Custom Driveshafts

Since fitting 17″ wheels and tyres I`ve broken 7 outer CV joints, stripped the teeth off one 3rd gear and snapped 2 driveshafts. The Driveshafts both snapped at the same time and 3rd gear stripped the trackday immediately after fitting brand new CV joints.

Whilst I carry new driveshafts and CV`s, this ongoing failure isn’t something I am happy with. I can get the car back on track in 30 minutes, but that’s half an hour of tracktime missed. I don’t go to trackdays to fix the car.

 

The outer CV has been the weakpoint. The MK2 ones were swapped to the VR6 larger ones when I switch to 5×100 hubs years ago.  I did have the option of the MK4 style, but until the Gearbox was strong enough, all I’d be doing is moving the weakpoint into the gearbox. It’s easy to change a CV joint, less so a gearbox on a trackday….

 

The Gearbox is now strong enough to cope so I am finally able to fit stronger Cv joints 

 

The MK4 CV is similar design to the MK3 type, same spline then a waisted section leading to a threaded part. The problem with this is that whilst the CV itself is stronger, the weakpoint is still the thin part before the thread

6 of the 7 failures have been at exactly this point, shearing at the thinnest part of the joint

 

Simply swapping to the MK4 ones of the same design wouldn`t change that. However the R32 and some other high power models use the bolt through type instead. The threaded bolt goes through the centre of the entire joint and there is no stress riser where the splines finish.

 

The bolt actually finishes in the grease chamber behind the cage

 

Looking at them side by side, the weakpoint is obvious and that`s exactly where it always fails. The choice of outer CV was decided. The MK4 R32 bolt through style 

 

The inner CV was easy. The Golf MK4 inner CV`s are 108mm and the inner drive flange fits into my 100mm diff. The splines are the same

 

Even though the difference is only 8mm, the actual joints are significantly different. The 108mm uses M10 bolts to attach the CV to the flange, the inner race, cage and balls are all noticeably larger

 

108mm inner CV ball vs 100mm inner CV ball

 

There are no driveshafts that fit these CV`s available that are a direct fit into my Golf, so custom shafts were the only option. The MK4 shafts are 29.5mm across the splines, the MK3 24.5mm. That 5mm doesn`t sound much, but when the shafts are placed end to end the difference is significant

 

To make the custom shafts, cut a VW shaft in half, degrease the inner and outer CV and remove the rubber boot

 

Source some tube thats a snug fit over the shaft, slide onto one half of the VW cut shaft

 

Fit the inner and outer CV`s, bolt into place on the car, securing the inner CV to the drive flange and ensure the outer CV bolt is tightened fully

 

Remove / wind down the coilover spring platform and put a jack under the balljoint. Raise and lower the driveshaft and note the plunge of the inner CV.

The driveshaft is too long on this photo, it`s pushing the inner race too far towards the gearbox and the end of the driveshaft would impact to the driveflange with the shock causing cage failure

 

This is with the driveshaft too short, the cage will allow the balls to fall out under high steering lock situations

 

With the inner race sitting in the same position as on the MK4 golf, moving the wishbone through full travel never allows the driveshaft too far in or too far out

 

Once this is set the sleeve is tacked onto the shaft, rotated and tacked on the other side

 

Repeat on the drivers side and you have 2 driveshaft templates of the correct length

 

Remove the CV joints and these are ready to send to be manufactured.

 

I now had to decide who was going to make the driveshafts. The choice was between Dave Mac Propshafts and Satchell Engineering. Dave Mac make Gripper and I`m absolutely delighted with the one in mine, but after speaking to both companies, something Satchell do really struck a chord with me.

 

The driveshaft failure I had was across the stress riser where the shoulder that locates the inside edge of the inner race sits, it is shown in RED on this photo. The sharp change of direction is where the shaft would most likely fail if it was going to.

 

Guess where my shaft sheared ? EXACTLY in that place

 

This is a solid driveshaft but it failed in the weakest point of the design

 

Satchell have also seen many shaft failures in this exact area and rather than have a raised shoulder, they have each alternate spline the correct length to seat the edge of the inner CV. The rest of the splines are a few mm longer to ensure there isn’t a weakpoint in one circumference of the shaft, by stepping them like this they’ve seen a massive decrease in shearing at this point. That thought process and solution really appealed to me and after speaking to Colin and Tony I sent off my 2 template shafts

 

The new driveshafts are sent for hardening after manufacture and arrived today

 

The stepped spline design is pretty self explanatory compared to the original stepped shoulder

 

The inner and outer CV`s were cleaned ready to be greased

 

I`ve had extremely positive results with Redline Cv2 grease in both CV joints and wheelbearings, the joints were densely packed with grease then fitted to the driveshafts.

 

The complete shafts were fitted to the car and only time will tell if they are as robust as they appear. I have no doubt they will be as despite a lot of research I was unable to find any negative comments about the Satchell manufacturing process or their driveshafts.

 

I’m sure you’ll be thinking “well if the CV’s, driveshafts and gearbox won’t fail, what’s the weakpoint now?“. I believe the answer is that there isn’t one. The R32s are not known to break CV`s or driveshafts so all I expect to happen is either get better traction out of the corner or if it overwhelms the tyres, they’ll simply spin up. 

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