CV's, the good the bad, ect...
03-17-2007, 11:49 AM
#1
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Thread Starter
CV's, the good the bad, ect...
All this talk about CV's when they are and are not more likely to break etc..., got me thinking that maybe it's a good time to get all of us up to speed before myths grow into legends.
First off, my background: I acquired a 1st gen 4runner in the mid 90's. I had never 4 wheeled but have always been a gear head. I was working full time as an engineering lab tech and going to school part time for mechanical engineering. My friends were engineers/4wheelers and taught me much. I'm one of those people who is totally incapable of leaving anything alone. I love to tinker. I installed my lift kit myself and began this little journey modifying this and that. I broke stuff, fixed stuff, learned to weld, used my truck for design projects in school, etc... In 2004 a thread popped up about ball joint spacer overseas and a friend an I decided to start SDORI which was nice because I was one poor college student. I got my bachelors in mechanical engineering at SDSU. I'll have my MSME here at SDSU shortly in advanced hybrid and general automotive design. I have been inside, around, and out of the 1st/2nd gen suspension so many times it's hard to believe and got to take part in dispelling many myths like, for example, the one where people thought you needed stiffer torsion bars when you cranked them up to "hold the lift". In fact, the load on the torsion bar goes down when you crank them up due to increased a-arm angle with respect to the force of gravity.
On to the good stuff....
Let me start by putting IFS CV's and solid axle birfields into perspective. If you compare a stock IFS CV to a stock birfield and put 33" tires on each truck, you will break way more birfields than CV's. They are not weak when compared to a stock birf. The reason the solid axle can tolerate larger tire sizes is because the weak birf has been specially treated to make it strong. Guess what, that same heat treating process can be done to a CV joint just as easily but more on that later. The point of this paragraph is illustrate that our IFS CV's are not "weak", they just haven't been modified to be excessively strong.
Ok, let's take a look at what conditions break CV joints. To break a joint at all you need one thing, torque. Assuming that you have your foot in the pedal and therefore have torque from the engine, you need traction. Traction without torque won't break a joint and neither will torque without traction. Traction is linearly (or very close to such) related to the force of the ground on the wheel. Another factor that can increase the likelihood of failure is angle. The steeper the mean angle the more likely the chance of failure therefore it is desirable that our suspension be compliant to make life on the CV easier when torque is highest.
Now lets look at the relationship between traction, angle, and breakage. When weight on the wheel is highest, one hopes the angle is least. What I mean is when you have a lot of weight on the wheel the suspension, if set up properly, is compressed and CV angle is minimal. When the angle is steepest, there is little or no weight on the wheel and therefore no traction so no torque so no breakage. If you have an open front diff, you only have as much torque on either joint as that of the front wheel with the least traction. With a locker you have max torque on the wheel with the most weight on it. If you like to wheel with your foot to the floor all the time you are going to break all sorts of things all the time and all bets are off.
CV joint and wear: We are off roaders and therefore build our vehicles for special purposes. Often, we have to make trade offs to save one part at the expense of another. If you increase the clearance between your a-arms, the CV's are at a steeper angle and will wear more quickly. But, the real questions as I see it are two fold. One, does the increase in wear even matter? Two, are the trade offs worth it?
One: CV joints last hundreds of thousands of miles. A 50% decrease in life might mean 100K miles instead of 2. Even if you run your CV's at an extreme angle and lessen the life to 10K miles, how long will it take to run that many miles in 4 wheel drive? Keep in mind that freewheeling ADD is not loading the joint so it won't wear out before your truck is rotting in a junkyard due to other reasons. My point, average CV angle (say +1.5" lift over stock) just isn't that big of a deal when it comes to wearing out the joint.
Two: The tradeoff for accepting more CV wear are increased compression travel and clearance between your front wheels. Increased travel will allow the suspension to absorb energy that would otherwise be passed on to the chassis. That's fancy talk for saying that when the a-arm hit the bumpstops force get really high really fast and you risk bending/breaking things. That's when the rear a-arm mounts start to spread. Increased clearance means you hit the front crossmember much less on rocks, etc... That is a good thing in my experience as that knocks out alignment, etc... So to sum up, we each need to decide for ourselves if it is worth a small amount of CV life (a part one can swap) to extend that of parts we can not just bolt when they bend like our a-arm mounts and increase our truck's overall capability.
