Do ya think bigger U joints will help?

[MAXIMUS]

Hi all,

I've blow my u joints apart (badly) in my 280zx(406sbc).

Seems like they go right at the U joint.

Anyone think that if I get bigger u joints for my 1/2 shafts,I may "fix" the problem?

[BRAAP]

I wasn't aware that bigger U-joints were available for the Datsun half shafts? At least I haven’t seen any posts about these larger U-joints. Please share if you have heard of such U-joints. Currently, most people step up to the CV axles.

 

Being as you have the semi trailing arms that are known for severe aggressive squat under launch, (I’ve heard of guys altering the geometry of the semi trailing arm in an attempt to limit that squat under launch conditions, though not sure if that is a help or a hindrance for the hard core strip chassis set ups), but being as you most likely have to deal with all that squat under launch, and as a result, severe U-joint angularity, (the steeper the U-joint angularity the weaker the U-joint is by design. The less angle you have in the U-joint, the stronger), it seems like the CV axle is your logical choice. Unless, you can keep the car from squatting so much, and if so, then just follow the guidelines the other successful hard care drag racing U-joint users have done in regards to U-joint brand choices and set up.

[MAXIMUS]

Hey Braap,

I've got a guy here in Toronto who will modify my 1/2 shafts to accept a bigger U- joint.

Think it's worth a try?

[JMortensen]

I know you're not asking me, but I wouldn't do it. Like BRAAP says, the angularity of the joint causes it to be used in a position where it is not strongest. While a stronger U-joint might hold down more power, it's still being used at a weak angle in your ZX due to the semi-trailing arm suspension design.

 

CV joints don't have this problem with angularity (up to a point) and it's already been proven by others that they can hold down a lot more power than the 1/2 shafts. I'd put your money into CV adapter pieces and get the CV's in there instead.

[Daeron]

Look up CV Joints in wikipedia and read up.. it will open your eyes.

[Pop N Wood]

I don't know guys, they put U joints in semi trucks and cement mixers. I had a Ford Fiesta that once popped a CV joint.

 

I thought the main reason auto manufactures went to CV's instead of U joints is they are smoother.

 

While it may have been proven that of the commonly availble units for a Z, the CV's hold up better than U joints, I think you can throw that idea out the window when you start talking about other sizes of U joints.

[Daeron]

from wikipedia:

Early front wheel drive systems such as those used on the Citroën Traction Avant and the front axles of Land Rover and similar four wheel drive vehicles used Hardy-Spicer joints, [READ: U-joints] where a cross-shaped metal pivot sits between two forked carriers (These are not strictly CV joints as they result in a variation of the transmitted speed except for certain specific configurations). These are simple to make and can be tremendously strong, and are still used to provide a flexible coupling in the propeller shafts, where there is not very much movement. However, they become "notchy" and difficult to turn when operated at extreme angles, [READ: outside of their tolerance, which (at speeds seen in automotive use) is a bit more than ten degrees, the number 17 comes to mind but I cannot quote that specifically] and need regular maintenance. They also need more complicated support bearings when used in drive axles, and could only be used in rigid axle designs.

 

U joints work great, WHEN the axle in question does not depart from a straight angle greatly. However, when the axle is put at angle, the U joint is overly stressed because it is at (or beyond) the limit of its functioning range. CV Joints have a functioning range about twice that of U joints.

[jnjdragracing]

We worked with ujoints for a long time. We tried various configurations as well. The main problem with ujoints is the angle of load. Need to setup the car squat when launching for the ujoints to be straight, not in a bind.

 

We finally went to cv joints and have had great success with them. My brother Jerry finally achieved the 1/8 mile in 5.8 seconds on ujoints which was his goal. Did 1/4 mile at a best of 9.21 at SEZ#6 with ujoints.

 

To me they are too unpredictable. I have seen them break to often and it takes a hard digger to the left, we usually would break the drivers side. But at SEZ#6 we broke both at once.

 

I would highly recommend CV joints.

