Author Topic: Halfshaft shimming (again)  (Read 1596 times)

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Offline Fotog

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Halfshaft shimming (again)
« on: Tuesday,October 22, 2019, 05:31:13 AM »
I've put about 10 miles on my car since I got it going.  '73 Twin Cam with a 352 gearbox.  I think I should check out the shimming of the half-shafts since I don't know their status.  I understand that I should shim it so that the fit of the roll-pins is tight while still being able to install them through the two holes involved, in the half-shaft and the transaxle output shaft.

I have read a lot, but a few things....

Is this described in the shop manual?  I don't see it. 

Why is this so important?  What are the consequences of not attending to this?

Do I need to dismantle the rear suspension, hubs, etc.  in order to separate the driveshaft yoke from the transaxle output shaft.  Even if I don't need to do this, maybe I should, to check that the hub splines are properly done with Loctite, bearing spacers seem correct (whatever is involved there; obviously I'm foggy), etc.  I've seen a few things on this car that are questionable, so what about things I can't see?

If it isn't necessary to dismantle the rear suspension / hubs, etc. then how do I do this shimming?  I think I've seen someone (maybe J.B.) mention that it should be done at something like every 3000 miles.  How do you extract the half-shaft from the transaxle output if the rear suspension is still in place?

Thanks!

Offline BDA

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Re: Halfshaft shimming (again)
« Reply #1 on: Tuesday,October 22, 2019, 07:30:53 AM »
The half shaft is the upper suspension arm so it carries axial suspension loads. If it is not shimmed properly, you could break your roll pin and then if the half shaft doesn't come off the tranny output shaft, the tranny will be subjected to shock loads from the half shaft which it is not designed to take.

The shims go between the inner  u-joint and the tranny. Jack up the rear of the car and drive out the roll pin with a punch. You can then pull the half shaft off the output shaft. Somebody else might be able to describe this better but the idea is to fit as many shims under the u-joint as you can and still put the roll pin back in. You can use a light to see if the roll pin holes line up when you push the half shaft against the tranny. Add shims till they just line up. You don't need to disassemble the suspension any further than that. As for checking it periodically, JB would know much better than I.

As for checking for Loctite on your hub splines, that won't be necessary if you know the PO did not monkey with it.  If it still concerns you, you could check. Taking the hub off the stub axle would require heat. I have been told by a knowledgeable person (not here) to use red Loctite (the proper color is green) so it's possible if the hub doesn't come off with just a puller, and you can't tell the color of the Loctite, you might have red. I'm not qualified to say whether it must come apart and be rebuilt correctly but it probably should. If you do take it apart, you might as well check your spacer. It should be hardened (so a file should not bite into the spacer) and there should be no mushroomed ends or other deformities. Since it's all pretty much taken apart, you could take the opportunity to replace your bearings. The manual is good for all this.

Good luck!

Offline Gmg31

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Re: Halfshaft shimming (again)
« Reply #2 on: Tuesday,October 22, 2019, 07:42:07 AM »
All of the above Plus:  It is very difficult to slide the drive shaft off the spline if you don't disconnect the bottom suspension arm.  Also the splines are an odd number and it will only go back together one way. 

Offline 4129R

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Re: Halfshaft shimming (again)
« Reply #3 on: Tuesday,October 22, 2019, 08:01:35 AM »
You can use a light to see if the roll pin holes line up when you push the half shaft against the tranny. ]

It is much easier to use metric drill bits of the correct size in the hole where the roll pin was.

If the drill bit won't go in when the shaft is fully pressed against the gearbox casing, then you have too thick a shim. Just keep adding thin shims until the drill won't go through and remove the thinnest shim until it does.

Offline Fotog

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Re: Halfshaft shimming (again)
« Reply #4 on: Tuesday,October 22, 2019, 08:36:41 AM »
Thanks for the advice.  Much appreciated.
All of the above Plus:  It is very difficult to slide the drive shaft off the spline if you don't disconnect the bottom suspension arm.  Also the splines are an odd number and it will only go back together one way.
By "bottom suspension arm", you mean that transverse "lower link"?