Max CV angle and suspension travel: "Back in the day" many of us experimented with our 4" bracket kits to see just how far up our suspension can travel without issues. Rockstomper make kits that greatly improved up travel. I made my own out of aluminum stock which retained the stock bumpstops and angled them in appropriately with that of the a-arm at full compression. The CV is a rotating part so there is not up/down as far as it is concerned. Therefore, the CV can tolerate as much a-arm up angle and is can down. The long and short of it is that my old '89 with BJ spacers and my home grown up travel kit had 14" of travel. I had a Trutrac in the front diff and never broke a CV joint. The joint did not bind at all ever. Many of us did this mod, it was "the" mod to do. My point here is to illustrate the capabilities of modified IFS and show the limits of our CV shafts so we don't unnecessarily worry ourselves.
An aside: Many of you might be shocked at the amount of travel available to our trucks with a 4" kit. Well don't rush out and buy one until you read on because this comes at a cost. One, if you have 15 years and 200K miles on a set of ball joints, they have worn within that window. When flex them farther the unworn part is now going in to the socket. This will wear them out wicked quick. I know this from experience. When you replace them and they operate over the wide range from the beginning, they last and last. I this too from experience. Bracket kits fall out of alignment a lot. Bracket kits sometimes fracture as they are often cast and therefore prone to brittle fracture. I know that from yet more experience. Finally, if you have like I did a bracket kit with t-bar crank and eventually spacers, that much lift in the back will likely give you driveline vibes which can be really expensive to fix. For me it was $500 driveshaft with a double cardan joint.
So, the best for CV wear is obvious, bone stock height. The worst for the chassis and crossmember is obvious, bone stock height. The tradeoffs are up to each individual to decide for themselves.
Now, lets talk about making CV's stronger. Without cryo treatment, before the Longfield, the Toyota axle was falling off the map as far as rock crawling was concerned. I'll be straight to the point, we can cryo treat our CV's and increase the strength. If anyone wants to run 35's or whatever and enough are interested, I will do the research and source a heat treater. Metallurgy has come a long way and there is no reason us IFS guys can't take advantage of those gains.
My fingers are now tired.
Frank
First off, my background: I acquired a 1st gen 4runner in the mid 90's. I had never 4 wheeled but have always been a gear head. I was working full time as an engineering lab tech and going to school part time for mechanical engineering. My friends were engineers/4wheelers and taught me much. I'm one of those people who is totally incapable of leaving anything alone. I love to tinker. I installed my lift kit myself and began this little journey modifying this and that. I broke stuff, fixed stuff, learned to weld, used my truck for design projects in school, etc... In 2004 a thread popped up about ball joint spacer overseas and a friend an I decided to start SDORI which was nice because I was one poor college student. I got my bachelors in mechanical engineering at SDSU. I'll have my MSME here at SDSU shortly in advanced hybrid and general automotive design. I have been inside, around, and out of the 1st/2nd gen suspension so many times it's hard to believe and got to take part in dispelling many myths like, for example, the one where people thought you needed stiffer torsion bars when you cranked them up to "hold the lift". In fact, the load on the torsion bar goes down when you crank them up due to increased a-arm angle with respect to the force of gravity.
On to the good stuff....
Let me start by putting IFS CV's and solid axle birfields into perspective. If you compare a stock IFS CV to a stock birfield and put 33" tires on each truck, you will break way more birfields than CV's. They are not weak when compared to a stock birf. The reason the solid axle can tolerate larger tire sizes is because the weak birf has been specially treated to make it strong. Guess what, that same heat treating process can be done to a CV joint just as easily but more on that later. The point of this paragraph is illustrate that our IFS CV's are not "weak", they just haven't been modified to be excessively strong.
Ok, let's take a look at what conditions break CV joints. To break a joint at all you need one thing, torque. Assuming that you have your foot in the pedal and therefore have torque from the engine, you need traction. Traction without torque won't break a joint and neither will torque without traction. Traction is linearly (or very close to such) related to the force of the ground on the wheel. Another factor that can increase the likelihood of failure is angle. The steeper the mean angle the more likely the chance of failure therefore it is desirable that our suspension be compliant to make life on the CV easier when torque is highest.
