A good friend of mine has a nice older model 4 Runner. We noticed something strange on the back axle that I was hoping someone here could explain to me. It is a metal rod that begins just off to the left of the rear pumpkin. Located there is a rubber bushing. The metal rod extend upward and accross the rear. It ends just above the leafs. I can't remember where it attaches exactly but I think it might be right to te frame. Our guess is that is would somehow measure the angle of the rear axle but there are no wires or sensors that we can see.

Id like to know what it's called. What it does. And can we take it off without hindering safety. Thanks!

 

Sounds similar to a panhard bar on a 3rd gen, but I'm not sure if they are on 1st gens. Got a pic?


EDIT: I'm not sure where I got 1st gen from , I guess I was just assuming....

 

Sorry no pictures. I know that would probably help allot. I just looked up some photos of a Panhard bar and it's a good guess. This metal rod really wouldnt provide much support though. The diameter is only the width of a pencil.

I can also tell you it's not custom and it looks like a cable at first, but upon closer inpection it's definately a solid rod.

 

That doesn't sound like a panhard rod to me if its the diameter of a pencil! I'm outta guesses.

Welcome to the forum by the way!

 

Thanks for your help. I'lll keep digging around. I'll try to take some photos this weekend. Ive got a camera but my internet connection is limited. I'll shoot to have them up by next Wedneday or Thursday

Thanks! Seems like a nice place with allot of information.

 

Hey Tom, you assumed 1st gen because he said 4runner and leaf springs. Leaf spring'd trucks don't use panhards since the leaves locate the axle left and right.

Ryan, I think you're talking about the brake proportioning valve. I don't think 3rd gens have them so Tom wouldn't have known. It's a sensor that tells the braking system how much weight is in the back and thus proportion more braking power to the front or rear accordingly.

After lifting the truck, some people will just disconnect the rod at the axle and zip tie it up to the frame. That will fool the sensor into thinking there is a heavy load and proportion more braking to the rear. All Pro does that to all the trucks they work on, but they always have pretty big tires intalled too. However, if you do that you probably run the risk of locking up the rear tires before the front in an emergancy braking situation. If that happens you will quickly loose control and swap ends.

 

I looked up Brake Proportioning Valve and I found a picture, although it's not a great one. I circled it in red. It shows it attached to the axle. Unfortunately the spare tire hides the rest. Looking at this picture do you still think it's the part of the Brake Proportioning Valve?

 

Yup Pretty sure.

 

sa-WEET. Good one Steve. I learn something new every day around here.

 

From what you described it seems like that's what it is. The placement and range of motion would make total sense. I didn't see any measuring mechanism other than the rod itself, but it was pretty muddy under there. Thanks again for the help!

 

That indeed is the LSPV rod. (Load Sensitive Proportioning Valve) Its purpose is to measure the distance between the axle and frame. In theory when you have a lot of weight back there the frame rides lower and it adjusts the brake bias to provide more rear braking power.

Only problem is that over time the springs sag so it thinks there is more weight than there really is causing the rear brakes to lock up sooner than they should.

I have heard of people disconnecting it and tying it to the frame with bailing wire to keep it stationary and get lots of rear brake power. I don't reccomend it but some yahoos out there like it that way.

Edit:

I thought of more to say. Simply disconnecting it and letting it droop will give you less rear brakes or maybe none at all since it will think the rear tires are in the air. Its the upper end where the LSPV is that measures the angle of the rod. Its bendable and that' how to adjust it to get the right brake bias with saggy rear springs.

Having slightly more rear brakes can be good and help prevent warped front rotors since the fronts would not have to do so much work. However if you adjust it too much the rears will lock too soon and you might find yourself un-intentionally backing into guard rails or ditches at high speed.