Driveshaft came adrift

[gridgway]

The n/s driveshaft came off today. Fortunately it was at slow speed changing into 2nd at about 20mph coming up to some lights. 3 of the 4 bolts came out and there is damage to the heat exchanger and clutch cable by the looks of it. The man from the RAC couldn't get any bolts back in. I'll see if I can take the bolts out tomorrow, I expect they are nadgered. Anyone experienced this? Any ideas on what else might be collateral damage? Would it have damaged the gearbox - maybe an output shaft bearing? They are 4 bolt flanges, are they known for this? Might the bolts have pulled out or just undone themselves (for some reason)?

Thanks
Graham
IMG_20190831_193835 by graham Ridgway, on Flickr

[Gary71]

I used to get this on my Golf (same bolts) I found it was simply not cleaning the flanges of grease enough to ensure the clamp load is maintained after torquing the bolts up.

[rhd racer]

Hi Graham

Yes, I had this several times on the 914 before I updated the drivetrain to match the power. However, I can see from the photo on the other thread that it is c1968 car, and therefore the large CV joints which are right for the year and pretty robust items (in fact, I had my driveshafts made to accept these CVs so they are good for pretty sensible horsepower). You may not have damaged the output shafts - usually the bolts simply undo for the following reasons;

1. All four bolts are fitted, but the roll pins set missing (x2 per CV joint). These prevent the twist under load
2. Bolts torqued correctly but Schnorr washers not fitted (these are serrated to prevent the bolts undoing)
3. The spreader plates not fitted (though appear they are in your photo)

If you have points 1 and 2, you have either been unlucky, they were not correctly torqued, or you are running a bit too much power for them to take (though usually you would snap bolts or the CVs themselves would destroys themselves rather than undo). You could, as a safety blanket lock wire them but you will know this from racing. I would do this with new bolts and washers having had a failure.

If you have wrecked the threads, I have a feeling that Chris at Fennlane reproduces output shafts.

HTH
Wayne

[gridgway]

Thanks Wayne. Where do the roll pins go? Do they just locate the CV joints to the flange?
Graham

[911hillclimber]

Agree with Wayne.
Had this a few years ago on my 911 (915 with 3.2 engine.)
The bolts simply come undone.

Take them all apart and clean and inspect.

Remove and replace the bolts and the special washers and clean them etc before simple re-assembly.
I wet my bolts with a spray of WD40 and a wipe 'dry' with an oily rag...

Trick is to torque them correctly, and that can be hard to do at the box end. I put all my extension pieces together and that allows accurate wrenching to the spec in the Haynes book, the torque wrench is outside of the wing this way so easy to get a good straight twist on them.

Never come loose since.

The tight fit of the scroll pins are essential to stop any shuffling between CV and box drive flange. They go in the 2 smaller holes in each CV and are diametrically opposite each other.

Those big CV joints are really robust, I changed mine last Xmas, they were the original 1973 items and have been through hell with me on the hill climb starts etc.
Fresh GKN CV grease called for. (Merlin Motorsport)

[gridgway]

So I had to get the car in the garage today on some skates that look like they will work ok, but the wheels are too small!
IMG_20190901_164905 by graham Ridgway, on Flickr
IMG_20190901_165014 by graham Ridgway, on Flickr
Got there, then took the bolts out. A bit of a mess really. I can't help but think that the output flange will be knackered too. Look at the RH bolt, that is truly nadgered!
Is it possible to remove the output shaft/flange with the box in the car? How does it come out? Is it just bolted in?
IMG_20190901_175951 by graham Ridgway, on Flickr

[911hillclimber]

On a 915 box the flanges are bolted into the diff with a large centre bolt, early boxes may be the same.
They have a spline on them that goes into the diff and have a big taper roller bearing and oil seal, should pull out readily iirc.

Before you do that I would get new cap head bolts and screw them into the threaded holes to see if they stand perpendicular to the flange face or are crooked.
The threads are normal metric corse, so easy to buy a tap and run it down the threads if needed.

This is why I suggested you remove the shafts and clean everything, new bolts etc, all available from Type911/design911 and OPC. You will need these parts anyway.

The flanges are not soft steel but cast steel alloy, a drop of good stuff, so probably ok.

[gridgway]

Thanks Graham, I've got the metric coarse threads in my collection of taps, so I can run them through. My main question was whether I can just remove the bolt in the middle of the flange and pull it out.
Graham

[Bruce M]

If it’s circa ‘68 901 box then only remove one at a time. The centre bolts around that time have a pin on the end that 1) holds up the spider gears inside the diff 2) wear away resulting in a destroyed gearbox.

Ask Jury what happens if you remove both at the same time. I think he fell for that Porsche booby trap.

[gridgway]

eeek, I'm definitely only removing one side!
Graham

[Bruce M]

These are what they look like when worn down and about to kill the gearbox..

[911hillclimber]

Gulp!
I was offering checking the tapped holes while the flanges were in the box, if the bolts are screwed in and look straight and don't wobble around a lot then with new hardware, clean and screw back together.
I did not know that issue about the early boxes, sounds like you end up taking the box out and snowball through a rebuild....

[gridgway]

The box was refreshed a year ago so I'm not expecting any wear.

I'll need to try again with a fresh M10 bolt to see if the threads behave ok. I guess I'm just anticipating issues. Having had it come apart once, I'd be unhappy bolting it up if it's not 100%.

[Bruce M]

If it had a recent refresh, I’d expect the weakness to be solved by upgrading with 914 parts. Easily done (if it even had the ‘68ish issue in the first place).

[rhd racer]

I would run a tap through in situ Graham and leave the flanges in place, then rebuild with new bolts and washers per the above, checking the roll pins in place

Cheers
Wayne