 

Oh I forgot to add, with the CV joints our best 60ft. to date has been a 1.32 60ft. The original CV Joints halfshafts with Modern Motorsports Companion flanges are still on the car with out failure so far. So I guess we are a pretty good test to what would hold up under drag conditions. I hope I did not jinx ourselfs for Pinks All Out - Bristol TN.

 

 

John

[Pop N Wood]

from wikipedia:

 

 

U joints work great, WHEN the axle in question does not depart from a straight angle greatly. However, when the axle is put at angle, the U joint is overly stressed because it is at (or beyond) the limit of its functioning range. CV Joints have a functioning range about twice that of U joints.

 

That says nothing about the relative strength of the two devices

 

Here is a link to a Cardan joint shaft that is rated for over 4000 ft-lbs of continuous torque.

 

I guess if what you read on Wikipedia is correct than the CV's on Z car should be good to something greater than that.

[JMortensen]

Why are we arguing over the relative strenth of CVs and U-joints? It's been done previously several times. CV's are better when the angularity is a factor, and ZX suspension has more severe angularity issues than the Z. Relatively speaking the U-joint is the stronger device (size for size) when used without angularity, but that isn't the case in the Datsuns. To put this in perspective, the 68 510 comes with the exact same U-joints and halfshafts that the jnj guys were using. The original app was a 100 bhp sedan. Compare to a 300ZXT CV which was designed for a 3000 lb sports car with 300 bhp. So size for size is not a parameter of our comparison.

 

It's not a mystery which is the stronger unit in practical terms, and in the ZX application upping the size of the U-joint still doesn't address the angularity issues. As an aside, http://www.wolfcreekracing.com makes a CV setup for 510s which have similar (but worse) angularity issues. A 510 picked up 3% whp on a dyno just by installing these CV's simply by eliminating the binding of the U-joint at severe angles.

[Pop N Wood]

Because it is all about options. If he can come up with a cost effective way to put in bigger U joints then that might be worth pursuing.

 

Past arguments, and I have been in quite a number of them, have concentrated on the relative strength of U joints and CV joints that were commonly available on Z cars or can be readily adapted to a Z car. I have already agreed that given that limited set of choices, then CV's are considered the better choice.

 

But that doesn't answer the question of "will bigger U joints fix the problem".

 

The answer is obviously "yes, but....."

 

Or should we just shut the site down and direct every question to the search feature because obviously if it is possible then it has already been talked about?

[JMortensen]

I realize the shutting down the site comment is sarcastic, but in all seriousness there are still plenty of NEW discussions and innovations to be made with the Z, and we really don't need to start rehashing old stuff to keep new posts coming in.

 

I'm all for pursuing theoretical arguments but I didn't realize that's what you were going after. In practical terms though, the issue has already been settled. And although you can undoubtedly install a larger U-joint on the back of the ZX that will survive drag launches with a 406, unless you had a real love for U-joints I think going to the trouble to install them would be a waste of resources.

 

In theoretical terms, the suspension design of the ZX is still going to be harder on U-joints than it will be on CV joints so you'd still need a relatively larger U-joint than CV joint to handle a given power level. Shall we continue the theoretical discussion now?

[jnjdragracing]

Added more info at bottom....

 

We worked with ujoints for a long time. We tried various configurations as well. The main problem with ujoints is the angle of load. Need to setup the car squat when launching for the ujoints to be straight, not in a bind.

 

We finally went to cv joints and have had great success with them. My brother Jerry finally achieved the 1/8 mile in 5.8 seconds on ujoints which was his goal. Did 1/4 mile at a best of 9.21 at SEZ#6 with ujoints.

 

To me they are too unpredictable. I have seen them break to often and it takes a hard digger to the left, we usually would break the drivers side. But at SEZ#6 we broke both at once.

 

I would highly recommend CV joints.

 

Oh I forgot to add, with the CV joints our best 60ft. to date has been a 1.32 60ft. The original CV Joints halfshafts with Modern Motorsports Companion flanges are still on the car with out failure so far. So I guess we are a pretty good test to what would hold up under drag conditions. I hope I did not jinx ourselfs for Pinks All Out - Bristol TN.

 

 

John