U joint critical speed.

[Geoff Weeks]

There are aftermarket brush band covers, if that is where you hole is,

[Geoff Weeks]

10 minutes ago, Joey Mack said:

Thank you for the starter part number... I spent over an hour trying to find one..  

I've got the factory parts manual, so if you need numbers for something, ask.

We might want to take this to some other place, because the thread topic is more about U joints in general. I'm new here so not sure where it should be.

 

[Joey Mack]

Good Idea..   ''Sidetrack area'' will work..   

[mechohaulic]

go for it Jojo - I like competition in off topic=LMAO 😂 . interesting to watch and learn as members relate their vehicles  and exchange knowledge.

[mechohaulic]

3 hours ago, Vladislav said:

Pretty interesting subject to discuss, thanks for lifting it up.

Honestly I don't remember hearing about those crytical speeds in the past but the effect sure makes sence. My guess older day's engeneers were familiar with that. Otherwise they wouldn't design shafts with intermediate carrier at all. Probably the road speeds were less in those days, especially for trucks.

Vlad

not only were road speeds less in those days = the roads weren't that well made to achieve high speeds. considering all mechanical items were basically an " over-kill" in design back then such as 55 K lb rears. all the heavy torque arms  and springs being replaced today with air bags , driveshafts possibly weren't a major factor. also other then west coast type units how many long wheel based trucks were there, if they were long . the shafts were made to suit.

[Geoff Weeks]

IDK, the 1940's roads were hard top in many places, 45-50-55 were not unreasonable. The truck in question seams to have been pressed into military service, it has the "military" steering wheel and there is a patch for a three point antenna mount. There is a hole in the dash that may or may not have been for a "spy in the cab tachograph".

 Interestingly the GVW is 16500, which is low for this model My other is 21500. It may have been spec'd for a set job, but at that time it just may be what was on hand at the time.

[Geoff Weeks]

Called this Am, the new shaft is finely ready for pick-up this afternoon. I will get it tomorrow and report back on how it works out. They said they had a delay in getting the slip-spline or slip yoke ( I don't remember which) and that is why it took so long. Not a problem, as I don't drive the '41 often.

[doubleclutchinweasel]

59 minutes ago, Geoff Weeks said:

Called this Am, the new shaft is finely ready for pick-up this afternoon. I will get it tomorrow and report back on how it works out. They said they had a delay in getting the slip-spline or slip yoke ( I don't remember which) and that is why it took so long. Not a problem, as I don't drive the '41 often.

I'll bet you'll be very happy with the results.  Keep us posted!

[Geoff Weeks]

Ran to Omaha, and picked up the shaft. Rain stopped enough for a while for me to put it in. Took it 12 miles and back to put 20 gal of gas in the new tank. I think we have a winner. I can run up to gov speed in O/D and while not silky smooth it isn't trying to tear itself apart. 55-60 is good enough. Speedo doesn't work correctly at present but I was keeping up with traffic, Tach wasn't at gov speed, so likely 55 -58 without problems.

Old and new shaft. Old has the old diff and carrier bearing yokes on the ends, so that is why it looks floppy. New shaft is 3 1/3" old is 2 1/2". The bigger shaft looks none to big on a truck of this size.

[Geoff Weeks]

Forgot to check the carrier bearing temp, didn't want to crawl back under in the wet. I'll check next time it is out.

[Vladislav]

Hope for the deal to be done.

So what the theory says on the crytical speed? Is it higher for fatter or heavier shaft? Or did just that "seat of pants" engineering work out well enough?

And what's up the bearing temp? Do you worry on extra stress put on it by larger shaft? Or did you just serviced it and wanted to check?

[Geoff Weeks]

I guess shafts with cross and bearing type joints set up a standing wave at  one RPM (critical speed). The size of the shaft and the length determine when that happens. To avoid it, you can make the shaft bigger or shorten each section.. Also they found that at exactly 1/2 the critical speed you can also get a vibration so while you can pass through that speed, you don't want to run at that speed for very long.

