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WB One-tonner Tailshaft broke?

Started by _Viper_ , Mar 05 2014 11:42 PM

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9 replies to this topic

#1 _Viper_

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Posted 05 March 2014 - 11:42 PM

Hey guys, Friends WB one tonner was on the Dyno the other day... Pretty much stock 308, TH350 with the original 6cylinder diff 3.55 Ratio or therabouts.

Was doing 150kph wheel speed when suddenly BANG it peeled open right in the center like a banana... No real damage except to the exhaust and a touch on the floorpan, engine/box seems fine..

Im just curious what the cause is? I know tailshafts have a critical rpm they should be kept under But being a 1-tonner shaft in a pretty much stock 1 tonner I wouldnt of thought it to be a problem? was only doing about 4000rpm at the time too... Surely thousands of 1-tonners have gone over 150kph.

Spoke to Phil at final drive and he recommended a 2-peice shaft as a replacement but didnt really provide any answers on why it would have broken...

Inside of the shaft was not rusty...

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#2 dattoman

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Posted 06 March 2014 - 12:04 AM

I doubt any 6 cyl 1 tonner ever cracked a real 150kmh

30+ year old metal fatigue ?

Crook shaft that was lucky to live as long as it did because it sat behind a gutless 6 all its life ?

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#3 myss427

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Posted 06 March 2014 - 08:42 AM

A stock 308 is not going to break a 3.5 inch tailshaft, has to be more to it, bent out of ballance? I cut one up years ago to put behind a toploader and they have thicker wall size and larger turbo 400 uni's. Would have to be a problem somewhere!

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#4 76lxhatch

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Posted 06 March 2014 - 09:52 AM

Length and diameter are trade-offs; short shafts can be smaller diameter than long ones to cope with the same torque.

A tonner shaft is getting quite long (which is why a 2 piece was suggested) so any small issues with it were probably made a lot worse as soon as it got out of balance. It wouldn't normally be under a lot of load at those revs either.

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#5 TerrA LX

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Posted 06 March 2014 - 10:07 AM

Did it split open along the seem?

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#6 rodomo

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Posted 07 March 2014 - 08:50 PM

I had thoughts of a one piece tailshaft in the Grease Slapper early in the build as I was having vibration problems at high RPM on the front straight at Sandown.....................Aussie 4 speed and Salisbury 2.78

I Swapped in a VL wagon Borg Warner diff (3.45) so I had to change the diff end yolk on the shaft and that also meant the centre bearing no longer lined up..........

Onyhoo...........I went to a tailshaft joint with all my measurements and they told me to stick to the 2 piece as a single shaft is no good after about 4500rpm.

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#7 _Viper_

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Posted 07 March 2014 - 10:15 PM

AFAIK Torque is not the problem (unless you have monster torque I guess) as the tailshaft see's the most torque In first gear, More to do with Tailshaft RPM but thats why I was confused as I thought in a stock setup they would have been fitted with a tailshaft that can handle what a stock car is likely to acheive. and top gear of 1:1 and 4000 or so rpm is well within stock limits I would imagine, so yea must have been a pre-existing fault/old and worn. Whatever the case a new 2-peice shaft will be fitted and not have to worry again.

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#8 Ice

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Posted 07 March 2014 - 10:25 PM

Jesus christ you did a job on that clint

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#9 _Viper_

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Posted 07 March 2014 - 10:44 PM

After getting the car back on the hoist we saw the extent of the damage...

The exhaust I just made copped a hit, no biggy tho was on a straight section so just cut it out and replace

Floor was hit in 2 places, 1 spot easy to knock out, the other crushes one of the crossmember type of braces... will need to cut it off and fabricate a new piece as its crimped.

But worst was that it also hit the fuel tank, creased quite bad in one spot and I dont think it will pass rego with it like that :(

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#10 Oversteer

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Posted 07 March 2014 - 10:45 PM

Only needs a small dent in the side of the shaft to drastically reduce its strength...have seen situations where too longer seat belt bolt has touched the shaft under load and bang !