Testing the rear locker: Dash light just blinks

[Beej]

Hey folks,

How do I definitely test if the rear locker is engaged?

I though my rear locker was not engaging. So I read the Overhauling lockers pdf I found here on the forum; it described in detail the rebuild and suggested ways to test the lockers before rebuilding. I figure I have mostly bad luck so I went ahead and bought the rebuild kit (after checking the fuse and after driving the truck on gravel all sorts of back and forth and round and round). Before the actual rebuilding however, I grabbed the ladyfriend and headed to the driveway to do some more of the tests. Why not?

I stuck my head under the rear end (of the truck ) and had flip the switch for the rear locker. I heard a noise!! It was even a rather authoritative noise. You might call it a clunk.

I read that if the locker engages but the dash is still blinking it is likely a bad positioning sensor.

Before I go out and buy one of those; how do I test if the rear locker is really engaged?

The only way I could think of was to lift all four wheels off the ground, put it in neutral and try and spin a rear wheel to see if the others moved as well? There's got to be an easier way? I do think I'm missing something.

Thanks in advance for any replies. I'm holding out hope that its just the positioning sensor but before I plunk down the cash, I'd love to be sure.

Thanks again.

-- Beej

 

[excessive]

you'll know because when you try to turn, your rear wheels will resist turning. you'll hear/feel the rear tires scrubbing. only do this type of test on an unpaved surface .

 

[inkpot]

You only need to lift up the rear axle and then engage the locker. If you can continue spinning either rear tire independently, then it is not engaging.

 

[Squash]

find some dirt and drive figure 8's.
Locked will scuff, unlocked will be smooth

 

[bajaphile]

^ Yes. I have been able to get several lockers to start working this way. Most of them were never used in 15+ years.

 

[Beej]

Ok, drove around on some gravel. It was smooth.

One last question because I'm not trusting my brain right now. Does the truck need to be in 4 wheel low to lock rear diff?

 

[Beej]

When I drop it in low and hit the switch, it seems like there's more scuff when the rear is engaged but it's tough to be certain.

It scuffs a bit just from having the center engaged.

Also, point of information. The front does engage when asked. 100% certain as I locked it during my front axle rebuild.

 

[DancesWithMutts]

Do you have a CDL switch? If so, you need to have the center locked in order to lock the rear, if not, I think you need to be in 4Lo with the transmission in L but I might be wrong on that.

 

[Tools R Us]

Ok, drove around on some gravel. It was smooth.

One last question because I'm not trusting my brain right now. Does the truck need to be in 4 wheel low to lock rear diff?

The CDL needs to be locked and the lights (ABS & CDL) on, for the axle lockers to work.

 

[LINUS]

When I drop it in low and hit the switch, it seems like there's more scuff when the rear is engaged but it's tough to be certain.

It scuffs a bit just from having the center engaged.

Also, point of information. The front does engage when asked. 100% certain as I locked it during my front axle rebuild.

Did you notice how the blinking fr locker "idiot light" went solid when locked?
(It should have if fr locker pos sensor works)

If your fr locker is working, and you hear sound from the rear, I'd go do a ton of "figure 8's" in a dirt lot before jacking it up, cycle the crap outta the lockers & see if that doesn't improve the situation.

After that worry about tearing into it, since that is going to only cost $$ the minute you find parts needing help - going nuts in a dirt lot is free & fun!

 

[Beej]

Alright, thanks so much for all replies. Here's the status.

Do you have a CDL switch? If so, you need to have the center locked in order to lock the rear, if not, I think you need to be in 4Lo with the transmission in L but I might be wrong on that.

I do have the CDL switch.

I have tried in 4hi and 4low and driven around in circles. Wasn't confident I was hearing enough scuffing so I replaced the position switch. Bought it from Napa, cleaned connections, installed. Light still blinking.

Before I pull the locker off, I finally put the damn thing up on jack stands.

When I turn a wheel, the other wheel turns the opposite direction. I can spin em for days; still blinking.

My understanding of the lockers is they gotta be spinnin the same direction so I'm going to go ahead and pull it and rebuild.

I think I'm out of tests?

Thanks again!

 

[LINUS]

Alright, thanks so much for all replies. Here's the status:

My understanding of the lockers is they gotta be spinnin the same direction so I'm going to go ahead and pull it and rebuild.

Yep, you got problems - locked, if you just lift 1 rear tire (or both) the lifted tire shouldn't spin, or both in air, should spin together.

The nice thing on the rear is the inspection port/window - to the left of the driveline/3rd member as you look at the axle under your 80, there's a plate ~3x4" you can pull to see how far the actuator moves the "tuning fork"-shaped part that moves the dog gear to lock the axle.

Seems it's below liquid level from memory, so verify your fill plug isn't frozen before pulling the drain plug and/or inspection window to see what your actuator travel looks like.

Break torque on both your fill & drain plugs ahead of popping the 4-6 bolts on that window, just so you know you can refill your diff with either the used or new diff fluid. And a 3qt pan if you drain it are needed - 6 pt socket (22mm?) is best for the fill/drain plugs, even if you need to go buy one ahead of getting in there & doing the job. HTH.