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Fri Jan 14, 2022 4:52 am

It's been a long time since I've posted here, but I've done a load of searching and reading and I can't find an answer to this question. If I've missed it, please point me in the right direction.

I converted my Baja to IRS about 20 years ago, and for most of the time have run stock boxed arms, 944 CVs and stub axles, and Thing/Trekker driveshafts. I've never had issues with noisy CVs.

I've made myself some 3x2 arms (3" longer and 2" wider), which I'm running with VW bus axles, 944 CVs and stub axles. The CVs are a fresh set that I've polished and clocked, and they have brand new high angle boots.

The travel is limited so that the CVs are happy at full droop, and there is plenty of plunge available at all points of the suspension travel.

My issue is that the CVs are noisy under acceleration, and I'm concerned that I'm damaging them. I've tried my original CVs and the newly polished ones, same deal.

So my question is, does the angle of the driveshafts from above matter? My understanding was that with 3x2 arms you don't need to move the gearbox, and in all my static testing the CVs were happy with this setup. On a stock setup the hub sits forward of the gearbox output flange, but with my new arms the hub sits aft of the gearbox output flange. Under acceleration is the driveshaft being pulled into the gearbox by the torque?

So on your 3x2 or 3x3 setups have you moved the gearbox back? If you've moved it did you go with the full 3", or is there a magic middle point?

Or is is something else I've missed? You guys have lot more experience with longer IRS arms than me so your advice would be appreciated.

Fri Jan 14, 2022 7:42 am

You don’t need to move the gearbox for longer arms. The CV joints don’t care what direction the axle moves. Backwards, forwards, up, down… makes no difference so long as you don’t exceed the articulation and plunge of the joint… figure 25* is about the max for T4 cv joints, which is what non-turbo 944s used.

Fri Jan 14, 2022 11:01 am

It is not only the movement of up and down angle of degrees you also have to account for angle of degrees the offset between CV flanges too.
You have to add to the total.
Meaning you can get more up and down angle of degrees if CV flanges are straight across from each other.

Also do your replacement CV joints have the same size balls as your old ones?
If CV balls are larger you won’t get as much angle out of them.
Type 4, 924 CV balls are 17.5mm verses a type 2 that are 20mm

Fri Jan 14, 2022 11:20 am

Vanapplebomb wrote: You don’t need to move the gearbox for longer arms. The CV joints don’t care what direction the axle moves. Backwards, forwards, up, down… makes no difference so long as you don’t exceed the articulation and plunge of the joint… figure 25* is about the max for T4 cv joints, which is what non-turbo 944s used.

That's what I thought. Any idea what the issue might be, or am I being over sensitive to the sound?

Fri Jan 14, 2022 11:26 am

jsturtlebuggy wrote: It is not only the movement of up and down angle of degrees you also have to account for angle of degrees the offset between CV flanges too.
You have to add to the total.
Meaning you can get more up and down angle of degrees if CV flanges are straight across from each other.

Definitely, I would be able to get more vertical travel by moving the gearbox back so that the flanges are lined up, but I'd rather not if possible. I've limited travel so that the CVs spin happily during static testing.

jsturtlebuggy wrote: Also do your replacement CV joints have the same size balls as your old ones?
If CV balls are larger you won’t get as much angle out of them.
Type 4, 924 CV balls are 17.5mm verses a type 2 that are 20mm

Yes, they're definitely Porsche CVs with the smaller balls. I actually got rid of all my spare type 2 CVs during this process to ensure they didn't get mixed up. But whatever the CV is, they were fine during static testing. I would say I've played it very safe with my limiting as they're running at about 17/18 degrees.

Fri Jan 14, 2022 2:51 pm

FireDancer wrote: I would be able to get more vertical travel by moving the gearbox back so that the flanges are lined up, but I'd rather not if possible.

Honestly, it’s a bit of a wash. I found that cv joints of this type are significantly impacted by plunge. If you are near the limits of plunge, you loose articulation before the balls max out in the cages. Yes, you will have lower articulation for a given travel if you move the box back, but you increase your plunge by doing so. You may find it is actually better with the gearbox where it is because they won’t plunge quite as much. You run out of plunge a lot faster than articulation in most cases.

