Huge clunk when driving
daarrve
10-19-2010, 07:19 PM
Today when going home I had the tow/haul button on, rpm's were around 2200, I disengaged the tow/haul and when the rpm's returned to "normal" there was a big clunk, the whole truck shook. I did the same procedure twice more to see if it would do it again, and it did, only one more time though, then it was smooth, I am thinking this in not normal. My truck is a 2000 Silverado, someone has suggested that this is the transmission having problems. What does it sound like to you guys, at the time my speed was about 90 kph which is about 55 mph. It was kinda sudden and made me nervous but as I stated it did smooth out and didnt do it for the rest of the trip home.
Blue Bowtie
10-19-2010, 09:02 PM
Operating in Tow/Haul mode increases transmission line pressure via the PCS (solenoid in the pump body) to assure positive engagement of clutches and the band to prevent slippage and damage. Tow/Haul mode also changes the shift points (in engine RPM versus road speed). to maintain lower gears longer and hold off the TCC lockup longer.
Operating out of Tow/Haul mode generally results in lower line pressure and lower RPM shift points.
Changing out of Tow/Haul at that road speed could be causing the TCC to lockup as soon as Tow/Haul is off and line pressure is still high. This could result in a harsh lockup. That could eventually damage the carbon clutch disc in the torque converter as well as the input drum in the trans. It could have also been the point at which OD engaged from 3rd range, and this could also have occurred at higher line pressure. The combination of shifting to lockup and changing to OD simultaneously could be causing a very harsh shift out of direct and into over running. The front planetary set and sprag clutch could be taking a beating from this, as well as the relatively fragile reaction sun shell hub and rear planetary input gear.
I would consult the owner's manual and avoid switching into and out of Tow/Haul if possible. If you are towing, keep it active. If you are driving normally with a normal load, keep it off.
It may also be good to drop the pan, fluid, and filter and inspect the fluid and pan interior for signs of debris or glitter. That would be a bad sign, but catching it sooner than later can save a lot of cash.
Operating out of Tow/Haul mode generally results in lower line pressure and lower RPM shift points.
Changing out of Tow/Haul at that road speed could be causing the TCC to lockup as soon as Tow/Haul is off and line pressure is still high. This could result in a harsh lockup. That could eventually damage the carbon clutch disc in the torque converter as well as the input drum in the trans. It could have also been the point at which OD engaged from 3rd range, and this could also have occurred at higher line pressure. The combination of shifting to lockup and changing to OD simultaneously could be causing a very harsh shift out of direct and into over running. The front planetary set and sprag clutch could be taking a beating from this, as well as the relatively fragile reaction sun shell hub and rear planetary input gear.
I would consult the owner's manual and avoid switching into and out of Tow/Haul if possible. If you are towing, keep it active. If you are driving normally with a normal load, keep it off.
It may also be good to drop the pan, fluid, and filter and inspect the fluid and pan interior for signs of debris or glitter. That would be a bad sign, but catching it sooner than later can save a lot of cash.
daarrve
10-20-2010, 09:23 AM
This morning as I was going to work I didn't put the truck in tow/haul mode, I didn't even use the cruise control and it did the same thing but as everything warmed up the clunk disappeared. My route to work if hilly and there are 2 major hills so it gets a good workout. In town as I was pulling away from a stop when the tranny changed gear it shifted hard again then went away, shifting ok once again. I am wondering if the transmission pressure control solenoid valve might be bad, can anyone help? Thank you for your input Blue Bowtie.
j cAT
10-20-2010, 05:42 PM
This morning as I was going to work I didn't put the truck in tow/haul mode, I didn't even use the cruise control and it did the same thing but as everything warmed up the clunk disappeared. My route to work if hilly and there are 2 major hills so it gets a good workout. In town as I was pulling away from a stop when the tranny changed gear it shifted hard again then went away, shifting ok once again. I am wondering if the transmission pressure control solenoid valve might be bad, can anyone help? Thank you for your input Blue Bowtie.
you do have a problem with your transmission. you description to me appears to be possibly worn tranny componets or bad fluid.
what fluid are you using ? If dexron III replace the fluid and filter. make sure the fluid level is correct on level ground when the transmission is hot.
switching in and out of tow mode will not cause your problem as you described..2000 silverado LT 4X4 ...
hard shifting is usually from slippage so slight you will not feel it.
PCM will sense this and command max line pressure..
In tow mode the line pressure is increased but should not cause it to be max which is very harsh. under engine loading the shift points are extended for less transmission heat generated..
When you do tow/haul anything do not use 4th gear ..this is how to destroy these trannys very quickly.......
clunking is most likely U joints or the transfercase bushing / yoke sticking ..could be rear diff pinion issues/wear as well........
you do have a problem with your transmission. you description to me appears to be possibly worn tranny componets or bad fluid.
what fluid are you using ? If dexron III replace the fluid and filter. make sure the fluid level is correct on level ground when the transmission is hot.
switching in and out of tow mode will not cause your problem as you described..2000 silverado LT 4X4 ...
hard shifting is usually from slippage so slight you will not feel it.
PCM will sense this and command max line pressure..
In tow mode the line pressure is increased but should not cause it to be max which is very harsh. under engine loading the shift points are extended for less transmission heat generated..
When you do tow/haul anything do not use 4th gear ..this is how to destroy these trannys very quickly.......
clunking is most likely U joints or the transfercase bushing / yoke sticking ..could be rear diff pinion issues/wear as well........
muff34
10-22-2010, 10:34 AM
[quote=j cAT
When you do tow/haul anything do not use 4th gear ..this is how to destroy these trannys very quickly.......
4th gear?? Are You referring to OD??
When you do tow/haul anything do not use 4th gear ..this is how to destroy these trannys very quickly.......
4th gear?? Are You referring to OD??
j cAT
10-22-2010, 11:36 AM
[quote=j cAT
When you do tow/haul anything do not use 4th gear ..this is how to destroy these trannys very quickly.......
4th gear?? Are You referring to OD??
when towing/hauling heavy load you are to use 3rd gear only.
also using the tow mode selection.
If you do not use 3rd gear the transmission overheats and then it rapidly wears out the componets due to fluid being damaged from excessive heat ....
this automatic transmission has 4 speeds correct ?
If you have been using OD/4th gear to tow haul this is why you have this problem. you may very well need much more than a solenoid.
When you do tow/haul anything do not use 4th gear ..this is how to destroy these trannys very quickly.......
4th gear?? Are You referring to OD??
when towing/hauling heavy load you are to use 3rd gear only.
also using the tow mode selection.
If you do not use 3rd gear the transmission overheats and then it rapidly wears out the componets due to fluid being damaged from excessive heat ....
this automatic transmission has 4 speeds correct ?
If you have been using OD/4th gear to tow haul this is why you have this problem. you may very well need much more than a solenoid.
Automotive Network, Inc., Copyright ©2026