The Secret Life Of The Universal Joint - Uses, Limits, How They Differ From Constant Velocity Joints 

Theres a channel called Garage Fab that has a great video on how U joints work. He built a model of a drive shaft and diff that articulates up and down with sprockets on each end to show the difference in speed at each end of the drive shaft at different angles. It's a great watch

Tony! My man! I've learned countless things from your videos since I first found your channel, but the part at the end where you recommend drilling the strap bolt bores all the way through and using long bolts has got to be the top of the heap! I've lost count of how many times where every last exact thing you said will go wrong with the short bolts has happened to me. And yet, I never considered drilling the holes all the way through. 24k gold advice. Thanks!

This is important. When you weld a driveshaft, the yokes on both ends must be aligned. That is, if vertical on one end, the yoke on the other end needs to be vertical, too.

Hmm.. Here's the thing. That joint at about 12:00 is not a constant velocity joint. It is a slidable T-joint. It just makes axle length change easier, because the "sliding" is done in better lubricating conditions than splined shaft and bore. Constant velocity is only achieved when bearing balls, hold in a perfect plain by a special retaining cage, ride in very complicaded trajectories curved on both inside and outside, both shell and inside "thingy" of the CV joint system. Usually it's 6 balls and 6 curvings because it's easier machinable. But this system used in most all front wheel drives outer joint, does not allow axial movement, and the inner joint must do that, and to also be really constant velocity, inner joint must be even more complicated. Some manufacturers don't even use true constant velocity for the inner joint, they use 3 bearings at 120deg, riding on 3 tunnels also at 120 deg which also is not constant velocity config. But does allow change in length, and in front wheel drives where it's used, the angles on inside are always smaller. On the outer side there's the suspension movement plus steering the wheels that is. Now about vibration on joints, a detail that does minimize vibration is the U' s must be timed, ie not random angle positioned, so the two vibrations mostly cancel each other. Keep up the good content, far better than what we see on tube. Have a good one.

sometimes there is harmonics from different panels around the shaft, some people think that is a vibration

Thanks for explaining how to get the zerk fitting to be compressed, as this concept isn't always clear. The crosspiece is weakest there, and lends weight to getting a sealed unit. As an aside, I came across an odd interchangeability. I had taken the rear driveshaft from my '91 Bronco to be serviced at a driveshaft shop. There was another driveshaft (customer's) that was clearly similar dimensionally to mine, but casting where it bolted to the rear axle was slightly different, but swappable. It belonged on a similar vintage Chevrolet Blazer. How that happened when the Blazer had a different wheelbase was noteworthy.

Dispelling wives tales and recurring myths. Love this guy, he knows stuff.

A drive shaft with 1 joint front and back, is a double cardon joint with a really long cage. As long as you dont have so much angle that the U joints dont bind, and both joints are parallel, the speeding up and slowing down of the driveshaft created at the tailshaft is cancelled by the opposing joint at the pinion. In a perfect world. Real world it might he off a touch from perfect as the car moves

You don't get "bind" from u joints, even at pretty big angles, as long as they are used in pairs, they are properly timed, and the drive and driven ends are parallel.

We had a Speedway Car had no rear suspension and the uni-joint would seze up, thanks for sharing, all the best to you and your loved ones

UTG, I enjoyed this video, thank you. Here is a lesson learned. A friend had a 1950 dodge which he restored years ago. It had a strange vibration when accelerating around 35 -40 MPH. Well with a flat head engine not much acceleration was actually happening but the vibration was like an unbalanced wheel. But was not. It was a worn drive shaft trunion. We turned the drive shaft around and walla no more vibration on acceleration. BTW Lincoln Mark 7"s had the constant velocity U joints. A cheep source.

These last two videos have made me very glad I installed air bags in my truck's rear suspension. My goal was to level the truck when towing in order to improve handling and braking. I hadn't even thought about the drive train geometry causing binding while I'm also demanding that it transmit maximum torque.

I never really thought about the compression on the fitting. That makes sense. Why I like your channel, I always learn something.

It is random stuff like this that makes the channel a bonus find! I love this kind of stuff, I am a nerd at the end of the day.

Most Toyota 4x4 have those double uni-joints CV joints in their tailshaft,never was told it's a CV joint thanks for sharing,all the best to you and your loved ones

Thank you for this video im in the middle of putting a new rear end in my streetrod i will definitely pay attention to how i install the u joints i didn't know about the orientation

Learned something new today, about installing a joint with the grease fitting hole in the drive compression position! Thank you UT!

