Load Sensing Valve Delete?

[GeneralDisorder]

Working with a member on his A0 brakes. Considering deleting the Load Sensing Valve since the A1+ trucks including my A1R don't use it and seemingly have no issues without it. Here's the A0 pneumatic diagram and the A1R pneumatic diagram.

It would appear they simply deleted it. The later diagram has the Modulating Valves for the ABS but AFAIK the ABS has no ability to replace the function of the LSV.

We have already upgraded the rear brake cans to the A1R type 12 cans but are not really seeing the braking improvement that we expect based on my experience with my truck and the older style pedal assembly. Perhaps it could be the LSV needs adjustment but then - if the engineers just deleted it after the first generation of trucks and it's really not serving a useful purpose I would rather just get rid of it entirely.

 

[biscuitwhistler37]

Yeah they just deleted it entirely. From the schematic, I gather the lsv applies brake pressure relative to brake pedal pressure, not pedal position, similar to one of Chryslers electronic braking "innovations", wherein the brakes would apply harder and faster the harder and faster the pedal was pressed. Deleting the LSV and running the line straight to the relay valve would, in theory, change that to where brake pressure applied to the wheels is relative exclusively to pedal position.

 

[Ronmar]

Well ABS does perform the function of the load sense valve by helping to control/prevent lockup on a light rear end. These valves are 1/6 pressure input to output when lever pulled all the way down(empty bed/light rear end) and 1:1 when the suspension is compressed enough to allow the lever to reach its full up stop(heavy load).

it has a vent on it but I have not had a chance to determine yet if it vents pressure when the lever moves like might happen during heavy braking/nosedive to help control lockup.

I have removed the control linkages on hydraulic versions on trucks I have lifted/modified over the years, and I install a turnbuckle from proportioner to the body to allow me to tune the rear brake response to match the weight. In a stock pickup, used to carry varying loads I would leave it.

For my RV, I may remove the cable and install a turnbuckle also as the weight should be fairly constant. But if it does vent pressure during heavy braking weight shift, it may be useful. I guess the next evolution of a turnbuckle would be to put in a linear actuator and I could tune it from the cab.

disconnecting the cable should give you 1:1/full output pressure, same as if the valve was removed. Take it to a dirt road and do some max performance braking to see how it works for their situation

 

[GeneralDisorder]

Ah I see! So the LSV effectively just reduces braking when the truck is light while the ABS tackles the problem from the other direction - preventing wheels from locking up when the truck is light. Got it.

I'll pass that along and he can decide what to do and how to tune it.

 

[STI2NR]

My cable is at full slack so this thing sits at full pressure all the time. If I removed it entirely and put a t manifold in its place what would happen?? I noticed it has 1 input and 2 outputs IIRC.

 

[Ronmar]

My cable is at full slack so this thing sits at full pressure all the time. If I removed it entirely and put a t manifold in its place what would happen?? I noticed it has 1 input and 2 outputs IIRC.

What truck is this on? the normal load sense valve only has an input(drivers side) and an output(pax side) port. On the A0 they Td the input so it also fed I think, the trailer brake protection valve and the anti compound valve. The output on the passenger side feeds the brake relay valve…

 

[GeneralDisorder]

What truck is this on? the normal load sense valve only has an input(drivers side) and an output(pax side) port. On the A0 they Td the input so it also fed I think, the trailer brake protection valve and the anti compound valve. The output on the passenger side feeds the brake relay valve…

Yeah it just has one in and one out. There's a T on the on the passenger side right at the valve. Apparently even though it was fully in the "up" position, deleting the valve made a HUGE difference. I'll let him post his findings.

 

[STI2NR]

I was quite surprised by the results. One 1/4" npt coupling is all I needed to make this work. The difference is night and day. My valve may have been broken so I am not sure if others would see the same results. Now combined with the upgraded rear cans and all new lines plus new diaphragms up front I have a ton of braking power.

Video is still uploading as I type this but here is the link for when it is complete

 

[Ronmar]

sounds like it was not working right. You can bench test it. Regulated pressure source on the drivers side port, say 80-100PSI, and a pressure gauge on the passenger side port. Lever against the up stop, output pressure should = input pressure, (1:1), just like your pipe fitting.

As you lower the lever the output pressure should decrease to 1/6 the input(6:1) at the down stop. According to the adjust procedures I have seen, that is how you set the bottom stop adjust bolt and locknut(passenger side of valve body).

my only concern would be at a fixed 1:1 with the pipe coupling, that you now may have too much rear braking when it gets slippery out Or on dirt.
gets pretty annoying when the rears lock up just thinking about touching the pedal

i tune them on dirt…

 

[STI2NR]

sounds like it was not working right. You can bench test it. Regulated pressure source on the drivers side port, say 80-100PSI, and a pressure gauge on the passenger side port. Lever against the up stop, output pressure should = input pressure, (1:1), just like your pipe fitting.

As you lower the lever the output pressure should decrease to 1/6 the input(6:1) at the down stop. According to the adjust procedures I have seen, that is how you set the bottom stop adjust bolt and locknut(passenger side of valve body).

my only concern would be at a fixed 1:1 with the pipe coupling, that you now may have too much rear braking when it gets slippery out Or on dirt.
gets pretty annoying when the rears lock up just thinking about touching the pedal

i tune them on dirt…

I just got done bench testing it and no pressure was getting through at all, totally blocked off in all lever positions. Something inside of that unit failed and I don't know if the truck has been that way the entire time I have owned it. Now I know why it was so hard to get my truck to come to a stop. I wonder if this caused only my front brakes to work? I was relying heavily on my pacbrake to bring my truck to a full and complete stop. I would stay at least 100 yards from anyone in front of me knowing I had a really difficult time stopping. I can see why now.

