Just been speaking to TSR regarding the 020 disintegrating diff syndrome. I was always under the impression that this was caused by the diff rivets giving way! I've just been told that this is not the case and it is the diff pin giving up that is the culprit. Is my leg being pulled? Anybody want to confirm this for me?
The diff pins are the main pins that hold the bevelled gear inside the diff. These don't tend to give up. Even Tubs's bevelled gear blew to pieces before the pin!! What you said is correct. The diff rivets(although you could call them pins, but infact are rivets) are the problem. Over the years of abuse, the rivets start showing signs of shear points, where the crownwheel and diff housing are bolted together. Where the crownwheel is constantly being put under pressure, it is in-effect, trying to turn on the diff housing, which eventually leads to the rivet shearing in 2, and spitting the half which doesn't have a 'fitted' (tight) fit out of the box. If your gonna be hammering the box it would be well worth having a new set of diff bolts fitted. While your there and the box is in bits, have a complete rebuild with new bearing and seals. Makes sense in the long run.
Both are correct, however, the rivet head popping off is the more common one that I've noticed. The shaft the bevel gears ride on should be secured in the housing by 2 lockrings, to prevent it sliding out. VW opted to ditch the lock rings, and modify the rivets being used to do the job of the lockrings. The rivets on each side of the shaft now used enlarged heads, which acted as a stop for the shaft. Over time, the shaft, which can float until it hits the enlarged head, will beat on the head of the rivet, knocking it off, and allowing the shaft to slide out, causing the SMS. The more common problem I've seen is as you described, where the regular rivets simply pull apart, and the loose head gets spun around by the ring gear, usually caught up between the ring and pinion gears, and in the process ruins the R&P and machines a hole through the case. Here is a pic of a rivet I had drilled the head out of (6mm bit, then 12mm bit), and when I knocked on it with a chisel, instead of just the head popping off, the shaft inside actually finished breaking and the rivet came out like pictured. Normally when you drill them, the head only pops off, and you drive the old rivet shaft out of the diff. VW used the larger heads on some diffs with the proper lockrings, sort of a double safety, and I have seen on some where there are no lockrings, yet the shaft is grooved on each end for a lockring. Some diffs use a non-grooved shaft, and the larger rivet heads are all that is used to stop the shaft. The bottom line is that the diff needs bolts installed. Rivets simply do not do the trick, and trying to use an already stressed rivet head to do double-duty by securing a floating shaft is just asking for it. Lockrings on the shaft, bolts on the diff. After that all you have to worry about is normal wear on the bevel gears, as they seem to get pitted and cavitated over time. Broke
Lol, you are a PROPER vortex user you photo junky Too true though, it the heads of the rivets that pop. VAG used enlarged heads on 2 of the rivets, the ones either side of the diff. pin in the centre of the diff. These have a tendency of coming off and destroying the box. As said, rivets that have been in the box for any length of time or millage aren't upto the job and should be changed.
Yeah, but the usual Vortexer posts pics of silly crap, or will use a pic of a car just for thread views and so on, but I like to use them to help explain things a bit more....like the rivets that actually snap in half in the middle, I suspect because of high axial loads presented by the helical cut gears. The same reason you don't want to re-use the 5th gear securing bolt, the big hollow XZN 12mm bolt...the side loads from the helical gears is too much for a used fastener. I was talking to a guy at Bentley Publishers who was teaching students 020 rebuilds, and they would re-use that 5th bolt for classroom use, and he said the bolts would break with regularity after being re-used, with the shouldered head simply popping off. I've also posted a pic in the engine mount thread here in these forums, in case the guy wants to go hunting junkyards for the old style bracket. Here, since I've been labeled as a photo junky, here is a Vortex style posting (though I must admit, I did post this pic on the Vortex too ) (it is my mean ass fat cat) Broke
Never had a problem with the bolt to be honest. I know there's alot of force being applied to it but, the bulk of the force is being directed onto the inputshaft itself not directly onto the bolt. Regularly I've seen 12.9 bolts shear on the head, only due to constant re-assembly and torquing up of components in work, likewise if that bolt is being re-used for teaching examples. I'd be more inclined to worry about the circlip holding the opposite helical fifth on. Frequently I see this gear quite sloppy on the shaft. Could easily help premature were of the clip and its resultent failure.
Not true in respect to the load direction, the helical cut 5th gears load opposite of what you stated. Under forward driving forces, the driving 5th gear (and sync) are forced towards the 5th gear 12mm bolt. The opposite driven gear is forced away from the circlip (or lock plate on 2.0 trans). All that is holding the driving 5th gear and sync assembly on is that 12mm bolt...and the shift fork being locked onto the selector tube....but that shift fork stands NO chance against the axial loads, so in essence, it is only the bolt holding 5th onto the input shaft under driving forces. To be honest with you, I just repalce them both in a rebuild, and I don't have to give it a second thought Broke Edited by: Broke
Okay dudes - Cheerz for all the help So I need to have the crownwheel bolted to the diff? Yes? Whats are the lockrings for? Where do they go? If I get these two things done as well as a full rebuild then 140 brake is never going to kill it?
