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My '79 4x4 Pickup has a "one-in, one-out" LSVP and has NO bleed valve/nipple. Only a decent sized hex on top which, if I undo it, I'm pretty sure will shoot the valve rod and a bunch of springs into the air...! SO the quiz is, Does this need bleeding (in the regular order R/L, R/R, F/R, F/L, LSVP ? Is so how? If not, and I'm bleeding the four wheel cylinders should the springs/axle (and LSPV) be under normal conditions, or is it ok to do it on a lift with the springs/axle hanging way down? The LSVP seems to be working just fine, so I don't want to replace it , but my brakes are a little spongy so I'm trying to figure how to get them back to normal.
"One-in, one-out" LSPV does it need bleeding - or does bleeding the rear wheel cylinders take care of it?
The LSVP doesn't have a bleeder because it's not meant to be bleed. It;s only job as far as I can find out, is as a switching valve between front & back brake systems. If 1 or the other fails, it allows hydraulic pressure to keep going to the unaffected system, so you at least have half braking power in the event of loss of fluid to either the front or back systems. The position of the wheels/axles/springs shouldn't make any difference in brake bleeding. I've bleed brakes with the vehicle on the ground or on a lift & it make no difference.
2 other things. The order you listed for the wheels when bleeding is a little off. Unless the FSM manual states otherwise, it's always been right rear, left rear, right front, left front; further away to nearest to the master cylinder, in order. Second, (& not to disparage anyone's knowledge or ability ) bleeding brakes can be a bit of an art. There are the normal things, like making sure the master doesn't run dry, a tight fitting hose on the bleeder to make sure it doesn't draw air back in, pumping up brake pedal 4 or 5 times then just cracking open the bleeder enough to let fluid flow, closing bleeder quickly before pedal gets to the bottom (floor), etc., etc. I've always done the wheel cylinders/calipers twice in the order above just to be sure I get all the air out. A vacuum bleeder helps too, if you are trying to do it alone.
The LSVP doesn't have a bleeder because it's not meant to be bleed. It;s only job as far as I can find out, is as a switching valve between front & back brake systems. If 1 or the other fails, it allows hydraulic pressure to keep going to the unaffected system, so you at least have half braking power in the event of loss of fluid to either the front or back systems.
I don't know if that is exactly what this LSPV is supposed to do. My understanding is that it reduces the braking power to the rear wheels under harder braking scenarios (as the weight transfers to the front of the vehicle) so that you don't lock up the rear wheels as easily. Hence the name Load Sensing Proportioning Valve.
I don't know if that is exactly what this LSPV is supposed to do. My understanding is that it reduces the braking power to the rear wheels under harder braking scenarios (as the weight transfers to the front of the vehicle) so that you don't lock up the rear wheels as easily. Hence the name Load Sensing Proportioning Valve.
yup, that’s what it’s for. 1 line in from the master, one line out to a T for both rear drums. As the bed load increases, a rod (fixed at the axle) acts on the LSPV and modulates the pressure to the rear drums as the angle of the rod changes. So the question remains, does it matter if I bleed the wheel cylinders on a lift with the axle/ springs hanging way down, or on the ground under normal load conditions?
Last edited by Rusty Bob; 01-12-2019 at 01:59 PM.
Reason: Typos
I didn't make any special provisions when I bled my system...I don't think there is a need to have the truck sitting any differently than just on its wheels in the garage.
01-11-2019, 09:10 AM
) bleeding brakes can be a bit of an art. There are the normal things, like making sure the master doesn't run dry, a tight fitting hose on the bleeder to make sure it doesn't draw air back in, pumping up brake pedal 4 or 5 times then just cracking open the bleeder enough to let fluid flow, closing bleeder quickly before pedal gets to the bottom (floor), etc., etc. I've always done the wheel cylinders/calipers twice in the order above just to be sure I get all the air out. A vacuum bleeder helps too, if you are trying to do it alone.
