jeffi Posted March 8, 2010 Share Posted March 8, 2010 Hi all, I've got the diff supported on the top bolt but when I pivot the diff to fit the bottom bolts I can't get either of them to bite. The bolts fitted when the diff was on the bench, albeit they had to be exactly aligned with no play. I think the issue is the top bush is compressing under the weight and so the bottom hole is about 1mm out from the hole in the bush - which is enough to stop the bolt biting. I'm concerned about using brute force given that the diff casing is aluminum and the threads with be soft. There's no play in the bushes for the bolts to wriggle, so everything is pretty tight on the tolerance front. I've got the right bolts and not mixed them up - similar looking imperial ones for the engine mounts won't go through the bushes. Any good advice? Perhaps a few lagers and sleeping on it may help... but it might have been the earlier lager that's impeding progress tonight... Jeff Link to comment Share on other sites More sharing options...
Rattie Posted March 9, 2010 Share Posted March 9, 2010 Yo Jeff! Been there, done that. You actually have to put the bottom bolts in first, so that it's the top one that's a bit out. Then you hammer the top one all the way through, making sure you a) have all the washers in the gaps and b) the s0dding chamfered washer under the s0dding head of the s0dding bolt! Guess which one I forgot... Basically you see how the long bolt is chamfered at the tip? That's to enable it to force its way through the slightly misaligned bushes and diff casing holes. It would appear that most of the metric chassis are a bit off in this dimension. Either that or it's "design feature" to give more positive clamping of the diff. Take your pick 😬 Martyn R300GRR SV trapped in Dartford until IVA on 12th March!!! Link to comment Share on other sites More sharing options...
Bricol Posted March 9, 2010 Share Posted March 9, 2010 Stick a jack under the diff to take the weight . . . Bri Link to comment Share on other sites More sharing options...
MartinH Posted March 9, 2010 Share Posted March 9, 2010 Hi Jeff Yes, I had the same problem. Martyn B has given as pretty full answer there but just a couple of tips that worked for me: I did the job from under the car on my own with the car on the highest setting on the stands Instead of putting top bolt in first, get a long screwdriver that is thinner than the top bolt and slide it all the way through where the top bolt will go. Now you can hang it there taking the weight while you get the bottom bolts in. When you put the bottom bolts in, don't tighten them all the way up yet.. My top bolt was not chamfered at the tip so I tapered it myself on the bench grinder. This is so you have a chance at getting it through the holes when the bottom bolts are in. Now slather your top bolt in copper grease, and whack it with the biggest hammer you can find through the top holes. It feels wrong but its the only way. I had to drift mine in and out a few times to get the right washers in. I am on the side that thinks it is quite a good design as when it is in - it sure aint gonna move again! Good luck. Cheers Martin Edited by - MartinH on 9 Mar 2010 09:50:43 Link to comment Share on other sites More sharing options...
Englishmaninwales Posted March 9, 2010 Share Posted March 9, 2010 Had my differential in and out loads of times. Much easier to manage the spacers if you hang the diff by the top bolt and then fit the lowers, and as mentioned above using a trolley jack to give you the final alignment for the bottom bolts. Easier with the boot floor out. Link to comment Share on other sites More sharing options...
Graham Perry Posted March 9, 2010 Share Posted March 9, 2010 Long thinner screwdriver through the holes is a great help as said. It gives you 'wiggle room' to get the other bolts through. I have always found a second set of hands is a great help as well Link to comment Share on other sites More sharing options...
Pete-B Posted March 9, 2010 Share Posted March 9, 2010 Yup, support the top with two undersize bolts then put bottom bolts in but don't tighten. Remove one of the small top bolts and hammer the long bolt in, removing the other small bolt as the long one goes through. As for the spacing washers, measure and find how many you need then tape these together by wrapping a narrow piece of tape round the edge of them (ie Circumference), job done. Peter Edited by - Pete-B on 9 Mar 2010 14:34:16 Link to comment Share on other sites More sharing options...
myothercarsa2cv Posted March 9, 2010 Share Posted March 9, 2010 There's a how to on my website John _________________________ myothercarsa2cv Bugsy: '82 2cv6 😬 Talloulah '08 1.6K Classic Link to comment Share on other sites More sharing options...
