Front wheels not engaging

hdcoffeeboy
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Front wheels not engaging

Unread post by hdcoffeeboy » October 11th, 2015, 8:46 am

I spent last weekend at the Portland Sand Dunes (stupid good fun: http://www.portlanddunebuggyclub.com.au/), but on the second day out on the sand I couldn't engage 4WD. I've looked over all the forum threads here on the topic, and done a fair bit of research outside of that.

When I put the 4WD selector it 4H or 4L, the solenoid in the engine bay (the one that controls the front diff actuator) buzzes or ticks rapidly, as though it's failing. The thing is, the buzzing/ticking only occurs if I wiggle the selector, and not if I leave it alone. Now I know it could be a faulty wire, but fact that it responds to movement in the selector says to me that it has to be the 2WD-4WD detection switch in the transfer case. If it was wiring or vacuum, the issue would either be constant, or it would happen independently of me wiggling the selector.

I'm not getting a 4WD light at all (flashing or otherwise), which as I understand it is right. The light would be on solid if the 2-4 detection switch was engaged AND the front diff was engaged; it would be flashing if only one was engaged. With a faulty switch, the system doesn't know that 4WD has been selected, and the front diff doesn't engage, so it doesn't even identify a fault - it just thinks it's still in 2WD... right? Hence, no light.

So... my guess is that I need a new 2-4WD detection switch in the transfer case. A MB811554, if I'm not mistaken: http://www.aliexpress.com/item/SWITCH-T ... 5,201560_1

I know this has been posted in detail before, but my symptoms are slightly different, and I'm looking for a second opinion on my diagnosis...

Thanks!
Tim

2004 Challenger LS Auto. Build-up photo gallery.

Ron04
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Re: Front wheels not engaging

Unread post by Ron04 » October 12th, 2015, 6:43 am

I'd say there is a good chance your diagnosis is on the money. I had a switch go but didn't get the buzzing bit, it simply didn't do anything.

Sam Pato
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Re: Front wheels not engaging

Unread post by Sam Pato » October 12th, 2015, 9:44 am

The default position for the front actuator is engaged (in 4wd). When you start the car in 2wd the vacuum pushes the actuator and disengages it. Its quite unusual to lose 4wd - usually you get the flashing light and the front remains engaged (so you have 4wd).

My guess would be that your actuator has seized in the 'in' position. They get crap in them over time and rust inside and then it becomes too hard for the vacuum to push

That said the 4wd light should flash as soon as there is a conflict between the sensors on the transfer case and those on the front diff. So no lights is a bit hard to explain if you have got the transfer case in 4wd.

The connector for the from diff switch is just in the driver side wheel arch. You can do some tests by putting a wire across it and seeing if you get your 4wd light back.

I eventually went with the free wheel hubs and wish I'd done it sooner. Should be some pictures on here somewhere.

Cheers


Sam
1999 Challenger, with Dual airbags and LSD
Mods: Does a roof rack count?

hdcoffeeboy
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Re: Front wheels not engaging

Unread post by hdcoffeeboy » October 12th, 2015, 10:03 pm

Thanks for the responses, guys.

Sam, I get what you're saying. It should be pretty easy to confirm whether the actuator is working, since the pin should move to the "out" position when the engine is off, and the "in" position when it is running and in 2WD. If that's the case, it means that the actuator, the solenoids and the vacuum system are all in working order, and that leaves only the switch in the transfer case failing to get or pass on the signal that the car is in 4WD. I'll test that, and I'll also try putting some current across the solenoid to see what happens.

The plan is to add a Lokka to the front diff, along with free wheeling hubs. At that point I'll rewire the 4WD light to the transfer case switch, and leave the front diff permanently engaged. But current funds don't allow for that, and even when they do I'll need that switch to work, so (if my tests prove me right), I'll be buying a new switch shortly.

Thanks again for the advice.
Tim

2004 Challenger LS Auto. Build-up photo gallery.

Sam Pato
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Re: Front wheels not engaging

Unread post by Sam Pato » October 13th, 2015, 2:56 pm

Putting some current across the solenoids is a good idea - they should click if they're good.

FWIW - you can get a set of ASIN copy freewheeling hubs off eBay for about $100-. Assuming the actuator isn't seized all you have to do is pull the hoses off it and it'll stick in the engaged position (mine had seized so I pulled it apart and stuffed it with washers so it was always engaged). Then (assuming you don't have ABS) you can forget about the solenoids switches etc. If you have abs then throw a relay into the front diff sensor circuit using the solenoid power as a switch - I think I described it somewhere on the board.

I reckon that the eBay hubs is the cheapest fix (unless you get lucky and can just swap one solenoid for a pattern one) and you're probably going to do it sometime in the future anyways. Saves a lot of guess work now and into the future. I understand that the transfer case switches are a pain to get to.

Cheers


Sam
1999 Challenger, with Dual airbags and LSD
Mods: Does a roof rack count?

