Will the 4L80E shudder at highway speed

[96GMC7.4l/454]

Hey newb here just registered…
I have a 96 GMC C2500 suburban. There were two of the 3/4 ton made from my understanding. The light one has a GVW of 7800lbs and the heavy has a GVW of 8600lbs. Mine is the heavy and unless I’ve been misinformed only trucks over 8000lbs came with the good stuff. My truck or burban whatever has the 4L80E trans and a 14 bolt full float rear end driven by a 7.4L 454. My question is can the 4L80E trans shudder at highway speeds. I’ve had a shudder and can not find the source. I’ve rebuilt the entire front end from the frame out and changed wheels and tires completely, there are brand new shocks on all four corners new trans mount and soon to have new motor mounts for good measure. Without mounting a camera to my chassis I don’t know what is causing this issue and it’s not consistent. I’ve heard of some transmissions causing this but they were in older Ford trucks. Any input is welcome and I’m always open for knowledge. Thanx in advance

 

[THEFERMANATOR]

A failing torque converter can most definitely give a shudder while running down the road. Hook a scanner up and monitor calculated gear ratio to see if it stays solid and watch converter slippage. If it's slipping bad enough to shudder I would expect to see it on the scanner.

 

[Stoney]

Two things I've had cause it, rear tranny mount bad, and bad carrier bearing..

 

[96GMC7.4l/454]

A failing torque converter can most definitely give a shudder while running down the road. Hook a scanner up and monitor calculated gear ratio to see if it stays solid and watch converter slippage. If it's slipping bad enough to shudder I would expect to see it on the scanner.

If the torque converter were slipping wouldn’t I notice that in unusually high rpm while driving?

 

[96GMC7.4l/454]

Two things I've had cause it, rear tranny mount bad, and bad carrier bearing..

I’ve replaced the tranny mount twice. Once when I first got the truck almost 4 years ago and recently. This truck doesn’t have a carrier on the driveshaft. I appreciate the information though.

Two things I've had cause it, rear tranny mount bad, and bad carrier bearing..

 

[MrMarty51]

And U Joints.
Many years ago. I had a very old Triumph motorcycle. 1957 6-T Thunderbird. When driving at high rates of speed, sometimes it would have this weird vibration. Let out of the throttle and slw down, then speed back up and the vibes would usually go away.
Tore the engine down. Discovered that the right side main ball bearing around the cranking shaft had been spinning in the crank case.
Fixed that with a good used case and all was good.

 

[Rockabillyrat]

Sounds to me like it might be the torque converter slipping. You need to monitor TCC slip speed on the scanner. When the PCM commands TCC lockup the slip speed should be under 50 rpm. I like to get on the highway and put as much load on it as I can without causing a downshift (preferably up a hill) and watch for the slip speed to increase. Also sometime a shudder like that is easier to see when you graph the slip speed on the scanner.

 

[WarWagon]

I have had a failing TC clutch feel like it's rapidly shifting as the ECM released the TC clutch and the reapplied it as it noticed the slipping. I had to have a scanner on it to see the TC on/off status change as it changed status quickly.

Raise the vehicle on jackstands with a good SHTF stopping distance in front of it. Wind it up in the air and see if you can see hear or otherwise locate the problem. If not it's load biased like a trans. Don't forget to check the rear wheels in case there is a loose hub bearing.

Check the oil in the diff.

From a bent axle, bent rim, to a bent driveshaft. No, I didn't ask the dealer that took it in trade when I overheard the mechanic say the rear axle was bent on a 1/2 ton. Ended my interest in it because how it may have got bent. Didn't want to know or get any of it on me. Bad luck would be a tire problem or tire shop that isn't balancing tires well. You have thrown a weight 1 mile from the tire shop sometime in the past, right?

 

[96GMC7.4l/454]

I’ve replaced the tranny mount twice. Once when I first got the truck almost 4 years ago and recently. This truck doesn’t have a carrier on the driveshaft. I appreciate the information though.

And U Joints.
Many years ago. I had a very old Triumph motorcycle. 1957 6-T Thunderbird. When driving at high rates of speed, sometimes it would have this weird vibration. Let out of the throttle and slw down, then speed back up and the vibes would usually go away.
Tore the engine down. Discovered that the right side main ball bearing around the cranking shaft had been spinning in the crank case.
Fixed that with a good used case and all was good.

oh man!!!… I really hope it’s not a spun bearing I’m not financially able to do a build right now being a single dad of two without any assistance or even child support. ( it drives me crazy all these worthless people that get state assistance but if you work hard and try to make something of yourself and be a good example of a man for your children to set a standard to for their definition of a man or a dad then you don’t qualify for assistance because you’re trying. sorry… ranting a bit.) As far as U-joints I’m going to replace them this weekend I’m not even sure if they’ve ever been done but they don’t “clank” or make any noise but it can’t hurt.

 

[96GMC7.4l/454]

I have had a failing TC clutch feel like it's rapidly shifting as the ECM released the TC clutch and the reapplied it as it noticed the slipping. I had to have a scanner on it to see the TC on/off status change as it changed status quickly.

Raise the vehicle on jackstands with a good SHTF stopping distance in front of it. Wind it up in the air and see if you can see hear or otherwise locate the problem. If not it's load biased like a trans. Don't forget to check the rear wheels in case there is a loose hub bearing.

Check the oil in the diff.

