Jon Singh

Hi All,

So I'm hoping you guys could give me a hand trying to diagnose this problem.

I recently bought a 94 f150 2wd, auto tranny with 65k miles on it. Looks like it had been sitting for quite sometime as the previous owner passed away 2 months ago (and he had been sick for at least 8 months prior) and his wife and daughter didn't really do much with it.

here's my issue. When I accelerate, everything is fine until about 40-45mph. Once that hits, IF i'm accelerating it will vibrate pretty hard, the whole truck will shake/vibrate pretty bad. The best way I can describe it is that it feels like i'm running over those bumps in the middle and side of the road (the plastic/metal ones on major streets), like lots of them and really fast. If i'm not accelerating and just coast, the issue goes away. If I go under 40mph the issue also goes away.

From my initial research online I decided to change out the u-joints on the truck. I changed them out but the issue still exists (though its a smoother ride for sure). Also 3 of the tires were balding really badly and the 4th tire wasn't even the right size, it was smaller. So I went and changed out all 4 tires, but the issue still exists. However, they told me that they could not align it because I needed new tie rods.

I'm a bit stumped. I have noticed that if the truck is cold and I take it out for a drive, it does not do this vibration/shaking thing for at least 20 minutes. It's almost like the truck needs to warm up before it starts to show the issue.

Other maintenance things I've done, oil change and I swapped out the heater hoses after i sprung a leak.

Any help or pointers or things to look at would really help. I really hope its not a transmission issue, it only has 65k miles on it so I really hope not. It seems to shift just fine but it does shudder from time to time when it does but it seems like this is kind of normal. It doesn't yank back and forth or anything when the tranny down or up shifts.

Thanks again
Jon



Cliff notes:
Truck vibrates heavily under acceleration starting at 40-45mph. (vibration feels like im running over lots of bumps really fast)
Seems to happen once the truck is warm, not cold.
Changed out u-joints
Bought new tires
Issue still exists
Please help!

fltdriver

If they say your tie rods are bad they probably are.

My advice to you would be to replace tie rods and anything else you can afford to do from this list:
Shocks
Upper/Lower ball joints
Inner/Outer wheel bearings

You should be able to do it for around $100, not counting the TRs, then go in and get an alignment. Also before you get the alignment would be the time to replace the front springs with standard moog 820 for factory, 824 or 844 to bring the front end up a couple of inches to reduce the forward rake.

Before I get an alignment I try to do everything that could possibly need to be done in the next couple of years, that way I'm not paying for another alignment before the vehicle needs new tires.

Brandon587

Do you have a check engine light on? You could just have a really bad miss or more than one. My buddie's 5.4 f150 with individual coil packs per cylinder vibrated bad up hills and accelerating. Check engine light came on and it was a miss fire , replaced the coil and all is good. I would check to make sure all wires are pluged in to the spark plugs and cap, check the cap and rotor condition, and spark plugs. While your checking spark plugs, a compression test wouldn't hurt either. See how even the compression is.

88xlt

If you select 2 or 1 on the gear selector does the vibration kick in at the same speed? You won't want to go 40 MPH in 1, don't over rev the engine.

There is talk of torque converter shutter. Also possibly in the ear end. It could be an engine miss, but seems like it would do it slower.

Jon Singh

No check engine light on yet but I did pick up spark plugs, wires and cap this weekend to put in during the week, Im going to give it a go this evening and replace them all

Jon Singh

Ill try that tonight with gear 2

ncranchero

Do a search on "Crown Vic torque converter shudder" as that sounds like your description. A lot of the Police Interceptors in our fleet experienced this, some with only a few thousand miles. (4R70W) My own Interceptor did it. Ford reps came down, instructed us to add a bottle of FORD Limited Slip Additive (yes, positive traction additive) to the affected vehicles. Crazy huh? It works! So if you can determine if it is TC shudder you can fix it for under $10. It fixed mine in a few miles!

Jon Singh

Thanks for this! I think this is my problem, Im gonna pick up some of this dr. shudder stuff i keep reading about that helps and is cheap. If thats the issue I might just end up doing a flush and putting in some Mercon V since it has anti-shudder component and go from there! I'll update this thread once I have more information for any other future people who have this issue.

ncranchero

I can recommend only the Ford Friction Modifier that Ford Motor Co specified.

Jon Singh

Hi ncranchero,

i just want to thank you, I went picked up some motorcraft friction modifier (same oz's, pretty sure exact same thing). Put it in, drove around and within a few miles the issue has improved dramatically. In fact at this point after driving maybe 15 miles the only time I feel it is if I'm barely applying throttle and around 40mph, and what I feel is nowhere near the same. If I'm giving it the usual amount of gas i don't feel it all. I think that residual shaking might actually be misfires that aren't being reported yet because if I gun it, when it hits the 40-50mph range it doesn't vibrate anymore but for that range the sound of the engine changes to not as loud. In fact the shaking is more like an audible vibration now and not so much something I feel.

I will continue to post updates once i change out the rotor, distributor cap, wires and plugs to see if that residual shaking goes away! (again, much much much much much much better!).

In any case, does anyone know if its safe to put in some more of the friction modifier, maybe two of the bottles (total of 8oz) or better to play it safe and keep it to only 4oz?