 

[GeneralDisorder]

Well. Given his truck is 24k lbs, and my truck (M1079 A1R) is 21,500 lbs..... I have essentially the same setup he has now and I have no issues with my rear brakes locking up - indeed I have never been able to get my ABS to activate. He is so close to the GVRW and doesn't plan to ever not have a habitat on the truck so I doubt it's ever going to be an issue in practice.

 

[Ronmar]

I wonder if this caused only my front brakes to work? I was relying heavily on my pacbrake to bring my truck to a full and complete stop.

yep, with the proportioner blocked, you only had front brakes, and the pacbrake… i would definitely test it close to home when it gets slippery out before I deliberately took it too far out into those conditions…

 

[Ronmar]

Well. Given his truck is 24k lbs, and my truck (M1079 A1R) is 21,500 lbs..... I have essentially the same setup he has now and I have no issues with my rear brakes locking up - indeed I have never been able to get my ABS to activate. He is so close to the GVRW and doesn't plan to ever not have a habitat on the truck so I doubt it's ever going to be an issue in practice.

Probably not at that weight as it should have been at or near 1:1 output anyway, but i would still skid pad it at the first opportunity just to make sure it behaves OK. I have overdone it before and too much rear brake is definitely no fun when it gets slippery. I mean I like drifting and all, but not at 11ton

 

[STI2NR]

yep, with the proportioner blocked, you only had front brakes, and the pacbrake… i would definitely test it close to home when it gets slippery out before I deliberately took it too far out into those conditions…

That explains my lack of confidence in the brakes. I feel so much better about it now.

 

[aw113sgte]

M1096 A1R here and when my abs was not functioning, I could easily lock my rear brakes and get going sideways. Load sensing valve makes a lot of sense and I would leave it. There is a reason race cars are fitted with brake bias adjusters.

 

[STI2NR]

M1096 A1R here and when my abs was not functioning, I could easily lock my rear brakes and get going sideways. Load sensing valve makes a lot of sense and I would leave it. There is a reason race cars are fitted with brake bias adjusters.

It does not make sense in my situation as the one I have is completely blocked as in no air goes through it at all and I was relying on just my front brakes and pac brake to come to a stop. If I hit the brakes hard that would explain why the truck would try to wander back and forth while coming to a stop since the front brakes were working hard to stop the truck. My truck will always weight at 12 tons or more so having that valve made no sense more so when it is completely blocked off.

 

[Ronmar]

It does not make sense in my situation as the one I have is completely blocked as in no air goes through it at all and I was relying on just my front brakes and pac brake to come to a stop. If I hit the brakes hard that would explain why the truck would try to wander back and forth while coming to a stop since the front brakes were working hard to stop the truck. My truck will always weight at 12 tons or more so having that valve made no sense more so when it is completely blocked off.

Yea at your weight, your cable was slack and should have been full on and would have been delivering full braking if not blocked. I wonder how much suspension unload and weight shift you get during heavy breaking? Havn't panic stopped one of these heavy yet

With a working valve, If you get much nosedive, that cable should pull on the lever and reduce rear brake force as the rear suspension unloads, same as you would ease off on the rear brake on a moto as you bear down on the front…

 

[GeneralDisorder]

M1096 A1R here and when my abs was not functioning, I could easily lock my rear brakes and get going sideways. Load sensing valve makes a lot of sense and I would leave it. There is a reason race cars are fitted with brake bias adjusters.

Yeah but that has the upgraded rear cans for the planned armor package, is light as hell (bare chassis as delivered), and is a 6x6 with twice as many brakes in the back. The 6x6 trucks, especially when running light, have tremendously strong brakes being they aren't *that* much heavier when not loaded and have 50% more brakes just by virtue of the extra axle.

I've NEVER been able to activate my ABS. Need to try that on snow/ice at some point. The 4x4 trucks just have less braking capability per unit of vehicle weight. Most of the habitat equipped MTV trucks I'm familiar with are weighing in around 28,000 lbs. While the 4x4 trucks are closer to 24,000 lbs fully equipped. That's 1 braking wheel per 4,666 lbs for the MTV, and 1 braking wheel per 6,000 lbs for the LMTV. This is even more pronounced when you consider that 2/3 of the MTV braking is in the rear where weight transfer when braking makes the load effectively lighter directly on top of the axles..... So *in general* the 6x6 trucks just usually tend to feel like they have more responsive brakes and it wouldn't surprise me that you could lock up your rear wheels rather a LOT easier than my truck.

And you'll need a LOT more weight to get close to your GVRW with an MTV. So yeah - I would seriously consider NOT deleting the LSV if you have an A0 6x6 that's not REALLY heavy.

 

[aw113sgte]

Are the front A1R cans larger than the backs? When checking my brakes I noticed the front shoes showed significantly more wear.
Edit: yes, 5.5"dia for rear, 6"dia for front

 

[STI2NR]

Yea at your weight, your cable was slack and should have been full on and would have been delivering full braking if not blocked. I wonder how much suspension unload and weight shift you get during heavy breaking? Havn't panic stopped one of these heavy yet

With a working valve, If you get much nosedive, that cable should pull on the lever and reduce rear brake force as the rear suspension unloads, same as you would ease off on the rear brake on a moto as you bear down on the front…

I will do some more testing obviously as we use the truck for overlanding and what not. At that point I will know how the truck behaves much better. For now I am happy to have rear brakes and a truck that can override the pac brake which I don't recall ever having before.