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Old 08-24-2010, 07:55 AM
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Jacket Jacket is offline
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Default bleeding and LPSV

My brake saga continues.... My brakes are still spongy, and require a pump or two to get them up to a comfortable level of firmness for normal driving. Two calipers have been replaced, 3 new soft lines between the frame and axles, and 1 new hard line on the passenger front. I went to bleed them for a 3rd time last night.

RR - a bit of air at first, but then a solid stream of fluid
LR - no air to speak of.
LSPV - With my wife pumping the pedal, we had streams and streams of air coming out the bleeder. It just kept coming and it seemed like the more times she pumped the pedal, the more air we could find. After pumping down the MC to about 1/3 capacity twice, I moved on.
RF - no air
LF - no air

back to the LSPV, but still the the lines seem to have an endless supply of air. I did one last pump and bleed at each corner, and again at the LSPV. Brakes are still waaaayy spongy.

Anyone have an idea of what could be going on? Seems like the 4 corners are fine, but the LSPV has an air source of some kind. Suggestions?
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Last edited by Jacket; 08-24-2010 at 10:31 AM. Reason: Getting my acronyms correct....
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Old 08-24-2010, 09:23 AM
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Not sure why there is endless air coming out of the lspbv, but in my endless brake bleeding hours on the 80 and gallons of fluid, the technique I found worked the best was this.

Using a motive, put 10 psi on the system and open whichever valve you want to bleed. Then with that valve still open, go stomp on the brake pedal pretty hard, but let up on the pedal VERY slowly. Repeat a number of times. Even with that 10 psi on the system you don't want to draw any air back into the lines from the bleed valve so that's why I didn't let up at normal speed.

I did this with two people (had an assistant pound the brakes, and let up slow) while I watched the fluid come out. None got sucked back in, and the sudden increase in pressure really forced some air out that just the standard Motive or standard "pump 3 times, open valve, close valve, repeat" method didn't get.

The benefit to using the motive is you can already have the valve open and fluid moving when you stomp on the pedal. Suppose you could do this just with gravity bleeding method too.

I do recall that I got quite a burst of air out of the lspv, but it only went for about 5 seconds and then fluid came out. Unless the valve is bad or the system has a leak somewhere, can't imagine that more air is getting into the system?? Though if you did softlines, hardlines, calipers, etc I would imagine it took me a whole lot more fluid than 2/3 of the reservoir twice to get the lspbv bled correctly.

2 cents from a noob.
corey
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Old 08-24-2010, 10:44 AM
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Thanks for the response. The "2/3 of the reservoir twice" comment was just for last night's bleed session and the LSPV valve. I've been through 3 of the tall jugs (32 oz's) over the course of the entire bleed saga.

A few other comments - I'm not losing any fluid, so I don't think there are any leaks. I just can't figure out where all the air in the LSPV line is coming from. I did run the MC dry when I broke a hard line a few weeks back, so unfortunately air was probably introduced through the top. But I thought I got all this air pushed out in the first and second rounds of bleeding.

I've read a few different threads on bleed techniques for Yotas with the LSPV, and it seems that consensus is that this valve should be last one you bleed (after each of the 4 corners). So that's what I have been trying.

Any other tips/tricks?
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Old 08-24-2010, 11:47 AM
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I do the LSPV last. My order is right rear, left rear, right front, left front and then LSPV. I use a Motive pressure bleeder. Dunno what to say other than keep bleeding until no air comes out. I've always wondered why it can be tough and think it depends on the position of the LSPV. If you push the rod up so that you get maximum rear flow then maybe it's easier than if the rod is cutting off fluid flow and you get a pocket of air stuck behind that is just trickling out. I have no reason to believe this other than just a hunch.
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Old 08-24-2010, 12:33 PM
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well, the actual rule of thumb is to always start at the highest point first in any system, so the lines that have the funky coil off the master, regardless of position are the ones to get first, then the lspv.

I could never get a real firm pedal in an 80, and I don't know many people that have one. 80's brakes are mush when good.
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Old 08-24-2010, 12:40 PM
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you sure your master cylinder isn't leaking air?

seems like it's not since air is only coming from the LSPV..
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Old 08-24-2010, 12:51 PM
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Quote:
Originally Posted by Beater View Post
well, the actual rule of thumb is to always start at the highest point first in any system, so the lines that have the funky coil off the master, regardless of position are the ones to get first, then the lspv.
Wonder about this, like a slug of air got (or is getting) into the master, which settles in the next highest spot at the LSPV. This might explain why Toyota says to do the LSPV last, air that does not burp out of the master would accumulate there.
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Old 08-24-2010, 01:36 PM
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Quote:
Originally Posted by rover67 View Post
you sure your master cylinder isn't leaking air?

seems like it's not since air is only coming from the LSPV..
I thought about that too, but couldn't get past the fact that the 4 wheels seemed fine.
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Old 08-24-2010, 01:41 PM
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I guess I could just go nuts on the LSPV line and couple more big bottles of fluid and see if I can get it to clear. It just seemed like the more we pumped, the worse it got. And we kept going and going with what felt like an amount of fluid that could have gone around the block and back. Maybe I underestimated the number of twists and turns in that part of the system?
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Old 08-24-2010, 01:41 PM
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Quote:
Originally Posted by Jacket View Post
back to the LSPV, but still the the lines seem to have an endless supply of air. I did one last pump and bleed at each corner, and again at the LSPV. Brakes are still waaaayy spongy.
Seems to me that if you are not introducing any air into the system via leak or running the MC dry again, and you are still getting air out of the lines, then you are bleeding it correctly and just need to keep after it? Even after I bled mine with at least 2 gallons and all possible methods, and robbie came by and bled the brakes again, he still got a little air out of one of the calipers.
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