Hi all,question on my speedo please ,its in mph but is out by quite alot .When i am going 50 kph ,its shows as 55 mph on speedo ,also when going 80 kph it shows on spedo as 70 mph .I took out the speedo gear cog from the tranny and its the yellow with 20 teeth so could anyone please recomend what colour cog to change to? Tranny is a th350 .Thanks in advance
lookoutas,
Apr 7, 12:24am
It sounds like you've got a bob each way here. It's almost doing a conversion from miles to K's at 50 - then it fair loses ground at 80K. So changing drive cogs will only work at one end.
Best you go find something that gives you a GPS readout, and forget the speedo.
tiles,
Apr 7, 12:27am
cheers ,might do that ,was hoping that if i change to a red cog with 17 teeth ,it may have worked
I seem to remember one of those convertors for sale on here a while back.
tweake,
Apr 7, 12:43am
gps is not a legal speedo. you must have an accurate(ish) speedo. so still needs to fix the stock one.
theres plenty of speedo repair crowds around that will have gears or converters.
lookoutas,
Apr 7, 12:46am
OP's problem is that it's over-reading at 50, and under-reading at 80. So changing the ratio at one end will work, but chuck it all t'hell at the other.
If ya need helping with were to go - get a navigator. If ya need help to stop getting tickets - get a radar detector with a GPS readout. Mine's cooling down after the weekends workout.
tiles,
Apr 7, 12:52am
OP's problem is that it's over-reading at 50, and under-reading at 80. So changing the ratio at one end will work, but chuck it all t'hell at the other.
If ya need helping with were to go - get a navigator. If ya need help to stop getting tickets - get a radar detector with a GPS readout. Mine's cooling down after the weekends workout.
cheers guys,might just use a gps unit for now and look at repairing the speedo later on
macman26,
Apr 7, 12:59am
How to get it accurate and on the cheap. 1. Work out the positions on your speedo. 2. Take it out. 3. Paint face of speedo. 4. draw your new speed markings. 5. put back together
tiles,
Apr 7, 1:01am
good idea ,might look ugly but will work ,cheers
macman26,
Apr 7, 1:13am
Just work out how far out the odometer is out and write x 0.62(or whatever it works out to) next to /under it.
tweake,
Apr 7, 1:56am
no its not. at 50kmh its reading 88kmh and at 80kmh its reading 112kmh. a gear change will get it close enough.
you have to have a working speedo for WOF. so he still needs to fix it.
ralphdog1,
Apr 7, 2:01am
76% high @ 50k 40% high @ 80k Sumfink is screwy
tiles,
Apr 7, 2:01am
yes correct,just googled and i think if i increase the teeth of the cogit will decrease the speedo?
lookoutas,
Apr 7, 2:18am
It's reading MPH tweake.
I have two cars with MPH, and 1 with KPH. The KPH one is doing 103-4 with the speedo on or about 110 (but not a gnats over) I wouldn't have a clue where the MPH speedos match. They're both different, so the GPS is the best option.
I know you have to have a working speedo for a WOF. But within what accuracy are they required to be? I sounds like OP's is rough enough.
lookoutas,
Apr 7, 2:39am
When the speedo is reading 55mph - The car is going "slower" than the reading @ 50kph. When the speedo is reading 70mph - The car is going "faster" than the reading @ 80kph Hence, if the same percentage of inaccuracy continued as at 50mph (which it won't do exactly) - when the speedo is reading 70mph as OP stated, the car should only be doing 63.63636364kph.
treachug,
Apr 7, 4:11am
Need a bit more info. Look inside trans where speedo cable fits & advise drive gear colour (& number of teeth if possible) What diff ratio? What tire size (eg 235/45x17)
tweake,
Apr 7, 4:55am
i did see it a while back, 10% error i think it is.
tamarillo,
Apr 7, 5:02am
Think you're right, it's based on aussie adr which is 10%, hence the 10% allowance on speeding tickets. still waiting for the 4 % to be tested in court. Surely theirs a lawyer who's been booked for 105 who'll take this to court on grounds the speedo is only expected to be accurate to within 10%.
tweake,
Apr 7, 5:14am
i think there is a catch in that speedo's are meant to error on the slow side. so to get done for 105 your speedo would be reading up to 115kmh.
tiles,
Apr 7, 11:20pm
255/60/15 tyres,cog is 20 teeth and yellow dont know what the diff ratio is cheers
lookoutas,
Apr 8, 4:49am
You're not gunna fix it.
When your speed is 50, the speedo is running at 110% by reading 55. When your speed is 80, the speedo is running at 87.5% by reading 70. If you knock 10% off the gearing to make 50 = 50, the 10% off at 80 will mean the speedo will be reading 62.
The best OP could do is make the speedo correct at 80 by increasing the drive by 12.5%, but this will make the reading at 50. 61.25 (to be exact) What it will be at 100 is anybody's guess.
macman26,
Apr 8, 4:55am
You may need to strip it down and clean and lube it. I just rebuilt an old speedo for an old cruiser for a mate recently and some of the old grease and oil goes quite sticky. That may be some of the problem. Also check the spedo cable. Pull the inner out. Check it, clean it and give a lube with some light oil.
lookoutas,
Apr 8, 5:04am
You reckon it might be slowing down as it speeds up? Good call.
treachug,
Apr 8, 5:17am
Cool, now. Check the drive gear (the gear the yellow gear runs on - the drive gear is the one in the trans. Could be plastic or steel, but still a few variance of teeth) The driven gear is the one on the cable (driven by the drive gear) What sort of diff is it? Pretty important to know ratio but see how you go/what you can work out. What sort of vehicle is it? (not that it matters. just curious)
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