load sensor on rear axle

[jeff jones]

can anyone tell me anything about this unit my 89 comanche has this but not hooked up parts missing from it thanx much

[ORCA]

I don't know too much about it, but i'll be eliminating mine eventually. If you want i'll give you all the parts I end up ditching. :cheers:

[Eagle]

The FSM has a rather involved section about adjusting it, and the adjustment involves replacing some small parts that probably aren't available even from a dealer. Most likely you could hook up a rod to it without replacing the small parts, but I think it's wiser to eliminate it.

 

I suggest that because the one in my '88 blew out in a panic stop situation. Having had that happen once, I won't trust another one. It's actually a duplicate hydraulic circuit and there is a way to eliminate it completely. Two ways, actually, one using the MJ front combo valve and one using an XJ (Cherokee) front combo valve. There are advantages and disadvantages to both ways.

 

Let us know if you're interested.

[SomeNew Name]

I'm pretty interested in doing this with a MJ front combo valve, can I use one from a 92 on a 90? and if so I would love it if you can school me on doing it.

[Eagle]

You already have the MJ front combo valve. However, it's function is different from that in an XJ. In the XJ the front valve is both the brake system failure warning light switch and the proportioning valve. In the MJ, it's the brake system failure warning light switch and a by-pass to allow full pressure to the rear brakes if the front brakes fail. Under normal conditions, fluid/pressure is sent to the rear brakes through that height-sensing proportioning valve.

 

To by-pass (eliminate) it is easy. First, either run a new brake line from the fitting on the "nose" of your front combo valve body directly to the hose from the chassis to the rear axle, or

 

Trace the line from the nose to the rear, and somewhere near the back cut it and flare it, then run a short section of new line to the rear flex hose. I recommend using all new line from the front because the steel hard line to the rear seems prone to rust, and they eventually pop right about where the run past/over the fuel tank.

 

Having run a single line from the combo valve block to the rear flex hose, you can now either ignore the rear height-sensing valve and whatever tubing is left, or remove it. I'd remove it; why haul excess junk around, and give some mechanic or inspector an excuse to ask why you disabled it?

 

Now, there will be a left-over line or empty outlet at the front bottom of the combo valve body. This outlet was the line that would by-pass the rear height-sensing valve if the front brakes failed. You no longer need a by-pass, because you now have full braking to the rear, all the time. You need to plug that outlet. You can search around for a brass plug to fit it, or ...

 

... you can go to Lowe's or the auto parts store and buy the shortest 1/2" x 20 bolt you can find, along with a 1/2" O-ring. Bring them home, put the bolt in a vise, and cut it down to 1/4" in length. Slip the O-ring on it, screw it into the blank outlet on the bottom of your combo valve, and tighten it enough to make the O-ring seal. This isn't highly critical, because nothing goes to that port unless the front brakes fail, so normally there won't be any leakage. If it weeps a bit in the unlikely event that it gets triggered, so what? As long as it's tight enough to maintain pressure you'll be okay.