Help with confirming axle length

[Joel K]

Got a question for those familiar with Porsche 930 CV joint axles.

I am about to install my axles in the SLC with a Graziano transaxle. I moved the engine/transaxle back about 1.5” in the chassis and just want to make sure the axles provided in the kit can still be used as is without adding spacers or ordering longer axles.

If I did not move the engine back the transaxle flanges would be about 1/2” in front of the wheel flanges. Now they are 1” behind. I used a triangular calculator just to see how the axle length could change. Based on the calculator the shorter axle would need to be only .03” longer so I am thinking that shouldn’t be an issue.

What complicates things is that my chassis is 10mm wider than a few of the other builders. Found this out when the front and rear engine mounts did not fit. This puts the lower control arms out a bit wider than normal. So considering this I wanted to double check if I am still good to go.

As delivered by the drive shaft shop the Passenger side axle is marked as 16”, and the Driver side marked at 19.5”

I measured them compressed and they are 15.5” and 19”. Fully expanded they are 17.125” and 20.625”. I measured them with the cv grease cap still on the CV joint but figure my numbers are within 1/16”. Also, what I think expands is the CV joint itself rather than the axle sliding in the CV joint if that makes sense.

Anyway, I installed the axles in the car and took some measurements of how much play they have. This is what I found…

Suspension position	Ride height	Passenger Axle Movement	Driver Axle Movement
At Ride Height	4.65”	.75”	.56”
At some Compression	2.65”	.875”	.625”
At Full Droop	6.15”	.625”	.5”

Since the axles can be expanded 1.62”, I figured the passenger side lines up with the CV joints pretty much centered and the Driver side with the CV joints pulled in about 1/8” on each side.




Anyway, I appreciate any help on the subject. Thanks!

 

[Scott]

One other way to think about it is to just measure as if you were buying new and see what the difference is. Assuming the car is aligned you put it on the floor. Then grab a welding rod and a pair of diagona cutters. Keeping trimming until you get a perfect fit then measure the rod on the bench.

 

[Joel K]

One other way to think about it is to just measure as if you were buying new and see what the difference is. Assuming the car is aligned you put it on the floor. Then grab a welding rod and a pair of diagona cutters. Keeping trimming until you get a perfect fit then measure the rod on the bench.

Thanks Scott, I did measure from flange to flange at ride height and sent that info off to DSS but the answer I got back didn’t make a lot sense to me so I just bolted them on to see how much play there was and see what others thought.

Here are the measurements I took…

Suspension position	Clock position on the flanges	Passenger Flange Distance	Driver Flange Distance
At Ride Height	12 o’clock	16.25”	20.0265”
At Ride Height	3 o’clock	16.25”	20.0265”
At Ride Height	6 o’clock	16.25”	20.0265”
At Ride Height	9 o’clock	16.25”	20.0265”
At full Compression	12 o’clock	16.125”	19.875”
At full Compression	3 o’clock	16.1875”	19.875”
At full Compression	6 o’clock	16.3125	20”
At full Compression	9 o’clock	16.25”	19.875”
At Full Droop	12 o’clock	16.4375”	20.0625”
At Full Droop	3 o’clock	16.4375”	20.0625”
At Full Droop	6 o’clock	16.4375”	20.0625”
At Full Droop	9 o’clock	16.375”	20”

DSS’s answer was that Driver side is good as is and the passenger side needs a .25-.5” spacer or longer axle. I didn’t go back to them yet based on the latest info, but to me it looks like if anything the driver side would need to be .25” longer and the passenger side is good as is.

Just figured I’d get some other opinions before I contact them again.

 

[Ken Roberts]

I seem to recall DSS telling me the length of the shaft is equal to the “flange to flange” measurement at ride height.

I agree with your conclusion Joel. For reference here is a picture of a ball sitting in the middle. The body is 1.5” wide. The ball is approx 7/8” wide. If it was a long travel dune buggy then I would be more concerned.

I’m about to polish mine up before reassembly. I bought some diamond buff bobs from McMaster Carr.

 

[Howard Jones]

When you call DDS back ask them if the 930CV joints "plunge" can accommodate the additional OVERALL length of the driveshaft assembly with both CV's installed. The answer is yes but I think you would be more comfortable hearing it from them

I am talking about the total "plunge" of both CV's combined and how much that varies the length of the combined assembly. Each CV will "plunge" about an inch or more so really it's twice the single CV plunge amount minus a safety margin. The complete assembly can vary in length at least that much. Ask DDS what they would like to see as a safety margin.