Only way to know is to play around with it.

Remove the transmission, and move it back a few inches with it supported with a jack, then cycle the arms and see what the difference is.

If you are not near the limits of plunge, moving the transmission back may gain you a small amount of travel. If you are near plunge limits, leave it where it is so the axle move in more of an arch than straight up and down.

Fri Jan 14, 2022 4:04 pm

I had a CV (new) that for some reason did not let the axle plunge smoothly, and was causing the CVs to make all kinds of noise when it hung up.

I replaced the center star, greased the splines on the new one real well, and the problem was solved.

Fri Jan 14, 2022 6:24 pm

You saying you polished the new CVs, are they moving freely? You want the CVs to be very loose. To almost like they are worn out. Making the openings in the CV ball cages so balls move freely.
On my own buggies I have stepped up to 930 CVs (one buggy is still type 4 CVs). I am using the Empi 930 race CVs, They are very loose fitting new. To the point if your not holding right the balls fall out.

Also if you are using a Bus transaxle, it being a hypoid design the mainshaft is not in the center like a Bug transaxle. It offset approximately 1/4in. Depending on how trans ais mounted you may come up with two different measurement between CV flanges.

Axle length does matter.
To find correct axle you need is to measure from center of each CV (the cup part) flange when they are parallel in height.
With this measurement subtract a 1/4 to 1/2in for correct axle length.
If you are using stock length axles the may not be long enough.

I am using the Empi chromoly axles on my buggies. Have had great luck with many years running them. They have long splines and no inner stop on them. Now I have had to shorten some of them to get correct length for different applications because unlike SwayAway they don’t make custom lengths only standard different lengths.

Sat Jan 15, 2022 7:04 am

Vanapplebomb wrote: FireDancer wrote: I would be able to get more vertical travel by moving the gearbox back so that the flanges are lined up, but I'd rather not if possible.

Honestly, it’s a bit of a wash. I found that cv joints of this type are significantly impacted by plunge. If you are near the limits of plunge, you loose articulation before the balls max out in the cages. Yes, you will have lower articulation for a given travel if you move the box back, but you increase your plunge by doing so. You may find it is actually better with the gearbox where it is because they won’t plunge quite as much. You run out of plunge a lot faster than articulation in most cases.

That's a very good point. Same principle as when we mount steering racks close to the beam to lower bump steer. Moving the gearbox so that the flanges are inline might cause issues with plunge as I'm not using long spline driveshafts.

Vanapplebomb wrote:
Only way to know is to play around with it.

Remove the transmission, and move it back a few inches with it supported with a jack, then cycle the arms and see what the difference is.

I did that when I designed the IRS arms. I'm building a Buggy and tested the setup on that chassis before swapping it onto my Baja. In static testing on the Buggy and Baja the CVs were happy throughout the travel, it's only an issue under power. I can do some more static testing though in case I missed something.

Vanapplebomb wrote:
If you are not near the limits of plunge, moving the transmission back may gain you a small amount of travel. If you are near plunge limits, leave it where it is so the axle move in more of an arch than straight up and down.

They're stock axles, so limiting plunge seems like a smart move. I'm glad I checked on here before moving the gearbox back 3".

Sat Jan 15, 2022 7:05 am

sailtexas186548 wrote: I had a CV (new) that for some reason did not let the axle plunge smoothly, and was causing the CVs to make all kinds of noise when it hung up.

I replaced the center star, greased the splines on the new one real well, and the problem was solved.

I'm using stock axles, so the CVs don't slide on the splines.

Sat Jan 15, 2022 7:14 am

jsturtlebuggy wrote: You saying you polished the new CVs, are they moving freely? You want the CVs to be very loose. To almost like they are worn out. Making the openings in the CV ball cages so balls move freely.
On my own buggies I have stepped up to 930 CVs (one buggy is still type 4 CVs). I am using the Empi 930 race CVs, They are very loose fitting new. To the point if your not holding right the balls fall out.

