Driveshaft Problems 1976 K20

[jdeere3010]

I have a 1976 K20 with a SM465 tranny and NP205 transfer case I have been working on a frame-off restoration all summer and decided to put a 4" suspension lift on it. Currently I am using 4" lift springs on the front and 4" blocks on the back (temporary). When I went to bolt the rear driveshaft on I found that it was too short. Fully extended right now, it is about 1/2 inch too short. The rear springs and shackles are installed correctly and I made no other changes to the driveline whatsoever. Has anyone else ever had this problem? Is it possible that someone else had put a different driveshaft on at one time? I didn't note how far the driveshaft was stretched out before i took it off but this still puzzles me. I am not a newbie to workin on the oobs chevys at all but this is the first time i have lifted one and never thought I would run into this problem. Any help would be greatly appreciated.

[jdeere3010]

In fact, I know of a guy in the area that put the same 4" rough country lift on an '83 K20 and never had a problem whatsoever.

[leveldowen]

Do you have it jacked up by the frame right now? Sounds like you need a longer driveshaft. It is possible that 4" on a short bed standard cab is enough facilitate a new driveshaft when combined with the already long 465/205 combo.

[jdeere3010]

All the weight of the pickup(motor, tranny, cab) is on the suspension right now except for the flatbed that was previously installed. It is a regular cab long box and I do plan to put the flatbed back on it. The flatbed is a homebuilt one and it really isn't that heavy so I don't think that it would make that much difference. Do you think that it is possible that somebody could have put a driveshaft from a short box on it at one time and made it work? I just don't understand why its so short other than the fact that it must have been stretched out a long ways when I took it off, but I really didn't look at it that close and never thought it would be a problem. Thanks again for your help.

[jdeere3010]

Would this thread be better off in the offroad forum?

[red suburban]

gonna need to get your driveshaft lengthened, usually you can find a local shop that can do that for a little money.

[jdeere3010]

Thats what I thought I would have to do but does anyone know why the difference between a '76 K20 and '83 K20 why the 83 (with same tranny/tc setup i think?) would work and not my '76? Is there a difference between K10 and K20 and working better for lifts? Not that important but im curious as to why the difference.
Also, what is the best way to correct front driveshaft angle with a 4" lift on a '76 with a Dana 44? My driveshaft has the cv joint at the transfer case end. I've heard of grinding the cv joint bind points but i think that is a bandaid fix at best and i have the rear crossmember that is bolted on the bottom and side of the frame which looks like a pita to lower if it is even possible. Any comments appreciated Thanks again

[96K2500]

My 80 K20 with same trans/tc had a 4" lift and stock driveshafts. When I bought the lift, I asked about driveline length and was told up to 6" would be fine on stock length with a standard cab longbed.

[Underpowered]

could it be that your D-shaft was not teh stock one from the truck?

my 77 k20 had a 4" lift on it , 350/350/205 drivetrain and the stock shaft was still in it.

[chevybig10]

Listen......I spent 8 years making every series of agircultural, heavy truck, aluminum shaft, carbon fiber shafts, power take off shaft known.

Any time the frame goes up your angles change and the driveshaft is now too short. Period.

When the frame goes up and the diff stays there your ats yoke on an outomatic pulls out quite a lot on a one piece driveshaft...or the slip and spline pull appart on a standard shaft.

If you have a 2 piece shaft the slip and spline WILL pull out as well.

Have your driveshaft lengthened.

Nnow here comes the really fun part. How are your angles? A universal joint can runat a maximum of 4 degrees without building up exessive heat and torque and tearing out quickly.

The shaft now points up more from the diff....so rotate your diff upwards to reduce the angle. The transmission now has the shaft pointing down more....creating angle...so lowering the transmission helps out. On a 2 piece you lower the steady bearing bracket to ease the angle on your poor u joints.

Now this is why I do not like high lifts on trucks....If you lower the tranny, you increase the angle on your front shaft ON TOP of the higher angle you already created with the lift.

MOST people want to save the rear driveline as they need it to get around and be reliable and keep ujoints in. The front ujoints are not needed as much so they can be sacraficed with angle.

So do you want to sacrafice the rear ujoints and driveline or the front?

That is the ****ty decision you must make when you lift your suspension.

The only time this is not so bad is with a pot style cv from the transfer case to the front diff...it is similar to a cv axle on a car...that can handle all kinds of angle...and they started putting them in around the 2002 mark only on 1/4 ton trucks.

You may create a high angle cv joint on the front to handle the increased angle....but running that much angle will wear them out prematurely as well.

Any other questions? Ps.....your front shaft will be running extended as well you must lengthen both front and rear driveshafts....cost is the pipe for each, 4 welds (2 on each) and they will want to balance the chafts as well.

[jdeere3010]

Honestly I don't know if the driveshaft on my pickup is the stock one or not. I bought the pickup early this summer and not knowing much about it at all. On the other hand I pretty much stole the pickup, paid 150 for the whole thing.

Anyway, as soon as I find another one with the same tranny/tc setup im going to measure its driveshaft and see whether or not they're different, or if anyone that has a pickup with this setup and would like to measure the driveshaft that would be great also.

Now, i do understand a little about u-joints and pinion angles and i realize that my angles are going to be steeper than normal and not ideal, but i don't think that a 4" lift on a pickup is considered a "high" lift and running a u-joint a little out of its ideal comfort range is not an uncommon occurrence.

I understand that u-joints will wear out quicker as the angle increases, but they still last one heck of a long time. And whats the big deal if you have to change u-joints a little more often, even to stay on the safe side. They're fairly inexpensive and easy to change so im not worried bout that.

I greatly appreciate everyone who has replied and helped me out. If anyone has any more info on driveshaft length, how far your driveshaft is stretched out with the same tranny/tc setup and 4" lift that would be great. I was puzzled too why this wouldn't work but that the joy of the build ain't it? It ain't my first disappointment with it and it isn't gonna bother me too much. Thanks again to all.

[DagoFast]

Get a longer drive shaft.

[79k104x4]

on my 79 RCSB iv got a four inch lift with blocks in rear that was already on the truck and im pretty sure you have to drop the transfer case and crossmember about an inch (i thought most kits told you that). anyway, there are 2 nuts stacked between frame and crossmember used as spacers from previous owner. Dont know if it makes a difference but mine has a TH350 and an NP203

[jdeere3010]

The kit i got said I may have to do that but i got the different crossmember that bolts on the bottom as well as the side of the frame. With this crossmember i would have to drill at least 2 if not 4 new holes and that is the reason i have not done it yet. If it comes down to it, i will do that but im also gonna try to find out if i can use the different style crossmember that only bolts onto the bottom of the frame.

I do understand that this won't solve my driveshaft problem and in the end I will probably end up with a differnt driveshaft, but I'm just tryin to find out what the f*** is goin on with with mine. I'm hopin that this might also help somebody else out someday when I do find the answer to my problem. Again, I appreciate everyone's help and advice.