Transmission Stumble & Clunk

[3800series2]

I've spent the last couple of days looking through forums and asking Google in many different phrasings but cannot find the exact issue I'm experiencing with my 2005 LeSabre with almost 130,000 miles.

Recently, if I decelerate/brake fast then immediately press the accelerator, the transmission seems like it hangs then slams into gear with a clunk. This will also happen if I am going through town leisurely, then accelerate abruptly, however this is more of a stumble than a clunk.

If it drive normally with light acceleration, like normal trips around town, stopping at stop signs for a few seconds or more, I don't experience any of the above and the trans shifts like butter in all gears.

The trans fluid has a few thousand miles on it. I suspect it may be a little overfilled from recent checks. I also am certain the front left trans/motor mount is smoked. The motor moves back a decent amount when revving in park and the mount looks bouncy. I plan to replace this in April when the weather is more favorable.

Thank you!

 

[BuickGirlFromMars]

I've spent the last couple of days looking through forums and asking Google in many different phrasings but cannot find the exact issue I'm experiencing with my 2005 LeSabre with almost 130,000 miles.

Recently, if I decelerate/brake fast then immediately press the accelerator, the transmission seems like it hangs then slams into gear with a clunk. This will also happen if I am going through town leisurely, then accelerate abruptly, however this is more of a stumble than a clunk.

If it drive normally with light acceleration, like normal trips around town, stopping at stop signs for a few seconds or more, I don't experience any of the above and the trans shifts like butter in all gears.

The trans fluid has a few thousand miles on it. I suspect it may be a little overfilled from recent checks. I also am certain the front left trans/motor mount is smoked. The motor moves back a decent amount when revving in park and the mount looks bouncy. I plan to replace this in April when the weather is more favorable.

Thank you!

Sounds like a classic transmission mount situation
There are 3 transmission mounts and 1 engine mount. the engine mount also could be at play. one is easy, one is less easy, one is moderately difficult, and one is much more difficult. The likely culprit is the easiest, the next two are the next likely culprits.
If you want to check to see if this is at play, open your hood then sit in the driver seat, and either boost up or stand up awkwardly or get a helper, and observe the engine while you shift to reverse, then neutral, then a drive range.
If you see the engine jerk and roll back-forth a lot, you likely need to replace something

The one is easy to inspect visually,. open hood and look down by the radiator fans by the ABS unit on the subframe, its a circular mount thats got a brakcet on it to the transmission.

The othere possibility is the subframe mounts (6) but less likely


IF These are not at play, youre likely looking at something damaged. based on mileage and age, im thinking its mounts. They are old and tired.

 

[BuickGirlFromMars]

If you decide to replace the mount, the aftermarket ones are known to fail soon after replacement and are not as good as the OEM.

The oem is 150$ but its very high quality https://www.amazon.com/Genuine-GM-25731375-Transmission-Mount/dp/B00GUGDASM

25731375​

 

[3800series2]

I was able to get the mount replaced today 😎

Fairly straight forward with a couple busted knuckles but got it done in an hour.

Now for a test drive to see if symptoms improved.

 

[silverbullet04]

Same issue with my 04 lesabre with 58k miles. Drives and shift perfect, especially after the transgo kit, new filter and fluid. If I do and quick stop at a stop sign and take off, I get a clunk. I also stall when putting the car into reverse at times, unless I come to a complete stop before putting it into reverse. Front round mount has been replaced, but issue is still there. Maybe my mount went bad again, it looks ok, but I'll have to have someone look at it while I power brake the car. If its not bad, I may replace the rear transmission mount. I heard that one isn't as easy as the front.

 

[3800series2]

Same issue with my 04 lesabre with 58k miles. Drives and shift perfect, especially after the transgo kit, new filter and fluid. If I do and quick stop at a stop sign and take off, I get a clunk. I also stall when putting the car into reverse at times, unless I come to a complete stop before putting it into reverse. Front round mount has been replaced, but issue is still there. Maybe my mount went bad again, it looks ok, but I'll have to have someone look at it while I power brake the car. If its not bad, I may replace the rear transmission mount. I heard that one isn't as easy as the front.

My issue improved a lot after the front mount replacement. I can drive as I normally do now instead of tiptoeing on the throttle. I can tell that the other 3 mounts may be a bit spongy but not completely gone yet. They are on my list but not an immediate concern.

The engine used to lift from the front mount about 2-3 inches. Now it's fractions of that. The mount wasn't completely separated but the bolts were floppy and the rubber looked like the grand canyon.

Next replacement is the front struts. I already have them, just need the time for replacement. I'm hoping the car will be super tight for a while then.

 

[BuickGirlFromMars]

Same issue with my 04 lesabre with 58k miles. Drives and shift perfect, especially after the transgo kit, new filter and fluid. If I do and quick stop at a stop sign and take off, I get a clunk. I also stall when putting the car into reverse at times, unless I come to a complete stop before putting it into reverse. Front round mount has been replaced, but issue is still there. Maybe my mount went bad again, it looks ok, but I'll have to have someone look at it while I power brake the car. If its not bad, I may replace the rear transmission mount. I heard that one isn't as easy as the front.

the stallin is a concern for me, id wonder about your torque converter or undiagnosed exhaust leaks (fueling corrections being far out, then stall maybe..?)

