lithium4750 Posted April 4, 2006 Share Posted April 4, 2006 I have a 5 speed tranny in my '74 260, and the speedometer isn't hooked up. My friend was telling me it would give me inaccurate readings even if it was hooked up because of the different gear ratios from the 4 spd to 5 spd. Does anyone know of an adapter that would fix that problem? Or any other kind of trick someone knows about? Quote Link to comment Share on other sites More sharing options...
AK-Z Posted April 4, 2006 Share Posted April 4, 2006 The way that you would get a inacuate reading would be, if the speedo gear didn't match the differential ratio. The speedo speed would be the same if you put the same speedo gear into any datsun tranny, as far as driveshaft is concerned. The gear gets its measurement in relation to the speed of the drive shaft, It the differential gear that would alter you readlings. So speedo gear has to match with the diff. So if all you did was swap out the tranny, then you would only need the speedo gear (the piece that the speedo cable connects to on the tranny) from your old tranny. Quote Link to comment Share on other sites More sharing options...
RB26powered74zcar Posted April 4, 2006 Share Posted April 4, 2006 Your issue has a easy fix. The piece that the cable attachs to on the trans is removable. It has a plastic gear on the end of it that determines the rotation speed of the cable, and by changing that out with the correct color plastic gear will correct your speedo. The problem is, you need to determine which one you need. Once you pull the speedo gear out of the trans and see what color it is (also the tooth count) and find out what rear end gear you have, then you can find out what color (tooth count) plastic gear you need to put back in the trans for your speedo to be closest to perfect.... There is a list floating around somewhere with the color/gear count combos that show which one should go in which trans/ rear end combos, but I don't know where to find it at the moment. Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted April 4, 2006 Share Posted April 4, 2006 In this link is what speedo gear to use with different diffs.....http://www.geocities.com/zgarage2001/engine.html LARRY Quote Link to comment Share on other sites More sharing options...
bjhines Posted April 5, 2006 Share Posted April 5, 2006 ummm.... he only changed his tranny right.....???? That would not change his speedo gearing at all.... Plug the cable back in and it will read exactly the same as it did before... You have to change tire/wheel size... or the differential gearing to need to recalibrate your speedo gearing.... Quote Link to comment Share on other sites More sharing options...
AK-Z Posted April 5, 2006 Share Posted April 5, 2006 ummm.... he only changed his tranny right.....???? That would not change his speedo gearing at all.... Plug the cable back in and it will read exactly the same as it did before... You have to change tire/wheel size... or the differential gearing to need to recalibrate your speedo gearing.... Speedo cable attaches to the tranny, not the diff. If he change the tranny AND the diff from the same car, then he wouldn't need to change the speedo gear. All he has to do is swap the speedo gear from his old tranny into his new one, if he did nothing to the diff. Quote Link to comment Share on other sites More sharing options...
lithium4750 Posted April 6, 2006 Author Share Posted April 6, 2006 Thanks guys that helps. I thought maybe that could have helped me out of a speeding ticket ha ha. But I guess I will have to use something else. But my speedometer is working nonetheless. Quote Link to comment Share on other sites More sharing options...
bjhines Posted April 6, 2006 Share Posted April 6, 2006 AK-Z..... Whaaaa?????..... like I said... if all he changed was the tranny... then he did not change the speedo calibration... It makes no difference what the tranny gear ratios are... at all....the differential and the tire/wheel sizes are all that matter... Plug the cable back in(to the new tranny) and it will read exactly the same as it did before... this assumes that the tranny was speedo geared for the same 3.54 rear end that 90% of hte Z cars came with... If he got a tranny out of a car that had a different rear end ratio then all he would have to do is swap the speedo gear housings from the original tranny to the new one.... PS dont swap the colored gear on the end.. swap the entire speedo gear housing... the offsets for the gears vary by ratio... so swap the whole speedo gear housing and it will fit properly. Quote Link to comment Share on other sites More sharing options...
AK-Z Posted April 7, 2006 Share Posted April 7, 2006 AK-Z..... Whaaaa?????..... like I said... if all he changed was the tranny... then he did not change the speedo calibration... It makes no difference what the tranny gear ratios are... at all....the differential and the tire/wheel sizes are all that matter... Plug the cable back in(to the new tranny) and it will read exactly the same as it did before... this assumes that the tranny was speedo geared for the same 3.54 rear end that 90% of hte Z cars came with... If he got a tranny out of a car that had a different rear end ratio then all he would have to do is swap the speedo gear housings from the original tranny to the new one.... PS dont swap the colored gear on the end.. swap the entire speedo gear housing... the offsets for the gears vary by ratio... so swap the whole speedo gear housing and it will fit properly. You Obviously didn't read that last part I posted. Th speedo gear needs to be changed to match the gearing of the diff because of the final drive. If he just swapped the diff with one from a different gear ratio, he would still need to swap the speedo gear to match the final drive of the new diff. Quote Link to comment Share on other sites More sharing options...
bjhines Posted April 7, 2006 Share Posted April 7, 2006 He didn't say he changed the diff... and I assume the tranny probably came from a car with the same rear end ratio... If not....I hope he has his old speedo gear... I was under the impression that there were only 2..or 3 different speedo gear housings.. and that they were different offsets to account for different speedo gear diameters...but that each housing was appropriate for several closely spaced gear sizes... in other words they took care of many gear sizes using only a few different housings...soo... it is best to keep the housings mated with the gears that originally came with them...but you can use one housing for several different plastic gears... as long as you know which gears are appropriate for which housings... swapping only the plastic gear is great if you need to $$buy$$ one new(instead of hunting in junk yards) and you only want a slight change to account for different tires sizes... it is a safe bet you can swap gears only 1 or 2 teeth different onto the same speedo drive housing.. other than that... I guess we are saying the same thing...My train of thought was on the idea that most of the Z cars had the same rear end ratio...so it is usually a no brainer....plug it in a go on your way... if there is a problem... pull the old speedo housing and gear and slap it in the new tranny... you don't need to know anything about gear ratios to do it correctly... Quote Link to comment Share on other sites More sharing options...
AK-Z Posted April 7, 2006 Share Posted April 7, 2006 If he just swapped the diff with one from a different gear ratio, he would still need to swap the speedo gear to match the final drive of the new diff. I said "IF", and I was saying that thats what he would have to do IF he did change the diff gear. Whether or not the donor car had the same diff ratio is another story. Quote Link to comment Share on other sites More sharing options...
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