F8X M3/M4 CF Drive shaft mod

[discoelk]

Driveshaft speed is directly correlated to wheel speed. Engine speed and gear do not matter. The shaft (heh) sounds out of balance or as someone else mentioned, the flanges are not welded true (misalignment issue).

[Radekxpl]

Originally posted by EthanolTurbo View Post
Food for thought: driveshaft is vibration free up to 8k RPM in 1st, 2nd, 3rd gear. It only vibrated at 80 mph in 6th gear and it was around 3k RPM the other night. Will test further. If it was the driveshaft wouldn't it vibrate at high RPM in any gear?

Negative. Driveshaft directly correlates to wheel speed. Engine is geared up through the transmission(really the other way around but that's not important). I.e. 8000rpm/4.227 in first, 8000rpm/2.528 in second.

60mph will always be a set driveshaft rpm, regardless of engine speed. This would only change if you had a different final drive ratio like a 4.10.

That is correct however using this https://www.drive-lines.com/php10/dlrpm.php driveline calculator its only true to certain speed vs gear your in at the time
for example: using 275/35/18 tire size in this example 25.6 tire diameter
M3 traveling in 3rd gear at 80mph which would be somewhere near 7600 engine rpm the driveshaft should be around spinning at 1754 RPM
where
if you traveling at 80mph in 6th gear driveshaft spinning at 871 rpm so roughly half the speed when it was in 3rd gear at the same speed, something doesn't add up here as EthanolTurbo mentioned it wasn't vibrating at 8k in 3rd gear which in that gear it definitely was spinning faster than in 6th going roughly the same speed.
Even if your doing 60mph in 3rd gear it’s still is spinning faster at 1295 then in 6th at 80mph at 871

Given this information either there’s more testing need to be done to confirm thats it’s only vibrating at high speeds in lower gear or maybe person testing can’t detect vibrating in higher gears since the engine is at redline and there’s more engine noise nvh associated at that time as well compared to calm cruising in 6th or there’s something else going on there 🤔

[mrgizmo04]

Food for thought: driveshaft is vibration free up to 8k RPM in 1st, 2nd, 3rd gear. It only vibrated at 80 mph in 6th gear and it was around 3k RPM the other night. Will test further. If it was the driveshaft wouldn't it vibrate at high RPM in any gear?

I was thinking this as well.

Sounds like the shop that did the balancing also thought the same thing, thus there is a problem at higher mph...

Sent from my SM-S911U1 using Tapatalk

[heinzboehmer]

Negative. Driveshaft directly correlates to wheel speed. Engine is geared up through the transmission(really the other way around but that's not important). I.e. 8000rpm/4.227 in first, 8000rpm/2.528 in second.

60mph will always be a set driveshaft rpm, regardless of engine speed. This would only change if you had a different final drive ratio like a 4.10.

Yes this. Driveshaft rpm is directly proportional to wheel rpm not engine rpm.

[discoelk]

Food for thought: driveshaft is vibration free up to 8k RPM in 1st, 2nd, 3rd gear. It only vibrated at 80 mph in 6th gear and it was around 3k RPM the other night. Will test further. If it was the driveshaft wouldn't it vibrate at high RPM in any gear?

Negative. Driveshaft directly correlates to wheel speed. Engine is geared up through the transmission(really the other way around but that's not important). I.e. 8000rpm/4.227 in first, 8000rpm/2.528 in second.

60mph will always be a set driveshaft rpm, regardless of engine speed. This would only change if you had a different final drive ratio like a 4.10.

[simonnim]

I checked with my local shop, they said no problem. But, I'll have to exchange it for another since the side of mines looks slightly damaged. They said about the same cost as the other invoice placed here a few pages back. I don't want to release shop but apparently according to the shop that I take my car to claimed they're the 'best' around here.

I'll test and see how the results are.

[Projecte46m3]

Food for thought: driveshaft is vibration free up to 8k RPM in 1st, 2nd, 3rd gear. It only vibrated at 80 mph in 6th gear and it was around 3k RPM the other night. Will test further. If it was the driveshaft wouldn't it vibrate at high RPM in any gear?

I was thinking this as well.

[EthanolTurbo]

Food for thought: driveshaft is vibration free up to 8k RPM in 1st, 2nd, 3rd gear. It only vibrated at 80 mph in 6th gear and it was around 3k RPM the other night. Will test further. If it was the driveshaft wouldn't it vibrate at high RPM in any gear?

