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Hi Guys I have fitted a 308 and TH350 from a HZ ute into a 1972 HQ Premier.I now have a problem with speedo reading to high.At 70kms it reads 100kms and at a 100kms it reads 140kms.I have talked to the local transmission guys and they dont seem to know a accurate solution.Has any one done this conversion and solved this problem.Thanks Mike.
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Obviously the HQ has a higher (numerically) rear axle ratio than the HZ.
The HZ most likely had a 2.60 rear end, while the HQ is 3.08 or 3.36.
You will need to change the driven speedo cog at the transmission end of the speedo cable to correct the speedo error. The tooth count of the cog required, will depend on what your HQs rear end ratio is, so find that out first.
Dr Terry |
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if you know how far out of calibration the speedo is, you could just leave it and drive at 140 on the highway and 35 around town
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Hi Dr Terry thanks for the quick reply.The plate on the input shaft says 3.08 but I want to change the oil so will remove cover and confirm in case it has been changed.Tyres are 235-60-14 if that has any thing to do with it.Current driven gear is 19 teeth but I dont know the teeth count on the drive gear but it is white.Thanks Mike.
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Yes, the tyres will make the issue worse.
I find the easiest fix is use the fact that each tooth on the driven gear will change your speedo by 5%. Rather than guesswork, find out how far the speedo is out exactly.
In NSW many our freeways have a measured 5km to check speedo error. Its actually odometer error which is easy to figure out. We drive the 5km & then compare that to the odo reading. This is easier, more accurate & safer than comparing actual road speeds.
Dr Terry |
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Just had a look, a standard HZ or WB with 195SR14 tyres (which are about the same as a 235/60/14) use a 19 teeth white speedo driven gear in a TH350 with 3.08 diff. The GM part number is 3987919. The one you have now is probably a 17 teeth Purple one for 2.6:1 diff, although my HZ parts catalogue doesnt list a 2.6 behind a TH350, only the WB lists it.
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Further on I have found that the drive gear has 10 teeth and the driven has 19.The local transmission guy is saying to fit a 8 tooth drive gear and this will get it close,does this sound right.Thanks Mike.
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klompy,hi,go to oldholden.com they have a live conversion for ALL trans /gear/rear /tyres combinations etc it is excellent,but all the above advice is right ,i just fitted a t400 in hq van same problem although i havent drove it yet i knew this was situation coming .
Jim in Adelaide |
Jim in Adelaide.. |
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