Rear Drum Brake Questions?
08-14-2008, 08:11 PM
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Rear Drum Brake Questions?
I see this little lever on the passenger side, inside the rear of the frame. It seems that both the rear brake lines connect to this lever that moves up and down. I have never seen anything like it and curious if this is for bleeding the line or what. (Im a noob here guys) I need to replace the leaking divers side rear wheel cylinder and have never done this before. I would like to learn more about it so I make sure to do it right. Just looks like two bolts so it should be easy but eh, what do I know? I see this lever and a bleeder valve so I am like Hmmm, what is this thingy LOL. Thanks guys
08-14-2008, 08:17 PM
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So how does this load sensing proportioning valve work exactly. Just seems like a lever that moves up and down and always returns to the center position it was in. Would really like to learn something here if you do not mind. Thanks
08-14-2008, 08:20 PM
#4
To honest i am not 100% sure. My guess, is that its just a valve that works based on the load placed on your truck. The lower the truck squats, the more brake pressure is applied to the rear brakes. Of course with todays braking systems there isn't any need for one, but it was pretty important back in the day.
08-14-2008, 08:22 PM
#5
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if you ever do a lift, that's the only time you have to consider either modifying it with a braket on the diff to raise the mounting point up, or bypass it all together with a proporsioning valve...
AND
when you bleed your brakes, don't forget to bleed that valve too; there's a bleeder screw on that thing just like wheel cylinders...
...wow, proposioning valve? that's why my name's superbleeder and not superspeller...
Last edited by iamsuperbleeder; 08-14-2008 at 08:24 PM.
08-14-2008, 08:24 PM
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To honest i am not 100% sure. My guess, is that its just a valve that works based on the load placed on your truck. The lower the truck squats, the more brake pressure is applied to the rear brakes. Of course with todays braking systems there isn't any need for one, but it was pretty important back in the day.
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08-14-2008, 09:28 PM
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It is a LSPV aka load sensing proportioning valve. There are 3 brake lines and a bleeder screw. One brake line T's for the rear tires. The other brake lines are the supply/return. As the bed squats down, more pressure is fed to the T, when the bed is empty, more pressure is fed to the return and less to the T. Take off the line for the wheel cylinder, and the two bolts. Swap out the cylinders. Bleed all four corners, then the LSPV.
08-14-2008, 10:07 PM
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It is a LSPV aka load sensing proportioning valve. There are 3 brake lines and a bleeder screw. One brake line T's for the rear tires. The other brake lines are the supply/return. As the bed squats down, more pressure is fed to the T, when the bed is empty, more pressure is fed to the return and less to the T. Take off the line for the wheel cylinder, and the two bolts. Swap out the cylinders. Bleed all four corners, then the LSPV.
Last edited by Ryan; 08-14-2008 at 10:09 PM.
08-15-2008, 07:06 AM
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DOT 4 has a higher boiling point than DOT 3. other than that, no difference.
do not use DOT 5 without rebuilding and flushing everything- it is not compatible with other brake fluids so cannot be mixed. in spite of a high boiling point, it is also slightly compressible so would cause a spongy feeling in the pedal.
DOT 5.1 is allowable but it's not necessary with your truck since you're not running a race rig.
If your truck does not have the arm going from the LPSV to the axle, your rear brakes are applying full pressure all the time. Not a big deal, but should the rear lock up before the front, the rear end will slide sideways.
The two lines coming from the front are not a 'supply' and 'return'. One is from the rear brake circuit of the master cylinder, the other is from the front brake circuit. Front brake pressure is used to help the valve limit rear brake pressure when the truck is less than fully loaded- a simple lever acting on a valve would blow apart under full brake pressure so the front circuit is used as an assist to the lever. There is no crossover between the two lines.
The lpsv bleed screw bleeds air from the line coming from the front brake circuit so that the valve can work properly. Bleeding the rear wheels take care of bleeding the other part of the valve.
do not use DOT 5 without rebuilding and flushing everything- it is not compatible with other brake fluids so cannot be mixed. in spite of a high boiling point, it is also slightly compressible so would cause a spongy feeling in the pedal.
DOT 5.1 is allowable but it's not necessary with your truck since you're not running a race rig.
If your truck does not have the arm going from the LPSV to the axle, your rear brakes are applying full pressure all the time. Not a big deal, but should the rear lock up before the front, the rear end will slide sideways.
The two lines coming from the front are not a 'supply' and 'return'. One is from the rear brake circuit of the master cylinder, the other is from the front brake circuit. Front brake pressure is used to help the valve limit rear brake pressure when the truck is less than fully loaded- a simple lever acting on a valve would blow apart under full brake pressure so the front circuit is used as an assist to the lever. There is no crossover between the two lines.
The lpsv bleed screw bleeds air from the line coming from the front brake circuit so that the valve can work properly. Bleeding the rear wheels take care of bleeding the other part of the valve.
