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Bang when engaging 4WD Low Range?


gillbot

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Bought this 1988 XLT Bronco II friday Nov. 21st. The dealer said the 4WD was busted and I knew it had to be the motor. Repaired the "touch drive" motor on it yesterday but didn't "test it" any since I had to do somw wire cleanup underneath. In the driveway today after some wire cleanup, I was testing out the 4WD to be sure it will engage. I had the tranny in Neutral (auto) and shifted to 4x4 and the light came on. I then shifted to low range and waited for a bit to be sure it was engaged. I put it in D and heard a LOUD BANG. I mean loud like I though the B2 was gonna wheelie or something! I immediately put it back into N and checked underneath but found nothing amiss. I went through it a few more times but it has yet to make any more noise and everything SEEMS to be working ok.

 

Anything else I should check? What is a good way to test the operation of the 4WD system sans getting it into the mud?

 

Also, what is the proper procedure for using the "touch drive" system? If I remember right, 4x4 can be egaged on the fly but low range needs to be stopped and in Neutral correct? Also, when I engage 4WD the light stays illuminated but when I engage the low range, the light just flashes till i put it in gear. Is this correct?

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Found this on the web, maybe it will help, maybe not... Good luck ;)

 

First thing is to look at the fuse, in which you said was o.k., then underneath the truck on the transfer case, there is an electric motor on the back that looks like a power window motor... this is your ingadgement motor, the smaller ribbed on is for the 4wd LOW range, which won't ingage unless the 4wd is ingaged. Look at the cannon plug (Electrical) connector leading into it, be sure it is clean, tight and there are no bare wires, this could cause grounding and ohm problems. Once that is done, with the truck in neutral, shift on a roll (still in neutral) into 4wd. Be sure you are off the pavement for this. If it DOES engage your orange light will illuminate... now if it DOES engage and you hear a lout ratcheting sound, this is telling you you have a problem in your auto-hub. if nothing happens, remove the transfer case engadgement motor and take it to an authorized shop or dealer for repair, or replacement. They generally cost round-bouts 65-85 dollars,

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graemlins/thumb.gif

 

Already disassembled the engagement motor and fixed it. I think it was all "frozen up" from not being used in a while. It only made the noise on the first time, no noise since. Hopefully it was just tweaking itself out.

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If for some reason the transfer case had not fully engaged into 4 wheel low when you put the tranny into drive, it engaged, and with the gear ratio on those in low, it will make a hell of a bang. The thing to do is try it again as see if it does the same thing. It shouldn't, also, it is very important that you not attempt to drive the truck on asphault in 4 wheel low. It can cause the transfer case to bind up requiring it to be removed. I have seen transfer cases bound up to the point that with all the bolts removed holding the case together, when hit witha hammer to pop the bind loose, the transfer case jumped 4 foot off the concrete where I was working on it.

 

Yours possibly was partially bound up and putting it in gear unbound it violently, which is typically the case when a transfer case gets unbound it's always violent.

 

The other reason this may have been the case is that if the touch motor was not operating, and I would guess that people were test driving the car before you, running a transfer case in 4low with the front axle unlocked can also cause binding in some transfer case. That in 2 high may not even be noticed.

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I think the problem was that the 4wd looks like it hasn't been used in years and i "broke it free" playing around with it. It hasn't made any loud noises since the first time but the 4wd system just isn't acting right. Feels like both front and rear axles have a locker in them but I doubt that's the case. I'm gonna tear into the front end and rebuild it anyhow, I just don't trust it since it's all rusty and looks like none of it has turned in ages.
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What I menat was it feels like there are lockers in the front and rear pumkins. It leans over as you corner and the tires probably hop a little. If that is what you are talking about then it is caused by the lack of a differential in the transfer case. You of course understand the need for a differential in the front and rear end. When cornering the tires turn two different speeds. Well the Front and rear axles spin two different speeds as well, the rear goes faster than the front. What is really happening is as you are turning the truck drops the nose because of the front and rear being locked together, you will only notice this on asphalt and concrete, and in a hard turn. Some newer trucks and the AWD cars have a diff in the transfer case, that allows the front and rear to spin at two different speeds. That is why they can be full time AWD.
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I know most full time 4wd systems have a viscous diff or something in the center. I'm just not explaining it well enough to convey the problem. This acts nothing like ANY 4wd vehicle i've ever been in sans a rock crawler with a locker in front and rear. None of my old 4wd B2's did this, nor dod my dads ranger or B2. I think there is a problem in the front section somewhere but I have to isolate it. With auto hubs this is hard to do. With manuals, i could put it in 4wd and leave the hubs unlocked to see if it binds, then put it in 2wd and lock the hubs to check there. with the auto hubs, it's too much work fighting everything apart so i'm just gonna refurb the whole front end.
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