Offline BDA

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Re: Halfshaft shimming (again)
« Reply #5 on: Tuesday,October 22, 2019, 09:01:10 AM »
Yes.

Offline Esprit2

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Re: Halfshaft shimming (again)
« Reply #6 on: Wednesday,October 23, 2019, 03:04:02 PM »
Forgive the cut-n-paste, but this is something I've posted before.

Removing the yoke doesn't require any special tools; however, it would be nice to have a proper 'roll pin punch'.   The end has a raised bump in the center.   The bump fits into the  hollow roll pin, and keeps the punch centered while you hammer on it.   It just makes life easier.   It should also be long enough to get the other end up above (or down below) the transaxle housing where you can get at it more easily with a hammer.

Tap, tap, tap won't get you anywhere.   Give it a good whack... just don't hit your hand.

With the roll pins driven out, the inner U-joint yoke may still fight you coming off of the output shaft.   To get it off:

Remove two of the wheel's lug nuts, and loosen the other two (across from one another).

Jack the car up and put it on stands with the wheels well off the ground.

Rotate the wheel until the two remaining lug nuts are up and down, grab the top of the tire (reach in, and wrap your grip around the top of the tire), pull outward firmly to take up any slack, then give it a firm jerk outward.   Using the tire as a pry bar, the yoke should pop the rest of the way off the output shaft without much effort.   Remove the wheel and continue with the rest of the task.

*~*~*~*
The yoke and the output shaft are both cross-drilled with matching holes for the roll-pin that secures the yoke to the shaft.   If no shims are installed, then while holding the yoke fully inward, the yoke will slide onto the shaft too far.   As a result, the roll pin holes will not align.   The inner shaft's roll pin bore ends up to far outboard relative to the yoke's bore... which by comparison is too far inboard.  If you use an awl/ ice pick/ small screw driver/ stiff wire, and slide it in along the inboard side of the hole through the yoke (the side closest to the transaxle), when it gets to the output shaft it will run into the step between the two bores, and stop.   On the other hand, if you slide the poker in along the outboard edge, it will just drop off the mis-match step, and keep going... and  that's not the condition you want.

Start adding shims, moving the yoke outward, and reducing the mis-match step to zero.   Then add one more of the thinnest shims, moving the mis-match to just beyond zero.   Now when you slide the poker in along the inboard edge, instead of stopping against the step, it will  fall off the step and keep going.   Slide it along the outboard edge, and the poker will stub it's toe against the smallest of steps (thinnest shim available... 0.005") and stop.   That's the condition you want.

After the yoke/ halfshaft are installed, insert the roll pin with the split crosswise to the halfshaft.   It can face either way, but it should be across the shaft, NOT along the shaft.   That orientation will allow the roll pin to act like a spring, and compress to slip past the small bore mis-match step.   With the step along the outboard side of the pin bore, the compressed roll pin will force the yoke inward, seating it firmly against the spacer sleeve/ diff housing journal.

If insufficient shim thickness were used, and the step was still on the inboard side of the pin bore through the yoke, then the compressed roll pin would force the yoke outward, lifting it off it's seat on the spacer/ diff housing journal.   Then the inward compression forces of the suspension geometry force the shaft inward when normally loaded,  or allow it to move outward when the suspension is lightly loaded (ie, getting 'light' going over a rise/ hump).   That little bit of loose motion can result in fretting wear in the spline joint, and result in a fatigue fracture of the roll pin.   It's important that shims are added until the pin bore alignment shifts from too far inboard, to just a minimum too far outboard.   None of which has anything to do with the transaxle's side nuts ("multi-tooth, multi-slotted ring-nut").

In the past, Steve Veris has sold the shims... check with him.   Or order them from RD Enterprises/ Richard Winter.   Failing all of that, they're the same size as the shims used to set the end-float in a GMC 4-71 supercharger, so get them from a GMC Truck Service Center.

*~*~*~*~*
The proper roll pins require not only the correct diameter x length, but also a slot of the correct, generous width.   Many of the Lotus Specialists used to sell standard 'hardware' roll pins with a very narrow slot.   That allows only minimal 'spring' compression during installation.   Once the slot closes up during installation, the pin effectively goes "solid", and an abusive level of hammering is required to drive it in.   That is NOT correct.   A correct roll pin never closes up 'solid'.   It still has to be 'driven' in, but not "hammered mercilessly" to get it in.

