PDA

View Full Version : bleeding and LPSV


Jacket
08-24-2010, 07:55 AM
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?

coax
08-24-2010, 09:23 AM
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?? :confused: 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

Jacket
08-24-2010, 10:44 AM
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?

DaveInDenver
08-24-2010, 11:47 AM
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.

Beater
08-24-2010, 12:33 PM
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.

rover67
08-24-2010, 12:40 PM
you sure your master cylinder isn't leaking air?

seems like it's not since air is only coming from the LSPV..

DaveInDenver
08-24-2010, 12:51 PM
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.

Jacket
08-24-2010, 01:36 PM
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.

Jacket
08-24-2010, 01:41 PM
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?

coax
08-24-2010, 01:41 PM
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.

corsair23
08-24-2010, 01:50 PM
I've read that for some, bleeding the brakes is one of the few things the OCD crowd will let a dealership do :)

Matt, did you bench bleed the MC after you ran it dry or bleed it on the truck? Never done that and hope to never have to but the procedure in the FSM makes it look pretty benign.

I've been lucky so far on both the 80 and the LX. I had never bled brakes before until a couple years ago. I've finally gotten decent as using the Motive power bleeder (key is a REAL tight seal) and decided that everytime I bleed the brakes I'll do a flush at the same time because trying to judge how much fluid to put into the Motive is a useless exercise in futility.

That said, I'm with John that even a well bled 80's brakes aren't something you'll write home about :)

I've contemplated getting those Speed Bleeders to make the pump and let up method a one person operation. But I'm not sure how you monitor whether air is coming out or not sitting in the truck push the brake :hill:

I might have to try Corey's technique next time of "aiding" the Motive with an extra push of the pedal...

Bikeman
08-24-2010, 07:09 PM
The one thing I don't touch on my 80's are the brakes. I let someone else do it with a power bleeder and have firm pedals on both.

Jacket
08-27-2010, 10:48 AM
This story is my experience verbatim:

http://www.expeditionportal.com/forum/showthread.php?t=4575

80 brakes seem to be frustrating to a lot of people.

I had it power flushed this morning, and they were unable to get the "mush" out as well. Seems like the Master Cylinder is the next likely part to be replaced. Does it make sense that the design of the 80 brakes would cause the LSPV to be the circuit most affected by a MC leak? I haven't read about a lot of 80 series MC problems, but maybe by letting it run dry during this process I dislodged a "fluid seal" and introduced a small air leak in the O-ring?

Has anyone else had to replace their 80 MC? Looks like I have a few choices: Marlin sells a big bore MC for the 80's, MAF has AISIN brand units, and of course there's OEM.

Bikeman
08-27-2010, 12:52 PM
Wow. Bummer, Matt. When the shop power bled mine, after getting it back, there was no evidence the LSPV was even cracked open.

rover67
08-27-2010, 01:14 PM
Man, I just don't get it. The only time I have had issues similar to what you are having was when I made the mistake of letting air into a system that had an ABS pump. It took me an eternity to get that thing bled until I found the right bleed screw.

after reading that other guy's post I feel like it's not the MC...

how much air is still coming from the LSPV? a lot?

corsair23
08-27-2010, 01:15 PM
Bummer Matt...

The longer you have the 80 the more you read about the little "nuances" of the rig...I never know what sort of credence to lend things you read about on here, MUD, etc. That said, little things like the problems people have encountered after running the MC dry, or folks that have busted off the vent line on the top of the radiator when replacing the spark plugs, or folks that have busted off the knock sensor when replacing the PHH, make me not temp fate when doing certain stuff and make me take extra precautions....

I haven't been where you are right now luckily for me because my skills wouldn't be good enough to get me out of the hole :hill:

DaveInDenver
08-27-2010, 01:32 PM
Wonder if running it dry could let a piece of debris flow down, scoring the piston bore wall or nicking a seal.

BTW, the Marlin 'Big Bore' MC is the stock Aisin FJ80 Non-ABS part, it's 'big' relative to the standard size Hilux. The FJ80 came with a 1" piston, which would upgrade a '79-'85 mini truck that came with a 13/16" piston. The potential upgrade for you would be to a 1-1/16" unit from a HD T100. But doing this with no other changes (primarily using the matching booster) might make the pedal even more mushy. BTW, I don't know if the FZJ80 has a different MC and I'm not sure how ABS affects your swap options.

I once went through trying to figure all that out. My truck was delivered with the 'big' bore master cylinder (what some people call the 'V6' brakes). The engine in the Hilux does not seemed to have been the determiner of what brakes you got, but rather if you have 8" or 10" rear drums (1986-1988 IFS I think had 8" but all trucks from 1989-1995 have 10" rear drums) and the caliper piston size. In any case with a FZJ80 you would already have at least a 1" bore master cylinder and maybe a 1-1/6" since some 4Runners (V6 from 1992-1995) and many T100 had them.

http://risingsun4x4club.org/forum2/showpost.php?p=105941&postcount=4

corsair23
08-27-2010, 01:41 PM
Matt, quick question.