Great video, the only thing that I can remember that you forgot to touch on is...... OUT OF PHASE.... U-joint, rubber insulation shaft that moves over time..... Splined shafts that people take apart and don't put together same way., ect.

That was a great explanation of U-Joint best practices. You might say something about phasing U-Joints in 2-piece driveshafts.

At my home track in the 1990s, we had a guy with a 74 Nova that ran high 13s low 14s with a 305 headed 350. He would chuck a driveshaft every few weeks, and garnered the nickname "Halfshaft" from it. I was running mid 11s to low 12s in a heavier Firebird with a 455 that would just about pull the front wheels and did a best of 1.59 60ft on slicks with 3.42 gears. I was doing it with a stock shaft, in a heavier car, with more power and a lot more strain on things. He was getting beefier and beefier driveshafts and spending money he didn't really have to keep it running. I told him that he didn't have the centerlines of the yokes aligned right, he said he did. So one day we checked it at the track with his car sitting on some 10" wide steel rims I had. Turns out the shaft was binding real bad, not only in the vertical plane, but laterally as well. The engine was tipped back too far and the front of the engine was closer to the passenger side than the drivers side, so it was tweaked side to side. It was nearly binding the yoke to the driveshaft it was so misaligned. He brought it over, we measured his subframe, it was crooked too, so we measured and aligned that, then moved the engine so it was straight front to back and not nose high. However with the leaf springs we couldn't do much without angle plates, but he never chucked a driveshaft again. If i remember right he picked up some ET too.

Thanks UT, great tip on compression of the grease nipple, I’m going to check my U joints today. I use a clinometer from a WW2 vickers machine gun to check the angle of my engine then set my pinion angle half a degree down from that reading. When I go to the drags I adjust the pinion down three degrees. I’ve replaced all of the factory trailing arms and panhard rod in my ‘71 LTD with adjustable rod ends for quick and easy adjustment.

You actually can put u-joint in backwards.... If you install it to the grease fittings in the back when it's installed you can't get a grease gun in between to greese it. Uncle Tony, So is the pinion snubber that Mopar designed to keep the driveshaft in line under acceleration? Great info here!

Uncle tony, klowny, and vice grip are all absolute geniuses

Do Not over tighten the u-bolts on a u-joint, if you crush the cap or distort it the bearings won’t turn = premature failure. It’s actually easy to over tighten. 👍

The compression of the zerk fitting is very interesting. I never thought about that. Usually people that race cars get solid u-joints.

How about the difference between a steel driveshaft and an aluminum one in relation to the various set ups?

I find the double cardan joint most often on 4x4 trucks on the front drive shaft

All U-joints are Cardan and when they are used as a CV style it is call a Double Cardan, which is a little more than just 2 u-joints slapped side by side. The real benefit of a double is you can run greater angles and also mis-matched angles with no vibration. That is why the vast majority of 4x4 with straight front axles have front drive shafts that use a Double Cardan to account for caster axle rotation.

I recently took my truck to a driveshaft shop. They rebuilt it and put in a new upgraded center slip yoke. Nice looking piece....but it vibrates. Started poking around. They just rammed in greasable ujoints and didnt check axial play. Also all the clips are black meaning they installed bulk clips for an aluminum shaft which are a different thickness then the standard copper ones, or the selection that comes in the bag when you buy good spicer ujoints. Rear u joint had enough play to feel and the others had the clip on one side flat and the other fanned out. Meaning the u joint is not centered and also buried into the caps. Wont rattle your teeth out but still a "whOOOm.....WhOOOm...WhOOOm" above 70kph. Also means they didnt road test it. Everyones in a hurry today to change parts and throw you out the door instead of doing an actual diagnosis LOL.

Thanks Tony, this extended info from the last video. Your illustrations showed perfect phasing of the front and rear joints of a driveshaft, excellent. But no explanation of the importance of phasing of joints. It is the most important aspect of the use of two joints in harmony. Thanks

I had a 65 Dart Charger with the 273 hipo. It had a 7-1/4" rear and I replaced it with a 8-3/4" rear from a 340 Dart that was trashed. I had to get the driveshaft shortened and I told them to balance it. Well it had a bad vibration at 65-80 mph. I thought it wasn't balanced but the driveshaft company said it was slightly bent? He apologized and said his people screwed up. He said it didn't need balancing? I installed it and everything was good up to 120mph. Glad they stood behind their work. Great video Tony I didn't check the pinion angle as it looked good and was a stock housing. That was way back in 1971.

Back in the day my 69 runner with a 440 4 gear used to explode u joints when you dumped the clutch- now I know why!