[0-60motorsports]

They said a 3-4 day turnaround. I have to work on sending them the specifics to get pricing. A rebuild used to go for $600-ish plus $150 to modify plus core charge. They don't have to replace the u-joints or center bearing. If I had to take a wild guess...$500 to weld the end on and balance? Its not hard...they usually turn a modify and rebuild around the same day.

Alright buddy I'll give you a call soon.

[bigjae46]

Thanks for the detailed info here regarding balancing your shaft LOL.

All kidding aside I'll call you in a day or two to decide as I know a few places I can get the DS from too. It'll all come down to budget for me. Thanks brother

They said a 3-4 day turnaround. I have to work on sending them the specifics to get pricing. A rebuild used to go for $600-ish plus $150 to modify plus core charge. They don't have to replace the u-joints or center bearing. If I had to take a wild guess...$500 to weld the end on and balance? Its not hard...they usually turn a modify and rebuild around the same day.

[liam821]

Looks like you can still buy these new from BMW for about $750 or so. Search for 26109882181.

[0-60motorsports]

I might have a solution through Powertrain Industries.

I believe that there are only a couple of rebuilders that can dynamically balance a driveshaft. Which makes sense because the equipment is large, expensive, and specific to balancing long shafts (lol), likely would need to balance thousands of shafts of break even. Think two large precision lathes end to end. I believe Powertrain Industries has a proprietary setup. Or at least that what I can remember from the sales pitch they gave me years ago.

I have an account with them and have facilitated over 30 rebuilds, some include modified driveshafts for 5 speed conversions. I have not had one complaint of a vibration issue that wasn't there before. I was going to go this route if 0-60 Motorsports wanted to enlist my assistance. I think this would be a straightforward modification for them. Likely can get it done at the same or lower cost that what I've seen here.

I will say Powertrain Industries uses non-OE parts. The issue, for me, has been the CV boot and the center bearing that they use. I did supply an OEM part for a couple of rebuilds. Then god help you if you move the CV joint at all...massive amounts of grease will come out. They overstuff the CV boot with grease. The driveshaft itself has been vibration free 6 years later and lots of track time.

Thanks for the detailed info here regarding balancing your shaft LOL.

All kidding aside I'll call you in a day or two to decide as I know a few places I can get the DS from too. It'll all come down to budget for me. Thanks brother

[bigjae46]

I might have a solution through Powertrain Industries.

I believe that there are only a couple of rebuilders that can dynamically balance a driveshaft. Which makes sense because the equipment is large, expensive, and specific to balancing long shafts (lol), likely would need to balance thousands of shafts of break even. Think two large precision lathes end to end. I believe Powertrain Industries has a proprietary setup. Or at least that what I can remember from the sales pitch they gave me years ago.

I have an account with them and have facilitated over 30 rebuilds, some include modified driveshafts for 5 speed conversions. I have not had one complaint of a vibration issue that wasn't there before. I was going to go this route if 0-60 Motorsports wanted to enlist my assistance. I think this would be a straightforward modification for them. Likely can get it done at the same or lower cost that what I've seen here.

I will say Powertrain Industries uses non-OE parts. The issue, for me, has been the CV boot and the center bearing that they use. I did supply an OEM part for a couple of rebuilds. Then god help you if you move the CV joint at all...massive amounts of grease will come out. They overstuff the CV boot with grease. The driveshaft itself has been vibration free 6 years later and lots of track time.

[Slideways]

That's unfortunate. Hopefully Altaran has better luck with the one he built.

[EthanolTurbo]

If the shaft is too long or too short, even by a few millimeters, your CV could be bottomed out. Worth asking Kevin how much free travel there was in the CV on install.

Also, if the flange at the transmission wasn’t welded very orthogonal, or the CV coaxial, it could balance well but still vibrate, depending on how they fixtured it for balancing.

These questions and the ones Epsilon posed are why I have to discontinue effort on this project. The juice isn't worth the squeeze at this point being this deep in.

Edit: the more I think about this, the more I think they botched the job. People have done this mod on E9x M3s with no vibration issues. These driveshafts were mostly pulled off running cars. It sounds like even one thing can set the balance off on these things so who's to say they took that into account?