Can,t Get The Driveshaft Installed

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
Grumpy..Long ago when I started this venture, transmission was a question,
and some folks here talked me into a 200R4 trans.
In the journey, if I recall, I was told to source a drive shaft from a vette with a TH350, as it would be the right length vs the one I had for my Th400. At the time, I did find myself one of those driveshafts.
So today, I'm finally getting to the point of reinstalling my drive shaft. I got the rebuilt trans all in place, the crossmember and all of that all buttoned up. BUT...
...can't get the drive shaft in at all. No room to get it into place. The original drive shaft had strap style u-joints on both front and back. This one has press in on the yolk end, so the yolk is attached. So it's about 3" too long to be able to stick it.
What is the trick. Please tell me that I don't have to go through removing torque converter bolts, and dropping the trans, or dropping the rear diff, just to stab a drive shaft....

The silver lining here is that it does appear that once IN, the drive shaft IS the right length, and won't need to be shortened/lengthened....
. I figured as out of whack as this is, it would be a "known" issue type of scenario converting to the 200R4..
This is about the only good pic I have right now. Because as of right now, I have everything tore back apart.
driveshaft-jpg.103321


If you look at the bottom center of the cross member, you will see the hole for the transmission tail bolts. The tail shaft of the trans lines up almost perfectly with the rear most edge of that box/hole. You can also see faintly, the ring stain on the yolk. That's pretty much where it will rest once inserted. I put the trans jack back under there, removed the cross member, and lower the trans down. But the motor mounts maxed out the angle and I was still a good inch plus of excess yolk length to even allow touching the hole. There is no room in the back to feed extra drive shaft back into, before pulling it back up inside. From what I have researched, the original had straps on both end, so you could stab the yolk, push it all the way in, and that 3/4" of slide gave you just enough to get the shaft into place.
I'm pretty sure I'm ripping the diff out, then reinstalling it. I think that will be less overall work than pulling the trans again, as well as not knowing what kind of finagle it's going to be to get the angles right reinstalling the trans.




Thx.



thank you for the posted picture
heres the correct and much easier to install corvette yoke:D

I hope you talked to a technician before ordering any parts and explained in detail your problem, so you verified you got the correct parts required

https://www.dennysdriveshaft.com/c976_combination_conversion_u_joints.html

https://www.dennysdriveshaft.com/p4...ombination_u_joint_1310_to_1330_series_g.html

https://www.dennysdriveshaft.com/p1...nsmission_slip_yoke_1310_series_u_bolt_s.html
hBXMTjQ.jpg


1607626661042-png.103322
CBEyjY59kwicJCV5yYY1DFD3tbVa24dT-TYQun2GDU1ghuNWKaYjf5gHzTSjLXZ5A_yCGoSY6QXq6SAjpqrEcIPQBaGxzg3nfT_kKhS54-foWBT9af45d_mv6vhQjlE


https://www.dennysdriveshaft.com/c976_combination_conversion_u_joints.html


conversion u-joints are readily available and not expensive
 
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On my 79 L82, the driveshaft is almost encased in the rear cross member attached to the differential. After removing the caps on both u joints, what needs to be done next to get the shaft out?


https://www.monstertransmission.com/700R4_c_3942.html

transtrength.png


length.png


most guys separate the yoke in the transmission as required to pull the yoke or push it into the trans to gain clearance then slide the drive shaft out
if you pull the yoke use rubber bands and a plastic glove on the trans tail shaft to limit fluid loss
in a few cases you need a bottle jack to raise the trans an inch after removing the rear trans mount bolts to gain added clearance

carefully slide the yoke into the trans tail assembly, until it bottoms out, then back it out about 3/4"-1"
you want a minimum of 3.5-5" of spline engagement, if thats available to handle the torque loads, more is better, as long as theres about 3/4" of room for the yoke to slide in further during suspension movement without bottoming out and binding,
and the u-joint will ideally be resting about 1"-3/4" back out of the tail of the trans to allow for suspension movement , if the yoke u-joint is mounted where it located back several inches during the cars operation, your exerting unwanted extra stress leverage on the trans tail shaft
yes it applies to almost all suspensions the only minor exception, is set-ups like the c4 with a solid link between the trans and rear differential where theres a c-beam limiting the changes in the distance the yoke can slide in and out.

this type of suspension only requires about a 1/2" fore & aft clearance

1612981855268-png.204409

http://www.grumpysperformance.com/transpline1.jpg

https://www.homedepot.com/p/LG-XL-O...RCH=REC-_-pipsem-_-202638590-_-312207723-_-N&
 
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Grumpy has your experience shown you that drive shaft u joints need replaced at xx miles and the side shafts tend to go xxx miles on swing axles?




the way you drive and environmental issues effect wear,
but by about 120K miles your easily due for new u-joints,
yeah theres millions of guys who don,t get that much mileage,
or get way more without issues, but thats a decent rule of thumb

http://garage.grumpysperformance.com/index.php?threads/replacing-u-joints.227/#post-266

http://garage.grumpysperformance.com/index.php?threads/u-joint-replacement-info.80/#post-102
 
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