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Ok here is the deal on rear truck brakes. Some large trucks (dump trucks etc.) have no front wheel breaks when you place most of the weight in the rear there is not nearly as much weight shift to the front it does not lift. A Toyota MH is all ways weighted to the rear it needs all the rear brakes you can give it under any circumstance . Backing up with drum breaks will be poor breaking because of the design of drum breaks they are what is called self energizing meaning the forward motion help apply them this does not happen in reverse. If you decide to adjust the proportioning valve adjust it for absolute max load because that is what it is.

I know that. I was just interested in a possible way to adjust the valve directly because adjusting the thingy that sticks out didn't do the trick.

Linda S

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I've never been 'inside' one, so hard to advise. With the rod disconnected, did the lever seem to move freely? Also, I seem to have read people who have simply removed the valve completely and hook the brake lines directly. I won't say if this is safe to do as I'm not sure if the valve performs a secondary function.

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I've never been 'inside' one, so hard to advise. With the rod disconnected, did the lever seem to move freely? Also, I seem to have read people who have simply removed the valve completely and hook the brake lines directly. I won't say if this is safe to do as I'm not sure if the valve performs a secondary function.

Thanks Derek for at least responding. Guess I'm just going to have to buy a factory service manual on ebay or something. Probably should have one anyway. I think I saw something on yotatech about removing it. Never done brake lines but can't be too hard.

Linda

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I doubt you'll find anything in an EBay FSM that's different from Post #1.

Computer is messed up. Too big to download. That's why I asked if I could just get a couple of pages of it. I'm better with paper anyway. On the ground next to me when I'm working.

Linda

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The entire ideal behind the valve was for the pickups the factory did not build MH's when the truck was unloaded it reduced the break pressure so that the rears did not lock up they were designed to carry weight so the rears on the pickup had a greater breaking force (drums vers. disks) So the bottom line it is of no use on a Toyota MH because there is no way they will lock up. It is way over weight.and does not have enough sweep area or cylinder size. It will not ware the shoes any more then having it it's all ready trying the hardest it can to stop the *&^% thing because the valve is all ready at the highest weight setting unless you jack the rear up with air bags. My Nova Star has 9 leaf spring packs it does not sit level on flat ground the rear is higher it has no valve (any more) the rear breaks do not lockup it does stop a touch better but still is no prize. The brakes are over taxed it is what it is.

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well I'm confused, will it do any good to adjust the bar shackle as in twoblock's top picture, or just wasting time, during panic breaking the front wheels lockup, and if its raining out forget about it, can't stop period, new shoes, turned drums rear, new pads rotors front, the only way i can lock up rears is with e-brake, not looking for lockup but would like to feel like I'm getting a little help from the rear, one thing i did notice last week on 1400 mile trip, i have always run with air bags full 90psi and tried this trip at 60psi just to feel the diff. in ride and i think the rears held a little better, could be my imagination, i was paying specif attention to breaks due to just having them done, anyways back to my original question, is the consensus here that i should or should not adjust the bar shackle to the proportioning valve?

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I just got mine back from some brake work and I still seem to be having a problem with the fronts locking up too easily. At first it was the left front locking and pulling the wheel over, so I put her in the shop and found out the right caliper was bad. So that got replaced. Now, both of them seem to be locking just way too easily for comfort.

Could it be that I just need to back the adjustment off to more of a rear-brake position? Could the valve be seized? Or is it something else entirely? I had the hoses checked out and they seem to be OK, and the mechanic didn't believe it could be the master cylinder, so what gives? I looked under there when I got the vehicle back, and it looked to be about neutral, maybe set a little toward the rear brakes. I'm waiting for the rain to stop so I can go to look again.

The mech said that I had strong pressure going to the fronts but not so much to the rear drums. I assume that is normal, being that drums don't need as much hydraulic pressure as discs do. But he repeated that 3-4 times in the half-hour we talked so I'm wondering if he meant that it was lower than it should be?

Of course I have had this RV for about a week and a half now, and it is my first Toyota, so this may be the norm for them and I just don't know it. If its not though, any information would be useful.

