hello. Could some one with a stock hight M1008, Please meassure the distance between the 2 pivot points (top to botton) on the rear load proportioning brake valve dog leg. Tha bracket I spot welded to make up for my lift kit, fell off and I can't remenber (5 years since) the meassurment, to keep it working right. Thanks.
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M1008, brake/cargo? load valve bracket
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GreenBull
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You may choose to remove it on a lifted M1008. Keep in mind that the function of the valve is to reduce rear brake force by metering fluid pressure made by the master cylinder. The intent is to prevent rear brake lockup. Llfts and oversized tires tend to increase suspention travel and increase dive/ weight transfer on hard braking. These can reduce rear brake effectiveness in certain situations.
My first questions to you is whether you have the capacity to evaluate the vehicles braking performance in both its normal expected usage and panic situations on wet/slippery pavement?
If yes, you want to test with the vehicle with the lightest GVW and valve arm full up first.
Based on my experience with lifted big wheel Chevrolet trucks you want all the brake force you can get and its a bad thing when you are heading anywhere back end first with the PRNDL in D. YMMV.
If the above test reveals the braking performance is to your satisfaction. You can bust out the duct tape and bailing wire or follow the TSB.
#88-320-5: REAR BRAKE SENSITIVITY (HEIGHT SENSING VALVE REMOVAL) - (Aug 3, 198
My first questions to you is whether you have the capacity to evaluate the vehicles braking performance in both its normal expected usage and panic situations on wet/slippery pavement?
If yes, you want to test with the vehicle with the lightest GVW and valve arm full up first.
Based on my experience with lifted big wheel Chevrolet trucks you want all the brake force you can get and its a bad thing when you are heading anywhere back end first with the PRNDL in D. YMMV.
If the above test reveals the braking performance is to your satisfaction. You can bust out the duct tape and bailing wire or follow the TSB.
#88-320-5: REAR BRAKE SENSITIVITY (HEIGHT SENSING VALVE REMOVAL) - (Aug 3, 198
Model and Year: 1984-86 C/K 30 SERIES 1987-88 R/V 30 SERIES
1984-1986 C/K 30 and 1987-1988 R/V 30 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 34897 and spacer (P/N 2355099) with a 3/8-16 x 1.38 bolt (PIN 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.
1984-1986 C/K 30 and 1987-1988 R/V 30 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 34897
and spacer (P/N 2355099) with a 3/8-16 x 1.38 bolt (PIN 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.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
AJMBLAZER
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Now that's interesting...
Hello and thanks for the reply. I just so happen to have 3 of 4 of the DMV inspection results. The brakes were check at DMV in Sep. '04 as purchased from the GSA with 59K miles, inspected with jack spare, full plus driver at around 5975lbs. brakes checked fron about 15 mph =OK. specs ALL OK with in tolerances. left to right and front to rear bias and ones again after the lift in April '05 as a safety courtecy after the 5.5" spring lift and on Humvee's 36" tires and wheels. Ones again OK pass The 3rd Sep. '06( I have lost it) but she pass OK The 4th. in Sep '08 after and D60 end to end rebuilt and ugrades of the Dana 60, including New callipers rear cylinder,SD pads and shoes, hardware and s/s braided lines, flush out and refill manually with DOT 5. The results were near perfect @ 6472lbs from 13.8 mph with cargo. and driver weight. This iOct. I put the 235x80x16 back for fuel savings and this past week from 45-55mph she wanted to bring the rear around. I look and found that the bracket extencion I had aded to comoensate for the 5.5 spring lift had come OFF. I think the height sensor valve works and work well at 6400lbs and the couple of times I PULL more the 2x times that weight.
Westech
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In my shop(s) we took the valves out.. 99% of the time they did not work worth a crap anyway. We would take the valves out and adjust the brakes a tad loose in the rear.
PS. Rest assure there are no "DUCK TAPE OR BAILING WIRE REPAIRS TO BE FOUND " that is part of the US, NASA program and a couple of Astronaouts are alive and thankfull becouse of it! Now after reading your TSB I am not shure if to redo the extension or do away with it alltogether???
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AJMBLAZER
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This has been discussed a few times on Colorado K5 - Full-Size GM 4x4 Restoration and Off Road Community and it's pretty well split. Some folks reengineer the system so it works with a lift. However a lot of others just got rid of it and none of them seemed to be having trouble. For sure no one was in a rush to reinstall it.
GreenBull
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The small tires less braking traction so It seems you want the valve. I can't picture your bracket mod. It seems to me that changing brackets may change the valves rate and that simply extending the link so the valve arm is at the correct position for no load curb height would be the better mod.
