Random driveline clunk when accelerating from a full stop

[mikez71]

Just a thought, but now is a good time to replace the transmission mount as well. You will be surprised how compressed that thing gets. start out with all three fresh.

Ordered one!

along with a delco-remy starter. Old one feels like a bunch of loose parts shaking around..

 

[TahoeTX]

I had a similar issue recently and it was the drivers side motor mount. With the new one it feels solid from launch and bump went away. It’s supposed to be a tough install on these trucks so I paid a shop to do it.

 

[KC 2013 Tahoe]

So it turns out Easter weekend was a terrible weekend to try and do the replacement. Too many commitments AND terrible weather.
Fast forward one weekend and have to say this was the most difficult motor mount replacement (most bloody too) I've ever done. Seems a lot of the videos are on 2-wheel drive models. As my Tahoe is 4WD, there's the transfer case and front diff that prevent any kind of access to the mounts and the bolts from below... none. I've replaced lots of mounts over the years and have a really good selection of wobble sockets, extensions, air tools, etc and this was an extremely difficult job, thanks mostly to the mount's heat shield getting in the way of getting at the four bolts going into the engine block.

Day-1:
Started Saturday morning at 08:00 with the idea to replace both mounts, but figured I'd start with the broken driver's side first. Started with the 3 mount to frame bolts which weren't too bad. What is the most frustrating are the four mount-to-block bolts which are largely done by feel as you really can't see them, other than the lower rear one which can be accessed through the wheel well after removing the wheel. Did have to pull the steering shaft coupler, the exhaust heat shield and remove the #1 plug wire and temp sensor plug. I'm fortunate as there's no salt corrosion (Arizona) so all the 10mm shield bolts came out easily.

I have a portable table that I put against the fender or bumper as needed, and using it to work from along with fender covers and moving blankets to protect everything I had to lay across the fender or front radiator cover. As I worked at reaching and trying to get to the bolts with various sockets and extensions, I noticed blood dripping all over everything. Turns out there's a connector block for the ECU/Ignition between the radiator and engine. The corner of it was as sharp as a razor blade. I didn't even realize how badly I'd torn up my left arm until the damage was done. Cleaned up my arm and filed down the edge so that wouldn't happen again. Turns out all the other brittle plastic harness connectors and such that are all over the place to a lesser extent also did a great job of tearing up my arms even more.

Took me close to two hours to get the other three block to mount bolts extracted. One of them fell down on top of the transfer case/diff and despite rounds of compressed air and a ton of probing with my really good magnet tool it apparently landed into a black hole to oblivion. Sadly so far this has been the "easy" part. Next came jacking up the engine with a 4x6 that I put at the rear of the oil pan and raised the engine as far as it would go. Took me close to an hour to wiggle, twist, contort the old mount until it finally came out. It was indeed broken in half. Tried for almost as long to get the new one in there, but it just wouldn't go in. Between unbolting it to remove the heatshield and applying an uncomfortable amount of pressure to the jack, I was finally able to get it in, but after re-assembling and trying to get that frickin' bolt/tab thing into the hole in the frame I'd blown another 45 minutes before it finally pluncked into place. By now it's 2PM.

Re-attaching the 3 frame-to-mount bolts was easy compared to all I'd just done. Reinstalled, but left them loose so I could still position the mount if needed for the other 4 bolts. Slowly lowered the jack and thankfully the holes all lined up well (at least the 1 that I could see through the wheel well). At this point having been under to move the jack, I also found the front anti-sway bar end link bushings had worn/disintegrated away, so stopped and picked up two replacement kits at O'Reilly. R&R'd them and it was now 4:30pm, so called it a day.

Day-2:
After Saturday's escapades decided there was no way I was going to mess with the undamaged passenger side mount.
Went through my parts bins and found a single 15mm bolt to replace the missing one, but it had a smallish 13mm head and no flange, so off to the h/w store to get a very similar, hardened flange bolt (M10x1.5). The most difficult part this day was trying to get the bolts started in the holes without risking cross-threading. Regardless of what extensions, flex sockets, non flex sockets I was unable to get the non-OEM bolt to start threading-in to any of the 4 holes. The OEM bolts have a special tip to aide in getting them to start threading.
Spent an hour and a half doing this, laying across the radiator support, balancing myself on my rib cage while diving-in as far as I could to try and do this. Finally set that bolt aside and had much better luck with the other three OEM bolts, but still another two hours to get them in and tightened up. Left the Lower front empty, as I'm going to order an OEM bolt at the dealer today at lunchtime and install it next weekend.
Re-installed everything else, snugged-up the three mount-to-frame bolts and got her back together. Was finished up by 2:30pm.
Took her for a test ride and the driveline clunk is gone! If this new mount ever breaks I will find a shop, as at 64 I've pretty much reached the limit for doing this intense level of repair work.

Again - My thanks to everyone on the forum for your advice and guidance. You guys were spot-on!