Rattie Posted March 9, 2010 Share Posted March 9, 2010 John, that's not a bad tutorial. On most of our metric chassis however, a rubber mallet might not be man enough to drive the top bolt through. I had to use either a deadblow or a brick hammer and a wooden drift. I can't remember now - my mind is blocking out the memory. It's definitelt in the realm of "really, this can't be right". I have to wonder how many diff mount failures we're going to see from the current crop of chassis. Martin, you slather all your bolts with copaslip! 😬 Martyn R300GRR SV trapped in Dartford until IVA on 12th March!!! Link to comment Share on other sites More sharing options...
MartinH Posted March 9, 2010 Share Posted March 9, 2010 Yep it needed some weight behind it. Bloody big lump hammer, but my bolt needed the extra taper putting on it using the grinder or even that amount of force would start it going through. The comment about copper grease was more to say that I put it all over the length of the bolt to aid the sliding through the holes rather than just the normal amount on the threaded part. Its one of those jobs that you feel really good about when its all over. Duratec R300 SV build in progress Link to comment Share on other sites More sharing options...
Area Representative Steve Wright Posted March 9, 2010 Area Representative Share Posted March 9, 2010 O.K. Jeff, you have been given some great advice. Now get on with it this evening and lay off the Stella visit Carrotland.co.uk Link to comment Share on other sites More sharing options...
Martin J Posted March 9, 2010 Share Posted March 9, 2010 *arrowup* *arrowup* John I thought you bench pressed your diff into possition & then balanced it on your head! Allright for you rowing types with muscles 😳 Link to comment Share on other sites More sharing options...
darren f Posted March 9, 2010 Share Posted March 9, 2010 It's not just the latest chassis- my K-series R300 was the same and diff is legendary self-build problem area, not at all helped by the fact that it happens early on. As said above, the over-riding feeling is 'this cannot be right'- a situation not helped during my build by the fact that the top bolt was actually very slightly over-sized- it would not go through the top hole in the diff- despite enthusiastic persuasian CC sent me a replacement machined down bolt that slotted straight through and recommended that I chamfer a lead-in to all 3 bolts. ISTR they said that the factory turn a lead-in to all their bolts to make things a bit easier. I did this and used a 'top-bolt-in-first' technique, got it all spaced correctly and the chamfered bottom bolts went in relatively easily. Link to comment Share on other sites More sharing options...
jeffi Posted March 9, 2010 Author Share Posted March 9, 2010 Thanks for all the good advice. Unfortunately I've stripped the thread out of one of bottom bolt holes when I tried one last go with the top-bolt-first method before attempting the bottom-hole-first approach. Here's what happened: I managed to use a combination of jack and wooden wedges to get the diff bottom hole as close in alignment as possible to the hole in the bush but both sides were still out of alignment by at least 1 mm - enough to impede bolt take-up. There's about 6-7mm of lateral movement for shims on each side but no perfect alignment for the bolt and thread with respect to the bushes. So then I tried filing down the bolts by taking roughly 3-4mm off the thread to create a threadless lead-in to help draw the bolt into the diff. This worked for one side fine and the bolt went in without a great deal of force - more than when it was on the bench but less than full torque Nm so I wasn't damaging the thread. Sadly when I repeated this for the other side, which had now become even more out of alignment, the bolt got halfway along it's thread then jammed. I didn't force it further and started to carefully undo it. Withdrawing it also took out the diff thread! Hooo-hummm, that's probably my build stalled now as the cost to put it through the PBC and IVA will now be spent on a sorting the diff. Anyone know how to make this a front-wheel car or do a conversion to electric? A mate who's pretty switched on with motorbike mechanics is coming over with a tap set to see if the thread can be salvaged, but we won't be able to make it bigger than an M12 as a larger bolt won't go through the bush and I'm not going to bodge the bushes. If all else fails I'll have no choice but to replace the diff or try and get it's casing replaced. Link to comment Share on other sites More sharing options...
