So I’ve got a 13 SI sedan. I’ve had an issue with a front end shudder under acceleration. I’ve checked (and had others double check) suspension components (she’s lowered a bit), wheels, tires, replaced axles, intermediate shaft bearing…

this shudder is on accel and decel, between 14&25mph though somewhat variable on where the shudder stops but seems to pick back up over 50mph or so. It’s intermittent but almost always there. If I accelerate rather slowly and smoothly it sometimes won’t happen, like whatever is “off balance” doesn’t catch or corrects well. It feels like a damn axle but I’ve replaced both sides twice before the intermediate shaft bearing. I’m limited with transmission knowledge so I’m wondering by if this could be the carrier bearings in my diff? Shifts relatively smoothly (classic notchiness). I feel a little…popcorn? type rumble under the vehicle when driving. Haven’t gotten it up in the air running to steth the tranny but I guess I should. Any ideas on that info so far?

i mean I guess it could be as easy as warped rotors but I just need some brainstorming.

 

Factory replacements on the half shafts? China junk is well, junk.

Also check your upper and lower engine torque mounts.

 

They are aftermarket shafts 😬 which I know can cause issues.

I’ll check the mounts for sure as well. I’m unsure of what the tolerances should be. I get a lot of bounce and can move the engine with my hand. I’d assume if one is bad I’d have less give? That’s crossing in to unfamiliar territory for me but I’m learning.

 

Engine mounts get soggy with age. I suspect your torque mounts might be contributing allowing the engine to move around creating a less than ideal CV joint angle. Plus the uncontrolled engine movement can certainly feel like a shutter at low throttle inputs.

Those torque mounts have to counter 1000+ lbs of force when you smash on the loud pedal in 1st gear and get traction. Stock Si is capable of 2,643 lb-ft of torque at the axle. So keep that in mind when looking at those torque mounts and how floppy they are.

 

tried to upload a video but couldn’t so here’s the link.

here is one of my actual mounts. Idk what the discoloration is but I don’t see any cracks? This can be pulled up on…

 

Second picture, upper torque mount is the one just out of sight under that AC line. The dog bone shaped aluminum bit.

The lower torque mount is bolted to the oil pan and goes to the sub frame. Also a dog bone shape.

 

oh yeah I’ve got replacements on the way. I just wasn’t sure if I needed to replace this one as well. I appreciate all the insight for sure!!!

 

Next question I have is this. Had a k-tuned s/cmc installed. Failed in 3mos. Changed out for stock and it looks like the fluid is fouled AGAIN. What other favors can foul the fluid so quickly?! No leaks.