I need help with a drivetrain problem!!!

[AlaskanJack]

Ok guys here it goes. I was hearing a thumping noise when driving, if I took foot off gas it would stop until I got around 20mph slowing down. If I am driving and take foot off gas it stops but will start up again when I give it gas. Its definitely not engine. My first reaction was to remove the front drive shaft to eliminate a u-joint or front diff problem. Thumping still there and its like a rotational thump kinda like when the bearings are going out in the t-case. So I decided it was the t-case and did a manual t-case swap from electronic. To my surprise when I took it out for test drive the thumping/clunking was still there. It had recently gotten worse which is why the t-case conversion took place.

Now some additional background. A4LD tranny I have had a problem with no OD and no Torque converter lock-up. I just recently discovered that my VSS plug was unplugged, appeared to have been like this for some time due to dirt build up on it, above the speedo cable on the t-case, I plugged it back in and 2 days later this thumping started.

Now here's my question does it sound like something in tranny, torque converter or possibly flywheel.

What would I hear if a torque converter or flywheel had a problem. Also when you take foot of gas should it feel like you just pushed the clutch in on an manual shifter.

 

[AlaskanJack]

Come on guys let me hear your thoughts

 

[MrShorty]

Don't have the whole answer for you, but I would expect if it were a problem with the flywheel/flexplate/torque converter, it would vary with engine speed rather than vehicle speed. These parts spin with the engine, so, if the knocking were coming from here, it would likely show up while the vehicle was stopped, in neutral, or whenever the engine was running.
Doesn't rule out the rest of the transmission, though.
I expect you've checked the u-joints.
How about something in the rear differential?

 

[NOTAJP]

My first thought would be everything behind the T-case. I know my drive shaft is worn out.

 

[AlaskanJack]

Nope its definitely in front of the t-case and behind the engine. I once thought I heard it with vehicle in park and engine idling but I think not.

Well when I take foot off gas doesn't that vary engine speed? When I take foot off gas the rpms drop to like 1500 rpms from 3000

 

[AlaskanJack]

oh one other thing which is why I was questioning torque converter. When it drops down to 20 mph going into a stop it sounds like an 18 wheeler stopping. I am not certain that I am explaining it correctly. Ever hear an 18 wheeler use its engine going downhill to slow down it goes tat tat tat tat tat or is it rrrr rrrr rrrr rrrr

Which is why I was thinking hopefully it was torque converter.

Anyone know a site that fully explains the function of a torque converter.

 

[Howard]

Here you go Jack a full explanation on torque converters.
http://auto.howstuffworks.com/torque-converter2.htm

 

[AlaskanJack]

Thanks Howard!

I am still looking for input on my problem

I went out front earlier and did some checking in reverse at 15mph no noise, at least I think. I am going to take it for a test drive where I can back it up around 20mph and listen. It appears to only make noise when torque is applied.

Is there a way to shut down the torque converter to eliminate it as a possible problem?

Edit: After reading some posts I thought I should mention that I am not getting any low engine braking either.

 

[Howard]

Jack I know this sounds silly but it isn't something like the engine moving on it's mounts and the fan touching the suround is it. I had one once that the mounts went soggy due to oil spillage and when I stopped quickly the fan chewed the radiator core. Apart from dismantling the torque converter I can't think of any other way of finding out. Good luck anyway.

 

[AlaskanJack]

Nope the fan is fine. engine doesn't rock at all.

It's definitely rotational like imagine you had a bad gear tooth in a diff and everytime it came around to that tooth you would hear a thump.

 

[V8BoatBuilder]

I was reading your first post about plugging in the VSS, as well as the dirt buildup that caused it to become unpluged. What you may want to do is find the transmission electrical harness (should be on the side of the transmission) and clean it with electronics cleaner (in an aresol can).

You may also want to search for TV cable adjustment, and drop the transmission pan and check he valve body. They do come loose. While your at it, check'change the ATF.

Before big items are replaced, start with the simple stuff.

Good Luck

 

[AlaskanJack]

Well it appeared as though it was purposely disconnected and wrapped around speedo cable. Don't know why someone would do that.

I will check those things but would they cause a thumping sound

 

[V8BoatBuilder]

My thought was that it is indeed a transmission/torque converter problem. If the transmission is not getting the proper electrical or mechanical control, or has an internal problem, it could be causing the thumping malfunction.

 

[AlaskanJack]

Well I am assuming that the first thing I should do is drop the tranny pan and look for metal shavings. Dang I just drained it and put in some Royal Purple. I should have looked at the fluid closer, but it smelled like holy hell so I just drained it. If I had to guess it smelled burnt, really bad. Oh wait I still have the fluid in a container I will check it out.

 

[AlaskanJack]

ttt

Come one Opera House, 410 find this thread!!!!!!!!!!!!!

 

[Opera House]

First, what is the history of this vehicle

Did you just find it in a cabbage patch. VSS unplugged, sounds like someone was trying to unload it quick. How long have you had it and has it changed in that time. The TC and the 3-4 (OD) are electrically controlled. Maybe the TC wouldn't unlock and the last person pulled every electrical connector to keep the TC from ever engaging. There is a connector plug just above the pan on the case. Forget which side. See if it is still plugged in. Have you ever had the pan off, done any work on the transmission? I've had 2 OD failures. Once with the OD drum /star washer failing and the other time the planetary snapped the welds. Even found needle bearings in the pan. No OD, lots of metal, but, never a single noise. How periodic is this? If it followed the engine, it would have to sound more like a buzz saw. Any strange shifting?

 

[NOTAJP]

I feel for ya man. I know nothing of slush boxes.

 

[AlaskanJack]

Re: First, what is the history of this vehicle

Originally posted by Opera House
Did you just find it in a cabbage patch. VSS unplugged, sounds like someone was trying to unload it quick. How long have you had it and has it changed in that time. The TC and the 3-4 (OD) are electrically controlled. Maybe the TC wouldn't unlock and the last person pulled every electrical connector to keep the TC from ever engaging. There is a connector plug just above the pan on the case. Forget which side. See if it is still plugged in. Have you ever had the pan off, done any work on the transmission? I've had 2 OD failures. Once with the OD drum /star washer failing and the other time the planetary snapped the welds. Even found needle bearings in the pan. No OD, lots of metal, but, never a single noise. How periodic is this? If it followed the engine, it would have to sound more like a buzz saw. Any strange shifting?

Well as for the history I have just discoverd that the tranny has been rebuilt twice in the past 4 yrs. And no the truck was going to the salvage yard for a broken RA arm. The previous owner seemed to know jack about 4x4's or fords. He definitely wasn't smart enough to unplug anything and heclaims the OD was working for him. But he is an idiot! I personally have not had the pan off. It happens as soon as I drive it and it is a noticeable thumping/clunking. Like I said I was thinking u-joints, front diff and then t-case. My buddy heard it and we both were thinking around the same areas. I have had occassional problems with it engaging into 1st. I would either wait and it would shift or sometimes if I gave it a little gas as the engine rpm's came down it would shift and off I would go. Maybe its not following the engine I don't know I even thought it was wheel bearings at one time but I went through them.

 

[410Fortune]

first find a hill, then roll down it in neautral, front hubs unlocked

is it there?

Now try it with teh hubs locked

is it there?

 

[AlaskanJack]

Originally posted by 410Fortune
first find a hill, then roll down it in neautral, front hubs unlocked

is it there?

Now try it with teh hubs locked

is it there?

Hmmmm interesting I will try it tonight. What if I can't stop???!!!! Well I guess I'll be Fred Flinstoning it!!! Yaabbaaa Dabba Dooooooo!!!! haha