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Discussion Starter · #1 · (Edited)
For those of you that have a drill press: (even better, if you have lathe)
Goal to see where the engine center is relative to the transmission.
Make a tool as below. I used oak, as it is better than pine. Aluminum would be even better.
Parts: 3/4" (19mm) drill bit
3/8: drill bit
1.5" x 1.5" (2x2) block
.38 spl laser boresight.
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The oak piece, I used came in a 3 foot length. The drill table must be locked, and wood (or metal) work-piece must be clamped against drill table. This is to minimize concentricity issues.
Make 3/4" (19mm) counterbore about 3/4" deep. Then make 3/8" thru hole, without unclamping part or moving table, that means table height is set as close to chuck as possible and still allow tool change.

I want to park some information.

 

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Discussion Starter · #2 · (Edited)
I don't know how to post a video. This is a screen grab of above center locator tool result. The projected transmission axis on my '81 GTV6 lands below the engine crankshaft centerline and slightly to the right. The video I made, shows that the circle made by the laser, while spinning the transmission yoke, is about 1/2 of the Alfa engine flywheel - driveshaft centering feature (I believe it is 26mm, so 13mm circle ). So the tool I made is fairly straight.
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The transmission is on new unmodified Milano front mounts (from Centerline) and new rear mount bushing.
Engine is on used front mounts, rear mount is new.
Body damage for my '81 GTV6 is unknown, but doors don't close very easily (requires a good slam), but I believe fairly straight. Previous owner riveted in a new driver-side floor pan. Super hokey.
Also, car is on jack-stands.

Anyways, if any body would like to contribute to answering this question:
Just where does the transmission input axis point to? My answer, is that it's not to the engine center but shown in image above.
 

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If you search the archives of this forum, you might find numerous mentions of the later Milano trans side mounts having an extra plate welded underneath which would serve to slightly lower the nose of the transmission. I am not sure if this is still the case, as I did not seem to have this issue with my GTV6 (my vibration issue, even after all new giubos/mounts and adjusting every which way, was caused by the driveshaft being slightly bent, balanced it using hose clamps, smooth as silk!).

You could try jacking up the nose of the trans by a small amount and see if this value equals the thickness of the extra plate of the Milano mounts; if so, cutting those off might solve your issue.
 

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Discussion Starter · #4 ·
There are other shims, between the subframe and the chassis, a thicker shim in those spots would lower the nose of the transmission. I installed what came with the car, I assumed it was stock.

I think the extra thickness at the transmission mounts serves to lift the front of the transmission, hence I was expecting the laser to point on the high side, since it has been mentioned that the extra plates do not belong on the GTV-6. It looks like I need more shims. It may be low for a reason, and that reason could be that, under a torque load, the nose of the transmission will rise. So I will try jacking the front of the transmission as you suggested.

For reference, if engine is at half load (cruising?? this is actually too much?) of 75 ft-lbs in 5th gear (0.78), and 4:1 rear axle ratio, reaction torque is 240 ft-lbs) Not sure how I would apply that, but a jack on the transmission front will do.

Meanwhile, for those who have the capability, it would be nice to know what Alfa intended for the axis of the transmission input shaft.

I think my laser is pointing about 3/4" to 1" low, and about 1/8" to 1/4" to the right.
 

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Haha, you are correct, I own and work on too many different types of cars and forgot the orientation of the Alfa transaxle mounts---they mount atop the forward crossmember, so any extra thickness would raise the nose of the transaxle.

You can experiment with washers above said cross member in an attempt to get the front and rear flanges to line up, and I hope that works out! I struck out trying to find a driveshaft shop to balance the Alfa transaxle driveshaft circa 2018 (in Southern California of all places), and that has probably gotten worse since 2020, hence the hose clamps after trying everything else (which worked out quite well). Please let us know how it works out.
 

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Discussion Starter · #7 ·
I wouldn't use the term alignment just jet.
The engine and transmission are where the mounts place them. The rear engine mount and rear transmission mount are centered as best I can, visually, since Alfa have not provided guidance marks for these bushings. Bumping the rear mount (to the left a bit) may help to bring the transmission input axis in line with the engine axis (left-right only, not up-down).

Also, I forgot to mention:
Regarding rear engine mount: The left side mounting stud (which is longer), actually is not fully installed. I need the tunnel mounting points to move to the right about a 1/16" so I can get the mounting bolts in. The reason I say left tunnel mount to the right, rather than right tunnel mount to the left, is due to half-a$$ driverside (US driverside) non original sheetmetal floorpan. I can slot (or enlarge) the mount hole to get it to fit.

Also, front radiator left side does have evidence of having been hammered straight. so car had a front impact. Left fender, front ledge (ahead of hood) probably was replaced, as they look okay.
 

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I occasionally ruminate about making a giubo from billet aluminum, or a hardwood, to be able to attach the front section of the propeller shaft to see where it lines-up at the center support. This would be all that you need for a non-transaxle model. For the transaxle cars, a solid center giubo would be required. A solid mount (for testing purposes only) to replace the center support might help too. Like @pangolin , I too believe that this misalignment is the cause of driveline vibration, and premature propeller shaft component failure. Anyone out there with a mill and a lathe, up for a project? @classicalfas??
 

