Do it properly, new shafts.
Do it properly, new shafts.
Hi, in my nova rally car I have to put spacers on the inside of the hub to stop the excess plunge. You have to do this on the harry hockley F20 shafts that i have fitted. You remove the coil spring and put the suspension through entire travel and measure the plunge. It should be between 18mm and 12mm at all suspension travel. Any more than this and the inner CV will run to far out, any closer then you run the risk of bottoming out the CV and destroying the diff.
Decent info, you can plan the shaft length now!!!Originally Posted by Novarally140016v
Thanks sir. Is that measured to the centre of the ball bearing and from the outer edge of the inner race? My measurement was about 21mm I think I remember.
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the easiest way to measure it is have the driveshaft fitted to the car, with all the suspension geometry set up as you are going to use it. Undo the driveshaft nut and push drivehshaft all the way in till the inner CV bottoms out. Using a vernier measure the distance from the end of the outer CV to a point on the hub. Then tighten driveshaft and measure the same distance. The difference between the two is the plunge.
I hope this makes sence?
Kinda does. So the two measurements should be within 12-18mm ideally. I suspect mine will be a lot more than that. This is all applicable to big block CV?
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not exactly. The actual numbers do not matter the difference between the driveshaft pushed fully in and the driveshaft nut tight should be between 12 to 18mm.
Thanks for the info. Also found a thread on Mig where Chris Astley mentions 15mm. Where did these numbers come from?
I've measured the inner CV total available travel as 40-42mm.
Drivers side is 22 mm at full droop, 25 mm on the bump stop and 26 mm at sitting height. This one has never posed an issue.
Passenger side that pops is 34 mm at droop, 40 mm on the bump stop and 39 mm at ride height. (Edited from 26 at droop hence comments below)
From this I suspect a 20 mm longer short shaft would be ideal based on 40 mm available travel unless anyone can justify the 12-18 mm measurement.
Last edited by Iain; 19-06-16 at 08:17 AM.
I was told the numbers 12mm to 18mm by Harry hockley Motorsport.
Are you running the same suspension geometry both sides?
14mm difference on one side to the other seems a bit excessive, considering you have 4mm difference on other side from full droop to bump stop?
I would not be making the shaft 20mm longer, you need a minimum of 12mm otherwise you risk the driveshaft bottoming out which will destroy the diff.
Am I not right in thinking that, if the CV has 40mm of available plunge you would want to see a max of 20mm plunge whilst at normal ride height, this would put the race in the middle of it's available travel and able to move 20mm out and also 20mm in?! So if Iain has seen 39mm at ride height then the CV is almost at it's outer limit of travel and isn't able to come out any further and this explains it's disintegration.
If the shaft is 15mm longer, then the plunge at ride height would be 24mm putting it nearer the middle of the available travel, would it not?!
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