Gary Lewis Posted November 18, 2018 Author Share Posted November 18, 2018 Thank-you for the updated pages Gary! That is great info! My son and his family arrive in a few hours, so I'll be scarce on here this week as we will have the whole family together under one roof! Otherwise I'd see if the factory shop manual has some magic words explaining how the load sensing valve works. But if any of you find it please post and I'll try to add them to the page. Link to comment Share on other sites More sharing options...
85lebaront2 Posted November 18, 2018 Share Posted November 18, 2018 My son and his family arrive in a few hours, so I'll be scarce on here this week as we will have the whole family together under one roof! Otherwise I'd see if the factory shop manual has some magic words explaining how the load sensing valve works. But if any of you find it please post and I'll try to add them to the page. Gary, it wasn't used until 1985, if you have the manuals for Big Blue it might be in there. I do know that there is no given adjustment for them, they come preset for full extension of the rear suspension. When I changed Darth's rear axle, I took the bracket off and lifted it up out of the way while I switched axles. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 18, 2018 Author Share Posted November 18, 2018 Gary, it wasn't used until 1985, if you have the manuals for Big Blue it might be in there. I do know that there is no given adjustment for them, they come preset for full extension of the rear suspension. When I changed Darth's rear axle, I took the bracket off and lifted it up out of the way while I switched axles. The master parts catalog actually shows a part number for 1984, but it is one-size-fits-all as opposed to the multiple parts used in '85 and later to make them specific to the springs/GVW. Anyway, I do have the 1985 factory shop manual and will see what it says re them. Since they'd have been new that year surely they wrote something about them. Link to comment Share on other sites More sharing options...
Romel Posted November 28, 2018 Share Posted November 28, 2018 The master parts catalog actually shows a part number for 1984, but it is one-size-fits-all as opposed to the multiple parts used in '85 and later to make them specific to the springs/GVW. Anyway, I do have the 1985 factory shop manual and will see what it says re them. Since they'd have been new that year surely they wrote something about them. What I have observed on my truck (Jan´s truck) is when the park brake was aplied over night, I release it, the truck is free moving. The first braking, the rear lock always. I have to really be careful to apply brake force to not lock it. Then it gets better, but any panic brakining the rear locks always. I have looked at the proportioning valve, the piston inside sitting in the middle, no light warning. I do have a rear load sensing valve above the rear axle conected, if I disconect it it moves free. The brakes bleed fine, rear, front. I have poured in gallons of brake fluid, flushed the system, no air anywhere. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 28, 2018 Author Share Posted November 28, 2018 What I have observed on my truck (Jan´s truck) is when the park brake was aplied over night, I release it, the truck is free moving. The first braking, the rear lock always. I have to really be careful to apply brake force to not lock it. Then it gets better, but any panic brakining the rear locks always. I have looked at the proportioning valve, the piston inside sitting in the middle, no light warning. I do have a rear load sensing valve above the rear axle conected, if I disconect it it moves free. The brakes bleed fine, rear, front. I have poured in gallons of brake fluid, flushed the system, no air anywhere. That's not a good situation, and is very unlike the situation I have on Big Blue. I wonder if someone has "worked on" the ride height sensing valve at the rear. I've found a couple of TSB's on it and will put them on the website and let you know when they are on. Link to comment Share on other sites More sharing options...
85lebaront2 Posted November 28, 2018 Share Posted November 28, 2018 That's not a good situation, and is very unlike the situation I have on Big Blue. I wonder if someone has "worked on" the ride height sensing valve at the rear. I've found a couple of TSB's on it and will put them on the website and let you know when they are on. I did find in doing the work on Darth that there are different size rear brake cylinders. If somewhere in the past the rears were changed to a larger size, it can make them lock up easily. One other item, when you did the Hydroboost change, if you didn't keep the original master cylinder, is the new one the same bore size? I did run into a similar situation on a 1978 Oldsmobile Delta 88 Royale with the 5.7L Diesel. Gm in their infinite wisdom decided despite the added weight of the heavier block and extra battery to use the V6 running gear under these cars. First problem was a complete failure of the front pads at around 20,000 miles or less (it's been 40 years) the solution, under warranty (TSB) was to upgrade the front pads to the B&C body heavy duty (police package) pads. The other issue though that the change aggravated was the tendency to lock the rear wheels any time you made a hard stop. I solved it by putting the HD rear shoes on the car which were a harder composition. If your rear shoes are fairly soft, that may be what you are seeing. Link to comment Share on other sites More sharing options...
Romel Posted November 28, 2018 Share Posted November 28, 2018 I did find in doing the work on Darth that there are different size rear brake cylinders. If somewhere in the past the rears were changed to a larger size, it can make them lock up easily. One other item, when you did the Hydroboost change, if you didn't keep the original master cylinder, is the new one the same bore size? I did run into a similar situation on a 1978 Oldsmobile Delta 88 Royale with the 5.7L Diesel. Gm in their infinite wisdom decided despite the added weight of the heavier block and extra battery to use the V6 running gear under these cars. First problem was a complete failure of the front pads at around 20,000 miles or less (it's been 40 years) the solution, under warranty (TSB) was to upgrade the front pads to the B&C body heavy duty (police package) pads. The other issue though that the change aggravated was the tendency to lock the rear wheels any time you made a hard stop. I solved it by putting the HD rear shoes on the car which were a harder composition. If your rear shoes are fairly soft, that may be what you are seeing. I did keep the original cast master, I hate it for turning the fluid into rusty poridge but oh well. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 28, 2018 Author Share Posted November 28, 2018 I did keep the original cast master, I hate it for turning the fluid into rusty poridge but oh well. I'm going with a 1990's F450 master cylinder, which is one of the plastic units with an aluminum cylinder, to replace the cast unit on Big Blue when I do the hydroboost upgrade. Anyway, I've added two Technical Service Bulletins to the website today: Brake Ride Height Proportioning Valve Brake Noise The first one discusses the rear proportioning valve and issues that can occur with changes to the suspension, but it may not help you, Jan. Link to comment Share on other sites More sharing options...
Romel Posted December 1, 2018 Share Posted December 1, 2018 I'm going with a 1990's F450 master cylinder, which is one of the plastic units with an aluminum cylinder, to replace the cast unit on Big Blue when I do the hydroboost upgrade. Anyway, I've added two Technical Service Bulletins to the website today: Brake Ride Height Proportioning Valve Brake Noise The first one discusses the rear proportioning valve and issues that can occur with changes to the suspension, but it may not help you, Jan. I just verified it must be the proportioning valve. If u aply slightly the brakes, and then go firm, they work as they should, the front suspension sinking and good stoping power. If u panic brake, the rear locks and the stoping power is limited, u slide like on ice. Link to comment Share on other sites More sharing options...
Gary Lewis Posted December 1, 2018 Author Share Posted December 1, 2018 I just verified it must be the proportioning valve. If u aply slightly the brakes, and then go firm, they work as they should, the front suspension sinking and good stoping power. If u panic brake, the rear locks and the stoping power is limited, u slide like on ice. When you say "the proportioning valve", are you meaning the one on the frame under the master cylinder? That's the one I think it probably is. But, there's the ride-height sensing one in the rear. Might it be malfunctioning or improperly adjusted? That one is supposed to limit rear braking with no load. How about disconnecting the arm from the truck, not the valve as the TSB says do not do that, and tie the arm in another position and try the braking? Perhaps you can figure out from that if it is the rear valve or not. Link to comment Share on other sites More sharing options...
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