08-15-2008, 09:17 AM
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DOT 4 has a higher boiling point than DOT 3. other than that, no difference.
do not use DOT 5 without rebuilding and flushing everything- it is not compatible with other brake fluids so cannot be mixed. in spite of a high boiling point, it is also slightly compressible so would cause a spongy feeling in the pedal.
DOT 5.1 is allowable but it's not necessary with your truck since you're not running a race rig.
If your truck does not have the arm going from the LPSV to the axle, your rear brakes are applying full pressure all the time. Not a big deal, but should the rear lock up before the front, the rear end will slide sideways.
The two lines coming from the front are not a 'supply' and 'return'. One is from the rear brake circuit of the master cylinder, the other is from the front brake circuit. Front brake pressure is used to help the valve limit rear brake pressure when the truck is less than fully loaded- a simple lever acting on a valve would blow apart under full brake pressure so the front circuit is used as an assist to the lever. There is no crossover between the two lines.
The lpsv bleed screw bleeds air from the line coming from the front brake circuit so that the valve can work properly. Bleeding the rear wheels take care of bleeding the other part of the valve.
do not use DOT 5 without rebuilding and flushing everything- it is not compatible with other brake fluids so cannot be mixed. in spite of a high boiling point, it is also slightly compressible so would cause a spongy feeling in the pedal.
DOT 5.1 is allowable but it's not necessary with your truck since you're not running a race rig.
If your truck does not have the arm going from the LPSV to the axle, your rear brakes are applying full pressure all the time. Not a big deal, but should the rear lock up before the front, the rear end will slide sideways.
The two lines coming from the front are not a 'supply' and 'return'. One is from the rear brake circuit of the master cylinder, the other is from the front brake circuit. Front brake pressure is used to help the valve limit rear brake pressure when the truck is less than fully loaded- a simple lever acting on a valve would blow apart under full brake pressure so the front circuit is used as an assist to the lever. There is no crossover between the two lines.
The lpsv bleed screw bleeds air from the line coming from the front brake circuit so that the valve can work properly. Bleeding the rear wheels take care of bleeding the other part of the valve.
Anyone if the Phoenix area want to give me a hand with this?
08-24-2008, 12:45 PM
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If anyone in the Phoenix area wants to give me a hand with a few things on the 4Runner, I am looking for someone who also has an air compressor so I can change out the control arm bushings with my air tools. Thanks guys
08-24-2008, 07:00 PM
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if you're driving a 4runner, the LPSV isn't as big a deal as it is on the trucks, since the runner is like a half-loaded truck anyways.
If you're gonna remove the valve, do it right and block the line from the front brakes with a good plug in the tee, and install a manual proportioning valve by the master cylinder on the rear brake line so you do have some means to compensate for loading the truck, else you might be chewing up front brakes or locking the rear up and spinning 'round at the wrong time
If you're gonna remove the valve, do it right and block the line from the front brakes with a good plug in the tee, and install a manual proportioning valve by the master cylinder on the rear brake line so you do have some means to compensate for loading the truck, else you might be chewing up front brakes or locking the rear up and spinning 'round at the wrong time
08-25-2008, 12:22 AM
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The connecting rod I have that was from the real axle assembly housing to the LPSV is cut up to the LPSV with only 3" left on it, hense the reason I thought it was a lever. Now I see it's purpose and it is no longer in use on my 4Runner. I can only assume it was cut like that when the previous owner had the 4" lift installed since it was no longer long enough to serve it's purpose. Now it sits level and even if I move it up or down it immediately returns to its level middle position. Hmm, not really sure if this matters or not or if I should even bother hooking it up but it has not made any difference in the braking that I could notice. I will likely be writing a DIY (Do It Yourself) thread on the rear brakes for anyone who would appreciate it. Do you guys think this would be helpful for some, even though it may be common sense for most?
I am considering a DIY for IFS upper/lower control arm bushing and bump stops and shocks, one for inner/outer Tie Rods, pitman arm, and idle arm, and alignments, and one for ball joints and maintenance, since I am already going to replace all of these parts this week. I just spent $900 for a good air compressor and all the tools required to get all this done. I will also likely be putting all the Toyota specs up with torque specs as well. What do you guys think, would these be good DIY threads for everyone to view and possibly help out? What section do you all recommend I post these threads in since I am still learning my way around this site?
I am considering a DIY for IFS upper/lower control arm bushing and bump stops and shocks, one for inner/outer Tie Rods, pitman arm, and idle arm, and alignments, and one for ball joints and maintenance, since I am already going to replace all of these parts this week. I just spent $900 for a good air compressor and all the tools required to get all this done. I will also likely be putting all the Toyota specs up with torque specs as well. What do you guys think, would these be good DIY threads for everyone to view and possibly help out? What section do you all recommend I post these threads in since I am still learning my way around this site?
Last edited by Ryan; 08-25-2008 at 12:25 AM.
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