98 k3500 7.4 speedometer bounce/ tcc lockup problems

[Loganshaw_6]

Howdy y'all,

I've got a 1998 GMC k3500 7.4 CCLB. Dash says 220k miles. Having a problem with my speedometer bouncing pretty bad past 65 mph. Depending on your speed determines how much it'll bounce sometimes up or down anywhere from 5 to 15 mph. While the needle bounces my scanner showed to match what the needle says. As all this happens my torque converter likes to lock and unlock in OD. I replaced the output speed sensor on the tail shaft housing on the transfer case with a Napa brand that I could get my hands on local and the problem seemed to get worse. Rather than starting at 65 mph it began at 55 mph. I cleaned the original sensor and popped it back in. Any recommendations on where I should start? Transmission was said to have been rebuilt about 15,000 mi ago but the transmission is slipping at wide open throttle in third gear. I've got a complete rebuild and transgo shift kit to go in just haven't found the time to actually pull the transmission and complete the task. Here's a video of the gauges.

 

[THEFERMANATOR]

I would be looking very hard at your transfer case for play in the output shaft. Problems like this are normally a bad sensor, metal on the sensor, or sebsor air gap us off because of wear in the slip yoke bushing or output bearing.

 

[Loganshaw_6]

I would be looking very hard at your transfer case for play in the output shaft. Problems like this are normally a bad sensor, metal on the sensor, or sebsor air gap us off because of wear in the slip yoke bushing or output bearing.

It doesn't appear that there is much play in the tail shaft I did however noticed there was a bit of metal on the sensor. I'm not too familiar with these transfer cases. There is a bushing in the tail shaft housing? Is there supposed to be transmission fluid in this housing from the transfer case. Mine does not have a slip yoke on it. I have a feeling that this is cause by the sensor since I replaced it and it only got worse. Is there a write-up on how to check the air gap or what I should be looking for when I remove the housing?

 

[FellowTraveler]

What t-case do you have? There should be a tag on it.

 

[Loganshaw_6]

What t-case do you have? There should be a tag on it.

Unfortunately there is no tag I have searched everywhere all my other trucks have had tags

 

[THEFERMANATOR]

Unfortunately there is no tag I have searched everywhere all my other trucks have had tags

1 tons normally got a borg warner t-case. I believe it's a bw4470 in a 98.

 

[Loganshaw_6]

1 tons normally got a borg warner t-case. I believe it's a bw4470 in a 98.

Yes I do know it is a bore corner for sure. I have since replaced the output speed sensor with an ACDelco sensor and now the speedometer starts to jump at about 75 mph Rather than starting at 60 mph. I'm also not having as many problems with the torque converter locking and unlocking but it does happen occasionally. When the needle does bounce It can go as far down as 60 mph.

 

[GM Guy]

Any updates on this?

I have a 95 K3500 6.5 5spd 4wd that is twitching, and I just replaced the speed sensor on the end of the transfer case. no change.

Im suspecting the VSSB, as this issue popped up all of a sudden, and I cant feel any wear in the rear bearing or bushing.

What are the failure signs of a dying or dead VSSB?