The Stovebolt Site Forums The Shop Area The HiPo Shop 1 piece or 2 piece driveshaft?

How much modification to convert to 1 piece driveshaft in a 3200TF truck? Heidts front susp with tci leafs in rear (SBC with TH400 and locker Ford 9" diff). I think I found a donor driveshaft that can be cut, 2003 Ram 2500 Quad cab 2WD (4 inch dia aluminum).

Unless the transmission you're using is a LOT longer than the one that was in the truck originally, you're headed for a truckload of trouble trying to stretch the driveshaft. There's a reason for using a 2-piece shaft, (length of the frame/chassis) and unless you believe you're smarter than the engineers who built the truck it would be wise to stick with what it was equipped with originally.
Jerry

I was expecting a driveshaft range of approx 62". The TH400 appears to be longer than the granny 4 box that was removed. I haven't completed the measurements yet. But the removal of the support bearing crossmember would be a point of no return. This isn't an issue about being smarter that the typical engineer and more of an questions for others that have converted. To those that have converted,was there a driveshaft clearance issue. I'm just asking, bc obviously what was in there and whats going to be in there is not remotely close to what was original.

The other question I have providing I continue down the road of 2 piece driveshaft. The SM420 has a flanged yoke at the end, whereas the TH400 uses a slip yoke housing at the end. This configuration would modify to use a slip yoke at the front of the forward driveshaft and a slip yoke at the front of the back driveshaft. Will the 2 slip yokes work like this? With the 2 piece setup, I intend to shorten the front driveshaft and the rear driveshaft will probably maintain the original length (with the exception fitting a chevy to ford 9" u-joint for the 9" yoke).
Again, what have others done with the 350(in my case,383)/TH400 combo?
Even at around 62" for a one piece driveshaft, critical speed is near 7200RPM. Not any RPM range that engine is going to be remotely close to.

If your center bearing (supporting the center u-joint at the front half of the driveshaft) is going to be fixed to the frame (as it should be), then you really only need a slip joint on the rear section of the driveshaft. That's where the shortening of the driveline is going to occur with compression of the suspension. But if the tranny you're planning on using has a slip connection, it won't hurt to include that on the front section.

I don't see why you cannot use a one piece driveshaft. The SM420 is much shorter than a TH400. When I replaced my torque tube system with a new rear end and a newer SM420 (last one GM made; has backup light switch), I wanted to use a one piece driveshaft. My 1980 long box pickup with TH400 had a one piece driveshaft and my 2010 pickup has a one piece driveshaft, but the driveshaft for the 1954 would be longer due to the short transmission. I spent a few hours looking around the local wrecking yard trying to find a one piece driveshaft that was long enough without any luck. Finally had to settle for a two piece driveshaft with steady bearing out of a long box truck with manual 4 speed. My local transmission shop cut the shaft down and balanced it for me. I asked the pro at the shop about using a one piece and he said the length would be too long. I should have talked to him before going to the wrecking yard.

Thanks. By rough guesstimate, lets say the sm420 is a little over 10", add a bell housing and that adds 6"-8". I would expect to lose 11" - 13" inches of front driveshaft (Short housing TH400 is approximately 29"). Now new question, How much HP can the center support bearing withstand? As my 383 is near 500hp. The stock center support bearing had the 235 (little over 120hp) and SM420 in for a few years and is showing signs of cracking. What are you using for center support (on a SBC with a little HP)?

Thank you for a 1 piece perspective. The concern I have with the 1 piece is clearance. Once the third member and transmission angles are set, I would need to clear a 4" - 5" diameter driveshaft (aluminum) or at least a 3.5" steel. Did you have clearance above the driveshaft if you were to install a one piece driveshaft (in your 54)?. I expect the ride height of my truck to fall 3" from stock. I know these are speculations, but I'm trying to plan for contingencies once the MII suspension transformation begins. Rear leafs will be TCI.

Check around and see who the mud boggers and rock crawlers are using to build their shafts. In my hometown we have a guy who has been doing drivelines for 40 years and it is amazing at what he can do/build for the above mentioned as well as race cars, antiques to tractor trailers. A good driveline man is worth the money. He can recommend shafts for strength, and all kinds of joints. see if one exist in your area.

You're very correct about that. We have driveline service of West Sacramento. Been around ever since I could remember. They built the driveline for my 383 when it was in my Malibu. They recommended the diameter and balanced the driveshaft. I never had a problem with their work or products.

Yes, I would have had enough clearance for the one piece. The shaft from the trans to the steady bearing drops about 2" - the second shaft slopes down to the rear end. A one piece (if it was possible) would cut the corner.

Yes, indeed.

Update today. I tried to stay with the two piece driveline setup, but it now looks like one piece is the only option. As was explained by the driveline shop, the intermediateshaft is an extension of the transmission tailshaft and the angles cannot be adjusted, as there is not enough room above the support bearing crossmember to allow the intermediate shaft to position straight through the support bearing. I still have all my parking brake cable setup attached to the crossmember. My option is to have a portion of the crossmember cut out and insert a tubular driveshaft loop in between. This will allow for a 3 1/2" one piece driveshaft with approximately 3.5 degrees of shaft angle. I was hoping the intermediate shaft could angle down and the rear shaft would extend to the differential, but it doesn't work that way. So the truck heads back to the fab shop one more time. Bummer

I believe your only issue with using the one piece shaft in your application is that it sounds like you have lowered the vehicle and that would cause interference with the driveshaft center support crossmember. I just finished installing a 3 speed overdrive in a 59 3200. We removed the SM420 4 speed and had a drive shaft made with a slip joint. The new shaft was made with a 3 1/2" tube and was 63" - u joint to u joint C/L. The driveshaft shop had no issues with making the driveshaft that length. There were no clearance issues.
If I remember correctly a 55 3200 with a factory 3 speed or 3 speed OD trans uses a one piece shaft. The 4 speed is much shorter and uses a flange, hence the 2 piece shaft.
Fred

In my 51, 3600 truck I changed the SM420 for a T5, went from a two piece (front enclosed/rear open) drive shaft to a custom made one piece. Had it made at a big truck drive-train shop and only took about 45 minutes.

I did leave the pillow bearing mount in place in case I ever wanted to go back stock.

No issues of any kine...Works great.

Mopar, couple questions about the T5. Did you need an adaptor to connect to the 235? What kind of RPM difference did you see at 55 MPH?

Mopar, couple questions about the T5. Did you need an adaptor to connect to the 235? What kind of RPM difference did you see at 55 MPH?

No adapter used on my 216 engine (original size in my 1951 3600). I did shorten the input shaft and throwout bearing collar to match the ones on the SM420. Lugnutz has some excellent how-to vids on the various options.

I don't have a tach, but according to one of the online calculators, with my 31" tall tires and 4.57 gears I was turning 2738 rpm with the SM420 at 55 mph. With the T5 I'm running (1352-222) and it's .72 5th gear, 55 mph is now 1948 rpm.

790 rpm less.

Calculator I used http://www.blocklayer.com/rpm-geareng.aspx

Thanks. I'll check Jay's site. Wonder if the 235 and 216 have the same block/clutch housing config/pattern?

The bolt pattern/configuration of clutch-housing to block would be the same.

Flywheel teeth counts and pilot bushings might be different.

Clutch release/throwout bearing heights/lengths might be different, but the total height/length of the clutch assembly would be the same (plate, pressure plate, and release bearing).