Ron04
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Re: Front wheels not engaging

Unread post by Ron04 » October 13th, 2015, 4:09 pm

Sam

That first bit about default position's not entirely true, the default position with no vacuum is 4wd. If the actuation system is in good condition and can hold vacuum there is a large tank which holds the actuator in the 2WD position when the motor is off. So when you start the car the actuator is already in the 2wd position. When you engage 4WD the switch de-activates the solenoids which releases the vacuum and you get 4wd. One of the many activation faults i've had was the 4wd light would flash for a couple of seconds when I first started then go out, when driving it would randomly come on (due to no manifold vacuum) and the actuator would release resulting in some ordinary noises from the front diff, this problem turned out to be a loose hose so i was loosing vacuum, once fixed the actuator then held in the 2wd position as it should

Sam Pato
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Re: Front wheels not engaging

Unread post by Sam Pato » October 13th, 2015, 6:02 pm

Hi Ron,

I'm aware of the accumulator tank but I'd always assumed that the vacuum leaked down once parked up. But like you say it probably stays charged up or you'd get a flashing light every start up.

Looking at it this way - it might be the case that a failure at the transfer case switch would mean that the solenoids aren't switched to release the vacuum and hence no front 4wd (which I'd found puzzling). That said pulling the hoses off the solenoid should release the vacuum (and engage front diff) if you're in a tight spot.

Cheers


Sam
1999 Challenger, with Dual airbags and LSD
Mods: Does a roof rack count?

hdcoffeeboy
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Posts: 44
Joined: January 28th, 2014, 11:06 pm
Location: Mount Evelyn, VIC

Re: Front wheels not engaging

Unread post by hdcoffeeboy » October 13th, 2015, 10:03 pm

Yup.. I have ABS, so I'll have to factor that in.

I still think it's the switch in the transfer case, rather than the solenoid or the actuator, and that's a $25 part (see my OP), so in the short term that's still the cheapest fix.

I'm a little wary of cheap eBay freewheeling hubs since a friend of mine had one fail half way up a hill in the high country. When the time comes I'll spend a little more, I think.
Tim

2004 Challenger LS Auto. Build-up photo gallery.

Sam Pato
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Re: Front wheels not engaging

Unread post by Sam Pato » October 15th, 2015, 12:49 pm

I looked into the free-wheelnig hubs and as far as I could tell the real ASIN ones were the best, however they're hard to come by and the only new ones I could find were in the US (about $350-400- from memory). The AVM ones had poor reports but the cheapo ebay ASIN copies seemed to have better feedback. That said I never leave home without my original solid hub.

I'd be interested to hear what your final diagnosis is on the switches. Have you changed the 4wd selector bush? I'm wondering if the poor switch contact is because your bush is in poor nick and hence the lever is not contacting the switch correctly. If you haven't its worth having a look at it. A good thing to fix if you're going to be well off the beaten track.

Cheers

Sam
1999 Challenger, with Dual airbags and LSD
Mods: Does a roof rack count?

Ron04
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Re: Front wheels not engaging

Unread post by Ron04 » October 16th, 2015, 6:40 am

The best thing I ever did was get rid of the vacuum actuator and fit free wheeling hubs, no more hassles, once it starts playing up it seems to go on and on.

I used the Wixxer bracket and completely removed everything else and also fitted the relay to simulate the front diff sensor which keeps the ABS happy.

Try the wreckers for free wheeling hubs, I found a set of 2nd hand factory fitted Aisins off a Triton for $150

hdcoffeeboy
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Joined: January 28th, 2014, 11:06 pm
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Re: Front wheels not engaging

Unread post by hdcoffeeboy » October 24th, 2015, 8:22 pm

Sam, re the hubs, I've heard the same thing that Ron found for himself - you can pick up Triton hubs from the wreckers. I may go down that path in the end.

Re the selector bush, I don't think so. The switch in question is a ball-bearing switch inside the transfer case, so it's switched by the movement inside the case, not the movement of the selector itself... and the transfer case is going into 4WD-H and 4WD-L OK, as far as I can tell. That said, I've seen a selector bush go before, and our whole group had to wait quite a while til we could get the car back into 2WD to limp back to camp, so I will probably add one to my spares eventually.

I've disconnected the two solenoids, one at a time, and I get the same sound. It's unlikely to be both of them, so I'm guessing it's neither, and that it is the switch.

Thanks for the advice, guys.
Tim

2004 Challenger LS Auto. Build-up photo gallery.

hdcoffeeboy
Here and there
Posts: 44
Joined: January 28th, 2014, 11:06 pm
Location: Mount Evelyn, VIC

Re: Front wheels not engaging

Unread post by hdcoffeeboy » October 25th, 2015, 2:12 pm

BTW, I confirmed today that by unplugging both of the solenoids, the front diff stays engaged when I start the engine (since that's its resting state when the engine isn't running). So when I want to go 4WDing, all I have to do is disconnect those leads. It's not a fix, but it will keep me going until the new switch arrives.
Tim

2004 Challenger LS Auto. Build-up photo gallery.

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