Did you replace all of the soft lines? I ask because I have it in my memory bank that someone in the club had issues with brakes and it turned out that one or more of their soft lines was loosing its integrity and what would happen is when you hit the brakes the pressure would cause the line to "balloon" and reduce the pedal effectiveness.

Granted, as I recall this was on a FJ40 with really old lines...

Jacket
08-27-2010, 02:41 PM
Man, I just don't get it. The only time I have had issues similar to what you are having was when I made the mistake of letting air into a system that had an ABS pump. It took me an eternity to get that thing bled until I found the right bleed screw.

after reading that other guy's post I feel like it's not the MC...

how much air is still coming from the LSPV? a lot?

Last time I did it, it was just a few bubbles. Becky said the pedal felt good resistance so I cranked it closed. Felt pretty good going around the block, but the next day the pedal went to the floor a couple of times.

Honestly - it seems like it goes in intervals. Like it'll be just fluid and maybe a few bubbles, but if I keep allowing my pedal pumper to push more fluid, it eventually "finds" another pocket of air - so much so that you hear it crackle when it enters the tube outside the bleeder. That behavior might lend itself to a leak in the MC.

Bummer Matt...

The longer you have the 80 the more you read about the little "nuances" of the rig...I never know what sort of credence to lend things you read about on here, MUD, etc. That said, little things like the problems people have encountered after running the MC dry, or folks that have busted off the vent line on the top of the radiator when replacing the spark plugs, or folks that have busted off the knock sensor when replacing the PHH, make me not temp fate when doing certain stuff and make me take extra precautions....

I haven't been where you are right now luckily for me because my skills wouldn't be good enough to get me out of the hole :hill:

I'm barely qualified to be a shade tree mechanic, but I've bled enough brake systems successfully to know that this is a serious anomaly.

Wonder if running it dry could let a piece of debris flow down, scoring the piston bore wall or nicking a seal.

BTW, the Marlin 'Big Bore' MC is the stock Aisin FJ80 Non-ABS part, it's 'big' relative to the standard size Hilux. The FJ80 came with a 1" piston, which would upgrade a '79-'85 mini truck that came with a 13/16" piston. The potential upgrade for you would be to a 1-1/16" unit from a HD T100. But doing this with no other changes (primarily using the matching booster) might make the pedal even more mushy. BTW, I don't know if the FZJ80 has a different MC and I'm not sure how ABS affects your swap options.



Good to know Dave - thanks. The Marlin MC is probably the same Aisin unit that MAF sells for 80's. And I wonder the same thing about debris or something affecting the MC when it ran dry. I'm going to try and do a pedal test on the MC this weekend and see if I can detect a leak.

Matt, quick question.

Did you replace all of the soft lines? I ask because I have it in my memory bank that someone in the club had issues with brakes and it turned out that one or more of their soft lines was loosing its integrity and what would happen is when you hit the brakes the pressure would cause the line to "balloon" and reduce the pedal effectiveness.

Granted, as I recall this was on a FJ40 with really old lines...

Not all the soft lines, just the ones that extend from the frame to the axle housing. So I suppose your theory is possible, although I keep coming back to the fact that its just the LSPV circuit that seems to be packed full of air. The four corners push out fluid and nothing more.

TIMZTOY
08-27-2010, 02:51 PM
Yes : letting the master cylinder "can" (but not always) damage the seal. Rendering the master cylinder defective.

- you don't need to bleed the lspv thingy unless you opened the lines to it directly. Or drained the system. The fluid pass threw it.

- I've found that the best way to bleed a troublesome system such as yours is a "one man brake bleeder" which is assentally just a tight fitting hose on the bleeder then submerged into a bottle filled about 1" with brake fluid. Because when you pump, the air comes out. But when you relese, it sucks fluid In, not air. Do this about 1/2 - 3-4 of the resivior. And you should be golden. If that dosent work un-bolt the rod to the diff and force it all the way up to take out all the slack in the piston essentially "top dead center " =( less volume to fill)

-Do not use pressure bleeders on vehicles with ABS ! You can distroy the motor. This is why tool manufacture stoped producing them. And you can only find vacume bleeders Now.

- I use vacume bleeders, the one man bleeder and the 3 pumps methods of bleeding. And the most affective method is the 3 pumps but you have to close the bleeder while the stream is still flowing solidly. And not after the flow stops. And open the bleader slowly. If you open it fast. Even with NO air, it will look like there is air Because of how it's shooting out.