LOUD bang in front under hard accel

[briantf]

This is on a 98 XLT 4x4 that two different Ford factory garages refused to update with new GEM software.

Now at 81K, the thumping under moderate acceleration below 45 MPH has turned into jarring thumps. It's very noticeable, almost like the motor mounts (it kicks the floorboard, the passenger can feel it). Unfortunately, no other motor mount symptoms manifest.

Given a clicking noise when backing up in 4Lo, I hoped it was binding in the drivers side CV. That was an inexpensive and straightforward R&R and it didn't resolve a thing. When I pulled the front driveshaft and it looked just fine, I figured that wasn't the cause.

I'm driving it today in the rain, and got the thumping to repeat quickly by flooring it from a stop sign into a left turn. A THUMP followed by a staccato thump-thump-thump-thump that went away as speed passed 50 mph made me think case engagement. At the next stoplight, I engaged 4Hi and floored it in a straight line. Silence.

Given that it seems that additional damage has ocurred, does anyone have any ideas about bushings or other rubber bits that may have gotten damaged by the contstant lock/release of the buggy GEM unit? It's LOUD and THUMPS, wherease prior symptoms were thump, thump type sounds (per Ford Dealer #2, could not confirm transfer case noise, off-road type tires prevented diagnosing - for BFG AT KO's fer cryin' out loud).

It still seems just fine off road, but it bugs the heck out of my wife when she's powering up an on-ramp and the CLUNK.....CLUNK, CLUNK starts in.

Checked the U joints on the front shaft, it's not wiggly, but does still rotate to take up slack as it did at 20K.


I'm really puzzled, and not inclined to trust the Ford dealers to do anything other than swap parts until the sun comes up.

Thanks for any suggestions.

Brian in CA

 

[tenikiwon]

For What it's worth

Mine did something like that when starting and stoping. Didn't do it all the time and didn't see that bad. I put a lighted switch to disable the AUTO and when it was off then nothing, whenit was on I would see the light pulse telling me that the 4x4 was enguaging.

I had the t-case flushed and that took care of it. Now once and a while when I hard accel, it makes kind of a bang that seems to come from the drivers side front wheel, but it doesn't do it all the time.

When wheeling (this may be unrelated) I noticed when on a hard climb and getting no-where that the whole truck tumps and shakes. Almost as if the tranny was slipping and jumping gears. I don't wanna think about it if that were the case.

 

[Hoppy]

Does anyone know of a way to reprogram the GEM to keep this from happening? My 97 will kick in and out of 4wd while accelerating hard on slippery surfaces. I was wondering if there was some kind of time delay that could be done to this so the 4wd does not kick in and out steady?

Hoppy

 

[tenikiwon]

Almost got stuck

While getting lost on some contry roads I pulled into a enterance for a farm field ('bout a foot of snow) and put it in reverse (2WD) and the truck spun and sank. Then I poped it in 4WD and hit the gas. Several loud bangs were heard.

Later, on a hard surface I put it in 4WD again and accelorated normally. No noise. It seems like the noise come only when the tires break loose. It kinda does it in 2WD, but "almost" sounds like the front in still engauging. I have Control Trac with AUTO, but did the mod to disable it.

Could it still be enguageing? My switch is lighted and nothing lights up when it happens. What about binding? I'm goind to search after this.

 

[tenikiwon]

Did a search has some questions

Most of the posts concerning 4WD problems have delt with Gen1. Here are some questions seeing as though I'm Gen2.

1. Everyone says go with Manual Hubs. With the ControlTrac setup is this possible, does it make sence, why would I want to go with that setup.

2. Sounds like my problems could be a combination of many things, bearings, hubs, bushings, (ball-joints need replaceing too) Whats my best solution. I'm mechanically inclided if presented with the right tools. Can you easily take off the wheel and dig down and clean-up/rebuild each side? What is dealer cost vs DIY?

Thanks

 

[TPLYNCH]

Manual hubs are a no go. Your hubs are "one piece" and are already "engaged" 24/7.

Hoppy - Only the Dealer can reprogram the GEM as far as I know.

 

[Hoppy]

Ok, Thanks. Too bad though, we could probably do some pretty wild stuff with reprogramming the GEM if we could eh! Possibly make it drive by itself like Kit did on Knight Rider!

Ha Ha.

just dreamin!

 

[tenikiwon]

Knight Rider

hee hee hee, I'm already started. I have the light in the front. Now to get it to talke

 

[Fredness]

I used a double pole relay and connected it as desribed. The idea was to turn the switch on, energizing the relay to disable the TOD input to the Control-Trac. That way, if it fails, it defaults to Control-Trac. I already used it towing the trailer form a dead stop up a hill in 2WD Low. Awesome! No more noise on hard turns, and the vehicle handles better in town (on pavement).

 

[dogfriend]

Briantf

Check this thread and read my post. It sounds like it could be your problem

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