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Thread: crunchy box

  1. #1
    Tadpole Mi16's Avatar
    Join Date
    Mar 2004
    Location
    Melbourne
    Posts
    17

    Default crunchy box

    my 93' series 1 Mi16 has just dropped 3rd and 4th syncro, 3rd is the worst, it seems strange to drop those two gears? It's done 280,000kms, driven fast but not thrashed. I was wondering if this is a common thing on Mi's as i know of one other that has had the same problem.

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  2. #2
    Member
    Join Date
    Sep 2003
    Location
    Boolarra Vic
    Posts
    95

    Icon5 Only synchros - lucky you

    Mine ( S2 94 xu10 Mi16 ) had only a couple of hundred Ks less that 150000 on the clock when last week it "developed" a fist sized hole in the casing between the diff and the clutch. It probably happened when I turned the last corner about 8 km and 350 metres climb from home last monday night. I had sat on 100-125 Kph all the way up the hill. No noises or anything althoug the Mi has a pretty loud note between 4 and 5 thousand revs and all those curves are such fun in a good handling car.
    First I was aware was the smoke around the car when I stopped in the carport. Most of the 2litres of gearbox oil was all over the engine, gearbox, exhaust ( hence the smoke) and most of the underside of the car.
    I have taken it off and had a good look and cannot see any obvious 'reason' for what happened. There is no evidence of damage to the crownwheel and pinion or the sun gears in the diff which were both put forward as possible causes. The box has always in the 25 000 KM and 8 months that I have had it had weak synchros on 2nd and, to a lesser extent 3rd, espacially when cold and it was suggested that the bits of metal from these crunchy changes can get into the diff and cause problems but I can see no evidence of this. The three bulges on the pressure plate all have lots of dings where the 2-3 mm of alloy which separates the clutch and diff have been battered away. There are no large bits of alloy in the diff to speak of so it looks like the metal has been pushed out by the diff and then broken away by the rotating pressure plate housing.
    I have seen one other B3 box with exactly the same damage at Pugwreck and Hayden tells me that he has seen a few others like it.
    The one possible cause which remains is related to the mounting of the gearbox to the engine. The car had apparently had a new clutch fitted not long before I brought it and it whoever did it was pretty shoddy. There remained only two of the four bell housing to engine bolts - both the bottom two were missing, and only two of the three starter motor bolts were left. Also the two bolts securing the engine mount to the gearbox were loose.
    My guess is that under the stress of high power coming up the hill the drive torque has tried to twist the diff away from the gearbox flexing the bellhousing in such a way as to distort the alloy membrane between the clutch and diff into the path of the clutch pressure plate which has just shattered it into little pieces....

    I would be very intersted to hear other Ideas.

    Trevor Hoare

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