low speed shudder

[chris_maxwell]

1995 GMC K2500 long box. Between 0 and 15 MPH there is a vibration/shudder at launch and driving, any gear dosen't matter. I have had the driveline center bearing replaced (didn't feel it before then, but i was also missing a bolt out of the back of my gear vendor yoke), driveline has been rebalanced, 2 shops say the u-joints are good. Had the pinion angle corrected (truck is lifted 4" since new). I have seen there has been several recalls on the 2 piece driveshaft, but not on the 95. I don't think i can change to a 1 piece anyhow because of the auxillary transmission. I changed the differencial oil to synthetic. Where do i need to look now?

[JohnC]

Could you have changed the phasing of the U-joints while you were working on the center bearing?

[chris_maxwell]

Originally the phasing was incorrect, but when i carrier bearing replaced they phased them correctly, and then rebalanced the driveline.

[moondoggie]

Good Day!

Your signature doesn't mention it, but the text of your query says "my gear vendor yoke". I will assume you're truck has a Gear Vendors Aux. OD, like my pickup.

I had the same thing after I installed my GV. I made four 1/4" plates with holes for the carrier bearing holder. I added and/or deleted these shims until the shudder went away. So, I've got somewhere between 1/4" & 1" of shim under my carrier bearing holder; I'd guess it worked best at 1/2" or 3/4", but I'd have to crawl under the truck to be sure, & yours will likely be different anyway. The concept is, you might have to play with this to get the right driveshaft angles for your truck, or maybe with your lift there is no right amount of shims to put under the carrier bearing holder that will satisfy all driveshaft angle requirements. Then maybe you'd have to go to a one-piece rear driveshaft; a good driveshaft shop can tell you whether it would be too long or not. I remember asking about this myself when I installed my GV, but I can't remember what the max length was.

For a brief ride, I had the only 3/4 ton front wheel drive pickup in MN. After tossing the rear driveshaft into the box, I put my truck in 4WD & drove it ~ 15 miles to the driveshaft shop.

Good luck; please post your results; &...

Blessings!

[Big Green]

I had the same issue with my truck for years... gm replaced the pump 5 or 6 times trying to fix it. As I got more miles on the truck it got worse. My truck would even do it in neutral. Rev it to 950-1000 rpms and it would shake the truck like it had a dead cylinder.

A gear drive fixed it.

So, I suggest before spending another truck load of cash on the driveshaft parts that you check the amount (number of degrees) of slack in the timing chain. It sounds like a huge job but it's really not that bad. Just remove the oil fill tube on the front of your engine and then rotate the engine back and forth and measure the number of degrees the crank moves before the injection pump gear starts to move. Somewhere I've seen the spec but if it were me and there more that almost none I'd be thinking about a new chain or a gear drive.

My truck also had an intermittent (I'm talking 5 or 6 times a week) miss at high speed. It almost felt like someone turned the key off for a split second. This is also gone since the gear drive install.

Good luck
Big Green
'95 6.5 K2500 5spd, cooling mods, gear drive, JK exhaust, JK intake mods, and a host of other goodies, JK chip on order

[Hubert]

I have experienced the fuel metering shudders launching in my 5spd in 2nd gear. Never get it in 1st gear. Have'nt really heard of a lot of automatics having the same thing. But with harsher drive angles and GV maybe so. I have also had another vehicle give shudders/vibration in low rpms from stiff u joints and soft transmission mount. And because the driveline vibes also came from not having ujoints concentric ( I did not have a clip fully seated in a groove). Once I fixed my first attempt at the fix the new ujoints loosend up after a little while and quit the low speed vibes. I think you can seat ujoint caps too hard and the articulation will be tight and cause wobble vibration in driveline articulation.

The fuel metering shudders (for me) seems to come from fuel viscosity, cetane, and lubricity issues. I notice it when I run too much Lucas fuel additive or some fuel distributors. It comes from low rpm varing load the ECM trying to keep perfect balance of rpm/power. Dunno you could test it by power braking launch or something to rule out a fuel metering issue. See if you can make it come and go with more throttle/load at launch. If you think you can influence with application of throttle/load and if you use fuel additive skip a tank then change to stanadyne Performance formula for 1 or 2 tanks and see what it does. Not all additives are created equal neither are all fuel stations/distributors.

[chris_maxwell]

I seemed to have eliminate most of the shudder. I took it into a spring shop who didn't know how to shim the pinion angle correctly so I proceeded to do it myself. I fliped the riser blocks (3 degrees difference) and installed new U-Bolts. I have a little shudder left (I may be a little sensitive now that I have felt it once) but it is a 300% better. Once I get the U-Bolts to hold the final torque I may play with shimming the carrrier bearing slightly. I can live with what I Have now. Where is a good place to get some chrome 8 lug wheels that are easy to clean? Not much selection for the HD trucks.