Being a class 8 mechanic 35 years this is one of the things I diag and fix. Have box trucks with 4 driveshafts and air ride with a vibration I road test it. A drive will indicate u joint angle or out of balance. U joint angle will induce a vibration on acceleration or coast on light throttle the vibration will be less. Out of balance will be speed specific usually you can drive through it like a bad tire. I work at a Freightliner dealership that has 10 other franchises and other makes and send all these vibrations to our shop my foreman says my ass is better than any vibration analyzer that we have used because they tried when I was on vacation told it was wheel end I came back it was drive line imbalance.

Mike bought a 1 year old 1970 SS El Camino with 350 motor . Came over to Joes house from the car lot saw us out in his front yard punched it and had wheel hop blew the rear yoke and U joint and it took 2 months to find one .

Wow, so much valuable knowledge here. Thanks, Tony

More good stuff to know! Now I can't wait to check my old Mopars out to see how the driveshafts are angled. They are mostly stock so I assume they should be pretty much ok, but it will still be great to check out. And damn, I had never heard of the compression on the zerk hole. Another thing that gets overlooked a lot.

Very good explanation. Also, do not over tighten the u bolts on the joint caps, just a good snug tightening.Can create a vibration.

The case where I see ujoints fail due to lack of movement is subarus (and likely others, but i work on a lot of subarus). Since they have independent rear suspension with an almost completely straight driveshaft, the ujoints do not move enough to lubricate and they end up with terrible false brinelling.

Learnt my lesson the hard way with stupid strap type yokes One prop shaft on the ground at the side of the road later and point made 😆 U bolts for life! 😎

The double Carson joint you didn’t show was used at the rear of all full bodied GM cars. Cadillac had both front and rear double Cardons from the mid sixties. Their weak link was the centering ball in the joint. Especially at the rear, water would get in past the seal and rust out the ball, its cups, and the tensioning spring causing misalignment and vibration. The individual joints would be fine but you had to replace one because the cups were retained by injected plastic which got cut during disassembly. The ball was part of the shaft on early models so that meant a new, very expensive, shaft or a lot of very expensive precision machine work plus 4 new joints and two ball kits on the early Caddies.

As always another jem of knowledge from uncle Tony.

I don’t quite understand the putting the u-joint in compression, how exactly is that done? I know you explained it but I’m not catching on as to how

Great video UT! Now how about a video on what you need to use to measure the angles of the diff and tail shaft yokes and what can be done to correct it.

my CV axle snapped, so I welded the broke stud back onto the CV hub... 4918 filler and 3/4 inch cut out of the broke section 50/50 split on fracture location. oil field frack well filler rod... 1 inch stud becomes a 700hp SFI patch. 100kpsi joint

Another good lesson as usual. I was surprised, though, that you didn't mention anything about u-joints that have no grease fitting. I've always thought they were supposed to be stronger since there's no grease fitting hole.

I see your charger in the background. My first car was a 66 charger. Man o man I loved that car.

Even if you do not have a high performance application...never reuse the ujoint bolts and straps. They are not expensive...just keep 5 on the shelf and use new.

Again, another great video on this UTG. I'm in the process of converting a 1965 Dodge Dart GT to Manual Trans and a V8. The car came stock with the 225 Slant 6 & automatic with the "Ball & Trunnion" drive shaft, due to the lateral angle design of the early A-Bodies. To correct this (because of what I'm doing with it) I have to straighten out that angle in order to do away with the need for the Ball & Trunnion for the standard Ford Slip Yoke on the 3-speed manual that is being swapped into it. As you clearly stated, a Manual Transmission is completely unforgiving compared to that 1965 "Slush-Box" automatic that was in there. I've tried my best to explain this to others, but as you are finding as well... it's a tough thing to explain to people. If I was to just drop this engine and tranny into this Dart, following the placement Mopar did.... I will have extreme U-Joint wrap.

Nice and thanks UT. My 2 pence. As I recall when a u-joint goes bad and the needle bearings get worn or flattened and it starts to stick the u-joint launches the driveshaft forward into the trans output shaft making a loud clunking sound. That is if the smell of burning grease don't give it away first.

Just this afternoon I was running a rototiller behind my tractor and literally smoked a u joint that measure 1.5" x 4.25" across the joint turning around 1000 rpm, of course the angles are in the not good to absolutely not and beyond with a lot of jumping of the triller! O well just dollars to replace the joint and yoke $%@^. Didn't know about compressing the grease fitting Thanks for the info.Fred

If it's for high performance just use non greaseable because the cross is solid making them stronger

Thanks for this video!

Thank you!

