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Help! - 4LO acting like jackhammer

Old 05-16-2019, 06:01 PM
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Help! - 4LO acting like jackhammer

2000 4runner SR5 auto 4x4, no locker.

Tried putting in 4lo to get ready to pull out a trailer. I'm in neutral, at complete stop, shift to 4hi, then neutral, then grinding to 4lo which I eventually read is because the trans is slightly spinning and u gotta do it fast to prevent grinding. Ok that's one problem solved.

The next is when I finally get it in 4lo, I'm on the brakes and it just starts jackhammering so I immediately pulled it to 4hi. Try 4lo again and same thing. So I am only using 2hi now.

I tried searching but didn't really find anything similar to this. Hoping it's something with an actuator sensor or something simple. Scared the bejesus out of me. Hoping it's not something serious
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Old 05-17-2019, 03:32 AM
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What do you mean by jackhammering?




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Old 05-17-2019, 03:37 AM
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Imagine you're in a manual transmission vehicle. And you have it in 1st gear and you rapidly engage and disengage the clutch (let's assume it doesn't stall here). It happens at a frequency of maybe 2 or 3 hz. Fairly quickly. That's what I mean by jackhammering

I also noticed 4wd light did not come on

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Old 05-17-2019, 03:56 AM
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So it goes into 4H, and operates correctly once in?

On my 2001, if I need 4L, I place transmission into N, and then swiftly move the transfer case lever to 4L. No need to first select 4H.

Is this the first time you’ve tried to use 4L?



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Old 05-17-2019, 04:13 AM
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Light does not come on in 4hi either, I can't tell if it is actually working in 4hi.

I have used 4lo before, maybe 4 or 5 years ago. Don't use it often
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Old 05-17-2019, 06:44 AM
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If you have the J shifter I think the transmission should be in neutral before shifting into 4lo.
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Old 05-17-2019, 08:42 AM
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Yes j shifter type transfer case

I stated at the top that I was in neutral before shifting into 4lo.

Im pretty sure it starts jackhammering when I put it in drive (I may have left this step out in the original post). I honestly can't remember if it was in neutral for transmission or in drive when it was doing that.
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Old 05-17-2019, 09:18 AM
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I thought you had to go through 4hi, to get to neutral, then 4lo. That's what I remember the diagram on the shifter knob showing. Am I wrong? I'll look closer later today. Anyway that's what I did the other 3 or 4 times I've ever used it and no problems.

I never thought You can go directly to 4 lo from 2hi, because it did not show that on the knob diagram.
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Old 05-19-2019, 05:11 PM
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Is the jackhammering a noise or something you can feel? Does it happen when moving only or also when stopped?

Have you had any work done since the last time you used 4lo?
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Old 05-19-2019, 05:27 PM
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Definitely feel it. As I explained above it's like someone letting the clutch in and out rapidly causing that rapid forward and stop jerking action. This was at a complete stop, no I did not attempt to let the car roll as I didn't really want to let it keep doing that.

I've done all the work myself. Done spark plugs, changed all diff fluid, trans fluid, oils, steering rack bushings, had rear diff rebuilt by ECGS and put that in September 2018. Nothing besides that really.

Just FYI, I'm almost totally deaf so sounds are hard to hear, and not how I am able to diagnose problems. although I could definitely hear that pinion Bearing roaring

I asked them to reuse my ring and pinion since it looked excellent. I don't think they would've got my gearing wrong if they did what I asked... 2wd hasn't been an issue
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Old 05-19-2019, 07:30 PM
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When the rear was rebuilt, did they install a new ring and pinion gear?

i know you said you didnít roll anywhere, but that sounds similar to a mixed set of gears front to back.

Theother thing im leaning towards is a bent or misadjusted shift linkage for the transfer case so when you shift to 4lo, you are Stil half in lo and half in the hi teeth.
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Old 05-27-2019, 10:52 AM
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Tested a few things today.

Main vacuum line thru check valve is good

Get vacuum on the front line that goes down in 2wd

Vacuum does not switch to the back line when in 4hi

Electrical signal does not switch to other plug. So that's something. Seems for sure a bad switch

However, it does not appear to force into 4wd when switching the vacuum line. I may try rolling the truck after manually changing the vacuum line, but this is sounding like a failure with the actuator or switch or both... obviously hoping it's just the switch. Guess I have to try driving with reversed vacuum line to rule out the actuator itself.

I've tried looking but if anyone has a link to test the switch (I believe there are 2?)
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Old 05-27-2019, 02:18 PM
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Confirmed 4wd works when vacuum lines switched.

Bad switch but don't know which?

Will research further want to know tonight so I can get new switch tmw
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