Ok, so i had a read of a couple of threads on here, nothing really matched my circumstance other than saying what has happened, not the solution. read: http://www.calaisturbo.com.au/showth...tials&pa ge=8 (http://www.calaisturbo.com.au/showthread.php?t=133721&highlight=differentials&page=8) anyway, drags last night, MT ET streets on. r33 5speed, kaaz LSD, 3.9 gears, 480rwhp, 2step makes up to 8psi (didnt launch it flat out at 8, atleast i dont think i did). rear arms are boxed (steel rods down sides and a small plate across), upper controll arms adjustable. bushes on lower arms on diff are a little tired, upper ones were completely ****ed so were replaced prior, we were pretty sure we got the pinion angle at or extremely close to how it was prior! so i launched it and this happened: http://www.facebook.com/photo.php?fb...0&l=38b021f86b (http://www.facebook.com/photo.php?fbid=10150743388615400&l=38b021f86b) obviously i have snapped the rear uni, and the diff housing has twisted... so clearly somehow the diff housing twisting back put extra stress on the shaft and snapped it? also obviously i need a new housing now, but just wondering what i can do to stop this happening again? cars out of action for a while while i save up some $$ to try and sort it out propperly. just asking for recomendations as to what modifications i can do to stop this happening next time? I'm thinking: - new housing, welded axle tubes, possibly plates welded across - rear alloy hat to keep my diff safe, because clearly its not - ??stronger tailshaft/unis?? can the whole thing be toughened or will the yolk become the weak point (R33) (seeking proffessional advice from final drive!) - Brand new RUBBER bushes throughout rear end would a watts linkage help here? since the diff is out i kind of want to do it anyway, would the change in suspension geometry be more beneficial? just want to know what i can do to make the rear end tougher, completely ok with dropping around 2k on just diff/shaft, maybe even more... cheers, feel free to PM me if you have anything/contacts you want kept private. Jack

Hi Jack, I can't see much there unfortunately, apart from that it appears your lower trailing arms survived unscathed (usually what goes). Can you get under there and check if there is any lateral and posterior twisting to the upper trailing arm mount on the diff housing, and the housing alignment in relation to the chassis rails? It should be square, but I'm thinking it will be skewed, with one side of the diff housing closer to the rear of the car than the other (with subsequent twisting of the upper mounts). You'll probably find in the split second when everything in the housing has allowed the flex to the point where it is now the uni has fractured and given way, hitting your floor pan (visible damage there). -Don't go for a rear alloy hat/diff cover; it'll make no difference -Don't go for a Ford EA-AU style watts linkage, as this won't impact your launch stresses noticeably, and will consequently become a weak point in your suspension (diff/cover is not a strong mount point) -Get a Hardy Spicer uni and yokes as part of a tailshaft rebuild (looks like it hasn't been done before; balancing is important) -New bushes yes, but it might be worthwhile considering aftermarket OEM style bushes in some points and urethane (the blue stuff) OEM style in others Lastly, perhaps a softer spring for use only at the strip?

Thanks Tim, you make up one of the three people on here i can rely on for straight to the point informative answers like that. especially in this kind of situation. (88chaser and NZ EVLHSV being the others). i've been at uni all day, pretty hungry to get under there and have a good look. i was thinking something must have given way in the rear as well. anyway, cheers for the feedback on parts, i'll take that info with me to the diff shop i will be going to see.