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We tried the laser to set up the first series 275GTB engine / transaxle with the one piece drive shaft and solid couplers. It was good for ball-park, but soon as you drove the car, chassis flex told you some more shims were needed. These cars had 4 point engine mounts and 3 point transaxle, so engine up-down was matched to the transaxle tail housing hanger, then left and right correction done with the front 2 transaxle mounts. Once you figured it out, by trial, they ran smooth until mounts settled, but by then either couplers or shaft splines required a refresh. Ferrari changed this system 2ce more before the 4 cam cars with a torque tube connecting the bell housing and transaxle.
 
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Much heavier, but by then Ferrari was making other racers. Only the earliest 275's had the open shaft.
 

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Discussion Starter · #12 ·
Yes, it seems all of the modern solutions use torque tubes. Also I include Mazda's "PPF' bracing of the diff to the engine an equivalent to the torque tube, of course Mazda doesn't require the ends to be concentric.

I think Alfa intended for the 'static' axis of the transaxle input shaft to intersect below the engine axis, to allow for the torque reaction at the transmission. I wonder by how much?
Also, was the right offset, intentional, like to compensate for engine motion? Or possible body tweaking that I may unfortunately have.
 

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Between post #6 (Sportiva: “Have you included the engine offset in your static alignment?” and yours, above, pangolin, there’s an interesting twist (LOL) to the tale in there somewhere, it seems.
Do tell.
 

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Discussion Starter · #14 ·
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Center bearing installed. Red dot is not axis center, but pretty dang close. For scale reference, nuts on propeller shaft is for 17mm socket.
Locus of laser is about 1-2 mm below and to the right of center.

At this time, I have no plans to try to straighten any of this. If other info shows up (meaning somebody does this on a straight car) and provides a reference to target.

Also, I did jack up at front of transmission, and it basically didn't budge. I think that transmission snubber may need to be adjusted, and maybe that's what I need to check for contact. I thought I did this, but maybe not.

And for those of you who have installed the driveshaft in a non-removable crossmember car.....***. Somewhere I read (on this forum) of somebody doing this without disassembling the driveshaft. How is this possible? I have lowered the transmission as much as possible with a jack on the dedion. Rear mount was not removed. Anyways...this is rhetorical, as I split the driveshaft.
 

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Many years ago I put the driveshaft assy onto my 75 GT all in one piece. It was VERY difficult, and took about 6 hours to get it in.
A couple of years ago I put the driveshaft assy onto my 86 GTV6; the 2 halves were together and the rear donut was on. But it was a lot easier on that car, as the 86 has the removable crossmember and the GTV6s have the pinch bolt, so I mounted the front donut and pinch bolt assy onto the flywheel first, and then slid the splined end of the driveshaft into the pinch bolt.
 

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Discussion Starter · #16 ·
about 6 hours
This is good info, if you did it again, would it be 3hrs? I didn't disconnect the shocks, should I have?
Anyways. it's enough info, that I will always split the driveshaft when installing/removing. I tried to get it in as one piece, but gave up, and andylarry mentioned center bearing, so I thought I should get that info, so I split the driveshaft.
 

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Discussion Starter · #17 ·
Transmission snubber is bent. Snubber was in contact with a rubber pad I glued to the transmission flat spot.
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Laser spot on center bearing with no snubber in place. Dot is in center divot. Locus of points is about 1-2 mm below, and a bit to the right.
 

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View attachment 1746611
Center bearing installed. Red dot is not axis center, but pretty dang close. For scale reference, nuts on propeller shaft is for 17mm socket.
Locus of laser is about 1-2 mm below and to the right of center.

At this time, I have no plans to try to straighten any of this. If other info shows up (meaning somebody does this on a straight car) and provides a reference to target.

Also, I did jack up at front of transmission, and it basically didn't budge. I think that transmission snubber may need to be adjusted, and maybe that's what I need to check for contact. I thought I did this, but maybe not.

And for those of you who have installed the driveshaft in a non-removable crossmember car.....***. Somewhere I read (on this forum) of somebody doing this without disassembling the driveshaft. How is this possible? I have lowered the transmission as much as possible with a jack on the dedion. Rear mount was not removed. Anyways...this is rhetorical, as I split the driveshaft.
Correct!! It was me, on a 1973 Alfetta! If you remove the front donut, the front "fork" of the driveshaft will pass thru the crossmember without disturbing the gear lever housing.
Other suggestion!! Mark precisely the position of the central removable fork vs splines!! This is of incredibile importance to preserve balance!! Far more important than marking front and rear halves reciprocal position: if you do not mark this last you have 33% probability to assemble them correctly. This means that in maximum 3 attempts you will find the correct reciprocal position. If you do not mark the splines, since these are very many, you will never find the correct reciprocal position again and will need to rebalance your driveshaft
 
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