I can get under my M1028 with a camara and measuring tape if you need a picture?
I can get under my M1028 with a camara and measuring tape if you need a picture?
Bracket
You are correct in that you have to retain the relative travel axis among the 3 pivot points in the valve bracket in order for it to work as intended. What I had done before after the spring lift was to ad a small extencion to the short upper bracket rod and another somewhat longer to the one at the botton this 2 rods are what made the dogleg, it retain the same travel distance and geometriy irelevant to the lift and tire size, in other words 2" of spring compresion had the same effect on the valve regardless of the added spring height it was adjusted for the 5.5" spring lift that is why the brakes work much the same before and after the lift. What happen was that since I did not know if the different tires and spring RATES or any subsecuent spring settleling would have an effect on its funtion, so I just tack welded both rods extencions and one fell OFF as I left it just tack for over 4 years. clearlly it had work and held longer the it should have. Now your TSB is making me reconcider everithing. But I still think that the valve was a good application IDEA from GM. The fact that they may stop working over a period of time or that they get out of wack after lift and suspetion mods is another issue
You are correct in that you have to retain the relative travel axis among the 3 pivot points in the valve bracket in order for it to work as intended. What I had done before after the spring lift was to ad a small extencion to the short upper bracket rod and another somewhat longer to the one at the botton this 2 rods are what made the dogleg, it retain the same travel distance and geometriy irelevant to the lift and tire size, in other words 2" of spring compresion had the same effect on the valve regardless of the added spring height it was adjusted for the 5.5" spring lift that is why the brakes work much the same before and after the lift. What happen was that since I did not know if the different tires and spring RATES or any subsecuent spring settleling would have an effect on its funtion, so I just tack welded both rods extencions and one fell OFF as I left it just tack for over 4 years. clearlly it had work and held longer the it should have. Now your TSB is making me reconcider everithing. But I still think that the valve was a good application IDEA from GM. The fact that they may stop working over a period of time or that they get out of wack after lift and suspetion mods is another issue
Bracket
You are correct in that you have to retain the relative travel axis among the 3 pivot points in the valve bracket in order for it to work as intended. What I had done before after the spring lift was to ad a small extencion to the short upper bracket rod and another somewhat longer to the one at the botton this 2 rods are what made the dogleg, it retain the same travel distance and geometriy irelevant to the lift and tire size, in other words 2" of spring compresion had the same effect on the valve regardless of the added spring height it was adjusted for the 5.5" spring lift that is why the brakes work much the same before and after the lift. What happen was that since I did not know if the different tires and spring RATES or any subsecuent spring settleling would have an effect on its funtion, so I just tack welded both rods extencions and one fell OFF as I left it just tack for over 4 years. clearlly it had work and held longer the it should have. Now your TSB is making me reconcider everithing. But I still think that the valve was a good application IDEA from GM. The fact that they may stop working over a period of time or that they get out of wack after lift and suspetion mods is another issue
You are correct in that you have to retain the relative travel axis among the 3 pivot points in the valve bracket in order for it to work as intended. What I had done before after the spring lift was to ad a small extencion to the short upper bracket rod and another somewhat longer to the one at the botton this 2 rods are what made the dogleg, it retain the same travel distance and geometriy irelevant to the lift and tire size, in other words 2" of spring compresion had the same effect on the valve regardless of the added spring height it was adjusted for the 5.5" spring lift that is why the brakes work much the same before and after the lift. What happen was that since I did not know if the different tires and spring RATES or any subsecuent spring settleling would have an effect on its funtion, so I just tack welded both rods extencions and one fell OFF as I left it just tack for over 4 years. clearlly it had work and held longer the it should have. Now your TSB is making me reconcider everithing. But I still think that the valve was a good application IDEA from GM. The fact that they may stop working over a period of time or that they get out of wack after lift and suspetion mods is another issue
GreenBull
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Glad to help. Its best when you get to make informed decisions.
I've just gotten an M1028 and still waiting on an SF97. Working on a two tank heated waste oil fuel system.
I've just gotten an M1028 and still waiting on an SF97. Working on a two tank heated waste oil fuel system.
tankie88
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I know this is an old thread.one of my rear brake pipes hes just split.I see in the TM's the M1009 has a brake valve on the rear axle.So i went to look and low and behold i aint got one.The pipe off the chassis goes to the flxie pipe and then dont to a T piece on the diff.Then goes left and right to the drums.I take it at some point the valve was knackered and was removed.