Rear axle displacement brake sensor thingy?

Hi there,
While wrenching on a friends Taco today, I saw some kind of sensor arm attached to the rear axle (in yellow, please ignore the red):


It goes to a hydraulic cylinder assembly (not included in this pic that I stole) that seems to then go on to drive both rear brakes.

What is this beast?

Near as I can figure it, it detects the vertical displacement of the rear axle, and could modulate the rear braking force by detecting a nose-down/tail-up attitude.

UPDATE!
Further digging makes me think that this is the rear proportioning valve, used to detect the tail-down attitude caused by load in the truck and modulate the braking pressure in response to the weight of the carried load.

 

Yep, thats what it does. More weight in the rear allows more rear proportional braking to take place.

 

Thanks!!!

 

yes, that is a Load Sensing Proportional Valve (LSPV)

It adjusts the strenght of the rear brakes according to what you are carrying in the bed. The heavier it is, the more it pushes the piston into the valve, allowing more brake fluid to the rear

 

OP, Sorry don’t mean to high jack your thread but it’s a related question. With a 3” lift how do you know how far this valve needs to be adjusted in order to work properly?

 

Raise it about as much as you raised the truck, also test it a couple times on dirt and pavement safely to determine that it isn't locking the brakes up too easily. That could cause tail happy handling and be dangerous in a panic stop

 

@Shubin If you lifted the rear 3" then you want to put the bpv bracket at the corresponding height (3"). Then do what Speedytech said and go test it to make sure the rear brakes are acting the way you want them to.

Taken from BAMF's website:

 

Awesome thanks guy. This is very helpful

 

I took mine right out along with the valve it controls and have had no problems.

 

What position is that whole assembly supposed to be at at regular ride height? When I did my relocation bracket, I noticed that whole assembly moves side to side, or up/down and "snaps" into place in either position when moving it.

 

IMO this excellent advice. Having the rear brakes lock before the front can cause a tail swap and then a possible roll over. The worst sort of crash.

I have recently installed an AAL to my ARB Dakar leaf springs and now the LSPV is out of adjustment. I will be doing brake lockup testing soon and want to disable the ABS system. I assume that disconnecting one ABS wheel sensor will disable the whole ABS system and not just the disconnected wheel.
Am I assuming correctly?

 

Actually it seems to be some sort of device for drying socks?

 

Just pull the ABS fuse, once the ABS dash light comes on you're good to go.

 

Thanks, much better idea.

 

I lifted my '04 over ten years ago and never heard of this thing. Does the flexible arm thing just need to be lifted, or is there something downstream of there that also needs to be moved?

 

The valve above works by sensing the angle of the "arm" that comes down to the axle, you just need to elevate it equal amount as your lift to get the arm into the proper angle.

I just cut a piece of metal and raised it 3.5", before doing this my truck felt as if all the braking was done by fronts only, now under heavy braking both front and rear would lock up about the same time.

 

I went to purchase the BAMF, but screw that sales tax thing. The damn part on the truck is just a threaded rod. Why not just screw on a threaded rod "extender"? Or, buy a piece of threaded rod and bend a new, longer one. ACE probably has the parts for $2. Beats $30. I guess I have been driving around with only front brakes for 12+ years.

 

if you make your own then just keep in mind the angles and make sure the threaded rod is strong enough so it won't bend under quick bounces.

 

Isn't it easier to just make a bracket that lifts it up though?

I think that extending the rod would work, but it's probably more complicated than it needs to be.

 

Well I got around to messing with mine more. My brakes all around had been neglected for so long in the past, and my rears never really worked much so I was riding on the fronts for the longest time. Wanted to wait as I had plans for tundra brakes and all new rears, which I finally got around to. But to my surprise (even with the lbpv bracket that was included with my (3") lift kit) my rears still didn't seem to work hardly at all after I replaced literally everything and adjusted everything. Decided to raise the arm even further via the adjustment nuts on that threaded rod, and it seemed to work better. Adjusted it one more time all the way up and maxed out, and they feel like they're working as they're supposed to now! Holy crap what a difference. But still couldn't get the rears to lock up. Thought about making another bracket to see if it would help even more, but it may be perfect as it is right now. Brakes work way better just with that adjustment. And you can see how far I adjusted it. So some people may need to adjust it even higher than you think, especially if your bracket is short and not adjustable like mine. Those multi-point adjustable BAMF brackets seem to be the better route to go.