The Stovebolt Site Forums The Shop Area Engine Shop Straight drive-shaft or no?

What are your opinions on having a straight drive-shaft made for my 66' LWB. It has rear coil springs and I'm tired of the carrier bearing going out. I've probably gone through six bearings of varying quality and manufacture. Please let me know if a straight shaft is possible. Thanks

Do what I did on my 68, I made an adapter(basicly a piece of thick angle iron) to mount a late model carrier bearing to the truck that way instead of hanging like the stock ones do it would be sitting on the plate I made. You may have to have your driveshaft modified because I was using the front shaft out of a 92 fullsize pick up in mine because of the longtail shaft automatic I was running....Joe

Why are they failing? It may be good to be sure you know before switching.

The two-piece shaft gains ground clearance and allows using smaller tubes. A single shaft will need to be much larger tube to provide the same strength, plus balance will be more critical.

A lwb is really too long for a single drive shaft. The length depends on tubing diameter and thickness. Center bearings normally last a very long time. Are your joints in phase and did you change the plane of the engine or the rear. If the plane has been changed a one piece shaft will fail in no time. I am assuming you are speaking of the center bearing. The carrier bearing is actually the bearing that supports the ring gear, but the center bearing is quite often referred to as a carrier bearing.

Over on another site they talked about the failure the after market bearing are having. Some folks went to far as to put new everything on the driveshaft & had them rebalanced & the bearing still went bad in less then a year. Most chalked it up to inferior overseas junk.
Some folks call them carrier bearings other call them support bearing or center bearing. Regardless they all mean the same thing, Google is your friend..Joe

That angle iron thing is a good idea but I don't know if I want to go that way. I was considering using a larger driveshaft off of a 3/4 ton that uses a "half-moon" bearing instead of the "teardrop" type bearing that I have now. I don't know why they are failing exactly but I have a theory that it is because my engine is 300+ horses which is much higher than the driveline was originally designed for. Generally the bearing itself doesn't fail but it's usually that the bracket actually twist off. Before installing the last bearing, I welded braces on it but it now sounds as though the bearing itself is going out. Everything on the drive line is at the same length as when this truck is manufactured. What exactly do you mean by plane Crenwelge? I am speaking of the center bearing, I just have always heard it called carrier bearing. Thanks a lot, Derry.

From over on 67-72chevytrucks.com & it seems some have ran a one piece driveshaft w/o problems.....Joe

I'll second that, and guess it's a balance or angle problem.

If you want to redesign the driveline have a look at this Tech Tip and the manuals linked in it http://www.stovebolt.com/techtips/driveline/setup/index.html
A driveshaft may look simple but there is a lot thought that goes into getting the right one for the job and installing it properly so it will last.

Before just swapping stuff around at least skim through the manuals and or ask a good driveshaft shop for help/recommendations.

Grigg

By plane he's referring to the angle of the driveshaft from level. If you change the angle of a driveshaft by changing the front or rear connections (raise or lower the rear end, different transmission with a lower or higher rear connector), you can often damage center bearings or u-joints quickly.

That doesn't sound like the problem you have. In the old days center bearings used to go out from too much vibration. Make sure your rear end isn't moving around on you (broken u-bolts or missing nuts on the axle mounts or badly worn springs mounts and shackles, etc.) and the transmission mount isn't worn excessively. If you can move the transmission from side to side, even slightly, by pushing on it, you've got a problem. If you can move the rear end in any direction (up, down, side to side, diagonally), you've got a problem.

Rear ends, when power is sent to them, want to twist upward. This movement is accounted for in the design of the drivetrain, including the sizing of the u-joints, the planes of the shafts and the location of the center bearing. But it depends on all the mounting points being firmly fixed, with no movement of the spring mounts or axle mounts allowed. Wear of any mount point can cause the rear end to move in unexpected ways, putting pressure on the center bearing in ways it's not designed to handle.

Also check all the u-joints. You could easily have a u-joint that's worn excessively, causing a vibration that's wearing the center bearing excessively. Any excessive movement (fractions of inches) translates into a constant vibration that puts tremendous loads on the center bearing during acceleration.

I wouldn't expect extra horsepower to cause this problem. It would be much more likely to shear the tips of the u-joints (which could lead to a bad center bearing eventually but would more likely manifest itself in a broken u-joint very quickly, especially if you're prone to jackrabbit starts or frequent burned rubber.

