CV's & axles-Swept back or not?

Mike330R

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I am in the process of a transmission upgrade. My original set-up had the trans CV cups and the trailing arm CV cups parallel to each other. The fab shop doing the swap says having the axle slightly swept back is best for CV longevity.

Can some of you explain why he says this and what you feel is the better set-up and why?

This is a 2700 pound sand car with a turbo Honda running 930 CV's.

Thanks for any insight!
 

Jess@HighAngle

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I kinda disagree with the slight back setting - c/v's usually like less then 24 degree's max and a lighter car - And remember Drive it like you stole it they like that too ! Jess
 

Mike330R

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If I understood his explanation correctly when at full droop the end of the trailing arms swings forward? Doesn't seem right but maybe I misunderstood?
 

Gonzo 5/1600

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If I understood his explanation correctly when at full droop the end of the trailing arms swings forward? Doesn't seem right but maybe I misunderstood?


Yes that is correct (if it is of VW type trailing arm design). When the trailing arms are level to the ground your wheelbase is longest (ignoring front suspension wheelbase changes) as the suspension compresses or droops from level trailing arms you loose a small amount of wheelbase since the wheel travels in an arc...

For best power transfer you want as little cv angle possible at ride height, under droop or compression a rearward angled axle will return forward as it follows the arc of the wheel. Depending on how much angle you are currently demanding from your cv's for ride height determines how you must configure them so as not to exceed their angular threshold before binding at the extremes of travel.

Sorry there's not a simple answer.:)
 

Mike330R

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Ok I can understand that. At full droop I limit the axles to 22'ish degrees or less. At ride height I have never measured but would guess in the 5 degree range or less.

So at ride height parallel cups seem best.
 

Mike330R

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Wilson your post was not redundant IMO.

You also said there are other considerations besides longevity but I look at it as wanting them to last as long as possible. This is not a race vehicle.

What other considerations are there?
 

F.P.O.

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At full droop both of the cups on your trans,& tire sides should be inline with each other, other wise you are going to have a compound angle on your cv's, this is fine if you have taken this into consideration, for every 1 degree back angle you have at droop you need to add 1.5 degrees to your cv angle. Do not worry about your back angle at ride height only at droop
 

Wilson

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After reading Gonzo's post and your reply, I felt that my response just said the same thing in different words. Essentially, you have to look at CV angles from both a horizontal and a vertical perspective. The angles are additive to some extent (vector sums). By properly selecting the "rearward" angle of the axles at mid travel, you can eliminate the horizontal component of CV angle at the "extremes". From the CV angles you mentioned, it probably doesn't make any difference in your case..... Race prepped 930 CV's are good to about 28 deg. or so. But, smaller CV angles are always better (for both longevity and power transmission)!

In our 5/1600 car, we are most concerned about power transmission but we are careful to limit our angles so that we don't "bind" at the extremes. The vertical location of the transaxle then becomes important for us (we want to maximize total travel but have body interference issues)..... For you, though, the location of the transaxle probably doesn't matter as long as you don't have "interference" issues.
 

Wilson

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It's 1.5 added? I read somewhere else it was .5.

Thanks for all the info.

A quick look at our setup shows that for every 1 deg forward or aft of the inboard CV centerline at full "droop" we add about .2 deg of total CV angle. Your mileage may vary. Figure .5 degrees and you'll be fine.....

Ideally, you'd want to choose a "back" angle at mid travel that exactly cancelled the forward movement of the axle at full droop.
 

FullsizeFun

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If you set up the cv's to be in line at full droop and have no forward or backward angle, this maximizes your droop, but will give you angle at ride height. More Angle at ride height creates more heat, robs power, and is harder on cv's and boots.

If you set it up to be in line at ride height, this will give you a compound angle at droop and will limit your travel.

You need to find a happy place in the middle of these 2 extremes. Depending on what is important to you, Travel or CV and boot life.

The cars i see that have excessive angle at ride height are the cars that eat up cv's and boots. Some cars I have seen with so much "back angle" at ride height that even at full droop the hub side cv is still Behind the trans side cv! No bueno

Every car out there is different, but I would set it up so that at full droop the hub side cv swings slightly past or forward of the trans side cv. This will minimize your angles at ride height.

Race cars spend more time at ride height than at full droop
 
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