From a bent axle, bent rim, to a bent driveshaft. No, I didn't ask the dealer that took it in trade when I overheard the mechanic say the rear axle was bent on a 1/2 ton. Ended my interest in it because how it may have got bent. Didn't want to know or get any of it on me. Bad luck would be a tire problem or tire shop that isn't balancing tires well. You have thrown a weight 1 mile from the tire shop sometime in the past, right?

I’ve changed wheels and tires completely to see if it was a bent or balance issue I’ll check more into the issue coming from the rear. Inside the truck it feels like it’s in the front or even-in front passenger lately I’ve felt like it feels more centered in the truck is why I question the trans . If I find anything I’ll post it. Thanx for your input

 

[Rockabillyrat]

TCC command should not go on and off under steady cruise. If it does then that indicates the PCM is seeing an input from a sensor telling it to command the TCC off like a bad TPS. TCC command should stay ON under cruise. If the TCC has failed mechanically it will show under slip speed. usually the PCM will command the TCC on and if it sees slip speed varying enough it will set a code and stop commanding TCC lock up.

 

[96GMC7.4l/454]

TCC command should not go on and off under steady cruise. If it does then that indicates the PCM is seeing an input from a sensor telling it to command the TCC off like a bad TPS. TCC command should stay ON under cruise. If the TCC has failed mechanically it will show under slip speed. usually the PCM will command the TCC on and if it sees slip speed varying enough it will set a code and stop commanding TCC lock up.

Well this may cause you think I’m dumb and when it comes to how a trans functions I would have to agree but I had to google TCC and PCM. So now that I’m up to speed I assume if this was the issue I would have a service engine light to get the OBD-II code P-0743 for TCC issues and I have no codes.

 

[Will L.]

No. It doesn’t always set a code that lights up the warning light. A scanner could show it if it’s way out, unless the computer is trying to compensate for it.

Yes from first ujoint back there could be something oddball causing it. But your description sounds like transmission...get a screen in there and rule that out right away or prove it. And no, you wouldn’t see a huge rpm jump.

If you can rule that out, start playing with moving around tires, looking at axle, ujloints.

 

[Rockabillyrat]

The PCM has a preset parameter is looks for to determine if it needs to set a code. It looks at slip speed over a period of time. If the shudder is not bad enough it may not set a code. I've had dozens of 4l80/6l80/6l90s have a TCC shudder and never set a code. Only way to see it is on a scanner.

 

[96GMC7.4l/454]

No. It doesn’t always set a code that lights up the warning light. A scanner could show it if it’s way out, unless the computer is trying to compensate for it.

Yes from first ujoint back there could be something oddball causing it. But your description sounds like transmission...get a screen in there and rule that out right away or prove it. And no, you wouldn’t see a huge rpm jump.

If you can rule that out, start playing with moving around tires, looking at axle, ujloints.

Where can I find this scanner / screen to use while driving you’ve referred to. How expensive is this test going to be?

 

[96GMC7.4l/454]

The PCM has a preset parameter is looks for to determine if it needs to set a code. It looks at slip speed over a period of time. If the shudder is not bad enough it may not set a code. I've had dozens of 4l80/6l80/6l90s have a TCC shudder and never set a code. Only way to see it is on a scanner.

Where can I find this scanner and what is the cost of performing this test?

 

[Rockabillyrat]

Where can I find this scanner and what is the cost of performing this test?

You need a scanner that can read PID data. So most of the cheap code readers wont cut it. My little Autel scanner does a good job for stuff at home. It was around $300 if I remember correctly. A good repair shop can diagnose it for you cheaper than paying for a scanner. But if you plan on working on your own truck owing a scanner is a must.

 

[WarWagon]

As far as U-joints I’m going to replace them this weekend I’m not even sure if they’ve ever been done but they don’t “clank” or make any noise but it can’t hurt.

Yes, Yes it can hurt. Don't throw parts at something: It's expensive, it may not solve the problem, and it may create a NEW problem. Driveshafts warp over time and use so when it's time for u-joints you are better off having a driveshaft shop straighten and balance it with new u-joints. After all you don't replace tires without balancing them.

 

[96GMC7.4l/454]

Yes, Yes it can hurt. Don't throw parts at something: It's expensive, it may not solve the problem, and it may create a NEW problem. Driveshafts warp over time and use so when it's time for u-joints you are better off having a driveshaft shop straighten and balance it with new u-joints. After all you don't replace tires without balancing them.

Well maybe you wouldn’t… you can balance tires without weights by rotating the tire on the wheel if you have the tools available. I’ve also cut down a drive shaft ground the old weld off the cup that is what the ears for the u joint are connected to or formed to however you would say it anyway after cutting the shaft cleaned up all surfaces and welded it back together without ever feeling like it had a balance issue. Mag I just got lucky but I prefer to do my own work to cut cost by more than 50% most of the time.

 

[THEFERMANATOR]

You can pick up vcxdiag on amazon for around $110 last I checked and it will give you full oem scanner ability through your laptop. Otherwise you could try something like the torque app with a bluetooth to obd2 dongle. The TCC lockup valve is a known problem area in the 4l80e. Sonnax and transgo both make a lockup valve with a scarf cut seal to correct the oem lockup valve. When you look at the scanner data watching tcc apply, it should ramp up to 96% in 1-2 seconds and hold around 96-98%, so don't be alarmed if you don't see 100% apply as pwm solenoids have max duty cycles under 100%. If your tcc slippage is under 40 rpm's, it will normally not code for a pwm apply tcc(the 4l60e for 98+ is a 150 rpm before it codes).