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Pickups Dodge Dakota Dodge Dakota Vibration
15 messages, Last post on Aug 20, 2008 at 4:46 PM
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My daughter's 1990 Dodge Dakota with the 3.9 L engine and automatic transmission with overdrive has developed a vibration. It happens when accelerating while in gear. If the gear selector is set to neutral while rolling, and the engine rpm is speeded up, the vibration doesn't occur. The vibration appears to me to be coming from the front of the pickup. The Haynes manual gives several possible causes, all related to the transmission or the drive shafts. Has anyone else experienced this vibration?
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Replying to: tjfitz (Sep 08, 2007 10:45 am) Regards, Dusty |
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Yes, it seems to be under load that the vibration happens. I was under the hood again yesterday and found that disconnecting the EGR valve from its vacuum source made the engine run smoother. (The pipe from the exhaust back to the engine has broken off at a weld and maybe had been causing rough-running. Also the engine would idle slower and eventually shut off when coming to a stop, but with the valve disconnected, that problem ended.) I took the pickup out for a spin and it ran well until I got to about 35 mph then the vibration began as before. It gets so loud in the cabin that you can hardly hear a passenger talk, and seems to me to be coming from "up front" rather than "from the rear". My daughter just speeds up and finds the noise isn't so bothersome at higher speeds! Anyway, I found that shifting the automatic transmission to second seemed to make the vibration less severe, although still there at 35 mph. Going to low or first seemed to stop the vibration entirely, although I wasn't going 35 mph in first. Putting the transmission into neutral and racing the engine to 3000 rpm doesn't produce a vibration, and there is no vibration when rolling down a hill at 35 mph in neutral. All that made me suspect that engine or transmission load is causing the vibration, but I don't know what to look for next. I'm hoping it isn't something complex like a transmission bearing or a seal. (I checked all the spark plugs and they were clean and correctly gapped and the wiring from the distributor seems secure. This is a throttle body fuel-injected 3.9 L engine.)
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Replying to: tjfitz (Sep 11, 2007 3:21 am) Regards, Dusty
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Replying to: dustyk (Sep 11, 2007 2:36 pm)
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Replying to: tjfitz (Sep 13, 2007 7:00 am) After doing a complete tune-up (plugs, wires, cap & rotor) it seemed to run fine for some time, then started to do the same thing. There were three occasions when he couldn't even get the thing started. Well, he was about to tear the engine apart, convinced that the timing chain was bad (he was listening to all of his Chevy friends), or a bad camshaft or bad valves. I was not convinced, however. Having his truck one day I went and got and installed new Mopar plug wires, cap, and rotor and that Dakota ran for another four years and 75,000 miles before needing another full tune-up. In that vintage especially the Power Train Computers were highly susceptible to disruption from random electrical impulses brought about by misfiring caused by poor ignition components. By the way, that '91 Dak is still on the road and has more than 400,000 miles on it (No tear down!). Best regards, Dusty
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Replying to: dustyk (Sep 13, 2007 5:01 pm) I took the cap and rotor and wires off and the rotor metal looked pretty rough. The contacts inside the distributor cap were what I'd call delaminated, with flaking metal. The wires seemed OK, but who knows? I put it all back together, and the engine started, but I can't road test it because I'm going to have to replace one of the metal brake lines after a leak developed at the "combination differential and metering valve" (name in my Haynes manual). I thought tightening the flare nut might help, but instead the leak got worse and I am hoping it is just the tubing flare inside the nut that failed and not the very pricey valve. |
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I installed new Mopar distributor cap, rotor and spark plugs wires. Then after some struggles I got the new long metal brake line installed. In the process I had to lower the fuel tank to get at some of the old line's hangers and in moving the filler hose I broke the plastic of the filler line housing and had to scout around in a junk yard today for another one. That was installed and all well. The bleeding of the brake lines for air went well, too, although I now have two alarms on the dashboard illuminated continuously: "ABS brakes" and "P Brake". I may have to continue bleeding the system because the brake fluid was dirty. I took the pickup out for a spin anyway and found the vibration under load is still there at about 35 mph in drive. In second it also vibrates at 35 mph although at a higher rpm. Shifting into neutral at that speed eliminates the vibration. Revving to high rpm in neutral doesn't cause the vibration. During the test drive, the rpm gauge began sticking and only gentle hammering on the dash would make it move. (The pickup seems to have a death wish!) The idle is very rough and the engine dies at idle unless I disconnect the vacuum line to the EGR valve. Using the ignition switch, I switched the ignition on and off three times and then left it on the fourth time and got these codes: 12, 12, 13, 14, 14. The information I can find seems to say those codes relate to the MAP or maniford absolute pressure sensor. |
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| I neglected to bleed the "hydraulic valve" on the drivers side above the rear axle. When that got done, the warning lights went out. Brakes are now good. This pickup has rear wheel antilock only. | |
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Yesterday I backed the pickup down the driveway, and as I shifted from park into reverse, there was a distinct "clank". Somewhere in the recesses of memory I recalled that clanking and vibration can be symptoms of a bad universal joint on the driveshaft. This morning I got up early, raised the rear tires off the pavement, supporting the rear axle with two stands and went to work trying to moving the u-joints. I have never done this before, but from what I read, any "give" at all might mean a bad joint, and the rear joint had give. I eventually got the rear joint disconnected from the differential and lowered it then pulled the front of the driveshaft out from the transmission, forgetting that transmission oil would be gushing forth, which it did, all over the driveway before I was able to get one of my wife's cooking pots under the stream. As far as I could see, there were no needle bearings left in the rear joint, so I took shaft and all to a local parts dealer/machine shop and they removed the joints and installed new ones. I put the shaft back into the pickup and added what I think was enough new transmission fluid then took the pickup out on the road. There was no more clank on shifting, and absolutely no more vibration even going as fast as 60 mph. The pickup now runs like a dream. When I asked my daughter how long the pickup had been vibrating before, she said about a year, and her sister had the same problem before she handed the pickup over to her! (That was the first I'd heard of it.) I think the brake line mentioned in an earlier posting in this thread probably failed by vibration fatigue. Also, my daughter drove the pickup from Idaho to North Dakota when she returned home about two weeks ago and about 50 miles from home stopped to rest and the pickup wouldn't re-start. She had to get roadside assistance at about 11 pm from a tow-truck and the driver found that the starter was hanging onto the engine by one loose bolt. I'd say the bolts had probably vibrated loose. "For want of a nail... ."
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