Like your videos alot. Always interesting tidbits of knowledge that I know took you time, frustration, money and pain to learn. In the past, when I had problem to fix, I used to have to go to the library (remember when people had to go to the library for answers?) and spends weeks trying to find answer for it. Nowadays, I can just watch a video, go figure. Anyways, could you possibly number your videos? When I do find a topic I want to explore, it's always a later video and I can't locate the earlier one in the sequence and can't tell when it was created. It just says 2 years ago, 4 years ago, 6 months ago. Thanks

Super Good Uncle Tony.

your a great Teacher ,Thanks

This information is superbly helpful

Broke many ujoints until someone told me to tryout a Spicer joint which was great untill that torque found another weak spot! LoL Thanks UT! 😎

cardan joint...found on the front driveshaft of all 70s jeep cherokees. they were great until they came apart and knocked the side of the transmission off. thats the only reason i ever had to change a th400 in a cherokee

The roller bearings needing to roll a little is part of why even with an independent rear the driveshaft still has a little bit of angle to it. Generally if it’s perfectly straight it tends to cause the joints to wear a little spot with the rollers as they’re basically just sitting in one spot rubbing.

I'm a little crazy with the grease gun. Some would say I over do it. But it keeps the joints alive. Good video as always

I need to check my u joints now and see if I have them properly installed on my sbf powered 90isuzu short bed single cab drag truck.

That Ball and Tenion joint I had to buy full rebuild kit just to buy rubber boot I’m putting a 55’ DeSoto 291 in a Model A that I got in basket case has a 48’ Ford front axle 69 Impala Disc Brakes (4piston like Vette) I put Lincoln v-12 front main spring . Has a 55’ Chevy rear axle (had 283 SBC when purchased). I have a Franklin Quick Change Rear Axle and 3 short tailshalf 727 Cores all three are 2 different u-joint & 1 ball & pin with parking brake like old powerflite My wheel base is 10 1/2” shorter then stock Model A frame , 3 1/2” front axle is behind spring & rear axle is 7” in front of spring . I was told a fiberglass 33’ Willy’s Coupe may fit my frame But in mean time I have a 29’ Coupster Steal Ford Body was a five window coup that had a full steel flat roof from factory it was cut off and lower part of roof panels were missing I had only the roof top to just under the top door hing top three inches of roof top. I had it in my yard and my dad tossed it out and a scrap man got it before I could save it. Unfortunately my dad also tossed out a matching pair of Hemi valve covers , I was going to have chromed plated, 😢 That roof hurts me more then those valve covers in a way. Most Model A Coupes had cloth top Mine didn’t and it was factory I wish I had the original Ford Engine this car came with. Oh yeah

You should check and see if they make a yoke there takes u bolts for for the differential you're working on. I've got a Dana 80 one of the bolt holes on the yolk broke. I did some research and found a yolked it took u bolts

Wow I had totally forgotten about the ball and trunion joint been a long time

Just stumbled upon "Kim fixes things" and she is in your shop, appears you are an equal opertunity mechanical guru, good for you. I'm not there yet

Since we're on the subject of drivelines, I'd like to see a video dealing with the various "series" of u-joints. For example, the differences between a Spicer 1310 and a Spicer 1330 and what joint is best suited to what application.

Yes, my fine thread bolts are getting crappy on my diff yoke.

The 2 U-joints cancel each other out. the only thing that will cause vibration is the varying driveshaft speed but the wheel speed will be constant

There is also the CV joints that have a bunch of balls in them. There is no shaft but the inners and outers form to the balls. Kinda like splines. Hard to explain. You see those on front wheel cars all the time.

I have a question. Is there a strength difference between the flange mount style yoke like on a foxbody and the older u-joint style yoke. Obviously I'm talking stock for stock. If there is a difference do you think it's worth changing from one to the other?

You the man!! Ty very much for sharing your knowledge,!! Now if you could let me know why dog barks at chem trails!! Awesome job!!

I have 8 of them in my 87 Ford ranger 4x4 3 in the front differential and 2 in the front drive shaft and 3 in the rear driveshaft good times

Driveshaft phase! What you said, regarding the up-down angles of the transmission, driveshaft, and pinion yoke, also holds true for side-to-side settings - which will come in to play when you introduce a rearend with an off-center pinion to a car with a perfectly centered transmission and driveshaft. If your engine and transmission aren't dead-nuts straight and the rearend pinion yoke is, then you're out of phase in that geometric plane. The important part is that the transmission output shaft/yoke is parallel with the pinion shaft yoke in both the up-and-down, and side-to-side, planes, which achieves proper phase. It's easier to perfect the side-to-side plane. The up-and-down plane is best set for the operating conditions in which the car spends the bulk of its time.

