Load Sensing Valve Modification?

[QuasarDecimari]

Hey everyone!

 

A while ago, I was checking up on my rear axle's gear oil, and I started looking more closely at the strange device attached to the rear axle carrier. The one coming from under the body, attached to the axle by a spring. After a few minutes of scrolling through the factory service manual, I found that it's the load sensing valve. Essentially, the design of this valve makes it so that the vehicle can detect when there is a lot of weight in the trunk of the vehicle, or you're pulling a trailer, as the spring attached to the axle relaxes tension and the lever on the valve pushes upward, changing the valve position. This, in theory, allows the vehicle to distribute a little more braking power to the rear brakes.

 

However, this only really applies if your axle is still the same distance from the body as it was when it was stock... Mine being 7" taller than stock in the rear, I can imagine that isn't going to do anything anymore, with how stretched the spring is.

My question is, how important is the operation of this valve? I have temporarily secured it so that it remains pressed in all of the time, to try and see if I can get more smooth braking in the rear, but I don't assume that it does much in the longrun.

 

I added a picture from the FSM of the device and its operation.

 

Edited January 12, 2019 by QuasarDecimari
Typos :P

[Slartibartfast]

The service manual has a table with front/rear brake pressures with the truck loaded and unloaded. The adjustment procedure has you hook up pressure gauges on the front and rear brake circuits and check the bias loaded/unloaded. Adjustment looks like a really vague process, with the allowable range for loaded/unloaded overlapping each other.

 

The WD21 and the 2WD R50 don't even have LSVs, they just have a fixed prop valve in the master cylinder. I'd expect an LSV without its linkage to act the same as the fixed prop. Provided the rears don't lock up first, it's probably fine. Might be interesting to do some hard braking tests to see if you can tell the difference between the LSV at its maximum and minimum settings.

[TowndawgR50]

Ive looked into this as well. @hawairish and I had discussed options a while back but since Im converting my rear brakes to discs its getting deleted anyways. 

 

I cant say for sure but I feel like my lift has negatively effected my rear braking performance due to the LSV not being in the correct position. I mostly notice it durring long downhill descents off road, with the front brakes taking the brunt of the work and the rear not even locking up under moments heavy braking where the front does. 

 

 

 

[QuasarDecimari]

I cant say for sure but I feel like my lift has negatively effected my rear braking performance due to the LSV not being in the correct position.

That’s exactly what I was thinking when I figured out what the valve was for. I knew by lifting it, that valve became obsolete.

Might be interesting to do some hard braking tests to see if you can tell the difference between the LSV at its maximum and minimum settings.

Not a bad idea. I have it fastened right now at max, and I remember when I did that and went for a drive afterwards, I could tell a slight difference. My front bumper didnt nosedive as bad and braking just felt smoother, like it wasnt going to launch me out of the windshield. I could always conduct some tests with braking times and how level the vehicle stays when braking, if anyone is curious enough.

[RainGoat]

Hmmm, very interesting insights. It is these little things that often get overlooked & can have real impact on drivability & safety. Regardless of what we choose to do with them, better to understand the consequences than not. Sway bar deletes, CV angles, driveshaft lengths & missing links come to mind. I am very interested in having the group puzzle this out more.[mention=37543]TowndawgR50[/mention] observations definitely trouble me a little.@QuasarDecimari seems to have a fix & possibly something that should be recommended on all lifted R50s. I’d like to hear more of our knowledgeable members chime in!

[QuasarDecimari]

QuasarDecimari[/mention] seems to have a fix & possibly something that should be recommended on all lifted R50s. I’d like to hear more of our knowledgeable members chime in!

I can definitely run some tests as soon as I can, to see what sort of impact the valve has, especially with a lift. My take on it, while some things are always questionable, the engineers put it on there for a reason, not just for extra accessories. If tests are conclusive that the valve does indeed enhance rear braking with a lift, I can’t imagine it’ll be hard to make a writeup on a bracket that could fix this. I could probably design and fabricate one in a day.

[dezm]

Following!


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[mjotrainbrain]

This is interesting to hear about.  My QX4 didn't have one so I never looked into what it did, definitely sounds like something that should be taken into consideration when lifting!

[mjotrainbrain]

These threads leave some questions unanswered, but may contain information handy to anybody who plans to dig into this further.

 

 

 

[QuasarDecimari]

This is interesting to hear about.  My QX4 didn't have one so I never looked into what it did, definitely sounds like something that should be taken into consideration when lifting!

 

I was waiting for you to come along with input!

 

From the looks of the second posting, it seems rather important. The user explaining it gives quite a bit of detail about the impact it makes. Maybe I’ll go ahead and get out the grinder and some steel, see if I can’t make an extended bracket.

 

(I swear the search feature on Tapatalk Mobile is absolutely useless. I tried searching for threads related to this and it just finds stuff completely unrelated...)

[mjotrainbrain]

3 hours ago, QuasarDecimari said:

 

I was waiting for you to come along with input!

 

From the looks of the second posting, it seems rather important. The user explaining it gives quite a bit of detail about the impact it makes. Maybe I’ll go ahead and get out the grinder and some steel, see if I can’t make an extended bracket.