They're nice and lose, like the one shown in this video: https://www.youtube.com/watch?v=wsIn3z7dbjc
Not my video, but my CVs are all like that.

jsturtlebuggy wrote: Also if you are using a Bus transaxle, it being a hypoid design the mainshaft is not in the center like a Bug transaxle. It offset approximately 1/4in. Depending on how trans ais mounted you may come up with two different measurement between CV flanges.

I'm using a Thing/Trekker trans, so type 1.

jsturtlebuggy wrote: Axle length does matter.
To find correct axle you need is to measure from center of each CV (the cup part) flange when they are parallel in height.
With this measurement subtract a 1/4 to 1/2in for correct axle length.
If you are using stock length axles the may not be long enough.

I'm trying to get a setup that works with the axles I have, custom axles are expensive in the UK. When I built the arms all these measurements were good.

jsturtlebuggy wrote: I am using the Empi chromoly axles on my buggies. Have had great luck with many years running them. They have long splines and no inner stop on them. Now I have had to shorten some of them to get correct length for different applications because unlike SwayAway they don’t make custom lengths only standard different lengths.

Good to know in case I need to swap out the axles. Thank you.

Fri Feb 04, 2022 5:58 am

Can I get some expert eyes (and ears) on my videos?

Here is the plunge on the CVs at ride height, both sides and from a couple of angles:

RHS in motion from behind:

And from above:

LHS in motion from behind:

And from above:

I'm not running crazy angles, but they're not as smooth as I'd expect from freshly poshed CVs when they're put under power.

Fri Feb 04, 2022 11:13 am

Maybe it's an optical illusion but it looks like the outers have more of an angle than the inners. Seems impossible !! Also, It looks like the outers are at a too severe angle. Visualizing what I am seeing it seems like the inner race and balls would be very near or beyond the edge of the outer race.

Fri Feb 04, 2022 11:31 am

rayjay wrote: Maybe it's an optical illusion but it looks like the outers have more of an angle than the inners. Seems impossible !!

The GoPro fisheye lens doesn't help here, so it could be that.

In which plane do you mean? Front to back the CVs are parallel. Side to side, the stub axles have slight negative camber.

rayjay wrote: Also, It looks like the outers are at a too severe angle. Visualizing what I am seeing it seems like the inner race and balls would be very near or beyond the edge of the outer race.

I have measured the angles and it's within what the CV is meant to be able to cope with, but the rake on the driveshaft will reduce that. Under power testing seems to be very different to static testing.

When I get the chance I think I'll need to lower it a spline and test again.

Fri Feb 04, 2022 1:20 pm

You are going to have to take the boot off, reassemble and then be able to look at the innards of the joint while you spin the tire.

Fri Feb 04, 2022 7:16 pm

What about clocking the inner and outer cv to each other?
There used to be a tech page from outbacksubaru but can’t find it.
Basically you want the bolt hole on the outer cv with a big gap to line up with a bolt hole on the inner cv with a small gap.

Sat Feb 05, 2022 6:33 am

rayjay wrote: You are going to have to take the boot off, reassemble and then be able to look at the innards of the joint while you spin the tire.

Did all that before driving it, and the CVs span fine. It's just under power.

Sat Feb 05, 2022 6:34 am

tripicana wrote: What about clocking the inner and outer cv to each other?
There used to be a tech page from outbacksubaru but can’t find it.
Basically you want the bolt hole on the outer cv with a big gap to line up with a bolt hole on the inner cv with a small gap.

Yep, CVs are clocked already.

Sat Feb 05, 2022 5:29 pm

Have you measure how many degrees the axles are from being center flange to flange?
Pictures show that it looks like it may be there is a lot of off set between flanges and the rib part of boots are touching.

Sun Feb 06, 2022 3:55 am

jsturtlebuggy wrote: Have you measure how many degrees the axles are from being center flange to flange?
Pictures show that it looks like it may be there is a lot of off set between flanges and the rib part of boots are touching.

I've not measured that, but my IRS arms are 3" longer so I estimate that they are offset 2-2.5" as the hubs sit forward on a stock setup. That would put the angle in the 7-8 degrees range.

Lots of people run 3x3 and 3x2 IRS arms, so I can't be the first person to ask this question?