Gearbox oil / Propshaft connection questions

[sf4018]

I have some (dumb) questions about the propshaft/gearbox connection point...I remember when putting it together if there was oil in the gearbox it would pour out of the opening here the end of the prop shaft goes into. Why is the end of the gearbox open like that so oil can flow to the prop shaft? Is there any expected gearbox oil loss to the prop shaft? The reason I ask is I changed out the gearbox oil today and it seemed less full than it should have been and there are oil splatters on the universal joints of the prop shaft and at the back near the diff (the diff is fine), so it seems some oil was coming out somewhere. Thanks!

[MV8]

The slip yoke rides on a long bushing in the tail housing that requires splash like the rest of the box. With an irs, it doesn't need any since there is no plunging with suspension movement.

 

The tailhousing has a press-in seal around the driveshaft slip yoke. You probably just need to tap in a new seal.

 

If you ever have a speed based (versus rpm) drive line vibration, the bushing can be damaged. The vibe could be the driveshaft joint angles could be setup wrong (pinion angle versus trans output shaft angle) or the drive shaft needs to be trued and balanced by a driveshaft machine shop. I usually take a shaft to a heavy truck shop where they do that type of work all the time. New joints, tubing, and balancing is typically about $200 for same day service.

[sf4018]

Thanks so much @MV8,I did indeed have speed dependent vibration at close to top speed (124mph+), it comes on suddenly then when releasing the throttle it went away suddenly too. Don’t know if the stress log the vibration is causing the oil to come out faster maybe, dunno.

Is there anything to check while it’s all intact before taking it all apart?

[MV8]

I'd make sure the trans vent is clear so pressure can't build and force oil out somewhere else, clean everything, refill, run hard briefly and recheck so you can catch it starting to leak and find the source.

 

[sf4018]

The left and right driveshafts look a bit eccentric...

https://youtube.com/shorts/hZJro1IIAIU?feature=share

https://youtube.com/shorts/B1a8R7ZMDuo?feature=share

...but maybe spinning at lower RPM compared to the center driveshaft it's not that important, dunno, maybe that's normal.

 

Center looks ok at low speeds anyways, not sure if this is of any use...

https://youtube.com/shorts/bpUyGbaYsuU?feature=share

 

Time for a complete disassembly!

 

[MV8]

I think you have some damaged tripods inside the inner cv cups of the halfshafts but the diff is probably fine. Have you been bottoming out or getting airborne in the back end? Either way it is possible to damage the inners within the cups if the axles were designed slightly too long under some alignment specs and excess vertical travel. If that's the case you could just limit travel a little.

 

The clamps and boots can be reused if your careful taking it apart to inspect.

[sf4018]

2 hours ago, MV8 said:

I think you have some damaged tripods inside the inner cv cups of the halfshafts but the diff is probably fine. Have you been bottoming out or getting airborne in the back end? Either way it is possible to damage the inners within the cups if the axles were designed slightly too long under some alignment specs and excess vertical travel. If that's the case you could just limit travel a little.

 

The clamps and boots can be reused if your careful taking it apart to inspect.

Yes probably hopped over the curb at turn 3 at Road Atlanta a few too many times last weekend. I’ll add that to the list!

[jimmylukeii]

15 minutes ago, sf4018 said:

Yes probably hopped over the curb at turn 3 at Road Atlanta a few too many times last weekend. I’ll add that to the list!

Heading there Sunday!  If you hear back sometime, let me know.  I would love to see another 7 on the track around here.

 

Ever tried Talladega Gran Prix Raceway?  I would like to give it a shot.

 

[sf4018]

1 hour ago, jimmylukeii said:

Heading there Sunday!  If you hear back sometime, let me know.  I would love to see another 7 on the track around here.

 

Ever tried Talladega Gran Prix Raceway?  I would like to give it a shot.

 

I’m planning on seeing if we can get a track day for sevens to get together in the spring next year. Once the track day people release their schedules next month I’ll make a list of possible dates and locations.

[sf4018]

On 10/21/2022 at 5:24 AM, MV8 said:

The slip yoke rides on a long bushing in the tail housing that requires splash like the rest of the box. With an irs, it doesn't need any since there is no plunging with suspension movement.

 

The tailhousing has a press-in seal around the driveshaft slip yoke. You probably just need to tap in a new seal.

 

If you ever have a speed based (versus rpm) drive line vibration, the bushing can be damaged. The vibe could be the driveshaft joint angles could be setup wrong (pinion angle versus trans output shaft angle) or the drive shaft needs to be trued and balanced by a driveshaft machine shop. I usually take a shaft to a heavy truck shop where they do that type of work all the time. New joints, tubing, and balancing is typically about $200 for same day service.

One of the U joints on the driveshaft is very stiff. Here’s a theory about the gearbox oil loss: the drivetrain vibration at high speeds is caused by the bad u joint, the vibration from this causes the yoke to vibrate inside the gearbox, which encourages oil flow out past the yoke.

Does this sound plausible?

[MV8]

If it's stiff, I'm thinking dry and rusty inside which can cause it to orbit versus spin true, so yes. Since it is such a pain to access, you might consider having it checked for true and balanced at a machine shop or driveline shop. It may never have been straight to begin with. I'm guessing it was never greased since it is a 2018 model.  

[IamScotticus]

people want to assume that a prop shaft is correct as new from a manufacturer,  but balance is something to always check if you haven't verified it yourself.