He says at high angles it binds but what he's talking about i think is less binding and more the design as he was saying...at a certain point in the rotation because of the 4 point contact design it reaches a spot where the driven side of the joint has to spin slightly faster for a very brief moment for the joint to overcome the geometry and it can seem like a vibration...well it is a vibration...but it's caused by that tiny speed up and slow down more than excess play or an actual bind in my opinion... honestly a slightly worn joint can achieve a higher angle before experiencing the same effect...I'm probably making no sense and sounding like I've been whacked in the head by a driveshaft lol. From my experience if you actually bind a u joint it finds the weakest spot... which personally I'd like to be a strap...if you break a strap you know not to try that a second time and can rig it up well enough to get home with some repurposed metal conveniently already attached to the truck! Again sorry if my explanation makes no sense it's hard to describe but fairly easy to demonstrate with the parts.

When replacing the screw in bolts with bolts and nuts allways use grade 5 or better bolts

Uncle Tony your jeeps front driveshaft has a double Cardone joint at the transfer case

Thank you Uncle Tony.

HOWdy U-T-G, ... Thank ... YOU - "U" - Yew JOINTS ! Pretty ... but ... they are hard to keep "LIT" ! COOP the WiSeNhEiMeR from Richmond, INDIANA ...

Yep jacked up 4 wheelers put the drive shaft in a bind. I have never seen any vehicle with the drive shaft in a level straight line. My '80 Ramcharger has the cardan joint on the front shaft and it is a bitch to take apart and put back together.

I would like to see Uncle Tony address the issue of ring and pinion ratios and tire diameter. Does a shorter tire actually work out to mimic a lower rear end ratio in practice?

🥝✔️ I'm in Pickle Paradise now. Thanks UTG.

Wow now I know why i broke the yoke one time,pretzeled three drive shafts on my 70 340 swinger! 4 grand hole shots imput and output being equal caused these problems!!! Chevy guy’es hated this car…I sand bagged these guys’d,because with my holes hot ! Back in early 1970smopar for ever!!!! A body was king…340s and 430 gears ! Hell y’all

Great video. I always enjoy learning something new. Thanks for sharing

I didnt realize how much and how easy driveshafts can bind until I worked in auto salvage. I've been in a tussle trying to get at bolts in cars that no longer could be lined up. Still remember this one BMW driveshaft that taught me not to take all the bolts out of one side before loosening the other side. Still miss that job and how it paid. Minimum wage just to be there plus a set amount per part. The owner had a 'get as many parts off vehicles and on the Internets' mentality so it worked out great.

Hi Tony! Do you know anyone who has compared wear, load abilities, and resistance to operational grime with OEM new u-joints and a few popular aftermarket brands too?

Very good Tone, great info today. Most don’t consider this

You never want a card an joint to run at zero angle. The trunion will absolutely end up with false brinnelling. You always want 0.5 to 1.5 degree angle. Same reason Rzeppa joints don’t run at zero degrees.

How does one check to see if a U joint is still good or about to wear out??

You got any info on double Cardenas?

I always hated rebuilding the Cardan CV joints in the rear of early to mid 70's big GM cars. that spring between the joints was the worst. I invented new swear words working on them.

Great video! Can you please do a video for 1 second (or tenths) upgrades. Also show how many pounds/ upgrades to shave per 10th in the 1/4 mile . I would love to see a car RU-vidr do this.

A U-joint IS a cardan joint. The CV joint that you called a cardan joint is really called a double cardan joint. 1/4-20 is course thread, not fine. 1/4-28 is fine.

Let’s get back to the 4.0 rebuild!!

I have some drive line noise. I replaced the carrier bearing, Chevy s 10 extended cab truck. It was not really bad, but the rubber mounting was broken. I still have rumble under load. I checked the u joints, all 5 of them. They seem fine. I still think it is a u joint because the rumble is like on off on off like a u joint spinning. Any ideas.

Wow. Great to know! Thanks.

65 a body trunnion driveshaft with u-joint 14.5 lbs.

Simple, and true.

Great knowledge, brother.

The red Mopar joint you called a CV joint is NOT a CV joint. It functions as a conventional u-joint but is designed uniquely. It contains 2 balls that roll and pivot like the caged rollers would, AND they roll in and out to accept driveshaft length changes during suspension movement. Other designs use splined shafts on the transmission and yoke. The red joint has only a 2 axis design, not 4 like the doubled u-joint you later illustrated, a design that neutralizes the "velocity" differences. Therefore the red is not constant velocity. Think about it.