I recently had my transmission (700R4) rebuilt and I bought a new torque converter as well. This TC is a 2500-2800 stall. The company I bought from have been making good TC's for over 20 years and I have spoken to many of their customer's who are all very very pleased with the TC's (I will leave the company name out of this post as I have yet to determine the cause of my vibration)...

Anyway today was the first time I road tested my car. I wanted to take it easy on her so I just drove slow up my street... I immediately noticed a very pronounced vibration when I push the gas and the rpm's come up to around 1200-1500 rpms, I get it again at higher rpm's as well. At idle (400-600 rpms) the vibration is barely noticeable. We checked everything that could possibly give me vibration (exhaust, suspension, engine timing etc etc) and everything checked out fine. When my car is parked and you rev it up you can feel this hard vibration at these rpm's as well. I do have a new polyurethane transmission mount and I know that these mounts transmit more vibration but I am sure this is not causing it, I have a friend with an '88 GTA and he has the same mount on the same tranny.

I had my tranmission rebuilt by a professional certified GM AST transmission mechanic who does very good work as I know of several people who have had their tranny's rebuilt by him (the reason I rebuilt my transmision was to install better parts and after 17 years I think it was time). When I installed my transmission after the rebuild I got it installed by a certified GM mechanic (my good friend who also owns a 3rd gen Camaro). So I am 100% sure that the install/rebuild is right... we marked the driveshaft prior to removing it and all of the proper things to do when doing this job.

We never done anything to the engine (besides change the timing chain which we know for a fact was put back perfectly) The car was working fine (no vibration) before we tackled the transmission so I am baffled as to what could be causing the vibration. The car idles fine, accelerates fine (minus the obvious vibration), timing is rock solid and right on the money.

I am going to unbolt the torque converter from the flywheel, set her back down and see if the vibration disappears while in PARK and revving the engine. If it does then I will rotate the flywheel by one bolt hole on the TC and try again, if the vibration is still there then I will move it to the final bolt hole (there's only three bolts so there is only 3 possible bolting patterns). If the vibration is still there the company said that they will send me a replacement torque converter.

My questions are these..

1. Is what I am planning the proper way to isolate the torque converter?

2. If the vibration is still there after I unbolt the torque converter where can I look for this vibration...

3. I only drove the car approx 1 mile and was very easy on it... could I have done any other damage internally to my tranny if the TC is the cause of the vibration?


Any thoughts, comments, help would really be appreciated!!

 

Moving it shouldn't matter since it's not balanced with the crank.
If you can get it to vibrate in neutral ( or park), then unbolt the converter all together and shove it back away from the flex plate.
Start it back up and see if it still shakes.

 

I have never heard of going through that sequence. Seems kinda odd.

 

Tonight we took off the inspection cover and had a look at the torque converter spinning. You could see it wasn't balanced and was wobbling. Unbolted the torque converter and the vibration went away.

One question... with the torque converter let go will the engine surge and seem like it wants to die out? I wasn't sure if it was because I was low on gas ( you know these perfect guages we have ) or if it was due to the fact that the torque converter wasn't attached to the engine (thus throwing off some sensor).

Either way this weekend we will pull the new one (back it goes to the manufacturer) and put my old one back on....the old one should do me fine for the remainder of the summer.

 

That's why I pointed out the shortcut check.
The converter or manual flywheel creates a load on the engine and it's easier for the computer to stabilize the idle. Kinda like a big shock absorber.
Glad you found the problem. Sorry to see that it all has to come apart.

 

Even though you've found your problem, still want to put out this bit of info. I had a vibration after swapping in the TH400 and new converter, drove it like that for a few months. Finally decided to do something about it and just unbolted the converter and moved it to the next set of holes. Started up and no more vibration! I had to do that with another converter too. Both times I had people saying that moving it wouldn't make a difference and both times it did make a difference.

 

I'll be damned. Thats cool to learn

 

Somewhere, there has to be a sloppy or careless balancing technique. If the converter is built to a zero weight offset, then there should be nothing to counteract by rotating.
The only time i've seen this is with a malfunctioning converter. Currently I run a torqueflite in my vehicle and in these model trans', the converter can only be attached to the flex plate one way. If it vibrates, it's a lemon.

 

This is very interesting.....
Being "out of balance" and being "out of square" are two entirely different things.

Try rotating it to the next position and bolting it back down.
Go around the bolt pattern and tighten each one a little bit in sequence.
See if you can,by chance, get it to seat evenly.
This will only cost you a few extra minutes of work even if you don't get it to work.

try this and run it again while you or your buddy watches under the car to see if it straightens out.

There's a chance this may fix it and you won't have to pull everything.

Good luck with it.

 

Had another thought....

Your flexplate 'could' be bent.
(They are easy to bend)

This would cause the TC to 'wobble'.