 

 

[Geoff Weeks]

Still haven't checked the carrier bearing. When I was diagnosing, I dropped the rear shaft and ran the engine and trans in top gear at rated speed and noticed the bearing housing got warm enough you couldn't hold it for more than a few seconds. I figure 125-135 deg F. It got this hot in a very short time of running at speed. This truck uses a double taper roller with a spacer supplied by the bearing Mfg. I ended up replacing the bearing (s) although they looked ok. I'm not sure if it was on the tight side or not.

 I saved the old bearing and put a N.O.S. bearing in. I need to put the bearing in a press of vice and see if it has pre-load or any play. I think I might mic the present spacer for the old bearing and order one a few thousandths thicker.

It doesn't use the more common type of ball bearing in a rubber mount. It has a tubular housing that holds the double bearing and the housing is mounted in a "clamshell" mount with a rubber ring between the housing and clamshell.

 

Edited July 10, 2023 by Geoff Weeks

[doubleclutchinweasel]

Definitely sounds like the bearing spacer could be too thin (making for too little clearance).  Tapered roller bearings CAN run at zero clearance, but at reduced speeds.  Axial clearance of 0.003-0.007" is more common for higher speed applications.  They are pretty forgiving.

[Geoff Weeks]

I can think of plenty that run with pre-load. Spec for this bearing is .005-.008 measured at the outer race. Just feeling by hand, I think it is tighter than that.

[doubleclutchinweasel]

10 hours ago, Geoff Weeks said:

I can think of plenty that run with pre-load. Spec for this bearing is .005-.008 measured at the outer race. Just feeling by hand, I think it is tighter than that.

Sounds like you've pretty much got it figured out.  

We routinely build special tapered roller bearings for certain customers with zero clearance or even with preload.  But, these are typically heavy load/low speed applications.  The higher speed bearings always have clearance in them.

Of course, there are other factors to consider.  Depending on the application, the materials used in the assembly, and the way they are mounted, tapered bearings CAN actually loosen up as they heat up.  But, with a back-to-back mounting with a steel spacer in-between, they typically get tighter as they heat up.

Keep us informed!

[Geoff Weeks]

Pinion bearings are a good example of bearings that run "back to back with a preload and high (relatively) high speed.  In the case of the carrier bearing, they are factory (bearing mfg, not truck mfg) set and sold that way. I don't know if over the years, the  roller races have been changed, they're not supposed to be, the bearing gets changed as a unit. It is made up with "off the shelf" cone and a double cup outer race, but the spacer is selective fit.

[doubleclutchinweasel]

Yep.  One of the biggest challenges when designing a bearing assembly, or any other assembly for that matter, is to calculate what parts will grow in what direction and what that growth will do to the assembly.  Lots of factors there.  Coefficients of thermal linear expansion of all the different materials.  Type of lubrication.  Phase of the moon.  Neighbor's wife's bra size.  You name it.

One of the most fun things I have ever done is build precision machine tool spindles.  Tolerances in the millionths of an inch.  Things where the ambient temperature, and the temperature of your hands, affects the build-up.  Those have to be pre-loaded to run accurately, but will instantly burn up if set up too "tight".  Really enjoyed those, though.  One of those things where the extra time spent getting it "just so" pays off in seriously longer service life.  Dang.  Getting teary eyed and nostalgic now!😂

[Vladislav]

On 7/11/2023 at 1:40 AM, Geoff Weeks said:

Still haven't checked the carrier bearing. When I was diagnosing, I dropped the rear shaft and ran the engine and trans in top gear at rated speed and noticed the bearing housing got warm enough you couldn't hold it for more than a few seconds. I figure 125-135 deg F. It got this hot in a very short time of running at speed. This truck uses a double taper roller with a spacer supplied by the bearing Mfg. I ended up replacing the bearing (s) although they looked ok. I'm not sure if it was on the tight side or not.

 I saved the old bearing and put a N.O.S. bearing in. I need to put the bearing in a press of vice and see if it has pre-load or any play. I think I might mic the present spacer for the old bearing and order one a few thousandths thicker.

