Lord Flashart Posted March 5, 2009 Report Share Posted March 5, 2009 Hi all, Got myself a test meter that has an RPM function and tested the car. It shows that the tach fitted is way out of calibration. Is it possible to re-calibrate at home? If so how?? Flash Quote Link to post Share on other sites
Lord Flashart Posted March 7, 2009 Author Report Share Posted March 7, 2009 I'll take that as a no then!! Cheers Flash Quote Link to post Share on other sites
Nigel Lay Posted March 7, 2009 Report Share Posted March 7, 2009 I was waiting for replies as well , I would be very careful using one of these multimeter tacho's as they can be very inaccurate unless it is a professional unit (like the snap on). There is a way using the 50cycles from the mains as a reference which I used when constructing tacho's in the 60's when it was difficult getting a 1-10,000 rpm one. Will try to get the info out of my old books but I think most of them are in France and the memory is failing as to how we done it. Keep looking at the post, perhaps somebody will now chip in. Nigel (with TS952) Quote Link to post Share on other sites
angelfj Posted March 7, 2009 Report Share Posted March 7, 2009 Hi all, Got myself a test meter that has an RPM function and tested the car. It shows that the tach fitted is way out of calibration. Is it possible to re-calibrate at home? If so how?? Flash Flash, I agree with Nigel. The set up on these cars is so simplistic that there is very little that can go wrong. Before you invert more money, I would check the tach against the speedo. What I mean, knowing the final drive ratio and your current speed, you can calculate what the engine speed should be at that speed. I would do this in 2nd, 3rd and 4th gear. That way you have a wide range of engine speed. Another suggestion, if you have access to a simple hand-held tacho, the kind that has a rubber tip that you hold up against the rotating object, use this at the cable take-off on the differential. When this number is known, you can multiply it by the ratio of your TR tach. to get the correct reading. Your tach should read very close to the theoretical number. If it does not, then you know the problem is in the tach and not elsewhere. good luck Quote Link to post Share on other sites
Kiwifrog Posted March 7, 2009 Report Share Posted March 7, 2009 Flash Is the Tachometer consistently inaccurate ? ie always reading over or under by a certain amount ? I had one that always read 500rpm too low, the solution was to take the tacho out take the face off move the needle to 500 rpm block the needle support (gently) pull the needle off and replace it pointing at 0. Be careful though as the mechanism is very fragile Cheers Alan Quote Link to post Share on other sites
Lord Flashart Posted March 7, 2009 Author Report Share Posted March 7, 2009 Cheers all, The tach is all over the place at the moment, which is why I think the portable is probably correct. The tach shows red line at 65mph and then starts bouncing between the stop and 4500 at speeds over this. Also shows the idle at 1100rpm when the engine sounds like it's idling much lower. It does seem like it's worse in top gear, but I don't rev the thing too hard in the lower gears though. I think the tach probably needs a proper looking at by a professional but funds don't allow at the moment. Paul Quote Link to post Share on other sites
ianhoward Posted March 8, 2009 Report Share Posted March 8, 2009 The tach on mine is probably accurate at low revs, but have ascertained that it progressively gets more error the higher the revs... Hence at 70mph in OD top it indicates approx 3500rpm - that's with a 3.45 diff (NO comments Alec! ) I think I shall leave it to one of the recalibrating pros when I get home... Quote Link to post Share on other sites
Kiwifrog Posted March 10, 2009 Report Share Posted March 10, 2009 Cheers all, The tach is all over the place at the moment, which is why I think the portable is probably correct. The tach shows red line at 65mph and then starts bouncing between the stop and 4500 at speeds over this. Also shows the idle at 1100rpm when the engine sounds like it's idling much lower. It does seem like it's worse in top gear, but I don't rev the thing too hard in the lower gears though. I think the tach probably needs a proper looking at by a professional but funds don't allow at the moment. Paul I suggest you check the drive cable, if this is ok then the gauge more than likley needs cleaning and recalibration by a professional Cheers Alan Quote Link to post Share on other sites
Paul Down Posted March 10, 2009 Report Share Posted March 10, 2009 I suggest you check the drive cable, if this is ok then the gauge more than likley needs cleaning and recalibration by a professional Cheers Alan Certainly sounds like the drive cable. When worn, the inner bowden cable that is usually comprised of several smaller wire strands twisted together can disentegrate causing a loose strand to catch on the inner surface of the outer sheath. this can cause very erratic readings on the meter. As Kiwifrog suggests check the cable first. Quote Link to post Share on other sites
Lord Flashart Posted March 10, 2009 Author Report Share Posted March 10, 2009 Cheers all, The cable is new and fitting had no effect. I'll have to get it sent off. Paul Quote Link to post Share on other sites
Don Elliott Posted March 11, 2009 Report Share Posted March 11, 2009 (edited) Paul - It's the poor quality of your new drive cable that's causing your problem. If the end that fits into the tach is not just so, it will do all sort of horrible things. Compare yours to the photo where you can see the single red wire. Notice the center bit that is sticking out. If yours looks like this, file off the excess bit you can see till it is fluch as shown in the photo with all the coloured wires. Then test the tach again before spending big money on an expensive repair of your tach if the problem is not there. Edited March 11, 2009 by Don Elliott Quote Link to post Share on other sites
stuart Posted March 11, 2009 Report Share Posted March 11, 2009 I had a similar problem with the speedo cable on my 4. if you did the nut up on the back of the instrument to hold the cable in it would drag the needle and at times completley seize the needle at any point. Undo the nut and just engage the inner cable only and it works fine. The plastic top hat section at the end of the inner is too deep.Typical not quite good enough repro Stuart. Quote Link to post Share on other sites
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