 

(I swear the search feature on Tapatalk Mobile is absolutely useless. I tried searching for threads related to this and it just finds stuff completely unrelated...)

 

I didn't use the forum's built in search feature, I never do unless I'm trying to find somebody's profile.  I agree, it's very limited/challenging to use well.  I put my searches in Google prefaced with NPORA to get as many results from this site as possible.

[PathyDude17]

4 hours ago, mjotrainbrain said:

 

I didn't use the forum's built in search feature, I never do unless I'm trying to find somebody's profile.  I agree, it's very limited/challenging to use well.  I put my searches in Google prefaced with NPORA to get as many results from this site as possible.

I feel like if you put your search in quotations (sometimes you have to wait for the advanced search option to come up after searching a phrase the first time), you get pretty good results. Depends on the popularity of what you’re searching though. 

Edited January 14, 2019 by PathyDude17

[Slartibartfast]

9 hours ago, QuasarDecimari said:

I can definitely run some tests as soon as I can, to see what sort of impact the valve has, especially with a lift. My take on it, while some things are always questionable, the engineers put it on there for a reason, not just for extra accessories. If tests are conclusive that the valve does indeed enhance rear braking with a lift, I can’t imagine it’ll be hard to make a writeup on a bracket that could fix this. I could probably design and fabricate one in a day.

 

 

Seems like the easiest way would be to extend the bracket on the axle, but then it would be yanking the spring when the rear end articulates, which is less than ideal. The best way to preserve the geometry would be to make a bracket to lower the LSV towards the axle, but then you'd probably have to extend the brake lines.

And yeah, I just Google NPORA + whatever I'm looking for.

[QuasarDecimari]

 
Seems like the easiest way would be to extend the bracket on the axle, but then it would be yanking the spring when the rear end articulates, which is less than ideal.

Actually, I don’t think there would be much issue with this. I had it attached for the longest time with the 7” rear lift and the spring still seems to have retained its shape. Its a tough little sucker. This is what I was thinking of doing, ultimately. I can’t imagine it being too difficult to extend either, just a plate with a few bolt holes.

Regardless, I’ll still see if I can conduct some stop-times and hard-braking angles beforehand.



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[Slartibartfast]

I was thinking less of damage to the spring and more of your brake bias changing depending on which way the axle was flexed. The stock bracket has the spring connected pretty close to what I assume is the "pivot point" on the axle (assuming the diff stays about the same distance from the body as the axle articulates). Add seven inches to that arm and the end of it will move back and forth more as the axle flexes.

 

Enough to matter? That I don't know.

[QuasarDecimari]

The stock bracket has the spring connected pretty close to what I assume is the "pivot point" on the axle (assuming the diff stays about the same distance from the body as the axle articulates).

Definitely a key point, hence the reason it would be a desirable fix to lower the LSV, than to raise the spring mount. More work, definitely more work, but possibly more accurate.

I’ll have to put some thought into that one

[hawairish]

I'm late to the party, but I'll echo @TowndawgR50's comment in principle, noting that my 04 doesn't have an LSV.  But yes, by lifting the truck, the LSV be allowing the minimum rear proportioning available.  The valve is meant to increase rear proportion when a load is detected, but the lift basically does the opposite to an extent.  To restore the function, you'd likely have to move the spring arm up a few inches like Slart mentioned, but I agree that it might not matter much.  I'd just as well suggest disconnecting the spring and calling it a day, or otherwise finding a way to put the lever in a static position that simulates stock-height (or a loaded position if more rear bias is desired).

[QuasarDecimari]

  I'd just as well suggest disconnecting the spring and calling it a day, or otherwise finding a way to put the lever in a static position that simulates stock-height (or a loaded position if more rear bias is desired).

 

Welcome to the party!

That’s what I ended up doing when I “discovered” the valve. I fastened it to where the valve was always loaded for more rear braking. I’m waiting for the midwestern Colorado weather to allow for me to toy around with this a bit, sheets of ice and snow aren’t exactly ideal for brake checks!

 

[RainGoat]

 I fastened it to where the valve was always loaded for more rear braking.

[mention=36148]hawairish[/mention] &@QuasarDecimari How about a “How To” for those of not as mechanically gifted as the two of you. As this issue undoubtedly effects safety, it sounds to me like it should be part & parcel of any lift.

 

[hawairish]

15 hours ago, RainGoat said:

How about a “How To” for those of not as mechanically gifted as the two of you. As this issue undoubtedly effects safety, it sounds to me like it should be part & parcel of any lift.

 

It's more about braking efficiency, less about safety (not that brakes aren't a safety item).  Regardless of the valve proportion, you'll have braking power, but it may contribute to more brake wear up front over the long run.  I'd document something, but I don't have any reference since my 04 doesn't have an LSV.  Although my Frontier does, it's a slightly different design, and my truck's been lowered and adjusted enough to meet OE specs.  Similar concept of course, but I wouldn't be able to account for any differences.  I know the FSM has some procedural items, but you're right in that we might need some specialty instructions for lift.