The roll pin crosses two joint lines between the yoke's inside bore/spline, and the output shaft's OD/ spline.   If insufficient shims are used, then it's common for the roll pin to fatigue fracture along one or both of the intersections.   Once that happens, and the shaft & yoke move, creating a step in the roll pin bore, it can be an exercise in futility trying to drive the roll pin out (ie, the end you're pounding on hits the step, and stops).   In that case, it's more productive to use a 'broken screw' extractor to remove the outer stubs, center the inner stub, slide the yoke off, and finally drive out the inner stub."

Regards,
Tim Engel
« Last Edit: Wednesday,October 23, 2019, 03:14:53 PM by Esprit2 »

Offline Fotog

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Re: Halfshaft shimming (again)
« Reply #7 on: Wednesday,October 23, 2019, 03:19:53 PM »
Wow!  On the phone here, I haven't read this all but it certainly looks very comprehensive. I'll review it for sure. Thank you very much.

I've read some of your other posts about this in the knowledge base, but there are so many threads there that I missed the one where you posted this previously.

Offline surfguitar58

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Re: Halfshaft shimming (again)
« Reply #8 on: Friday,October 25, 2019, 08:11:23 AM »
Following this thread with great interest as I am about to embark on a transmission swap.

Question (one of many keeping me awake nights): What are the chances the pin holes will line up between my currently installed yokes and my new output shafts? With the splines, it would not take much angular misalignment for this to ruin my day.

Tom
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Antoine de Saint-Exupery

Offline BDA

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Re: Halfshaft shimming (again)
« Reply #9 on: Friday,October 25, 2019, 08:48:12 AM »
Tom, where are the yokes coming from?

Offline surfguitar58

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Re: Halfshaft shimming (again)
« Reply #10 on: Friday,October 25, 2019, 10:41:11 AM »
Tom, where are the yokes coming from?

The yokes are currently on the car, being driven my my existing 352 trans. The new 365 trans came without yokes, so I was hoping my existing yokes would slide onto the output shafts of the new 365 tranny and the pin holes would line-up with the appropriate amount of shimming. My worry is that without some serious drill alignment tooling back at the Lotus factory in 1973 or so, the angular alignment of the holes and splines might be different between my old yokes and my new tranny. Does anyone have experience with interchangeability of yokes and output shafts?

t
"A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away."
Antoine de Saint-Exupery

Offline BDA

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Re: Halfshaft shimming (again)
« Reply #11 on: Friday,October 25, 2019, 12:59:42 PM »
The yokes should fit without problem. I believe the holes and splines will line up. The holes in them and the output shafts are offset a little so they only fit one way. I had no problem going from a 365 to an NG3 so you should have no problems either. I just verified that in the parts manual.

Offline Fotog

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Re: Halfshaft shimming (again)
« Reply #12 on: Friday,October 25, 2019, 06:25:32 PM »
As a matter of curiosity, why are you changing transmissions?

Offline pboedker

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Re: Halfshaft shimming (again)
« Reply #13 on: Saturday,October 26, 2019, 11:52:51 AM »
When I replaced my 352 box with a 365 box, the holes in the yokes fit perfectly to the output shafts on the 365 box. FWIW.  :D
« Last Edit: Saturday,October 26, 2019, 02:08:27 PM by pboedker »
Peter Boedker
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Offline surfguitar58

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Re: Halfshaft shimming (again)
« Reply #14 on: Saturday,October 26, 2019, 07:34:22 PM »
As a matter of curiosity, why are you changing transmissions?

I’ve always felt I was reving pretty high just to maintain 70 mph highway speed in 4th gear, and the modest ratio increase of 5th gear would help. But the main reason is that my current 352 trans pops out of 3rd gear unexpectedly, suggesting the synchro is going bad.

The consensus seems to be the spline/pin hole angle is consistent. Thanks everyone for your input.

t
"A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away."
Antoine de Saint-Exupery