1 Piece Driveshaft Fitment Issues

[Shenker]

Hey guys,

First post here, loooong time lurker however. Ill introduce myself/car in another post later. Purchased my E30 325i coupe after about 10 years of searching. Doing a turbo M20 street car build with an occasional track day. Focusing on suspension/brake/driveline for now, but I have a spare M20 on the stand waiting for a build. Shooting for 400whp.

After a ton of searching i'm looking for some advice. Basically, what I've got going on here is my OEM D/S was shot, I took it to a respected and highly recommended (by my local E30 community) driveline shop to have the shaft rebuilt. Given the goals of my project I was recommended I move to a 1 piece driveshaft, after plenty of research we did some math and measuring, and I now have a 1 piece 3" tube steel shaft + aluminum guibo + some big boy (replaceable ;) ) u-joints and it is designed to hold well over the power figure I will ever put through it at critical speeds higher than it should ever see. Anyway... I was putting it in tonight for a test fit, as expected with any custom bits I've got some tweaks to make.

The shaft bolts up perfectly on the transmission end, on the diff end however the larger diameter shaft is contacting the "saddle" of the fuel tank ever so slightly. Right at the point before it goes through the subframe hole.
It is worth noting that I have the jack stands on the subframe, so the bushings are compressed as much as they ever will be, once the weight is off the subframe id expect another ~1/4" of clearance. The bushings are still OEM rubber so i'm potentially losing some clearance there. However I still think id like a little more margin of safety there. I have Condor 12mm solid riser bushings/diff spacers waiting to be installed (this winters project, although I was hoping to move the car). I have seen several LS/M60 swap guys run 3" shafts with this same issue.

The long and the short is, the way I see it, I have a few potential solutions. Which direction should I head first?
-Pull the subframe, replace with the condor bushings, hope it fixes it. The riser bushings will compound my issue, but the included diff spacers will likely put it right back where it is now... unless the OEM rubbers are THAT sloppy. I have RTAB/Diff bushings to go in as well. Seems like the obvious choice, but again, I would really like to move the car first.
-Diff spacers. Something i'm unfamiliar with, but I see some of the V8 guys do this... will everything still bolt up with JUST spacers?
-Clearance the fuel tank saddle. Something id like to avoid if possible. However I came across THIS article of exactly this. I would likely attempt this with the tank in the car still.
-Abandon the 1 piece, I was an idiot for trying something and it backfired lol. Ill need a new OEM D/S + output flange as mine has had some machining done to eliminate the centering bushing.

Any input is appreciated, I will grab some photos tomorrow. Thanks guys, happy to finally join the forum!

[hasa]

Something does not match here... One piece driveshaft, guibo, multiple U-joints.

Generally speaking (in theory) replacing guibo-style driveline with double U-joints+ single shaft require adjustment of crankshaft angle and pinion angle to match. It's not just a direct swap.

Also you must calculate the single piece driveshaft critical speed to ensure that you are not facing the self destruction speed when doing some top speed runs (if you do those).

Pictures of your parts might answer to many questions or doubts!

[Shenker]

Something does not match here... One piece driveshaft, guibo, multiple U-joints.

Generally speaking (in theory) replacing guibo-style driveline with double U-joints+ single shaft require adjustment of crankshaft angle and pinion angle to match. It's not just a direct swap.

Also you must calculate the single piece driveshaft critical speed to ensure that you are not facing the self destruction speed when doing some top speed runs (if you do those).

Pictures of your parts might answer to many questions or doubts!

I will get some photos today of the shafts/fitment. Essentially this is what I have, but from a local shop. On the front end, the guibo has been replaced with an aluminum "puck" between the G260 flange and D/S flange, on the back end the flange mates directly to the differential. https://driveshaftshop.com/product/b...ly-driveshaft/
From what I understand, I shouldn't have to adjust the pinion angles? Similar to how most 1 piece shafts on solid rear axle applications work (trucks/SRA cars)? The shaft angle on those is constantly changing with suspension travel (and usually quite a bit higher). Maybe I am mistaken, this car is hands down the furthest I have dug into custom parts/work for power. So Ill be forthright in saying I have a lot to learn.
Critical speeds have already been figured by the shop to be in excess of what the car should ever hit.

[Shenker]

The rusty strap looking bit above the shaft in this photo is the area that is being contacted by the shaft.





As far as critical speed goes, a couple of quick calcs gave me some hard numbers for you guys. The tube length is around 46". It is 58 3/8" flange to flange.
This yeilds a critical speed of 93XX RPM with a mild steel shaft. (I believe this is chromly)
9300 X 0.81 (5th ratio) = 7533RPM engine speed.
If this car ever sees 7500RPM in 5th, I've done something terribly, terribly wrong.

