vibration/shudder on acceleration (1 Viewer)

[wingnutter]

Been searching around and haven't seen this yet.

I've got a 94 80 with 230K. Yesterday after driving around for about 30 mins, I started to get a shudder/vibration when I accelerated normally.

It runs fine at speed, but if I gas it, it shudders. If I accelerate lightly (read: grandma speed), it gets up to speed fine, but if I give it gas at any point, at any speed the truck shudders pretty hard and there is very little power.

Starts fine, it idles fine in gear and in neutral. Also I can rev the engine in neutral or in gear (applying the brake) and I don't get any shudder.

Not too much recent work, other than checking/replacing fluids. Did the front axle rebuild about 10K ago...no other major maintenance.

Immediate idea is to replace the fuel filter, but outside of that...I seem to just be running down a list of things...spark plugs, wires, distributor...but I don't really know what else to look at.

Thanks in advance

 

[snowwolf]

I had exactly the same thing with my Lexus SC 400 I changed the auto box fluid and it worked fine after that, do a test and take the overdrive off, see if it does it then.

 

[archie]

Does it seem to happen when the engine is under load only(try it on an incline downhill)? When was the las time the driveshaft lubricated? If it does what RPM?

 

[wingnutter]

switching the O/D switch off doesn't seem to have any effect on the shudder

 

[wingnutter]

Does it seem to happen when the engine is under load only(try it on an incline downhill)? When was the las time the driveshaft lubricated? If it does what RPM?

incline, flat, decline, doesnt seem to matter. happens anytime i press down the accelerator. RPM doesn't matter, i can be at a dead stop and punch the gas and shudder. i can be cruising at 30mph and hit the gas and get the shudder.

it's been a while since greased the beast.

 

[gray]

Sounds maybe like the tranny. Is it almost like you are going over little speed bumps? Have you serviced the transmission, ever? Added any additives recently to "help" sluggish or soft shifts? These trannies do not like additives IME; just a high quality Dexron ATF. Often, adding additives makes a slight problem worse.

I would start with the basics; adjust the kickdown cable first. If you added any additives recently, you can drain out a few quarts via the drain plug, and then add fresh Dexron; see if that helps. If not, you can drop the pan, clean it and the fine mesh screen carefully, top it off, then flush the entire system with new Dexron ATF. If the fluid is already fairly clean from many fluid changes (this is the controversial part) you might consider jumping to a complete flush using either a BG cleaner and flush machine at a BG shop, or adding Lubegard tranny flush and then doing the flush.IMO.

 

[archie]

does it shudder when you lightly accelerate while tranny is in neutral? Just trying to see if it is engine related.

 

[wingnutter]

Sounds maybe like the tranny. Is it almost like you are going over little speed bumps? Have you serviced the transmission, ever? Added any additives recently to "help" sluggish or soft shifts? These trannies do not like additives IME; just a high quality Dexron ATF. Often, adding additives makes a slight problem worse.

Small speed bumps is a good analogy. No additives at all, just plain ol Dexron ATF. This problem didn't creep up, it just appeared the other afternoon. Hadn't been having any issues with power or shifting.

Going to swap out the tranny fluid tonight and see if that helps at all. If not, guess I'll drop the pan this weekend. Not really too keen on machine flushing, seems to cause more problems then it solves

 

[wingnutter]

does it shudder when you lightly accelerate while tranny is in neutral? Just trying to see if it is engine related.

I only get the shudder when I accelerate while moving. I've reved the engine in park, neutral, in gear with the brakes engaged. Nothing.

I can cruise at any speed without so much as a vibration, but as soon as I press the accelerator and give it any bit of power it shudder like going over series of "small speed bumps"

 

[archie]

i would punch the accelerator while coasting in neutral to a stop (in a safe place)and see if you could get the shudder. I think it's best to isolate the problem from engine, tranny, or driveshaft. It could be a engine motor mount, or something wierd with the driveshaft in addition to a tranny problem. Tranny problems usually creep up as small symptoms first so I have a feeling it might be driveshaft or engine related seeing you don't have any shifting problems.

 

[snowwolf]

all what you have said, was exactly the same as my SC400 Lexus, try the ATF change in the autobox, see what happens.

 

[wingnutter]

i would punch the accelerator while coasting in neutral to a stop (in a safe place)and see if you could get the shudder.

Just tried this, don't get any shudder when coasting in neutral. Pulled into an empty parking lot and tried the punching it in reverse. Get the same shudder.

Was there a recent sudden drop in ambient temperature just before it happened ie: is it below freezing in VA?

Nope...it actually was an unseasonably warm weekend here.

 

[snowwolf]

so you changed the tranny fluid? and still the same.

have you checked under the truck for any loose trany brackets, where bolts have fallen out? also check engine mounting bolts etc

 

[gray]

Possibly the tranny from your description of "shudder"; you could drain the fluid a couple of times and see what you get; if it is a bit less noticable, you may get lucky with more fluid changes.
Here is the link to adjust your kickdown cable, if you need it:

http://www.ih8mud.com/tech/80throttle.php

In my limited knowledge (hoping others will chime in later) the solenoids on the A440F, if bad, will not provide the correct pressures for the clutch packs and/or the torque converter to operate properly. Later today some trannies gurus will probably come on line and you'll get more specific advice I'm sure. But you seem to be saying that it still is shifting correctly, but shudders on acceleration, correct?

 

[wingnutter]

so you changed the tranny fluid? and still the same.

have you checked under the truck for any loose trany brackets, where bolts have fallen out? also check engine mounting bolts etc

I have checked under the truck and nothing looks amiss. Changing the fluid tonight.

But you seem to be saying that it still is shifting correctly, but shudders on acceleration, correct?

Seems to be shifting just fine. If I'm very light on the accelerator it shifts thru the gears just fine and I can get up to cruising speed. If i get on the accelerator like one normally would, it shudders regardless of gear or shifting point.

 

[concretejungle]

Got to throw this one out there guys...

Have you washed the engine lately?

 

[wingnutter]

nope...engine's nice and dusty

 

[archie]

Got to throw this one out there guys...

Have you washed the engine lately?

or gone thru any big water puddles? I was thinking that also! How about the age of the spark plug wires?

 

[wingnutter]

no puddles since i moved to the coast. wires have almost 25K on them...they are probably due, but they still look good.

 

[archie]

I would try spraying water from a water bottle onto the spark plugs and other wires in the darkness. You might see a spark on the wires that might be causing the engine to run rough.