Adjusting driveshaft angles with transmission mount

[Guest Anonymous]

Just had an idea... Would it be possible to adjust/fine tune drivetrain alignment (at the transmission end at least) by altering the design or mounting of the JTR transmission mount? You'd be able to adjust transmission output shaft angle, F driveshaft pinion angle, as well as R driveshaft pinion angle. This leaves us with with differential centerline angle, which can be adjusted by shimming/cutting at its mounts. This way, you can approach ideal driveline phasing and alignment, and all but eliminate drivetrain vibrations. Am I right about this or am I smoking crack? Are there any disadvantages to doing this, are there any adverse effects I haven't taken into account? I'd love to hear your thoughts on this as we may be on to something here...

[John Scott]

No, your on track here. Trouble is with some trans. placements the tail end needs to go up sometimes causing tunnel clearance problems. If you have the room to play, then try it. I've used shims under the mounts on my automatic with great results, in fact I should do the same with my T56. The new urethane mount really transmits the vibes. My engine transmission is low enough to raise the tailshaft another 1-1/2". I found a 1/4" raise was good for the auto.

JS

[pparaska]

If you're smoking crack, it hasn't affected your creative side yet .

 

I had to do just that (raise the rear of the tranny) to alleviate my u-joint angle problems. Check out my site if interested (Drivetrain mods). The one height I didn't mess with was the front diff mount. But Simon Z Build and others have made custom front crossmembers for the diff that allow that.

[pparaska]

Omar, putting the spacer in between the frame rails and the engine crossmember and lowering the trans tail 1/2" also will lower the engine and give more clearance.

 

The problem that can create is that it lowers the centerline of the transmission yoke even farther below the centerline of the pinion. This makes the u-joint angles even larger. That limits how far you can lower the engine/trans in a JTR conversion with the diff in the OE location, even with the aft end raised.

 

Remember, the centerlines of the transmission yoke and the diff pinion need to be parallel AND close enough so as to not cause large u-joint angles. Satisfying just one of these two rules is not sufficient. The parallel bit gets you equal u-joint angles (a good thing) and minimizing the u-joint angles comes from minimizing the perpendicular separation of the centerlines (although a small distance is desired, since a u-joint angle of at least 1 degree is desirable to fend off fretting).

 

HTH,

[Guest Anonymous]

Good point, I forgot that the tranny centerline is actually lower than the diff centerline. That's what you get for not working on the car much

 

If you could give me some kind of measurements

on the following I'd really appreciate it.

 

- delta height between tranny centerline and diff centerline using 1/2" subframe spacers, stock JTR tranny mount, and stock diff mounting

 

- tranny centerline pitch angle with the previous setup

- diff centerline pitch angle with the previous setup.

 

With the aforementioned numbers, I'll be able to experiment (on paper) with different layouts and such, but my engine will probably be another 1/4-1/2" or so closer to the firewall than yours, so I'm gonna have to adjust for that.

 

Ideally, I would have the tranny pitch at + 3-4 degrees and the diff pitch at - 3-4 degrees which, according to your spreadsheet, should minimize vibrations and make logistics easier (ease, fitment, clearance, C.G., etc) Whether or not I can do that is another matter, hopefully your numbers (and expertise will shed some light on the situation.

 

As an aside, I'm thinking of making the tranny mount out of aluminum due to its lighter weight and easier machinability. Do you think its lower fatigue strength might be a problem here or should I not be worried? What about strength, it should be strong enough right? Maybe I can make it out of 1/2" stock instead of 3/8".. I dunno

 

 

P.S. What's fretting?

[pparaska]

Fretting, that's when the wife or girlfriend starts to bit... Oh, THAT kind of fretting! It's when the wear pattern, fatigue and failure occur due to small oscilating motion between parts. If the angle of the u-joint is too small, this can occur and fail the joint prematurely.

 

I MAY be able to come up with some measurements, but it's not easy as I've tried before.

 

It's easier to just experiment with engine placement in many cases, as the measurements of the vertical offset of the centerlines are difficult to measure and prone to errors. I did make some measurements and I'll try to dig them up. I did basically the same thing you're attempting and drew it out on some big sheets of paper. I probably still have them.

[Miles]

I just finished installing a SBC and 89 World Class T5 trans into my son's 72 240Z. We used the Motor sports Auto (MSA) conversion motor and transmission mounts. The tranny mount was designed for the 700R auto trans, but it worked just fine with the t5. Using the Camaro bell housing the shifter comes right up the stock hole in the tunnel with a little trimming on the drivers side. The advantage of the MSA tranny mount is that it fits up in the tranny tunnel and you can move it up and down within a range of several inches to fine tune the angle of the ouput shaft. I just put an angle finder on the end of the output shaft while my son jacked the tranny up until I got the angle I wanted. We then bolted the mount in place. The differential is off horizontal by 2.5 deg. We have road tested the car and the drive train is smooth as silk with no vibrations. MSA does not put the engine as low or as far back as the JTR mounts, but this is fine for a daily driver. It depends on how you are going to use the car. Overall I would rate the installation of the SBC and T5 using the MSA mounts fairly easy. The hardest part was converting from a R100 diff to the R200 diff. You can get lots of help doing your V8 conversion through the folks here in the HybridZ forum. Cheers

[Guest Anonymous]

Pete, I've already gone over your entire site like 20 times so far, and I've found it to be EXTREMELY helpful. Thanks a lot for everything,you're an inspiration to all of us

 

I would be using a T5 which is relatively compact, so I should have some leeway with fitment, si? And Pete, why can't we use the 1/2" front crossmember spacers in conjunction with a 1/2" (+/- however much you need to get proper alignment) spacer at the JTR tranny mount to maintain the proper angle? This way you get the benefits of lowering the C of G a bit, and more significantly, gaining clearance everywhere. Between tranny and tunnel, dizzy and hood latch, and air cleaner & hood so you can fit more spacers or a taller air filter for more power. Granted we would be lowering the roll center by a bit, but that can be fixed with strut spacers right? Again, is there anything I've overlooked or haven't taken into account? Like steering shaft clearance maybe? Anything else? I still haven't really started work on my car, I'm just making observations and using common sense. Again, I'd love to hear your thoughts about this... thanks

[pparaska]

Thanks Miles,

 

That 2.5 degrees jives with my notes. Of course, I don't think my car was level when I measured.

 

I found that for my install, (with the rear of the diff raised about 1/2" with cutdown urethane Mustache bar bushings and the top large washer there removed) that the centerline of my tranny output shaft was about 2" above the pinion centerline at the pinion flange, and about 3" above it at the tranny yoke. The angle between the centerlines was something like 1.5 degrees, before I raised the rear of the tranny.

 

I like the sound of the MSA trans mount how it allows you to change the height of the tranny mount so easily!