[ForcedFirebird]

At 7000 rpm in 5th, your drive shaft will be going about 8600rpm. The final drive of the transmission is .81:1, so if the engine is going 7000, then .81:7000=1:8641 - the drive shaft is spinning 19% higher than the engine.

I've put some serious power through stock e30 shafts (500+whp), the only reason shops push a one piece is they have a machine that can balance them. Not many places have the 3 finger yoke and spline adapters for the machines. The shaft halves are balanced independently, and can be moved from one car to another.

I haven't found many people with BMW's that like the one piece once they are in. As hasa mentioned, the pinion and crank angles in a BMW are not conclusive to one piece. Also, not to mention, if you look at ANY make or manufacturer that utilizes an interdependent rear suspension always has a two piece drive shaft and Giubo's (flex disc). From Corvette to Camaro to Cobra Mustang, to Mercedes, to Nissan, to Toyota, etc etc.

One piece is more suited to a live rear axle, the splines at the front of the shaft move in/out of the transmission tails haft to allow the arc. If you have a one piece and your chassis, and your drive train moves in any way (chassis flex), it causes severe vibration since the length is rigid. Only time I have seen it work well was when using a yoke on the transmission side - otherwise the rigid shaft will not deflect and the vibrations will move to the car.

Not even the fancy, expensive carbon shafts avoid vibration issues. After warning my friend about them in his e46m3 race car, he dropped $1500+ on one, just to go back to stock.

Reputable new aftermarket e30 shafts are about $600. To contrast GKN OE replacement half shafts are ~$300, and the only ones we will use.

[Shenker]

At 7000 rpm in 5th, your drive shaft will be going about 8600rpm. The final drive of the transmission is .81:1, so if the engine is going 7000, then .81:7000=1:8641 - the drive shaft is spinning 19% higher than the engine.

I've put some serious power through stock e30 shafts (500+whp), the only reason shops push a one piece is they have a machine that can balance them. Not many places have the 3 finger yoke and spline adapters for the machines. The shaft halves are balanced independently, and can be moved from one car to another.

I haven't found many people with BMW's that like the one piece once they are in. As hasa mentioned, the pinion and crank angles in a BMW are not conclusive to one piece. Also, not to mention, if you look at ANY make or manufacturer that utilizes an interdependent rear suspension always has a two piece drive shaft and Giubo's (flex disc). From Corvette to Camaro to Cobra Mustang, to Mercedes, to Nissan, to Toyota, etc etc.

One piece is more suited to a live rear axle, the splines at the front of the shaft move in/out of the transmission tails haft to allow the arc. If you have a one piece and your chassis, and your drive train moves in any way (chassis flex), it causes severe vibration since the length is rigid. Only time I have seen it work well was when using a yoke on the transmission side - otherwise the rigid shaft will not deflect and the vibrations will move to the car.

Not even the fancy, expensive carbon shafts avoid vibration issues. After warning my friend about them in his e46m3 race car, he dropped $1500+ on one, just to go back to stock.

Reputable new aftermarket e30 shafts are about $600. To contrast GKN OE replacement half shafts are ~$300, and the only ones we will use.

See above photos, I do have a slip yoke in this shaft to account for chassis flex. I'm plenty safe on the critical speed as per calcs above.

I was ill informed about the capabilities of the factory shafts, I was under the impression that much over 300whp would risk eating the ujoints. I have come across a new Dorman shaft that actually has servicable ujoints. I think what I am going to do is order one of those, and revisit this shaft once I pull and refresh the subframe, and after the engine comes out later.

Thanks for the input guys! I believe ill be able to make it work at some point, but Id like the car back on the ground for now as its been on jack stands for a year and I need to move it..

[ForcedFirebird]

Ah, see the yoke now (Good call!) - I'm just getting old (eyes are going), and the pic is the size of my thumb on a 32" monitor.

I have a small shop that caters to e30's. We have built countless of them over 300hp, the stock equipment is extremely overbuilt. The ring and pinion are almost the same size in Camaro of the same generation. One car we built was over 7yr ago, makes 300+ whp, still on it's original 150k+ mile unit.

[ForcedFirebird]

For future reference, e30 equivalent to a domestic universal is a 1310...

How much power can a 1310 U Joint handle?
According to Spicer, the 1310 joint is rated at 400 lb-ft of continuous torque (down the track) and 800 lb-ft of short-term torque (launch at the line).