I've been posting the status of my transmission overhaul and torque converter change. One of you members wanted to know how my truck performs with the new converter... it's a 900 RPM Stall non-lockup torque converter.

At idle, the entire truck vibrates or shutters. Anything in the rear view mirrors look smears. Even with idle speed around 500 or 600 the truck vibrates. Oddly enough, even with the transmission in neutral, the truck still vibrates. What is the engine driving while in neutral that would still make the entire truck vibrate?

Once off idle, the truck runs great as just a pickup, ie: not towing.

When I hook up the trailer (5460# boat and trailer) it pulls ok from a stop. At highway speeds the new torque converter slips just like the old one. I've heard that after reaching stall speed, the lockup is still not 100% but more like 79% - 92% lockup. Mine seems more like 79% or maybe worse.

Going down the highway at 55 mph I can push the throttle and hear the engine spin up to max RPM without increasing truck speed. Is there something built into a torque converter that 'lets go' if the torque gets too high?

 

Sounds like you got a bad converter. Also, non lockup converters always slip. As far as vibrating, even in neutral, don't know. My first though is that they welded balancing weights on it as if it were going in a gasser with a cast crank (externally balanced). Does it vibrate at speed?

 

I'm with mhuppertz, and if it's not got weights on the converter then something wrong inside!

Could allso be a bad eng. or tranny mount? is the ex mounts still incasted with rubber?

allso if this converter was built for a gasser the stall will keep going up and so will the slip......as the torkconvert fins bend and tear off

 

If the motor is running then the flexplate and converter are spinning. So even in neutral if there is a balance problem you will still feel it. Check your flexplate and torque converter bolts to make sure nothing is cracked or loose. Also look for missing weights. I'm not sure about the balance on the cummins converters or the flexplate. The converter may have weights for balancing.

A torque converter is just a fluid compiling device. Take a glass of water with ice cubes in it and spin it. The cup will spin faster, but eventually the ice cubes will also spin, but never sync'd 100%.

It's just discs with louvers in it with a torque converter design with fluid being the 'connection'. So it's never locked at 100%. It's going to slip at full throttle also since it's not a mechanical coupling like a pressureplate/clutch setup. It takes a certain rpm for the discs and the fluid to couple.

Stall: For race converters used in cars they give a stall rpm, but this 'stall speed' will vary depending on the engine torque. As an example in my car I have a 3800 stall speed converter. It'll 'flash' higher than 3800 on the intial full throttle rpm rise, but it will stall near the rated rpm. I can start off in 3rd gear (manual automatic) and hammer it and the rpms will stay near 3800-4000 until the engine rpm and vehicle speed increase to the stall speed...then rpm will increase. But then it will also cruise at a lower rpm..that's where efficiency comes in. It's not always a 3800 rpm 'slip'.

Efficiency: The efficieny is going to be the ratio at a constant speed cruise rpm, not at take off or heavy acceleration. I guess you could say it's how efficent it couples with a contant torque load.

So I guess what i'm trying to say is that it's not going to rev to 900 rpm and lock up, but at 900 rpm it will be 'more coupled' than a stock coverter.

I'm no transmission expert...so if anybody wan's to add/correct feel free.

 

I think it very well could be a cracked flexplate, now that I have thought about it some more. It would cause the symptoms you describe.

 

Thanks for all the input, maybe others will chime in as well. For me, it's time to get the Bureau of Automotive Repair connected into the picture. (They'll probablly just do a $2M study and file it.)

[MHuppertz: Does it vibrate at speed?] No. As soon as I come off idle, plus a hundred or two RPM, the entire truck smooths out, quiets down and the images in the mirrors come into focus. At speed the truck runs smooth and quiet.

FlashGordon: I'll have to check if there are any external weights welded on it.

My major question now is: What is the input shaft driving while the transmission is in neutral?

My understanding: It is driving the centers of disengaged clutches and an oil pump.

Den: I've begun to understand torque converters in the last couple weeks but I really like your annalysis of the glass of water and ice cubes.

Your race converters allow you to flash to higher [than 3800] RPMs but will couple once the fluid gets up to speed. That sounds like I should try flashing the throttle and keep it there while the fluid coupling gets up to speed.

 

Dean,
Sorry to hear that your having trouble with your trans. Same thing happened to me, $3600 into the trans and the stock one pulled better. 4 or 5 trips back to the shop to get things right and they still weren't right. Had a poorly built billet converter, rpms would flash to 3000 rpm's and a poorly done shift kit.
This is the kind of crap I found when I took it apart to put my parts in. Unacceptable, for what I spent and I will be making one last trip up there in person to stir up some trouble. I would be assamed if I left that crud in there.


I had enough and decided to do it myself with Goerend parts.

I'm much happier with the new setup. Really makes the engine work, less throttle required to get it moving. Pulls hard right off of idle.

 

You mentioned you were idling at 5-600 rpm's that is where your vibration is coming from. The idle needs to be right up at 900rpm's in drive and the AC on then I bet the vibration will go away.

 

I thought that it was 750? but your right,

Captain Dean didn't you say that if you raised the rpm up a couple hundred the vibration gos a way?

 

900 RPM stall?

Why so low? Isn't peak torque around 1800?

Is the theory that if you have the stall that low you will get a larger powerband?

 

You know it may be 750 I don't remember for sure though. I do know the 500-600 he said it was idling at is way too low. Should raise the idle up untill it stops shaking anyways, as long as its below 900 when it stops shaking thats the problem.

 

It's better for the engine to idle slightly higher than stock idle settings any way. Keeps the oil and other fluids pumping nicer and keeps pressures up a bit if it sits for very long while running. There are little injectors that shoot oil into the bottom of the cylinders that will appreciate haveing the idle up a bit.

 

Because the person that sold him that converter doesn't know what they're talking about. If that converter truly had a 900 rpm stall it would be real hard to get the truck rolling with a load on it, maybe impossible because you wouldn't be able to spool the turbo.

Stall in a torque converter is torque dependant and the stall rpm will rise as the torque input increases.
I recently installed a Goerend converter and for example I put the trans in 1st gear, hold the brakes, and go WOT very briefly. 1300-1400 rpms is where my rpms stopped increasing. Now thats at a no or low boost condition, take the same condition with 10lbs of boost and more torque and the same converter will stall at a higher speed say 1600 to 1800 rpms.

Clear as mud, good. I didn't confuse anybody did I?

 

Try kicking the idle up to 750 in drive if it doesn't try to drive away too bad. These things shake something awful if they idle slower than that. I like mine to idle at 850, but I realize that would probably pull too hard in an automatic truck.

 

Well, I raised the idle until the mirrors focused. I don't have a tach but I suppose it's around 750 or 800. There is still a vibration but the only thing that rattles now are my seatbelt mounts.

This torque converter has to go and I will stop doing business with this guy. That leaves one other transmission shop on my side of the island. My other choice is to purchase a transmission jack and change it myself.

The Getrag is truely the best manual for these trucks however are there other manual transmissions that will fit and handle the workload?