Defender rev range

[Ranga]

I'm getting an old bloke down the road to check out why my VDO tacho is so inaccurate next week. Anyone able to advise what the idle revs are for a 300TDi, so he's got something to go by?

[MacFamily]

This post has some great info have a read
http://www.aulro.com/afvb/technical-chatter/29771-vdo-tacho-wiring.html

[rick130]

Idle revs on a 300Tdi are supposed to be 720 +-20RPM.

Most accurate way I know is to use an optical tacho on the crank pulley and calibrate the tacho to that.

The VDO tachs I've seen have an adjuster pot inside so that the indicated revs can be altered, but it does sound like it's possible someones swapped an alternator on yours and it's now running a different size pulley, L/R changed the pulley size between early and late Tdi's

[VladTepes]

yes that is exactly what they have done - his is not the original alternator. There is a limited range of adjustment - we couldn't get it adjusted down far enough to read properly. So given there is insufficient adjustent in the tacho itself, where to next ?

[one_iota]

When my alternator failed I was only able to get the new edition so I swapped over the pulley from the old one to the new one.

There might be someone here who has a clapped out old one with the pulley intact that could be used as a donor.

[rick130]

yes that is exactly what they have done - his is not the original alternator. There is a limited range of adjustment - we couldn't get it adjusted down far enough to read properly. So given there is insufficient adjustent in the tacho itself, where to next ?

Swap to the original OD alternator pulley.

I have an old VDO tach here that I used to use on my race cars and I could never get it to read low enough revs so never fitted it. As you've found, not enough adjustment in that adjustable pot. Not sure if there is something else internally that can be changed, (eg a resitor ? ) but at a guess it would cost more to do than another tach.

[steveG]

I just bought a new VDO tacho yesterday, and it has a few dip switches on the back to adjust the broad range, then the pot on the side for fine adjustment.

Is your one like that?
If so I've got the instructions here if it helps.

Steve

[weeds]

i still have my original pulley from when i upgraded to the disco alternator which youu can have for nicks

[Ranga]

Coincidentally, I did get my pulley fixed recently by MR (was squeaking like a stuck mouse!), but both before and after the tacho wasn't accurate, so I assume they replaced the pulley with similar.

Weeds - I'll have a look at your pulley when I come and take photos of your sliders.

[VladTepes]

steve - yeah tried all combos of the dip switches - still no luck. The pulley is obviously the culprit. Weeds I hear of these sliders but will have to look at Rangas pics and hear his report as I can't get over there any time soon.
Could your design be adapted to a 130 easiliy enough ?

[weeds]

Coincidentally, I did get my pulley fixed recently by MR (was squeaking like a stuck mouse!), but both before and after the tacho wasn't accurate, so I assume they replaced the pulley with similar.

Weeds - I'll have a look at your pulley when I come and take photos of your sliders.


steve - yeah tried all combos of the dip switches - still no luck. The pulley is obviously the culprit. Weeds I hear of these sliders but will have to look at Rangas pics and hear his report as I can't get over there any time soon.
Could your design be adapted to a 130 easiliy enough ?

vlad....you must nearly drive past my house every day

hows does monday arvo sound guys

[Ranga]

vlad....you must nearly drive past my house every day

hows does monday arvo sound guys

Vlad was referring to my tacho - his installation works fine, due to original alternator and/or pulley :mad:

When can I pop around and have a look?

[steveG]

steve - yeah tried all combos of the dip switches - still no luck. The pulley is obviously the culprit.

So if the tacho is reading too high, the pulley must be smaller than standard (ie higher alternator RPM for given engine RPM) ??
Just trying to get my head around it...
That would tie up with my 300tdi disco experience in that the later model belt doesnt fit the early 300tdi (its too small so the earlier pulley must be larger)

Would a simple frequency divider circuit work to bring the pulses down to a frequency that the tacho can handle?
Something like this: Frequency Divider Circuit (http://ecelab.com/circuit-frequency-divider.htm)

Steve

[weeds]

So if the tacho is reading too high, the pulley must be smaller than standard (ie higher alternator RPM for given engine RPM) ??
Just trying to get my head around it...
That would tie up with my 300tdi disco experience in that the later model belt doesnt fit the early 300tdi (its too small so the earlier pulley must be larger)

Would a simple frequency divider circuit work to bring the pulses down to a frequency that the tacho can handle?
Something like this: Frequency Divider Circuit (http://ecelab.com/circuit-frequency-divider.htm)

Steve

the earlier 300tdi, defenders at least, had a smaller pulley fitted to the alternator, when i upgraded my alternator i went with the larger output unit that is fitted to the disco's, at the time i brought the longer belt instead of changing over the pulleys