Now lets look at the relationship between traction, angle, and breakage. When weight on the wheel is highest, one hopes the angle is least. What I mean is when you have a lot of weight on the wheel the suspension, if set up properly, is compressed and CV angle is minimal. When the angle is steepest, there is little or no weight on the wheel and therefore no traction so no torque so no breakage. If you have an open front diff, you only have as much torque on either joint as that of the front wheel with the least traction. With a locker you have max torque on the wheel with the most weight on it. If you like to wheel with your foot to the floor all the time you are going to break all sorts of things all the time and all bets are off.
CV joint and wear: We are off roaders and therefore build our vehicles for special purposes. Often, we have to make trade offs to save one part at the expense of another. If you increase the clearance between your a-arms, the CV's are at a steeper angle and will wear more quickly. But, the real questions as I see it are two fold. One, does the increase in wear even matter? Two, are the trade offs worth it?
One: CV joints last hundreds of thousands of miles. A 50% decrease in life might mean 100K miles instead of 2. Even if you run your CV's at an extreme angle and lessen the life to 10K miles, how long will it take to run that many miles in 4 wheel drive? Keep in mind that freewheeling ADD is not loading the joint so it won't wear out before your truck is rotting in a junkyard due to other reasons. My point, average CV angle (say +1.5" lift over stock) just isn't that big of a deal when it comes to wearing out the joint.
Two: The tradeoff for accepting more CV wear are increased compression travel and clearance between your front wheels. Increased travel will allow the suspension to absorb energy that would otherwise be passed on to the chassis. That's fancy talk for saying that when the a-arm hit the bumpstops force get really high really fast and you risk bending/breaking things. That's when the rear a-arm mounts start to spread. Increased clearance means you hit the front crossmember much less on rocks, etc... That is a good thing in my experience as that knocks out alignment, etc... So to sum up, we each need to decide for ourselves if it is worth a small amount of CV life (a part one can swap) to extend that of parts we can not just bolt when they bend like our a-arm mounts and increase our truck's overall capability.
Max CV angle and suspension travel: "Back in the day" many of us experimented with our 4" bracket kits to see just how far up our suspension can travel without issues. Rockstomper make kits that greatly improved up travel. I made my own out of aluminum stock which retained the stock bumpstops and angled them in appropriately with that of the a-arm at full compression. The CV is a rotating part so there is not up/down as far as it is concerned. Therefore, the CV can tolerate as much a-arm up angle and is can down. The long and short of it is that my old '89 with BJ spacers and my home grown up travel kit had 14" of travel. I had a Trutrac in the front diff and never broke a CV joint. The joint did not bind at all ever. Many of us did this mod, it was "the" mod to do. My point here is to illustrate the capabilities of modified IFS and show the limits of our CV shafts so we don't unnecessarily worry ourselves.
An aside: Many of you might be shocked at the amount of travel available to our trucks with a 4" kit. Well don't rush out and buy one until you read on because this comes at a cost. One, if you have 15 years and 200K miles on a set of ball joints, they have worn within that window. When flex them farther the unworn part is now going in to the socket. This will wear them out wicked quick. I know this from experience. When you replace them and they operate over the wide range from the beginning, they last and last. I this too from experience. Bracket kits fall out of alignment a lot. Bracket kits sometimes fracture as they are often cast and therefore prone to brittle fracture. I know that from yet more experience. Finally, if you have like I did a bracket kit with t-bar crank and eventually spacers, that much lift in the back will likely give you driveline vibes which can be really expensive to fix. For me it was $500 driveshaft with a double cardan joint.
So, the best for CV wear is obvious, bone stock height. The worst for the chassis and crossmember is obvious, bone stock height. The tradeoffs are up to each individual to decide for themselves.
Now, lets talk about making CV's stronger. Without cryo treatment, before the Longfield, the Toyota axle was falling off the map as far as rock crawling was concerned. I'll be straight to the point, we can cryo treat our CV's and increase the strength. If anyone wants to run 35's or whatever and enough are interested, I will do the research and source a heat treater. Metallurgy has come a long way and there is no reason us IFS guys can't take advantage of those gains.