Well I guess the plane isn't my problem. I did just replace the rear U-joint last week as it had severe bearing wear. The rear end did have a bolt that had pulled through where it mounted to the truck but that was fixed with a large washer and welding. I have new coil springs and shocks installed. The transmission is mounted to the bell housing only. Is it possible that worn motor mounts can be causing this problem? The drive shaft has been balanced and looks to be in good shape. Perhaps it is my quick driving that is causing all this havoc on the bearing? I will go through today and see if anything looks broken or worn but am not optimistic to find anything. Thanks a lot, Derry

It's a poor design, pure and simple. Of course other factors make them fail sooner and the influx of foreign junk dosen't help much. I like the idea of changing it out for something more substantial.
Fred

Dellman, I'm not familiar with your year of truck, but most GM vehicles had a transmission crossmember that bolted to the frame. The transmission then mounted to the crossmember through a transmission mount, basically a metal plate with rubber bonded to it and a bolt hole on each side. This allowed the transmission a small amount of flexibility while supporting its weight and fixing it in position. I would check to see if the truck is supposed to have a crossmember supporting the transmission. Hanging a tranny off an engine with just the bellhousing bolts supporting it is a risk proposition.

If there is supposed to be a crossmember and yours is missing, I'd peg that as a major source of your center bearing travails. You can probably pick one up a the local junk yard for almost nothing and then buy a new transmission mount at your local parts store or online.

In fact, if there is supposed to be a transmission crossmember, if you go to a bigger, heavier driveshaft setup, you simply exacerbate the problem. I'd check that first, and fix it if it's missing, before even considering changing your setup.

Bad motor mounts are more likely to manifest themselves in excessive side to side movement when the motor is revved. I've seen broken mounts where the motor literally jumped up when it was revved (and the fan cut the radiator hoses even.)

rfs56trk, do you have some basis for the claim of poor design? I see this thrown out quite frequently when things aren't working right, but the cause of most problems is a lack of maintenance, missing or severely worn parts and/or a complete lack of understanding on the part of the person attempting to fix the problem.

For example, you will often hear, right here at Stovebolt, that Rochester Model B carbs are "awful", that they don't idle well, that they constantly leak, etc., etc. I have two on my truck. They don't leak, they idle fine and the truck runs like a scalded dog. They were rebuilt by a man who knows what he's doing.

The question I always ask is, would the manufacturer sell new vehicles that would fail early because of a poor choice of parts? Model B's were the standard carb for GM six cylinder engines for a number of years. Yes, modern carbs are better, but that's true of everything (in most cases.)

I doubt seriously that the driveline design of GM was poorly designed. I think it was probably state of the art for 1966.

I know when trucks moved to an open driveline in the mid 50s, this crossmember wasn't used. The transmission cantilevered behind the bellhousing. I'm not sure when it changed again to a support on the tailhousing, but there was a time when that crossmember was not being used.
It might be a good idea to put the crossmember in to support the tail of the transmission. Your motor being stronger than stock can cause some issues.

There was no cross member for 1960-66 Chevys with 3 speed short tail-shaft transmissions that I know of. I have another 66' 3 speed truck and have seen many other trucks of my year with 3 speeds and none of them have cross members. Curiously there are two bolt holes of the tail-shaft where is appears a cross member could be mounted but I believe that virtually the same transmissions were used on other models as well.

I owned a 66 C-20 for 17 years, it came with a 292 and a 3 speed. During the course of ownership I changed it over to a 3sp OD and had the driveshaft balanced. It had the center bearing that is the subject of this discussion. The center bearing is supported by a narrow mount with 2 bolts to the frame. It is very weak at that point, irregardless of any other issues such as worn u-joints.
It is the same system used in cars from about 58 through 64.
I probably replaced 5 or 6 of the center bearing assemblies during this time, only one of them was due to the actual bearing failing. All of them cracked at the spindly mount bracket.
I had a relative with the same exact truck that came with a 4 speed. It had a substantial center bearing with a collar that supported the assembly. I maintained the truck for him for many years and it had none of the problems that my truck had. I also worked in a number of shops and replaced many of these center bearings on cars and trucks of that era. It was a common problem.

Fred

My interest is in 50's GMC's because that my father used in his business and what I drove to school. We switched to Internationals in the 60's because we considered them a heavier built truck so I am not familiar with 60's GM. If indeed they did have a weak center bearing design, I would fabricate a cross member and use a heavier center bearing. A machinist can fabricate a bushing to accommodate the larger bore. As for off shore stuff, I despise Chinese stuff, but I just last week bought a center bearing for a 50's 3 ton. The cushion is made in USA. The bearing is SKF, made in Italy. I put Italian machining in the same class as German and Swiss.