The first "Hawk-Rod" resurrection, Roadkill style

Builderguy

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I agree! I would not get much done either if these were her work clothes.

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HawkRod

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OK. Time to tackle two things I am not thrilled with doing.
(1) Fix my tach again! I think the wire came loose again from the back, and the only way to get to it is to remove the instrument cluster. But the radio will pose a problem so I likely have to pull that too. Then drop the steering column and pull the instrument cluster for one &%$#@! wire! Damn it!

(2) Attempt to fix my driveline vibration. I shimmed the back of the transmission and the vibration was reduced, but not eliminated. But when I tried to shim it some more, the Gear Vendors Overdrive hit the transmission tunnel. Crap. So now I will cut out the transmission tunnel and try to shim the transmission some more. If this fixes the vibration, I will weld up and repair the transmission tunnel with a smile. If I doesn't, then I will be one peeved dude! We'll see!

OK, so time to dig into the interior.
20220403_154000.jpg


The console had to come out, as well as both seats, and the rear carpet had to be pulled back to get access to the tunnel.

Once I got stuff removed, I cut out the tunnel as needed. I then put extra shims in the transmission. I will throw the drivers seat in and test the car without welding up anything.
20220404_095631.jpg


But, next up I will go for the tach. This means it is unlikely I will have time to test drive the car today - most likely it will be Thursday or Friday (I am also finishing up taxes for the year too, so that will dig into my available time...)
 

qkcuda

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Hawk, if the combined drivetrain angle is causing the vibration issue, couldn't that have been adjusted at the rear axle?
 

HawkRod

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Hawk, if the combined drivetrain angle is causing the vibration issue, couldn't that have been adjusted at the rear axle?
Maybe. First of all, I am no expert with this. I have had this vibration for 30 years since I quasi-restored the car. I have tried almost everything to address it.
  • Rebuilt and rebalanced the engine (now twice - even a completely different engine).
  • Two completely different transmissions.
  • Balanced the drive shaft (now twice because it has been shortened for the Gear Vendor Overdrive)
  • Tried completely different rim and tire combo on the car
  • AND I have tried to shim the rear end up and down to no avail.
When I finally shimmed the rear of the transmission, this was the FIRST time I have ever felt any change with the vibration. So I am continuing to go after that area.

Am I doing it right? I really don't know - I am hoping for a good result... :lowdown:
 

zyzzyx

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So, have you narrowed the vibration down to the driveshaft or the transmission?
One thing you can try that is not scientific, is duct tape a washer onto the driveshaft
at different positions thirty degrees apart and test drive it and see if that helps. Do
this at the front and the back. This way you can get a better idea and it doesn't cost
you anything. Put a GoPro under the car and see what the driveline does. Try and
get a video of the movement of the driveshaft. Wow! Wish I were there to help!
Just cause the driveshaft guy says it's balanced doesn't mean squat!
 

HawkRod

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So, have you narrowed the vibration down to the driveshaft or the transmission?
One thing you can try that is not scientific, is duct tape a washer onto the driveshaft
at different positions thirty degrees apart and test drive it and see if that helps. Do
this at the front and the back. This way you can get a better idea and it doesn't cost
you anything. Put a GoPro under the car and see what the driveline does. Try and
get a video of the movement of the driveshaft. Wow! Wish I were there to help!
Just cause the driveshaft guy says it's balanced doesn't mean squat!
Agree. However, the driveshaft was recently shortened and balanced by a separate outfit with no change. It COULD still be the driveshaft but it seems unlikely.

When I test the car, if I still have vibrations I will try the washer trick and see what happens. As far as seeing it, I'll be able to see the top of the O/D unit while driving until I button it up!
 
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hyde-park

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HawkRod, As noted there isn't much left to change or redo. However if you are using any kind of polyurethane mount/bushing anywhere this might be something to look into. Motor mounts, trans mount, torsion bar crossmember mount, k-frame bushings, etc. Any of these could transfer a vibration instead of dampening it like the factory rubber bushing material will.
 

HawkRod

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Got the tach working again - it was a dirty fuse connection at the fuse block. Proof that one should ALWAYS look for the simple stuff first when diagnosing stuff. :poke:

I wish I could do something simple for this vibration issue! But I have some results of the additional shim in the tranny mount:
I drove the car and could actually lay my hand on the Gear Vendor's Overdrive since I now have this big, nasty hole cut in my transmission tunnel. The shim again changed the nature of the vibration. Before it was a harmonic that presented itself at speeds above 55 MPH. It was there regardless of engine speed or gear the transmission was in.
Now the harmonic seems mostly to be gone, but I now have a vibration when accelerating - even moderately. But the one great thing about the hole in the tunnel is I swear I could feel that the vibration was NOT in the tranny, but at the back of the car.

The ONLY thing that has not been changed on this car is the rear. Time to pull this and check this carefully, especially the yoke. I have rusty, crappy old 2.76 (?) open rear in my basement. I may throw that in and see what happens, although I am not sure that the old 2.76 is in very good shape.

I've GOT to find this issue soon - less than 4 weeks until departure on the trip! :eek::eek::eek:
 

zyzzyx

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Jeez! A gear vendor O.D. AND a 2:76? 80mi/gal!
Yeah, check that rear yoke. Shake it pull on it.
At least you're narrowing it down.
 

