Transmission (?) bucking while under load at higher speed

[Jules]

Greeting all, it's been a while...

While driving at higher speeds (100 / 110 kph) and above, the vehicle has started to buck / hard shudder when accelerating under load. Most notable when I accelerate to pass or need to pull up steeper hills. I can avoid the bucking by feathering the accelerator to increasing speed over a longer time/distance or by manually downshifting to increase RPM and momentum. However, if I give it too much throttle, it will buck hard until I let up on the gas. City driving seems normal (with the exception noted below.)

I recently had a ton of front end/suspension work done. (BIG mistake!) I needed to have new struts and shocks (Sachs/Boge) along with upper strut mount bearings. Fair enough. I had some slop in the CV joints so I authorized the replacement. Bushings were getting worn, so lower control arms as well. The right axle shaft wouldn't release (needed to be cut in two) so I got a new right front hub as well. All in, parts, labor and taxes, $4000 later I drove home. OUCH!

Next day I noticed front end shudder on accelerate so I returned to the shop to have the defective CV joint axle shaft replaced (they did both.) The car just isn't the same as it was pre-CV joint replacement. Front end feels somewhat lumpy/bumpy, I had the tires rotated and balanced, reduced air pressure to 30 PSI but it's still not smooth like before. It seems to 'pulse' on accelerate and has developed a whine (driver's side front wheel) that starts at about 50 kph and increases in pitch as I increase speed. Above 90 kph, my ear cannot detect the higher pitch of the whine. I should have just replaced the struts & shocks and left everything else alone. And now, the high speed bucking/shudder under load.

I really don't know if the bucking is front end CV joint related or a transmission problem. It will go back to the shop for warranty front end fixing as soon as I can get it in. If the bucking is transmission related, I'm hoping upon hope it is just a matter of reloading the transmission software.

Any ideas, comments of glimmers of hope?

Cheers
Jules

[JRL]

It would help to post your mileage
What you did with the front end should have no effect on shifting but I would check the transmission fluid level first, they may have lost some doing the axles and did not top it back up. This transmission is VERY fluid level sensitive, either overfilled OR underfilled.

Motor needs to be VERY hot (run for at least 30 minutes) on a perfectly level ground.
Engine running and idling, check the fluid on the engine hot level mark.

[hoonk]

I had some slop in the CV joints so I authorized the replacement.

Next day I noticed front end shudder on accelerate so I returned to the shop to have the defective CV joint axle shaft replaced

hard shudder when accelerating under load. Most notable when I accelerate to pass

The car just isn't the same as it was pre-CV joint replacement.

You are describing bad (stiff or cheap or poorly manufactured or worn out) cv joints (and yes, I understand they are "new")

What brand of axles are being put in your car? I have installed new aftermarket axles (at customers request) that vibrated worse than the old axles that were being replaced.

[mapper]

Also, double check for engine codes. Sounds like misfires to me. Mine acted similarly when the fuel pressure sensor went bad. Though mine was obvious engine stumbling. You seem convinced yours is different but your initial "bucking" comments suggests more than a CV, to me anyway.

[Jules]

The vehicle has 185,000 km, I'm the second owner, purchased with 60,000 km. The replacement CV joints / axle shafts are OEM Volvo replacement parts. Mechanic said it wasn't his first time experiencing defective axle shafts and didn't hesitate to replace the bad ones.

Note: On a quick drive into town this morning, I got the bucking at lower speeds when hard on the throttle (not super hard, just a little aggressive.)

[Jules]

Definitely not an engine hesitation or misfire, it's a hard, rapid bucking or shaking.

[MacNoob]

Sounds just like what my old Saab 9000 used to do when there was trouble with the turbo control system. Did they maybe leave loose or misposition some turbo control vacuum lines? It used to overboost/cut BANG like someone had briefly punched the brake under hard acceleration.

[hoonk]

The replacement CV joints / axle shafts are OEM Volvo replacement parts.

To me OEM just means that manufacturer makes some parts for a car company, but does not necessarily supply Volvo with their original equipment axles. Volvo axles are sold (at the dealer) as a remanufactured part with a core charge. If you had to cut the right axle in half to get it out, Volvo would not have accepted that as a rebuildable core.

A LF axle lists (in the US) for $582.26 #8252038, RF axle is $657.79 #8252053

Mechanic said it wasn't his first time experiencing defective axle shafts and didn't hesitate to replace the bad ones.

I have not hesitated to warranty new bad aftermarket axles either - but have never had a problem with axles purchased from a Volvo dealer.

[Jules]

OK hoonk, you've got me there. I was told they were Volvo parts from Volvo, not aftermarket, and I assumed, being Volvo parts, they were new and not rebuilt. I'm going to follow up on this to get the bottom of it. Thanks for clarifying this for me.

That said, is there any such thing as reloading / refreshing the transmission software? Is there any such thing as transmission software? With all the on-board computers I'm kind of clutching at straws looking for a (transmission) fix.

Cheers,
Jules

[Jules]

Nope, never touched the turbo controls. The shudder occurs when under load (not necessarily 'hard' acceleration.) I'm thinking the transmission can't decide if it should downshift or not, and rapidly switches from 5th to 4th to 5th to 4th, or 4th to 3rd to 4th to 3rd, until I let off the throttle. Just clutching at straws here.

Cheers
Jules