Motor Mount Height Question

[GoldenGorilla]

I get that, but height of lift might not mean their TC to DC angle is as extreme.

I mathed this, which kind of illustrates what I think happened. Assuming pinion angle is 0 degrees in both, the TC to DC angle becomes more pronounced with a belly tuck (without further lifting the motor to retain the same angle of drivetrain):

View attachment 710724

So physics-wise I have to think that if the pinion angle is the same, and the angle of the TC to DC must be the pain point. The only way to "fix" that angle would be to drop the TC to negate the belly lift (I know, money pissed away) or lift the motor up more to bring the angle back to where it began.

But yeah, I plan to also reach out to Tom's. You would think the "double" u joint at the TC would not allow this issue, but eh...

Your drawing is conceptually accurate. There are some 1/2" aluminum spacers on Summit that you can use for an in-between option. A 2 pack is like $6 I think.

https://www.summitracing.com/parts/AAF-ALL18766

 

[Hasselblad]

Your understanding of what raising and lowering the engine and transmission do to the ujoints is correct.

In fact in my illustration I have the pinion at 0 degrees, and if one were to rotate that to 1-2 degrees down, it would make that TC/DC angle even more pronounced.

 

[jjvw]

In fact in my illustration I have the pinion at 0 degrees, and if one were to rotate that to 1-2 degrees down, it would make that TC/DC angle even more pronounced.

At the end of the day, you want the platform that reduces the operating angles as much as is feasible and you want a pinion angle that does not result in vibrations. There may be some compromises to perfection between front and rear operating angles, front and rear pinion angles, and front caster.

A few things about my setup to wrestle with....

With a 4" spring and raised belly, the driveshafts are operating at about a 7" lift.

The rear has a center limiting strap to prevent the start of ujoint binding just before full shock extension on 12" shocks.

In addition to the front and rear being beyond their normal operating angles, they spin well above their maximum operating rpm.

I think I'm on my third rear driveshaft with many tens of thousands of miles on each one. There are no driveshaft vibrations and I accept that I will not be getting 100k miles before having to rebuilt or replace a driveshaft.

On the note, I tend to replace every other one because I am slightly paranoid about a worn centering pin taking out the transmission.

 

[Hasselblad]

At the end of the day, you want the platform that reduces the operating angles as much as is feasible and you want a pinion angle that does not result in vibrations. There may be some compromises to perfection between front and rear operating angles, front and rear pinion angles, and front caster.

Roger that.
I mean I still intend to pull the shaft and inspect the joints, but I am confident that dropping the belly back down will help to decrease that TC/DC angle. I'd do a higher MM, but again the existing one already gave me a headache pinching those wires between tub and trans and $$$$ to have someone get in there to repair them.

Actually that has me considering doing BOTH now that I think about it for 3 seconds as the spacers of the skid would free up the space to avoid pinch potential. Dropping the skid an inch and perhaps raising the motor another 1/2" could only help, right?




right?

 

[jjvw]

Roger that.
I mean I still intend to pull the shaft and inspect the joints, but I am confident that dropping the belly back down will help to decrease that TC/DC angle. I'd do a higher MM, but again the existing one already gave me a headache pinching those wires between tub and trans and $$$$ to have someone get in there to repair them.

Actually that has me considering doing BOTH now that I think about it for 3 seconds as the spacers of the skid would free up the space to avoid pinch potential. Dropping the skid an inch and perhaps raising the motor another 1/2" could only help, right?




right?

I would not do more than a 1" motor mount lift. There is a reason taller ones are difficult to find.

 

[That'll Buff]

@jjvw how do people with 4" of lift and the high up tucks like savvy or UCF make them work typically. I bring up the savvy specifically because I know it's only available for later models which are more likely to have the 241 and it is (from what I've read) the tightest tuck. Enough people have done them that I feel like there would be a common enough solution or at least check that people do to make it work. Maybe I'm wrong in thinking that. If for the 231 the SS SYE is recommended (lengthening the rear ds and helping the angle), then is a potential solution for the 241 to instead stretch the rear axle? I can't remember what you did, been a while since I went through your thread.

 

[jjvw]

@jjvw how do people with 4" of lift and the high up tucks like savvy or UCF make them work typically. I bring up the savvy specifically because I know it's only available for later models which are more likely to have the 241 and it is (from what I've read) the tightest tuck. Enough people have done them that I feel like there would be a common enough solution or at least check that people do to make it work. Maybe I'm wrong in thinking that. If for the 231 the SS SYE is recommended (lengthening the rear ds and helping the angle), then is a potential solution for the 241 to instead stretch the rear axle? I can't remember what you did, been a while since I went through your thread.

They make it work with a double cardan rear driveshaft and adjustable control arms.

I do not know if Savvy raises the t-case output higher than others. Or if it makes it's ground clearance in the middle section more effectively than others. Maybe a little of both.

One thing I do know is that on a TJ with a high belly and an outboard with 12" travel shocks on a 241 runs the very real risk of driveshaft bind at full shock extension because of the short driveshaft. That is why mine has a center limiting strap. A wheelbase stretch would also correct that. But the strap is much easier and has no meaningful consequences.

 

[GoldenGorilla]

In fact in my illustration I have the pinion at 0 degrees, and if one were to rotate that to 1-2 degrees down, it would make that TC/DC angle even more pronounced.

The rear DS angles are steeper and an issue frequently, but the front DS is a double edge sword to balance vibrations and caster. If you raise the motor, the front DS angles become steeper which introduce vibration there.

 

[Hasselblad]

The rear DS angles are steeper and an issue frequently, but the front DS is a double edge sword to balance vibrations and caster. If you raise the motor, the front DS angles become steeper which introduce vibration there.

I also have to think that even without the subject of vibrations, there would be less torque with an angle than a straight line in general, and more stress on that angle point even with a double U joint there. At least the front DS is hella longer than the rear.

I feel good about dropping the skid/DL, just wish the spacers would be getting here sooner than Sunday.