Kevin

 

[89Suburban]

So it turns out Easter weekend was a terrible weekend to try and do the replacement. Too many commitments AND terrible weather.
Fast forward one weekend and have to say this was the most difficult motor mount replacement (most bloody too) I've ever done. Seems a lot of the videos are on 2-wheel drive models. As my Tahoe is 4WD, there's the transfer case and front diff that all prevent any kind of decent access to the mounts and the bolts from below. I've replaced lots of mounts over the years and have a really good selection of wobble sockets, extensions, air tools, etc and this was an extremely difficult job.

Day-1:
Started Saturday morning at 08:00 with the idea to replace both mounts, but figured I'd start with the broken driver's side first. Started with the 3 mount to frame bolts which weren't too bad. What is the most frustrating are the four mount-to-block bolts which are largely done by feel as you really can't see them, other than the lower rear one which can be accessed through the wheel well after removing the wheel. Did have to pull the steering shaft coupler, the exhaust heat shield and remove the #1 plug wire and temp sensor plug. I'm fortunate as there's no salt corrosion (Arizona) so all the 10mm shield bolts came out easily.

I have a portable table that I put against the fender or bumper as needed, and using it to work from along with fender covers and moving blankets to protect everything I had to lay across the fender or front radiator cover. As I worked at reaching and trying to get to the bolts with various sockets and extensions, I noticed blood dripping all over everything. Turns out there's a connector block for the ECU/Ignition between the radiator and engine. The corner of it was as sharp as a razor blade. I didn't even realize how badly I'd torn up my left arm until the damage was done. Cleaned up my arm and filed down the edge so that wouldn't happen again. Turns out all the other brittle plastic harness connectors and such that are all over the place to a lesser extent also did a great job of tearing up my arms even more.

Took me close to two hours to get the other three block to mount bolts extracted. One of them fell down on top of the transfer case/diff and despite rounds of compressed air and a ton of probing with my really good magnet tool it apparently landed into a black hole to oblivion. Sadly so far this has been the "easy" part. Next came jacking up the engine with a 4x6 that I put at the rear of the oil pan and raised the engine as far as it would go. Took me close to an hour to wiggle, twist, contort until it finally came out. It was indeed broken in half. Tried for almost as long to get the new one in there, but it just wouldn't go. Between unbolting it to remove the heatshield and applying an uncomfortable amount of pressure to the jack, I was finally able to get it in, but after re-assembling and trying to get that frickin' bolt/tab thing into the hole in the frame I'd blown another 45 minutes before it finally pluncked into place. By now it's 2PM.

Re-attaching the 3 frame to mount bolts was easy compared to all I'd just done. Reinstalled, but left them loose so I could still position the mount if needed for the other 4 bolts. Slowly lowered the jack and thankfully the holes all lined up well (at least the 1 that I could see through the wheel well). At this point having been under to move the jack, I also found the front anti-sway bar end link bushings had worn/disintegrated away, so stopped and picked up two replacement kits at O'Reilly. R&R'd them and it was now 4:30pm, so called it a day.

Day-2:
After Saturday's escapades decided there was no way I was going to mess with the undamaged passenger side mount.
Went through my parts bins and found a single 15mm bolt to replace the missing one, but it had a smallish 13mm head and no flange, so off to the h/w store to get a very similar, hardened flange bolt (M10x1.5). The most difficult part this day was trying to get the bolts started in the holes without risking cross-threading. Regardless of what extensions, flex sockets, non flex sockets I was unable to get the non-OEM bolt to start threading-in to any of the 4 holes. The OEM bolts have a special tip to aide in getting them to start threading. Spent an hour and a half doing this, laying across the radiator support, balancing myself on my rib cage while diving-in as far as I could to try and do this. Finally set that bolt aside and had much better luck with the other three OEM bolts, but still another two hours to get them in and tightened up. Left the Lower front empty, as I'm going to order an OEM bolt at the dealer today at lunchtime and install it next weekend.
Re-installed everything else, snugged-up the three mount-to-frame and got her back together. Was finished up by 2:30pm.
Took her for a test ride and the driveline clunk is gone! If this new mount ever breaks I will find a shop, as at 64 I've pretty much reached the limit for doing this intense level of repair work.

Again - My thanks to everyone on the forum for your advice and guidance. You guys were spot-on!

Kevin

I salute you sir.

 

[KC 2013 Tahoe]

Never again... at 64 your muscles don't recover from the soreness quite as quickly, not to mention a lot of bruising across my chest from laying across the radiator support. Lots of Tylenol helps considerably, as did a cold beer when I was done!

Update - 4/15/2024: Purchased the missing Mount-to-Block bolt ($6.25) from local dealer. Installed it this Saturday morning. Still needed to remove the steering shaft for access, but it went right in. Reinstalled the steering shaft and had it all done in an hour. Has been clunk-free the past week... almost like driving a completely different vehicle! Didn't realize how much I'd been feathering the gas to minimize the clunk. Anyhow, sticking a fork in this repair. Done!