HawkRod

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Well, crap. That didn't work... ...you know what they say about when you assume...

So my rear differential is a 742 case based 3.55 sure grip. The spare junker open differential 2.76 is also a 742 based case. What can possibly go wrong with that swap?

So I pulled the axles fist. By the way, the old Timken bearings looked good. They were perhaps a little bit dry, but rolled smoothly and with no apparent issues. Then out came the 3.55 sure grip chunk:
20220407_220514.jpg


By the way, I have never rebuilt a rear, so I can't say I really know how to diagnose them. But I didn't see any funny wear on the teeth, and the yoke seemed tight. There didn't seem to be too much play in it either. I was kind of hoping for some "smoking gun" to present itself but no such luck.

So in went the 2.76 open diff beater chunk. I just got it in there and decided at that point to verify the yoke before I tightened it down and installed the axles.
Nope. No go. My 3.55 yoke takes a 1 1/8" U-joint. The 2.76 yoke takes a smaller 1 1/16" U-joint. :mad: I had assumed that since both were 742 cases that the yokes, and in turn, the U-joints, would be the same. Live and learn. :rolleyes:

Now, I know they make U-joints that can connect this to my driveshaft with 1.125" caps on one end and 1.063" caps on the other. But that is another $40, plus the work to swap out the U-joint, all for maybe 10 miles of testing? :poke:

I'm not sure what to do next. I'm not inclined to buy and swap out the U-joint too for a 1 hour test. Maybe I'm just better off trying to swap the 3.55 chunk with the 3.55 chunk in my 70? But I'd rather not tear into that car since it runs and drives perfectly... :(
 

qkcuda

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Its going to be cheaper and easier in the long run to just buy the u-joint Hawk. You can always resell it when you are done.
 

zyzzyx

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The same things happen to me too! Don't think for a minute that you're the only one.
Like a mouse eating an elephant, One bite at a time! Chomp Chomp Chomp.
 

HawkRod

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I've decided I'm going to abandon the installation of the old, beater, 2.76 differential.
First of all, the history of that rear is completely unknown. It even has a tight spot when turning the yoke, due to some kind of issue with the pinion gear. So if there is an issue, is that rear also a problem? I won't know.
Second, I have to deal with getting a U-joint in order to get it installed.

Instead, I am readying a donor patient, my 1970 Road Runner. It is a 100% working car. I KNOW that the rear does not cause any vibrations and works well in the car. It is also a 3.55 sure grip rear, so it is identical to what the 73 has. This will allow me to confidently determine if the 73 rear has issues causing the vibration.

I only have one lift, and the 73 is on it. So I will have to squirm around like a worm to get the 70 differential out. It's tight quarters, but it is what it is. Normally I park the 'Vette here and reserve the larger 3rd bay for the B bodies.
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Now I just have to hope the *&^$#@! rain stops; we're drowning here in the NE. :cursin: My yard needs to be cut, but is a complete swamp. The constant rain also doesn't help when I need to move cars outside and/or work with the garage door open, as I will need to do to pull the rear out of the 70.
 

qkcuda

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Been there, done that Hawk. If you use your floor jack and leave the pinion snubber on wrap a chain around it you can usually pull it straight out.
 

mpgmike

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The tight spot is on a pumpkin he was thinking about swapping in, not the one that's been in.
 

HawkRod

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Tight spot, eh? Me thinks you just answered your question.

The tight spot is on a pumpkin he was thinking about swapping in, not the one that's been in.

Correct. The tight spot is on the crusty old 2.76 differential that has been laying in the dust for god knows how many years. The 3.55 chunk out of the 73 Road Runner actually looks decent to my eyes, and seems to operate smoothly. However, in order to leave no stone unturned, I am swapping it out just to verify.
 

HawkRod

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So the donor patient is now resting comfortably. Getting the 3.55 differential out of the Limelight 70 really wasn't too bad...
20220409_165942.jpg


I then got it cleaned and installed into the 73. Again, pretty easy at this point.
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Then, I got my decal in the mail!
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I was excited so I had to put it on the car. The car has now officially been Christened for the trip!
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I had to break for a dinner engagement, so tomorrow will be cleaning up and installing driveshaft, axles, better backing plates (the 73's were worn - more on that later), new brakes and wheel cylinders. I also plan to use the brake drums from the 70 in case the ones from the 73 were causing the vibration. Hopefully by the end of the day tomorrow I will have had a chance to test drive it and see what is going on.

Oh, I can only hope the vibration is gone... :lowdown::lowdown::lowdown:
 

JDmac72chrgr

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"Like a kid in candy store" moment for you, huh Hawk? :lol: Roadkill!!

Great articles/updates, now when rains stops, and not working, 72 Charger comes out & he gets some "HAWK" work done, hope no vibrations, wow.
 

hyde-park

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I have been watching HawkRod's project as the posts are updated. The issue that the car has vibration issues and has a Gear Vendors overdrive was what I took particular note of. Whether those two points are related remains to be seen. I've read everything I could find on the internet about anyone who has good and bad luck with a Gear Vendors overdrive as I've been thinking about buying one myself. Some of those posts go back 15 years or so. A good portion of them concern vibrations. If it's just a case of tweaking the driveline angles, okay thats to be expected. Then I got to looking how the thing bolts on. If it's because the mass of the overdrive itself hangs way behind the trans mount and is unsupported thats another matter entirely.
 
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