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Adjust the proportion valve wide open, disconnect it and wire it open. remove it and replace it with a "T"

any of the three options will get you maximum braking to the rear wheels.

John Mc

88 Dolpnih 4 Auto

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Sorry I took a bit to answer. By the valve you mean the lever mechanism on the rear axle? I'm a little confused. I think it's time to download that manual.

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Yes, you want the valve wide open. The LSPV is the simplest attempt at making the braking system 'smart'. It's only got 1 'input' of information, the ride height. Add a set of air springs to the rear axle and this 1 'input' is all screwed up, fooling the valve into thinking you're not heavily loaded.

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OK, so I'm going to back the lock nut off to the top of the post. I don't have air bags so I don't have to worry about that.

Is it possible to go too far and end up with rear bias? That's probably just as dangerous as the problem I have right now.

Edited by straygoose

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I don't think you've got to worry about too much rear bias. But certainly, find a nice empty stretch of road and test them before going out onto a busy freeway! :)

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Best way to check brake bias for rears try braking down hill, if too much rear brake they will lock up as we don't have antilock. Another check is try stopping on a hill going backwards. If fronts lock up too easily try again and add rear braking via the parking brake, thats what I have to do with mine. I remember somewhere here another poster saying that's what they do. Now that all the brakes are done on mine will see what's what. When we did the rears at 85 K the shoes were 1/2 down.

vanman

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I don't think you've got to worry about too much rear bias. But certainly, find a nice empty stretch of road and test them before going out onto a busy freeway! :)

I kind of figure as much, since the locking up comes at slow speeds. It probably also happens at high (+35mph) speeds but I haven't had to get on the binders real hard out on the highway.

Sometimes though, I feel like it's still just locking up on one side (front left). Maybe its just because I'm on that side of the vehicle too, but it just feels that way to me. And like I said it seems to be locking up at slow speeds (10-20mph).

I'm not really up for testing her by slamming on the brakes at 40mph, seeing as I've only had her a couple of weeks and I'm still getting familiar with her handling, or lack thereof. Don't really feel like laying her over on her side just to see if she wants to stop quickly.

That would suck. Big time.

Edited by straygoose

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You can feel the difference driving normally. You can NOT adjust the arm to far, mine is wired up to the frame.

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/\ This is funny! +1 to DUN

/\

You can feel the difference driving normally. You can NOT adjust the arm to far, mine is wired up to the frame.

I'm going to back mine off either sometime today or tomorrow. If that fixes the problem great, but disabling it is something I don't feel comfortable doing. Thanks

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OK, I crawled under there, and once I realized it was a five minute adjustment (DOH!), I grabbed a couple of wrenches and commenced to cranking. I thought I might need to get her with impact tools or dynamite or something, but the whole assembly came apart in a minute.

I backed her off a good 1/2" as you can see in the photos. The shiny area on the threaded rod is how far I backed her off.

Took her around the campground here and she seems to be more balanced than before. The fronts still locked up, but it seems to take a lot more pressure on the pedal than before, so that's a good thing. I have to go into town tomorrow, so I'll check her out a highway speed then. I figure if worse comes to worst, I can always crawl under her in the WalMart parking lot and either back her off more or bring her back into a more neutral position. I do have about another 1/2" of adjustment to make if I need to increase the rear bias.

In the photos at the top of the post, it shows that the lever is held in place by two opposing nuts with lock washers. On mine there is only a lower nut with a lock washer, and the top nut is actually welded into the lever itself. Obviously an engineering change. I'm sure others have the same setup, so does anyone know when they changed it? Just curious.

This has been very helpful. Hopefully the problem is solved with just a little more adjustment to the bias. Thanks to everyone.

post-6508-0-26325300-1352047784_thumb.jppost-6508-0-95836000-1352047804_thumb.jp

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I don't remember if you have air springs or not, but if you do, change the air pressure will throw things off and you'll have to start adjusting all over again. That's why most advocate simply just adjusting it all the way.

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No, no air bags on mine. It does have spring helpers though. Will that change things?

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No, since they're not adjustable. Possibly when the helper springs were installed the valve wasn't adjusted at the same time. The helpers would fool the valve into thinking that you were lightly loaded, even though you aren't.

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