Hey mate. Been through this as well. Id probably look at getting a custom tail shaft as more than likely that one may now be bent and possibly it could have twisted the spline in the yoke up at the gearbox. I upgraded mine with 1 piece shaft with a Drift front yoke think its called a 1320 and oversized Uni's. Since then i have done over 50 launches at the track on slicks with no issues in the rear end. After doing the same as what you did I also have the boxed arms and installed adjustable upper control arms as i had bent 2 pairs of the genuine uppers. within just a dozen passes. I had Hardy Spicer make me 2 tail shafts. Both of which were never tested for trueness and both vibrated. This sending me into a spin on trying to overcome a vibration in the car when it was replaced. Because of course you would think they would test them before supplying them to the customer. However i did have some clearance issues with a 1 piece tailshaft, After some suspension work and pinion angle adjustment it seems to be working fine now. It may also pay to have a slightly larger spring in the back to allow more squat in the launch.

don't get a hardy spicer gearbox yoke as it is too soft and will twist in the splines and distort where the caps go in. happened to me after 8 runs. They are cheap chinese crap.. Final drive should be able to sort you something decent out tho, try run 1350 uni's front and back. As xchase said you won't have much room under there if you decide on a 1 piece, pretty sure final drive are doing a tuff 2 piece unit these days using xr8 cv joints. Pedders do a nice solid rubber mount for the diff and trailing arms which limits movements but isn't ridged like nolathane. Alloy rear covers are a good idea, as they have little jacking bolts in the rear to hold a small amount of load on the carrier bearing straps. so the cw and pinion don't try to separate under power/ jump a tooth and end up smashed. A mate had this happen to him ends up farking the diff housing. I've never see the welds brake out the axle tubes/centre dang. yea run couple small stitch weld on it. cheers Coz

cheers for the input guys. just got under there in the dark with a torch. checked all the arms.... seems like none of them have come out or appear bent, lower arms seem the same, upper arms felt good (couldnt completely see them... it honestly looks like just the diff housing has twisted about 20 degrees up... nothing else lol. so now im thinking what can i do to stop that... surely stitch welds wouldnt offer that much more torque resistance. i'll see what phil says. now im 99% sure theres no way we could have got the upper so wrong, but if they had that much pressure on them to be wanting to tip the diff back that much we would have noticed it wouldnt we? the way its sitting now is massively out.

From what you can see looks like the pinion angle was all wrong mate and tried to run the uni like an angle grinder. Need to have a clear thourough inspection of every area with some light

Watts link wont help, its expensive to do it properly too, and clearance might be an issue. I had a 2 piece tail shaft made from a guy in W.A, its awesome, 2 piece will spin faster with less vibration than a single piece any day of the week (So he tells me anyway) Its the same guy that made the tail shaft for Mark in PROVLT, he also warranties his work. PROVLT ran one of the alloy rear hats with the bearing supports in it, along with a solid shim as opposed to the standard pinion shim, im not sure what made the difference, but it stood up to a hell of a time, Mark gave that thing everything, all the time. If it was me, and I had to get a new diff, I would start with a 9" housing. G and J diffs can make housings to fit commodore at a decent price, and no doubt would freight it over for you if there was nothing local at the right price, everything for the inside of a 9" is cheaper, and stronger than any borgwarner, I would also have the upper arms checked for length, and have someone that actually knows what he is looking at set the pinion angle, its far more important than just making sure the uni survives, it will help with traction off the line. Probably weld a plate to each side of the upper arm brackets on the chassis, and if possible on the lower as well, its probably all over kill, but if it doesn't break again it has to be worth it. The bloke that made the tailshaft for me used ford uni joints as well. Probably first step would be to have the housing checked, it might be as simple as a broken uni, it happens.

Cheers guys. Just hoping the internals of the diff are ok at this point, if they are I will stick with the 78. Kaaz LSD near new and brand new 3.9s lol. 2k of diff that shouldn't break, so instead it breaks the next weakest point...

Chase has a good point re: tailshaft/gearbox intersection; I've managed to twist the splines on and NA before, so it's definitely an area worth some serious attention. If it looks like nothing has happened other than the pinion area, it's possible all of your bushes have been warped or torn in the mounts. Won't know until you take it out. How's the panhard?

When mine pushed forward i have a feeling that when the tailshaft yoke hit into the gearbox it may have damaged the gearset in the box. As the next time i used the car i blew the gearbox when changing gears after the repairs. Coincidence or just the next week link im unsure.

what are the chassis mounts like on the top arms? may have done somthing to the mount side