Pedal vibrations related to transmission gear/speed? 99 LX

[shtbrwn86]

Did a bunch of searching, but couldn't really find anything.

Recently noticed a vibration in the gas pedal when I was doing between 38-41mph on speedo. Today I noticed that I was accelerating at about 40 there was no vibration until the truck shifted into the next gear. Tested this a few times today where I would put it in 2 and I couldn't feel a vibration in the gas pedal as I passed 40mph, but as soon as I manually shift to D at 40mph the vibration came back. It also seems to help if I turn overdrive off since that just downshifts to third right? I do sometimes feel a similar vibration at lower speeds, 20mph or so, but the one at 40mph is more pronounced.

I thought at first it might be front u-joints, but that would probably be a vibration whether or not I am giving it gas? At least that's how the rears were when I changed them.

 

[bigredmachine]

I thought at first it might be front u-joints, but that would probably be a vibration whether or not I am giving it gas?

not necessarily, your putting s load on the u-joints while accelerating not coasting. coasting their just going for a ride so you might not feel it unless it was really bad. i would check the u-joints first then go from there, could be an issue with the torque converter when its going into lock up

 

[shtbrwn86]

not necessarily, your putting s load on the u-joints while accelerating not coasting. coasting their just going for a ride so you might not feel it unless it was really bad. i would check the u-joints first then go from there, could be an issue with the torque converter when its going into lock up

Interesting. I guess my rears were so bad I could wiggle the whole shaft easily with my hands. The front ones feel tight but they are also the same age as the rears. I guess I’ll pull the shaft and see if it helps. Hope that’s the case and it’s not the torque converter.

Transmission drives and shifts great otherwise

 

[JunkCrzr89]

not necessarily, your putting s load on the u-joints while accelerating not coasting. coasting their just going for a ride so you might not feel it unless it was really bad. i would check the u-joints first then go from there, could be an issue with the torque converter when its going into lock up

x2.

 

[bigredmachine]

Interesting. I guess my rears were so bad I could wiggle the whole shaft easily with my hands. The front ones feel tight but they are also the same age as the rears. I guess I’ll pull the shaft and see if it helps. Hope that’s the case and it’s not the torque converter.

Transmission drives and shifts great otherwise

best way to check is one hand on the yolk and the other on the shaft and check for rotational play and both vertical and horizontal in the joint. another option is to unbolt the driveshaft from either the t-case or front diff and check for stiffness in the joints by rotating the shaft through a greater range of motion that what it would be subjected to when bolted up and in position.

 

[shtbrwn86]

best way to check is one hand on the yolk and the other on the shaft and check for rotational play and both vertical and horizontal in the joint. another option is to unbolt the driveshaft from either the t-case or front diff and check for stiffness in the joints by rotating the shaft through a greater range of motion that what it would be subjected to when bolted up and in position.

I’m probably going to pull the whole shaft and see if it helps. If I’m pulling one side i Might as well pull the whole thing right?

 

[bigredmachine]

I’m probably going to pull the whole shaft and see if it helps. If I’m pulling one side i Might as well pull the whole thing right?

if theres binding in one joint or the other youll feel it with one end of the shaft disconnected. if your thinking that your probably going to be doing the joints or one of the joints anyways then ya just remove it and save a step in the process.

you can also lock the cdl if you have the button, remove the front drive shaft and drive it again to see if the vibration goes away to isolate the shaft as the source of vibration

 

[shtbrwn86]

you can also lock the cdl if you have the button, remove the front drive shaft and drive it again to see if the vibration goes away to isolate the shaft as the source of vibration

That’s what I did with the rear shaft and it was immediately obvious the joints were the issue.

 

[shtbrwn86]

If I pull the front shaft should I just address the u-joints at that time? I mean they have 255k on them. If I am going to pull the shaft my thought is I might as well just replace the u-joints. Hell, I paid $170 for a shop to press new joints in the rear and an entire new front shaft from McGeorge is only $260.

Thoughts? Sometimes I feel like the "new OEM OCD" of this forum gets to me and I make poor financial decisions

 

[shtbrwn86]

I greased the front ujoints yesterday and while my first drive that night didn't seem much better, today the vibrations seemed to have improved.

Oh well, I still went and bought some stuff... 10% off and free shipping plus no tax. I don't feel like this is a bad price for all this stuff. Two new OEM u-joints are $150 before tax and shipping online.

 

[shtbrwn86]

Well I installed am new OEM front prop shaft and the vibrations are still there.

When I’m driving at 40 mph and it starts buzzing in the gas pedal I can turn overdrive off it goes away. I can turn it off and on over and over again and it comes back when I’m in OD and goes away when I turn OD back off. Really hoping it’s not the tranny!