Bleeding rear drums (1 Viewer)

[fullthrottle]

So I've rebuilt the front and rear brakes. New cylinders and pads in the rear and rotors and calipers in the front.

Now I can bleed the fronts with no problem, but cannot get any fluid to come out the bleed nipple for either rear brake cylinder. I bleed the LSPV to make sure fluid was coming to there. Which worked fine.
Suspecting there could be a blocked line I completely disconnected one of the rear brake lines but still not a drop will come out.
I have the truck jacked up by its diff, so you would think the the LSPV is still sensing load and should let some fluid through.

Is there a bit of a trick to it or something?

 

[fullthrottle]

Just to add. It is possible the rear brakes weren't even working to begin with. Give the state of them when rebuilt.
A good portion of black (old) fluid came out of the LSPV when bleeding it. So either....

- The LSPV is stuffed.
- I need to disconnect the load sensing rod from the diff and lift it up to mimic full load.
- There is a blockage somewhere else.
- The problem lies between the work stool and spanner

 

[lacalvette]

When I opened the LSPV on my 86bj75, I figured that the oil in the bottom portion of the valve's body is stagniant and water can acumulate there after a while. Which can lead in a malfunctionning LSPV (corosion). Brake fluid should be flush periodically but I think the LSVP by it design is hard to be completely flushed.
Manually moving the arm is a good idea.
If not working you can disconnect the hard line from the front and see if there is oil there.
there is a tool which use vacuum to help bleeding brake system, work fine.

 

[sodafeld1]

Motive power bleeders are good, puts the hydraulics under constant pressure for bleeding. If there is no leaks.

Kind of sounds like you should give your brakes a complete service. They are important. At least have a look at your shoes and drums.

 

[fullthrottle]

Ok, so I've pulled out the LSPV and pulled it apart. To me it looks like the rod of the valve has worn down and so the arm (when pushed up) is not doing anything to the valve. So the valve always thinks there is no load in the rear, thus not letting fluid through.

Been trying to find a picture of a good valve to see how far it protrudes.

 

[fullthrottle]

Ahhhh finally found one and yep on mine the end of the valve rod thing can't even be seen protruding from the valve body, but in this picture you can clearly see it poking out.

Looks like another new part.....

 

[Felde]

Hi
Check out the various threads I did on the LSPV (search function is your friend).
And understand it's function...
With the vehicle sitting (driving) level, the LSPV is fully open (assumed to be adjusted accurately) and allows full brake power to the rear. When braking, the front sinks in and the back comes up, resulting in a greater distance of axle to LSPV. This is what the lever senses. The LSPV proportionally closes up the circuit to the resr and directs pressure (brake force) back to the front by opening ip the return line.
Notes:
- Protrusion of the pin is about 4mm.
- Movement (max) is about 2mm only! The system actually works with pressure (to press the pin outwards against the lever) and counter-pressure (from the lever), so testing it stationary is barely impossible.
- The bleeder on the LSPV basically bleeds the feed line and the LSPV body only.
The issue with bleeding the LSPV is this:
- When sitting stationary = valve to the front closed, makes the long return line part of the front braking circuit. Air in this line makes the front brake feel spongy and it doesn't bleed by the front bleeding nipples. As it is so long, it takes a lot of patience to bleed. In order to bleed this line, you need the LSPV to open the return line: You have to undo and drop the lever. (Again: with everything attached and the truck sitting, this line is basically sealed off). You bleed to the front callipers (which is a loooong way).
- 90% of LSPV male function imho is because of
a) Seized actuation pin (dirt / grime / corrosion). The rubber grommet may act as a cup and actually collect grime. Barely never anybody removes the grommet to clean and put some fresh grease).
b) Inappropriate adjustment. Again: The actuation distance on the pin is about 2-3mm only. Any change in distance of axle / frame affects this, e.g a lift, but also sagging springs or additional permanent load. Mostly this presses the pin into the upper position, where it then seizes as it would only move on hard braking then. Some people also think, measuring the distance for the lever and eyeballing the setting would do the trick; no, not if 1mm of accuracy matters. Some complete idiots even delete it, basically because they haven't understood it and think they are more clever than all these engineers at one of the world's biggest automotive companies.
- Malfunction of the LSPV result (when braking heavily = when efficient braking matters the most) in a) less braking power in the front (compared to a working LSPV) and b) the rear wheels locking earlier than the front, resulting in the rear to loose track; and off the rig flies...
- The workshop procedure (as per FSM) is, uhmm 'academic' and requires equipment usually not available to DIYs. Here is a procedure that works:
Post in thread 'What did you do on your 70 series today?' What did you do on your 70 series today? - https://forum.ih8mud.com/threads/what-did-you-do-on-your-70-series-today.804784/post-14738924
Good Luck Ralf

 

[Felde]

Ahhhh finally found one and yep on mine the end of the valve rod thing can't even be seen protruding from the valve body, but in this picture you can clearly see it poking out.

