99 Tahoe advice
 

I am a pretty decent mechanic as is my dad thats been helping me on my Tahoe but I need some outside opinions.

Over the past few months I have been battling some strange "shudder/vibration'. My truck is a 99' 4x4 tahoe with 5.7 and Auto tranny.



I have replaced the following:

Truck has 202K but we completely rebuilt the engine at 169K

Both front CV alxe assemblies, were worn and needed replaced

Pulled the front differential and replaced carrier and axle shaft bearings...all were worn.

Inspected all U-joints, they are in good shape.

After this took to a mechanic that said the shudder I was still feeling was the torque converter when going into overdrive.

Pulled tranny, t-case, etc...replaced torque converter, service tranny with new filter, pan gasket and fluid.


It was running good for about two weeks and this weekend on the way home from out of town the shudder is back. Only thing different is it seems to be less intermident and more steady. It also doesnt stop when I shift from 4th down to 3rd now as the mechanic suggested trying before to see if it was the overdrive. It it steady now around 40-65 MPH but not 70mph plus.



Any advice would be greatly appreciated, Im about to loose my mind over this. Im worried maybe the tranny is going out and its hunting season.

You guys know way more about this than I do but we had a similar problem with a vehicle turned out to be bad motor mounts, You couldnt notice them until the engine was at higher revs. We replaced them and the shudder went away.......

Or--

Your Tahoe caught wind of the election results and just said, "Ya know, F' it..."

Stink I had an incident recently with mine and it turned out to be plug wires. Only did it around 60mph. '96 w/ 240k rebuilt at 183k.

Blue, forgot to mention I changed plugs and wires when this first started too. Last year it did something similiar and it was a wire but didnt help this time. I guess Im gonna have to try and change em again.

Does it only do it in lockup, or does it do it all the time at those speeds? If it does it only while in lockup, then my next question is did you upgrade the valve body when you did the converter? 4L60E's from 95+ sufferred from lockup bore wear in teh valve body that causes them to slip or drop out of lock-up many times throwing a P1870 code. The most common aftermarket fix is to replace the PWM lockup valve with an on off style valve to eliminate the pulse width modulation lockup function(soft lockup feature), and makes it like another gear. GM and SONNAX use an oversized lockup valve in the valve body, but they suffer from the same issue down the road. Another VERY common issue that causes missing going down the road at cruise is the injector pod assembly. If it is the origanal non multi port updated set-up this could be your issue. Also make sure your cats aren't plugged, the EGR is working and not hanging open, and O2 sensors are NOTORIOUS for giving driveability issues in these without coding or for throwing misfire codes. Also make sure and put a PREMIUM quality cap and rotor in it as the crab caps are BAD about cross firing internally.

You need to narrow it down to wether it is a driveline binding issue, lockup kicking out, engine misfire, or loading up. Then go from there. And yes, I've worked on a FEW of these animals and the early V8 VORTEC can give you nightmares trying to chase issues in them as the OBD2 in them SUCKS.

ONLY, and I repeat ONLY use AC DELCO platinum or iridium plugs in these engines if you don't want misfires and studders. Also most wiresets you buy now are JUNK! I use teh CARQUEST premium 8MM silicone wires, or BOSCH from AZ. The DURALAST wires are garbage, and most of teh time run worse than 200K mile origanals.

Thanks FERM. I THINK I went with ACdelco on the plug. Wires were whatever advanced auto had. Im thinking Ill get some better 8mm next and double check my plug. I Havent done the rotor/cap in a while so that will be the first step.


Its after lockup at a steady speed.


and No we didnt fool with the valve body. What do you think ...it could be that?

Have you looked at the driveshaft? Or is this not the vibration type you are experiencing?

stink i've had best luck with the MSD cap and button or the blue marine cap and button with brass terminals. Wires best luck with Delphi or AC wires. plugs best for me have been either AC Platinum or Denso Iridium plugs.

I like the blue marine cap as well. have yet to have one of them fail me, but many of the black ones give all kinds of grief. ANYTIME there is a torque converter issue with a 95+ 4L60E the valve body should be teh FIRST thing addressed. Most any trans shop knows this, and I'm surprised one told you to do a converter instead of the lockup valve. It wouldn't hurt to put a TRANSGO SK or HD2 shift kit in teh valve body. Lockup will be alot firmer, but it will eliminate the possibility of converter slippage from a control issue which is a semi common issue on 95+ 4L60E's. And it wouldn't hurt to put a fuel pressure guage on it while it is doing it to make sure it is holding pressure. If it still has teh central unit with poppets on it, they NEED at least 42 PSI to open the poppits properly, but prefer 46 or better.