It doesn't use the more common type of ball bearing in a rubber mount. It has a tubular housing that holds the double bearing and the housing is mounted in a "clamshell" mount with a rubber ring between the housing and clamshell.

 

Ok, figured. When you mentioned a "carrier bearing" I got thinking of a bearing in a carrier, a pinion bearing. I always surprized the fact the axle reducer unit is called a carrier (and we even spoke about that on here). The "diff" term also doesn't sound technically correct since there are gears in the carrier also, not a diff only. But the things are as they are.

I think determining pre-load in a press or a vise is the right way to go. To my understansding for the particular task you have very light pre-load is needed. Fat or oil used in the original bearing was of much lower standards than modern materials so a bit of pre-load wouldn't make damage. At the same time play may give space for potential vibrations. And I doubt you need extensive pre-load having no plans for really big milage. 

[Geoff Weeks]

Terms can get confusing esp when "slang" and regional differences come into play.

 To be clear, I am taking about a driveshaft mid ship bearing and not anything contained in the rear axle housing. Yes the left and right bearing inside the axle housing are also called "carrier" bearings, because they support the (carry as it were) the differential, which is housed inside the carrier itself. Clear as mud, and the more I try and spell it out the more it will confuse things!

 Most longer wheel base trucks today have multiple shafts sections with the back end of each supported by a driveshaft carrier bearing, often suspended from above. Unlike the modern practice of hanging the bearing from two bolts, this one passes through the crossmember and is held in with a ring of 6 bolts

 This truck has the carrier or "midship" bearing where the shaft passes through the frame crossmember. The bearing must "float" on the shaft to allow for minor fore and aft as well as concentric adjustments of the whole housing 

 The double taper roller is supposed to have .005 to .008 of "slop" in the bearing assembly, so no pre load in this application. It runs in grease, and that may come into play as well. Bearings run in an oil bath can remove the heat, those in grease can not. (or not as easily).  To adjust the bearing, you select the spacer ring that provides the desired fit.

 Too tight and you risk the whole bearing spinning in the housing, too loose and you will introduce run-out and therefor vibration into the shaft.

 The problem I was having was, after running the shaft at max speed for just a few minutes the bearing housing was getting so warm you wouldn't want to keep your flesh on it for more than a few seconds.  It may be normal, or it may not, I have little to compare it to other than wheel bearings, which turn slower but don't generate anywhere near that amount of heat after hours of running.

[doubleclutchinweasel]

Believe it or not, too much grease can also cause a bearing to overheat at higher rpm. If over-greased, the whole thing can get heat-soaked because the excess grease can trap the heat. 
Our industrial bearings are typically filled 1/3 full. 

[Geoff Weeks]

Heat was there when  just the bearings were "hand packed" with no "extra" grease in the housing, so that isn't the cause in this case.

[doubleclutchinweasel]

Yep, Geoff. Sounds like a preload issue. 

[Vladislav]

I would also think so. Or better to say I just don't see any other reason. Grease overfill is excluded. May be normal in very theory but I wouldn't like such way of things definitely. So seems like setting some reasonable minimum play is the way.

Speaking the terminology I also use to have that feeling of getting more and more complicated the more I try to say clearer. I admitted on the forum a few times that American technical terminology is a kind of mess in many cases with plenty of terms of slang origin. I can state this relating to terminology used in Soviet Union design documentation. Although the most Russian technologies of 20th century were based on Western (mostly US and German) designs local engeneers made large job investigating and systemizing the info which followed by designing and establishing strict industrial standards. Those also conteined standartized names for certain parts, units, assemblies etc. Also it was prescribed of what should be called as a part, what is a unit or a assembly etc. Very important point when you read a (good) book of those times and you see a name (a term) used for a certain part that exactly same name would be used all over the book including text in pics, schemas and specifications. Unfortunately modern literature doesn't follow those standards being translated (inprofessionally in many cases) or just written by undereducated specialists.