My fingers are now tired.
Frank
03-17-2007, 01:02 PM
#2
Contributing Member
Hey Frank, I'd be interested in the cryo treatment even though I've never broken one (knock on wood). Would they have to be new CVs or would the cryo treatment work on used CVs? They didn't even talk about cryo treatment back when I took metallurgy. 
Last edited by mt_goat; 03-17-2007 at 01:03 PM.
03-17-2007, 02:32 PM
#4
Registered User
Thread Starter
This is especially helpful for cast parts where they tend to cool quickly forming lots of discontinuities and places for cracks to form.
Honestly, our IFS is very well designed with two weak spots. One is the CV's and the other the idler arm. Both can be addressed.
Frank
03-17-2007, 03:20 PM
#6
Registered User
Now, lets talk about making CV's stronger. Without cryo treatment, before the Longfield, the Toyota axle was falling off the map as far as rock crawling was concerned. I'll be straight to the point, we can cryo treat our CV's and increase the strength. If anyone wants to run 35's or whatever and enough are interested, I will do the research and source a heat treater. Metallurgy has come a long way and there is no reason us IFS guys can't take advantage of those gains.
I'd be interested to see what a set of cryo'd T-100 axles would run.
Or are we just talking about the cv's themselves? Do the shafts break easily? Would they benefit from Cryo treatment as well?
Now what about the 7.5" center section? Can this be treated or replaced with an 8" center section?
Last edited by deathrunner; 03-17-2007 at 03:22 PM.
03-17-2007, 03:21 PM
#7
Contributing Member
An excellent post, thank you ripster...Very good information.
I will disagree a bit here.
The idler arm is certainly a weak spot, but actually, the whole rest of the steering system is weak as well. I have bent my share of idlers, but have also folded tierod adjusting sleaves, and have see relay rods bent too...
Granted, those are under harsh conditions, but the rack and pinion set up of the 3rd gens is much more resistant to abuse.
In addition, the lower ball joint mounts, on the lower arm, are exceptionally easy to push out of the range where the truck can be aligned.
I'm not saying you are wrong, but i think toyota could have done better, becasue they really got it right with the third gens.
Anyway, this isn't to start a bunch of bickering, just adding in some personal experience and opinions based on my frustration with this set up.
The idler arm is certainly a weak spot, but actually, the whole rest of the steering system is weak as well. I have bent my share of idlers, but have also folded tierod adjusting sleaves, and have see relay rods bent too...
Granted, those are under harsh conditions, but the rack and pinion set up of the 3rd gens is much more resistant to abuse.
In addition, the lower ball joint mounts, on the lower arm, are exceptionally easy to push out of the range where the truck can be aligned.
I'm not saying you are wrong, but i think toyota could have done better, becasue they really got it right with the third gens.
Anyway, this isn't to start a bunch of bickering, just adding in some personal experience and opinions based on my frustration with this set up.
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03-17-2007, 03:29 PM
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Correct me if im wrong, but isnt the weak part of the CV the portion that holds in the bearings. This does not change if it is cryo/heat treated. The shafts themselves will hold more power than any toyota on this site can produce, but the bearing enclosure is that needs to be stengthened. When you find a solution to this mess, let me know cause i am VERY interested!
03-17-2007, 03:32 PM
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very interesting...great reasreach
i think the trade off you get with bj spacers is fine...plus you can't beat the price...i will also be tossing in new upper ball joints when i do it...as for the rear....chevys(which i have sitting on my porch sand blasted and ready) i always knew these IFS's had some good in them...even though everyone esle may not think so
i think the trade off you get with bj spacers is fine...plus you can't beat the price...i will also be tossing in new upper ball joints when i do it...as for the rear....chevys(which i have sitting on my porch sand blasted and ready)
i always knew these IFS's had some good in them...even though everyone esle may not think so
03-17-2007, 03:40 PM
#10
Registered User
hmmmmmmmmmmmmmmmmmmmmmmm.......................... ......................
03-17-2007, 06:02 PM
#13
Yeah, the rubber might be damaged.
Seriously, very informative post.
So what's got me all
is the torsion bar explaination, or lack there of. I just can't seem to get that idea to make any sense.
Seriously, very informative post.