You could check it with the TC unbolted. Do a good visual inspection of the flexplate while it's rotating at idle speed.

IT could be warped and not cause too much vibration with the TC unbolted because it's a VERY lightweight flywheel.

The torque converter is heavier and so could cause more vibration when it's bolted up and spinning.

Just an extra thought I'm throwing in here.

 

I have to ask.
If a converter is piloted to the center of the crank with a precision snout that's machined to fit a precision bored hole in a crank, how can you possibly bolt it out of square?

 

That's what I tried doing to mine first before turning it to the next set of holes, didn't work or seem to affect anything. Both the converter and flex plate were new, TCI's SFI aprooved flex plate and a Continental 9 inch converter which was 800 bucks.

 

That's usually caused by the pilot on the converter not seating properly into the crank. A speck of dirt or rust, a ding on one of the parts, etc. can cause it. Turning it doesn't really change the balance or how stuff lines up or any of that; it just gives the 2 parts a different point at which to mate and go all the way together.

 

We are 99.999999% sure it's the converter.... the box that it came was pretty banged up (broke through on one side) and when my buddy was looking at the converter last night (while it was on the car) he said "Do you know this converter has a dent in it?" ... I said "No! I know it got knocked around a bit but I never noticed any big dent" ... he said " Yup it's dented pretty good"

The manufacturer is sending me a new one today.....sucky part is I have to pull the new one out again... blah!! Least I don't have to drop the tranny completely

 

Yeah I noticed the lack of "load" when I turned the key... the starter really spun the engine over fast

 

AMRacer:

It's the same deal as torquing down your wheel studs ONE AT A TIME.
I don't know ANYONE that would do that and expect the wheel to run true.
You torque them down a little at a time in a "criss-cross" pattern until you get them all to the correct torque.
It's the same with the flywheel bolts....you use the same procedure.

Samo-samo with the three torque converter to flexplate bolts.

Make sense now?

BTW, the torque converter is NOT piloted to the flywheel or the flexplate.
It is LOCATED PRECISELY by the three mounting bolts.
Of course IS "piloted" on the pump input splines and the transmission input shaft.

At least that's the case on a SBC.
I don't know (or care) what the rest of the mfgs' do.

I think what you are visualizing is a manual input shaft and a piloy bearing in the crankshaft flange.

Automatics are NOT like that.

Ok?????

 

If automatics aren't like that then save a few ounces and cut the snout off that goes into the crank since it's unnecessary.
How many people at the factory ***'y line do you think they have going through all the gyrations you suggest?

 

I think they have none.

Computerized laser measuring equipment is used to ascertain tolerances on the parts. Converters are balanced and checked for 'straightness' and the bolts are torqued via computer driven machines.
Parts are new and clean. Techniques are devised to make things work in 9,999 time out of 10,000 or better.
Sometimes even with all that engineering YOU get the one that has a vibration or isn't just right.

Quite an environment compared to your or my garage or shadetree wouldn't you say?
I don't have 40 million dollars worth of machinery and computers to assemble my engine or tranny, do you?

That's why procedures are developed to get things to work when conditions are less than ideal.

There's good information in FSM's. Pick one up and read it sometime. There's be a lot of things in there you may scoff at.

Either learn procedures and techniques and use them or be ready for a lot of failure and heartbreak.

Sorry but that's the way it is in the "real" world.

It helps to have an open mind when you deal with things.
One of the hardest things to learn is "unlearning" a preconcieved idea.

But ce'est la vie. It's a free country. Everyone is free to believe what they believe and apply technique as they see fit.

I'm not here to argue any point, just trying to help out.

VetNutJim ..........Moving on now.......................

87ROCZ .... Good luck getting'er going.....

 

Yes, it is.

Look at a converter sometime. There's a round thing about 1½" in diameter on the front of it in the center. That's the pilot. It plugs into the crank. You're partly right, it's not like a manual, with a bushing and all; since it doesn't have to spin. But it definitely aligns itself positively to the crank by that method.

AFAIK all mfrs use some variation or other of that theme; all GM V8 motors, and all of the RWD 6-cyl motors that I've ever had to deal with, use the same diameter pilot in the rear of the crank.

The bolt holes are like almost any other bolt holes.... just holes. There's not "piloting" action provided by them, unlike starter or clutch bolts for example.

The pilot on the converter fits into this location on the crank.

 

What about the statement above that says

" Go around the bolt pattern and tighten each one a little bit in sequence."

Does this need to be done? I wouldn't think so but hey I'm new at all of this... my mechanic buddy never did that, he said it doesn't matter as the torque converter seats itself against the flexplate and he has done countless torque converters... but that doesn't mean he is correct.

I see the reason for doing this with a wheel/rim so maybe this should be done here as well...