302/AOD Violently shaking in 3rd/4th gears - Hot Rod Forum : Hotrodders Bulletin Board
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Old 02-10-2013, 02:03 PM
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302/AOD Violently shaking in 3rd/4th gears

I have an 87 Ford F-150 with a 5.0 and AOD. When the transmission shifts into 3rd gear the truck starts shaking violently. Kinda like when you apply the brakes on a vehicle with severely warped brake rotors, only this happens when you're not on the brakes, but on the throttle instead. It will smooth out as the speed increases, but does it again in 4th gear (OD) just not as bad.

I took it to two transmission shops. One says the bands are slipping and the transmission needs rebuilt. However there are no other signs of slipping, ever, and when pulling a trailer it is alot smoother driving than without it. I would think pulling a trailer would make it slip worse, and not just chatter. That particular transmission shop always tells you the transmission is bad anyways. Every one ive ever taken to them they've said is bad.

The second shop said its NOT a transmission issue, but rather an engine issue. The guy says the engine is about to blow up and has a dead missfire in one or more cylinders. There IS a slight miss in the engine, and but I think its either a vacuum/intake leak or low compression on one cylinder, So far I have tested the compression on 4 of the 8 cylinders, including one that i was suspecting had a problem (due to oil fouled plug) and found that all 4 of those cylinders had 150 to 165 psi - which is plenty of compression and not low by any means. Anyways, the 2nd guy says 3rd gear is direct drive and 4th is OD (both of which are true) and that the shake from the misfire is magnified in those gears.

It doesn't shake in 1st or second and the shake is the worst in 3rd gear at low speeds with light throttle applied. Push the pedal way down and it will downshift and the shake goes away. At higher speeds in 3rd gear it seems to go away or significantly lessen also, and OD it kinda shakes all the time just not as bad.

I don't know what the deal is. I really don't think its the transmission itself, but I don't think the slight misfire is the problem either.

BTW the engine had a fresh tune up in march. New plugs, wires, cap, rotor, coil, and oxygen sensor. And not cheap parts either. We're talking Motorcraft, MSD, Ford racing and Bosch parts.

Anyone have any ideas? Someone mentioned changing the transmission fluid, that the fluid might be "worn out", but I've always heard its bad to change the fluid if it hasn't been done in a long time. Even the transmission shop told me that..

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Old 02-10-2013, 02:34 PM
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Slipped balancer. Or out of balance flex plate. Basically the engine is unbalanced and the low high load low rpm situation magnifies the shake.
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Old 02-10-2013, 02:54 PM
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Not a balancer problem.
Most likely a throttle pressure problem.
You should check the linkage at the throttle body , there is a cable to the trans that regulates pressure at the trans. If the pressure is low, you can end up with a "shudder" at low speeds. It actually clutches slipping in the trans and can tear up your trans.
There is a procedure for setteing the throttle pressure for the trans.
A balancer or flex plate would shake in every gear at the same RPM s as it is related toengine speed. Your problem is associated with road speed and certain gears like 3 and 4 .
Its a good possibility that you have a clutch pack on the way out, but it cant hurt to check line pressure/throttle pressure adjustment.
It could also be the torque converter clutch slipping as it comes on in 3 and 4 .
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Old 02-10-2013, 03:20 PM
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Just discovered #8 cylinder doesn't appear to be firing. Take the plug wire off that cylinder and it does not make any change in the engine. The plug is firing and there is 165 psi compression. The plug is black and oily with crud on it. Not sure what the deal is?? It doesn't smell like gas either. Engine is fuel injected. Must be getting fuel or it wouldn't be cruddy or wet. The only thing I can think of is that the plug wont fire under compression maybe?
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Old 02-10-2013, 03:33 PM
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Quote:
Originally Posted by Torque454 View Post
Just discovered #8 cylinder doesn't appear to be firing.



The plug is firing and there is 165 psi compression.
Could be an injector not spraying

The way you described the problem it sounded more like a trans problem.
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Old 02-10-2013, 03:42 PM
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Faulty coil pack or possible slipping clutch in the torque converter lock up. Ford has a history with bad torque converter clutches. My E250 work van (117,000 miles) developed a shudder when going into OD. Flushed the trans and converter with new mercon 5 fluid and all is well.
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Old 02-10-2013, 05:30 PM
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f150 shudder

aod ford trans in overdrive by passes the torqe so is direcr drive,so if 1cyl has a dead miss when in od woud magnify the miss fire. i would solve the engine isue first.then check trans linkag(throtle pressure. an lik prev poster mercon trans fluid solves many trans isues
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Old 02-10-2013, 08:51 PM
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Quote:
Originally Posted by LATECH View Post
Could be an injector not spraying
Kinda leaning towards this right now. I just dont understand how a cylinder without an injector working is still managing to get the plug cruddy and wet/oily. #8 is the only plug that does not look normal.

Vacuum gauge was connected to the engine today. 19" of vacuum at idle, steady needle, no dropping or vibrating or anything. Firing order was checked and it was correct. Sprayed carb cleaner around as many places as I could (intake, vacuum connections, injector bungs, etc) without any change in idle speed or smoothness. Finished the compression test. All cylinders were 150 to 175 psi and the 150 readings were taken when i forgot to push the throttle to the floor so they may be a little higher if they were tested WOT like the rest of them were.

How are the injectors removed from this engine? Remove a few bolts out of the fuel rail, lift the rail up and off the injectors and then the injectors just pop out of the manifold?

Last edited by Torque454; 02-10-2013 at 08:58 PM.
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