What you can do is take the springs off the shocks, set the car on stands, jack the tire up and down through its normal travel range, and see if the driveshaft ever goes solid in length throughout the total normal bump/droop cycle. As long as the driveshaft still has some plunge left in them as the car causes the effective axle length to change when the suspension cycles through its vertical movement you are fine.

Measure/record the different DS lengths as you do this (both sides). Good to know before you call DSS.

If you do this then you will quickly see that a 1/4 of an inch SHOULDN'T have much effect. At static ride height, the "plunge" should be in the center of its range. The only way a 1/4 inch would make a significant difference is if the drive shaft length was so far off in length that you were very close to either pulling it tight or compressing it tight at normal ride height.

This is also a good exercise to determine just what the travel limiting element is. It cannot be the driveshafts, however.

 

[Joel K]

I seem to recall DSS telling me the length of the shaft is equal to the “flange to flange” measurement at ride height.

I agree with your conclusion Joel. For reference here is a picture of a ball sitting in the middle. The body is 1.5” wide. The ball is approx 7/8” wide. If it was a long travel dune buggy then I would be more concerned.

I’m about to polish mine up before reassembly. I bought some diamond buff bobs from McMaster Carr.View attachment 123782

View attachment 123781

Ken, Thanks for the pics and information. It helps me visualize what is going on. Your measurements seem to be consistent with what I am seeing. .75” movement on each CV, 1.5” total. The passenger side axle seems good since it moves .75” at ride height so the ball/bearing is aligning right in the middle of the CV which is probably what you would want it to be. The driver side may not be ideal, but is it good enough. That is what I have to figure out.

 

[Joel K]

When you call DDS back ask them if the 930CV joints "plunge" can accommodate the additional OVERALL length of the driveshaft assembly with both CV's installed. The answer is yes but I think you would be more comfortable hearing it from them

I am talking about the total "plunge" of both CV's combined and how much that varies the length of the combined assembly. Each CV will "plunge" about an inch or more so really it's twice the single CV plunge amount minus a safety margin. The complete assembly can vary in length at least that much. Ask DDS what they would like to see as a safety margin.

What you can do is take the springs off the shocks, set the car on stands, jack the tire up and down through its normal travel range, and see if the driveshaft ever goes solid in length throughout the total normal bump/droop cycle. As long as the driveshaft still has some plunge left in them as the car causes the effective axle length to change when the suspension cycles through its vertical movement you are fine.

Measure/record the different DS lengths as you do this (both sides). Good to know before you call DSS.

If you do this then you will quickly see that a 1/4 of an inch SHOULDN'T have much effect. At static ride height, the "plunge" should be in the center of its range. The only way a 1/4 inch would make a significant difference is if the drive shaft length was so far off in length that you were very close to either pulling it tight or compressing it tight at normal ride height.

This is also a good exercise to determine just what the travel limiting element is. It cannot be the driveshafts, however.

Thanks Howard, appreciate the feedback.

I’ve sent the flange to flange measurements to DSS. You can see them in post #3. Their recommendation was to add a spacer on the passenger side or buy an axle that is .25”-.5” longer. But based on what I am seeing that just doesn’t make sense to me. I think the driver side may need to be wider, but the passenger side should be ok since it has .75” of movement/plunge at ride height. So figured I’d ask on the forum.

Also to your point, I’ve taken the measurements with the springs off and moving the suspension from compressed to full droop. The least amount of plunge is .5” on the driver’s side at full Droop. So I’ll ask them if this is within an acceptable limit, If so, great and I’m good to go. If not then I’ll see what their recommendation is.

Joel

 

[Joel K]

Thanks again guys and special thanks to Ken who helped review some emails from DSS which I was not fully understanding.

First, there is a mistake in the original post. The total play in the axles are greater than I measured and stated. The grease caps were preventing the CVS to move all the way in.

Here was the net of it from DSS, each CV can move in/out a total of an inch. So the axle length with the distance of the CVs fully expanded to fully contracted is 2”.

When the axle is installed, at ride height the ideal amount of total axle play is 1”. That puts the balls of the CV centered. In general, they recommend to have .75” to 1” of total axle play.

In my case the pasenger axle had .75” which is ok, and the driver side had .5” which is not ideal. In my mind, it still may be good since the suspension has very little change in axle length from full droop to full compression.

At the moment I have a couple spacers fabricated which place the axles in the center of their range. At some point if/when I upgrade to the C7 bearings I’ll have new axles made to the perfect length.

 

[Bill Kearley]

I just cut and installed the axles after I used a piece of wood dowel the same diameter as the axle (because the inner and outer flanges are cupped). One won't get a true axle length using anything smaller in diameter. Removal of the shocks and springs made it easy. I cut the wood as necessary till I had 1/4 inch end play as I moved an upright through its travel.