My issue improved a lot after the front mount replacement. I can drive as I normally do now instead of tiptoeing on the throttle. I can tell that the other 3 mounts may be a bit spongy but not completely gone yet. They are on my list but not an immediate concern.

The engine used to lift from the front mount about 2-3 inches. Now it's fractions of that. The mount wasn't completely separated but the bolts were floppy and the rubber looked like the grand canyon.

Next replacement is the front struts. I already have them, just need the time for replacement. I'm hoping the car will be super tight for a while then.

What mount did you use?

 

[silverbullet04]

the stallin is a concern for me, id wonder about your torque converter or undiagnosed exhaust leaks (fueling corrections being far out, then stall maybe..?)

What mount did you use?

I'm pretty sure i have an exhaust leak on my rear manifold, I smell raw exhaust sometimes. I just haven't really got into messing around with it.

 

[3800series2]

the stallin is a concern for me, id wonder about your torque converter or undiagnosed exhaust leaks (fueling corrections being far out, then stall maybe..?)

What mount did you use?

I went with a TRQ mount since I live paycheck to paycheck and only drive the car 6,000 miles a year. The job was so quick that if it fails again, it wouldn't be a big deal to change it again.

 

[silverbullet04]

I went with a TRQ mount since I live paycheck to paycheck and only drive the car 6,000 miles a year. The job was so quick that if it fails again, it wouldn't be a big deal to change it again.

I originally bought one from Amazon which was trash, it lasted like 3 months. The one in my car now is from advanced auto and had held up good so far after 6 months.

 

[BuickGirlFromMars]

I went with a TRQ mount since I live paycheck to paycheck and only drive the car 6,000 miles a year. The job was so quick that if it fails again, it wouldn't be a big deal to change it again.

if you wear yours out, pumping it full of windo weld urethane may extend its life(for an almost equal cost, meh)
My anchor one was kinda decent esp since i liked to lean into boost all the time

 

[3800series2]

if you wear yours out, pumping it full of windo weld urethane may extend its life(for an almost equal cost, meh)
My anchor one was kinda decent esp since i liked to lean into boost all the time

I'd love an L67. I bet that is pretty addicting. A Park Ave Ultra has always been on the wishlist. I've owned 5 vehicles with the L36.

 

[BuickGirlFromMars]

I'd love an L67. I bet that is pretty addicting. A Park Ave Ultra has always been on the wishlist. I've owned 5 vehicles with the L36.

a lesabre isnt too hard to swap 🙂

 

[02LTD2.0]

a lesabre isnt too hard to swap 🙂

Really? Seems like it would be quite a labor intensive task!!!

 

[3800series2]

Really? Seems like it would be quite a labor intensive task!!!

From all of the videos I've watched, it's not much harder than changing the intake manifold out for the m90, Different belt, injectors, and possibly a tune?

 

[HotZ28]

If you decide to replace the mount, the aftermarket ones are known to fail soon after replacement and are not as good as the OEM.

The oem is 150$ but its very high quality https://www.amazon.com/Genuine-GM-25731375-Transmission-Mount/dp/B00GUGDASM

25731375​

Genuine GM 25731375 (hydraulic) Transmission Mount ​

Country of Origin: CHINA !🤣

 

[HotZ28]

a lesabre isnt too hard to swap 🙂

Could you explain what "isnt too hard to swap"? Are you referring to the trans mount, or an L67 conversion? I see some others are also confused with your post! 😵

 

[BuickGirlFromMars]

From all of the videos I've watched, it's not much harder than changing the intake manifold out for the m90, Different belt, injectors, and possibly a tune?

I meant swapping to an L67, dont top swap a L36 (in my opinion) the liklihood of damaging the engine and making granola in your transmission differential are too great. Swapping in a trans/engine is what i meant, because the PCM can be taken from like-year swaps (2000-2002 lesabre, 1999-2002 park avenue for donor. or bonneville 2000-2002. grand prix should but not sure if the trans will have the right transmission bracket provision. )
2003-2005 bonneville/park avenue to 2003-2005 lesabre.
I suggest these ranges to get matching transmissions/PCMs/engine updates

One can make a 4t65e into the HD if you have the final drive (differential) and the output and the axle shaft shooting out of it , and then match the wheel bearing to the park avenue ultra of the same year and side to fit the splines.

Really? Seems like it would be quite a labor intensive task!!!

perspective

from my perspective it would not be too difficult

If i didnt starve my final drive and grenade my trans my l67 would be a very happy/eager swap to a lesabre. im getting back to work here soon and if the right deal came across id upgrade a base trans and then just use my engine
like if i found a car with a blown motor , kinda thing


But yes labor intensive over all indeed

 

[BuickGirlFromMars]

Could you explain what "isnt too hard to swap"? Are you referring to the trans mount, or an L67 conversion? I see some others are also confused with your post! 😵

trans mount isnt too bad in the front of the engine bay either
Just a piece of wood and a jack to lift up off the mount and some sockets /wrenches

 

[silverbullet04]

I wouldn't dare put a s/c in my lesabre with the made of thin glass transmission thats in it now. If I ever decide to upgrade the trans, then I would consider a s/c.