So what's got me all
is the torsion bar explaination, or lack there of. I just can't seem to get that idea to make any sense.
03-17-2007, 09:59 PM
#14
Contributing Member
When you crank the torsion bar, all you've done is increase the angle at which the a-arm meets the frame, you haven't put any more stress on the bar...Essentially, the bar will "flex" (which is twisting) enough to hold the truck off the ground. It will "flex" the same if you have the a-arms level, or cranked for a lift.
People think that you are actually twisting the bar more, and thus will fatigue the bars, when you aren't really doing that at all. You are simply rotating the bar, which rotates the arm, which lifts the truck.
The reason for the harsher ride with cranked bars is becasue of the angle of the arm. This is difficult to explain without a diagram, so please bear with me, the terms aren't going to be very exact.
Basically there are two components of the force, "horizontal" and "vertical". The bar can only cushion the "vertical" force, not the "horizontal". By cranking the bars, you increase the amount of horizontal force, which is transfered to the frame, and you feel a crappy ride.
This is why BJ spacers are the best way to get 1.5" of lift w/out decreasing ride quality. You can maintain the angle of the upper a-arm at stock, and gain clearance too.
I'm sorry, i know that is a crappy way to put it, it would be easy to show in person, but damn impossible here. Anyway, clear as mud?
Last edited by AxleIke; 03-17-2007 at 10:00 PM.
03-18-2007, 02:57 AM
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another reason the IFS seems to be weaker is that they operate not just in 1 plane of movement, like the birfs, but in 2...
birfs just moves forward and backwards.
CVs goes up and down, forward and backwards...
granted, when you feed a 150:1 ratio torque even into a inner CV joint made for porsche 959s... even those break too...
ask me how i know... lol...
birfs just moves forward and backwards.
CVs goes up and down, forward and backwards...
granted, when you feed a 150:1 ratio torque even into a inner CV joint made for porsche 959s... even those break too...
ask me how i know... lol...
03-18-2007, 10:06 AM
#18
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Thread Starter
An excellent post, thank you ripster...Very good information.
I will disagree a bit here.
The idler arm is certainly a weak spot, but actually, the whole rest of the steering system is weak as well. I have bent my share of idlers, but have also folded tierod adjusting sleaves, and have see relay rods bent too...
Granted, those are under harsh conditions, but the rack and pinion set up of the 3rd gens is much more resistant to abuse.
In addition, the lower ball joint mounts, on the lower arm, are exceptionally easy to push out of the range where the truck can be aligned.
I'm not saying you are wrong, but i think toyota could have done better, becasue they really got it right with the third gens.
Anyway, this isn't to start a bunch of bickering, just adding in some personal experience and opinions based on my frustration with this set up.
I will disagree a bit here.
The idler arm is certainly a weak spot, but actually, the whole rest of the steering system is weak as well. I have bent my share of idlers, but have also folded tierod adjusting sleaves, and have see relay rods bent too...
Granted, those are under harsh conditions, but the rack and pinion set up of the 3rd gens is much more resistant to abuse.
In addition, the lower ball joint mounts, on the lower arm, are exceptionally easy to push out of the range where the truck can be aligned.
I'm not saying you are wrong, but i think toyota could have done better, becasue they really got it right with the third gens.
Anyway, this isn't to start a bunch of bickering, just adding in some personal experience and opinions based on my frustration with this set up.
Frank
03-18-2007, 10:08 AM
#19
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Thread Starter
Frank
03-18-2007, 10:19 AM
#20
Contributing Member
This is very interesting. I have heard much to the opposite regarding the 3rd gen. Do you maybe mean the 4th gen where all the steering we relocated up high an out of the way? 3rd gens have lots of steering rack issues from leaking to all out failure. They are much less tolerance of increasing the travel window than the 1st/2nd gen set up. Many people have compared the two side to side the earlier chassis have been judged much more durable. I haven't had a 3rd gen though so I can speak from personal experience.
Frank
Frank
I've had real good luck so far with mine even with a locker up front but I try not to turn much while the locker is engaged. I run an extra idler arm in the middle of the center link (or relay rod) though and that I relieves some stress on the factory idler and pitman arms.
Last edited by mt_goat; 03-18-2007 at 10:21 AM.
