- when raising the LSPV body and lever (tie to the car body) because the jack when it is at the maximum limit in the adjustment screw does not touch the pin, in this case the fluid pressure rises backwards so.
I understand, the lever is detached from the axle and tied up to the floor. In this position, the actuator pin is forced into the LSPV by the lever, right? This is actually achieved by tying up the lever; moving the LSPV body shouldn't be of much relevance in this.
Anyway, this indicates to me, the LSPV is working when pin gets actuated inwards.
- I lowered the LSPV body and also raised the jack ...
Not sure I understand what this situation actually is. I understand:
- Lever tied to adjusting screw on pivot point on axle (I guess, you call that pivot point a 'jack')
- LSPV body adjusted in a way that the lever barely touches the actuator pin. (*)
At least that's how it should be..
... in this case the fluid pressure should rise ...
You mentioned previously in the conversation that you expect the 'pressure to rise' [at rear drums]. That is actually not how the LSPV works. It is rather the other way around. Let me explain the function:
- When braking, the front wheels brake circuit is pressurised (= braking force). A line delivers this pressure into the LSPV.
- Inside the LSPV, the pressure tries to push that actuator pin from inside to out. But when stationary or on low speed, the lever outside is close to the pin, preventing it from being pushed out. In this situation, the pin inside has a gateway A open, which allows the full brake power to go to the rear brakes.
- Now, when braking from higher speeds, the front of the truck goes down, and the rear goes up. The higher the speed & the harder you brake, the more the rear goes up. The rear going up also means: Less dynamic weight on the rear axle / more weight on the front axle. This disbalance may cause the rear wheels to lock earlier than the front wheels. This situation would be dangerous as the rear would become instable and off you fly.. The LSPV prevents this this way:
- The rear going up increases the distance between axle and frame (where the LSPV is). Axle and LSPV are connected by the bowed lever. More distance in essence means: The lever is going down, ! giving the pin more room to come out ! (*)
- The pin now moving out is now actuating the LSPV: The gateway A to the rear brakes is gradually closed, and another gateway B is gradually opened, ! which makes a portion of the brake power to 'escape' from the rear brakes: The rear brake power is actually LOWERED (as there is less dynamic weight in the rear, requirering lower brake force).
The escaping brake power is directed into another line leaving the LSPV and tying back to the front brake. Thus, the front brake power gets increased (as there is more dynamic weight in the front, requirering more brake force there).
So, what might now be your situation...
Note this (*) : The actuator pin is mostly driven by brake pressure. It is springloaded internationally, so it 'should' reset on its own, but if old and dirty, this might not happen. Means: Tap the brakes before and after changing any setting in order to have the pin adjust to the new geometry.
The brake force you get with the lever tied up, is the max you will ever get from it in the rear. Your respective test showed there IS braking in the back in this case, so the LSPV is good. If the force is not sufficient over all, that is likely not the LSPVs fault. (But you didn't say it's insufficient).
The rear pressure will not increase, but if you fixate the lever just a tad too low, the pin moves out and it will reduce the force in the back.
Another fault could be if you adjusted the lever to the pin with the pin already being pushed out. In that case you would see no Initial brake force in the rear (which you would probablyonly notice on the first brake test, but it would gradually come in when adjusting upwards.
It's tiny increments! The max travel of the actuator pin is only 2-3 mm! So, missing that 'barely touching' by 1mm is a lot.
Under all circumstances do not force the pin upwards by fixating the lever with upward tension on it, though.
Other than that I can only repeat myself:
Push the lever up to make sure the pin is as much in as possible, then let off the lever a tiny bit so it barely touches the pin.
Fixate the lever in that position, with jack roughly in the middle of the adjusting screw. Tune in with the screw. Only if the screw gets bottomed out (not leaving about 10mm play each direction for the fine-tuning brake test): Move the LSPV on frame a bit in that case and start over.
Getting that presenting right is key.
Do the brake test for fine-tuning then.
Good Luck Ralf