Looks like another new part.....

Actual protrusion can only be seen correctly if the LSPV is mounted and slight brake pressure is applied. This makes the pin move out. Yes, there is a spring, but on older items the pin may not be smooth - move smoothly, and the spring may be tired.
Protrusion is 3-4mm only anyways.
Put some tape around the tips of some pliers, grab the pin (tape to not scratch the pin) and try to move it up & down / pull it down. Some resistance is normal, but it should move, but by ~2-3mm only.
Good Luck Ralf

 

[TreadingLight]

Some complete idiots even delete it, basically because they haven't understood it and think they are more clever than all these engineers at one of the world's biggest automotive companies.

This complete idiot bypassed their LSPV not because they think they're more clever than an automotive engineer, but because when presented with the choice of no rear brakes and 50/50 front/rear brakes, this idiot chose the latter. So dumb.

This idiot also put an LSPV project on their project list. But the LSPV is hard to adjust, hard to bleed, hard to maintain, and hard to modify for lifts. And it's effectiveness is dependent on getting all of the above just right. So it is on the list but not at the top of the list.

Sometimes one has to prioritize their efforts and be called an idiot.

Fine by me. This idiot is quite happy with their decision.

 

[sodafeld1]

I encounter idiots very often. If there is idiots on mud, they are the better idiot! My children think I am an idiot too. Never seems to be more idiots in human history at present. Astounding

 

[TreadingLight]

We're everywhere!

 

[OGBeno]

Someone has to win the Darwin Award this week!

I encounter idiots very often. If there is idiots on mud, they are the better idiot! My children think I am an idiot too. Never seems to be more idiots in human history at present. Astounding

 

[sodafeld1]

As long as she can stop by braking, preferably on all four corners, not too much of an idiot. I watch ratrodders do all sorts of wild stuff with brakes.
I too considered the lspv delete and installing a wildwood hydraulic tap from the master. But there is so many things I have to do that time does not allow, and she works, she stops well, so I leave her alone.
I am an idiot for having too many projects, can comfortably admit and say. But there is a range of idiots on a scale level. The high score idiots are winning

 

[fullthrottle]

Hi
Check out the various threads I did on the LSPV (search function is your friend).
And understand it's function...

Post in thread 'What did you do on your 70 series today?' What did you do on your 70 series today? - https://forum.ih8mud.com/threads/what-did-you-do-on-your-70-series-today.804784/post-14738924
Good Luck Ralf

Many thanks Ralf, that has been very insightful.

 

[Broski]

This complete idiot bypassed their LSPV not because they think they're more clever than an automotive engineer, but because when presented with the choice of no rear brakes and 50/50 front/rear brakes, this idiot chose the latter. So dumb.

This idiot also put an LSPV project on their project list. But the LSPV is hard to adjust, hard to bleed, hard to maintain, and hard to modify for lifts. And it's effectiveness is dependent on getting all of the above just right. So it is on the list but not at the top of the list.

Sometimes one has to prioritize their efforts and be called an idiot.

Fine by me. This idiot is quite happy with their decision.

Add me to the list of idiots for all the same reason
Except I’m a double idiot because I took the ABS out at the same time

The brakes work better then they ever have in my owner ship
I did add a proportioning valve

 

[fullthrottle]

You've convinced me, going the cheaper option....

No Brakes, Just Bull Bars

 

[Felde]

Sorry, it was not my intention to offend anyone.
Ralf

 

[TreadingLight]

It's OK. You gave me an opening so I had to run with it

 

[JuanJ]

Someone has to win the Darwin Award this week!

Hello,

Our society messed up with natural selection. There is a price to pay for it.

The human gene pool needs deep (and thorough) chlorination.

Just my opinion. No offense intended.




Juan

 

[sodafeld1]

I think it is wonderful that Ralf did a thorough write up on the lspv. Thanks Ralf!
I can understand both sides of the table some like it, some don't.
It is a simple thing. A valve which controls how much hydraulic fluid goes to the rear drums, controlled by an arm which is actuated by the weight of the load in the rear.
Here is an old toyota one and a new ebay one made by 'satan'..if you have the money go new toyota