Howdy folks. A few months back I bought a 81 D150 with an slant 6 and auto trans. After getting the truck I had to fix some minor issues and now finally starting to drive the truck as a daily driver. Last week I drove the truck 15 miles to town and it ran perfect. On the way home at 50 mph climbing slight incline I developed a jerking about every second or two but more so random. This occurres only in lockout and with light load. If I nail it it downshifts and no jerking.

A few weeks back I had the plugs out to observe the running condition and noticed two plugs white indicating a lean condition while the other plugs nearly fouled. At that time I was have carb problems and choke pull off linkage out of choke so that could explain the near fouled plugs. So, I cleaned the plugs up very good and drove truck 30 miles and no jerking, thinking my previous rich startup was messing up my plugs resulting in poor combustion at light load during cruising speeds.

Today I thought my problem was fixed and after 40 mikes the jerking came back and now I'm back to trying to find my problem. I've not checked anything except trans fluid level and it's good idleing in neutral. One symptom today was different than last time is that I thought I heard a substantial rpm change like it was trying to come out of lockup mode. I live in the UP of Michigan and my highways are snow-covered right now so they are rough and noisy so there's a chance I could of been mistaken but I really do think that this is a converter issue but I know very little about transmissions and torque converter's. I suppose I'll go pull all the plugs again and take a look at them because maybe I have a intake leak creating a lean condition but that wouldn explain a misfire, at least I don't think it would. The only reason I think it could be a misfire is because I've owned a few fords that had coilpacks that went bad and would cause this jerking or what seems like a transmission problem with a light load on a slight hill.

Where would you guys start first?

What about if you roll into the throttle more when it is jerking? If it keeps doing it as it was, it is likely a converter problem. If it changes substantially, then maybe lean mixture? Or, does come out of lockup when you roll into the throttle more? I am not a lockup converter 904 expert, but maybe others can chime in. Some of the valve bodies did not behave nicely.

Lou

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Home of Slant6-powered fun machines

Make sure the plug fouling/lean issue is fixed first. If the engine is not right, everything else is a crapshoot.

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Official Cookie and Mater Tormentor.

Yesterday I pulled the plugs and all nice and tan. Even though the cap, rotor and wires look okey, I'm gonna replace because they still may be old and allowing a spark to jump. I had to run to my Illinois for a few days but I did order tune up parts and will install Saturday. Thanks for the help guys!

904 with lock up is known to do that you could buy an animal shudder additive like wyns anti shudder or change fluid and put in the new chrysler atf. Also installing a transfer cooler helps.

I never heard of this additive, interesting! I did indeed install new plugs, cap, rotor, wires, fuel and air filter today. Took truck for a ride and no shudder but than again I only went 15 miles and the two times I experienced this shudder it was after 20 miles or so. I'll try an runit tomorrow but we been getting hammered with snow and I got no weight in da ole dodge.

Sounds like a typical ign. cable breakdown, do your tune-up.

I have been having a similar issue with my 88 Dipplomat 318/904 lockup. I have come to the conclusion it is the lockup clutch slipping. Only does it after 45 mph (lockup point), at more then light throttle application (but not to kick down). Very similar feel as a stick car with a bad clutch leaving a stop light. It does not feel as if the lockup is "hunting".

PS: Will not exebit the problem, at any throttle opening, below lockup point. Including wide open throttle, brakes locked stall test.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 225 nitrous
64 Valiant Signet
64 Valiant 4dr 170

Same here, I just did a tune up and so I do feel I eliminated the ignition. As we speak I have the trans pan off and doing a filter and fluid service. By the looks of things this appears to be the first time the pan has ever been off so even if this does not remedy the problem I'm okay in knowing it was a worthwhile attempt in my little feeble mind. My tires are all good, i've inspected the U joints pulldown twisted them so they all seem fine both of them, motor mounts and transmission mount are not a problem. I cannot live with this shutter problem so if it persists I'm going to have to pull the trans. I'll wait for that until I get more feedback from all you guys and other sources . This website is so valuable to me and how everybody has offered to help not on just this problem but a few others that I posted and the willingness to share knowledge is precious. I'm getting ready to put the pan on now and put some ATF4 in it and I'll post my results .

Hi Lenny,
Wow you are way up the in the beautiful part of MI.


I bet old mopar guys let alone slant 6'rs are few and far between there unless you find them in WI?

I was up in munising 2 summers ago.. It was nice.


Best of luck with your truck and shudder problem.

Greg

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Have you verified the kickdown linkage is adjusted properly?

If you want to disable the lockup function for diagnostic purposes, HERE is how you do it. It requires pulling the trans pan and dropping the valve body, but it really is a simple operation.

Note that what I originally thought was a bad converter or a shudder caused by a lockup problem turned out to actually be totally worn out clutches.

Reed, I have not verified the linkage is correct. I will though it you tell me how to do it 🤓

1 - Have an assistant hold the gas pedal to the floor (or a brick if no helper is handy) and crawl under he truck with a 1/2 inch box end wrench.

2 - Find the kickdown lever on the side of the transmission. Loosen the 1/3 inch set-bolt so the arm slides freely on the kickdown rod.

3 - With the gas pedal still held all the way down, slide the kickdown lever all the way to the rear of the truck until it either hits the internal stop or you run out of kickdown rod.

4 - Tighten the 1/2 inch bolt, crawl out from under he truck, let off the gas.

5 - Start the truck and take it for a test drive.

The best additive is lube guard instant shudder fix it is I small tube of friction modifier. Transmission shops usualy have it or I'm sure some were on line caries it

FYI- the transmission I disabled the lockup on that had worn out front clutches had this written in yellow grease paint on it: "add 1 quart red lubeguard."

It is better to fix the problem than to mask the symptom. I am not a fan of additives.