Sunday, February 13, 2011

McArlus Cars - 16

This is the long awaited driveshaft update.
After discovering a problem with the length of the driveshafts, and consequently running out of suspension travel, I have spent a lot of time (and beers) trying to find a solution.
To start with I have different length shafts.
I am sure that all of the shafts, I have six of them; have come from the same model car at the wreckers. I cannot say with certainty if they came of manual or automatics, but if I had to guess, I think I would have taken them all off manuals. It is important to remember that I only use the short shaft out of the cars. In the KA laser one drive shaft is about 300mm longer than the other, so to get six they must have come off six different cars and the shorter ones I have must have come off two different cars. Sometimes you can be unlucky.
I measured each assembled shaft fully compressed and proved it. Two of them are short and four of them are about 6mm longer. I then started to disassemble them to try to find the difference. In the picture that shows the outer end of three axles, all of the inner ends are aligned. The top one is a long, the middle a short and the bottom one is a modified short, but more on that later.
Once I had proved that the difference was in the axles, I really wanted to find out more information. I spent a lot of time on the internet and talking to driveshaft reconditioners without a lot of luck. Most of them said that it couldn’t happen, although a couple did say that it does happen from time to time, but that it wouldn’t matter. Unfortunately in my case it did!
I investigated all possibilities of a solution.
Ideally the short shaft that carries the sprockets should be shorter. However shortening it would mean that its internal splines would need to be deeper. Ideally the bearings that carried the shaft would need to be changed and located differently as well.
To fix the problem here would mean replacing the bearings, devising a new method of locating them on the sprocket shaft and having a new sprocket shaft made. Clearly this would be an expensive and inconvenient path to take, and despite it being to “right” solution, I wasn’t keen to redesign the shaft and bearing mounting, or spend the money and throw the current custom made parts away, or get shorter axles made.
I have had too many Bolwells to enjoy either of those solutions!
The other area that shortening was possible was in the axles that I had.
After first reassembly all of the suspension, and then moving it through its travel, I carefully determined what actually was the correct driveshaft length, making sure that the bumps stops on the coilovers were compressed before the driveshaft bottomed out. At this point I discovered that even the short axels I had were too long, so I had definitely made an error in the sprocket shaft length!
By closely inspecting the axels I tried to find where I could shorten them. In the picture of the outer end, it can be seen that the CV joint is held on by a wire circlip. This locates in the outer CV joint and prevents it pulling on and off the shaft. In my case there is no length adjustment in the outer CV joint, I don’t know, but assume it is always the case as on a front wheel drive car the outer end has to deal with suspension travel and steering.
 By looking closely at the wear marks on the axle (as in the picture) I could shorten the outer in of the axle by moving the circlip groove in by 7mm and then cutting the extra length off the axel (at the original circlip groove). In this way I was losing virtually no loss of spline engagement of the axle with the outer CV joint. This would solve my problem with the “short” axles.
With the “long” axles I also needed to shorten the inner end. This end is where the length adjustment of the driveshaft takes place. The bearing spline is located on the axle by a circlip on the outside end and bears against a shoulder on the axle on the inner end. All of this fits inside the large ‘cup’ and is held in by the large wire circlip in the picture. In this case there is about 25mm of length adjustment, with the bearing sliding in and out of the cup.
You can see in the Inner end picture how I have reduced the shoulder on the top axle by 4mm.
By reducing the shoulder on the axle (on my NEW lathe) I could then remachine the circlip groove and only lose about 1-2mm spline engagement from the axle to the CV joint bearing. I only then needed to remachine the circlip groove and again cut the excess length off the axel.
Although not the perfect solution, I think that this has solved our problem and I will keep a copy of this post in case I ever need to do it again!
Driveshafts Outer End
Driveshafts Inner End
Driveshaft & CV Outer
Driveshaft & CV Inner

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