MartinH Posted March 9, 2010 Share Posted March 9, 2010 Ah, thats really bad luck Jeff. Don't give up yet. Careful tapping and dieing can recover from a multitude of horrible situations like that. Worth investing in a good set if you don't have one. I bet if you recut both threads they will match up again. Let us know how it goes. Martin Duratec R300 SV build in progress Link to comment Share on other sites More sharing options...
jeffi Posted March 9, 2010 Author Share Posted March 9, 2010 Failing the old tap & die treatment, here's something a mate has used to recover from this:- here Link to comment Share on other sites More sharing options...
jeffi Posted March 9, 2010 Author Share Posted March 9, 2010 Things are looking hopeful:- Anyone use the Heli-coil - here's a YouTube demo:- I may do this on both sides! Link to comment Share on other sites More sharing options...
Bio Posted March 10, 2010 Share Posted March 10, 2010 Yes I have used Helicoil inserts on M6 and M8 threads. Also do a search for Time certs...Have been advised that these are a good alternative. Best of luck. John Link to comment Share on other sites More sharing options...
simonpa Posted March 10, 2010 Share Posted March 10, 2010 Hi Jeff, if all else fails, I'm currently removing a 3.92 diff from my car in order to put an LSD in. The old diff has only done 3k miles, so not even run in yet :) Still looks like new. I'm happy to sell or loan while you sort yours out - if needed. Cheers - Simon Link to comment Share on other sites More sharing options...
jeffi Posted March 10, 2010 Author Share Posted March 10, 2010 Thanks Simon very kind of you - I'll give the repair a try and report back. Hopefully armed with a repaired thread and better method as described above I should sort this out and not be too far behind schedule. Link to comment Share on other sites More sharing options...
Z3MCJez Posted March 11, 2010 Share Posted March 11, 2010 Helicoil is pretty good. On my tintop the bolts on the top of the engine had been overtightened (prior to my ownership) and of the 8 (or 10 or 12, I can't remember) only about 3 were still providing purchase. I had the whole lot helicoiled for about £250 and they're all absolutely fine now. They are low torque small bolts but I think the process is pretty robust. However, you may well find it cheaper to get a new casing. Or have a word with CC. They may replace the casing, given that the manual really isn't the right way to get the diff in. Jez Link to comment Share on other sites More sharing options...
myothercarsa2cv Posted March 11, 2010 Share Posted March 11, 2010 Thanks Rattie Mine was a metric chassis too, I'm obviously swinging the mallet better Admittedly though, it wasn't half out of line! Hi Martin I did indeed use my face 😬 Helicoil will do the job just fine, worked a treat on many a cylinder head in 2cv land for both spark plugs and manifold studs. John _________________________ myothercarsa2cv Bugsy: '82 2cv6 😬 Talloulah '08 1.6K Classic Link to comment Share on other sites More sharing options...
jeffi Posted March 11, 2010 Author Share Posted March 11, 2010 A good evening's work: I Helicoiled the well damaged thread and was impressed with the result. I then Helicoiled the good side to standardize. Interestingly before this, I tapped the good side with a normal M12 die and was amazed of how much ali dust was scraped out - goes to show it's worth tapping out all critical threads. I then used the suggested bottom-bolts-first approach and had them in all the way with my fingers - the top mounting with screw drivers in place. Then I fitted the top bolt, which only required a little force to knock through, and re-fitted the bottom and top with shims and got the diff central to within what looks like 0.5mm. The Helicoil gave me the reassurance that I could refit the bolts with ease and without that horrid feeling of cross-threading! They are also stronger than the original. Next time though I'll get someone to hold the diff when I drill out the holes before tapping - it's amazing how much they want to fly when the drill bites! So thanks for the advice re the new technique and the support. And thx Simon for the offer of a loan diff, but I'm now cooking on gas! There's a market for a new manual, with loads more pics and in colour too. Cheers Jeff Link to comment Share on other sites More sharing options...
simonpa Posted March 12, 2010 Share Posted March 12, 2010 Great stuff - well done! Colour manual? You'll be saying clams are outdated next! Link to comment Share on other sites More sharing options...
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