hello i buy my first dino 208 gt4 las week speedemeter works great, but, odometer works double fast than realty is.- when i travel 1 km, odometer put 2 kms? some one can help me?? what is the problem?? the clock, works to fast to??? more or less in 1 hour, run 4 hour ..... this car travel int time ....!!!!! maybe is other car to "back to future ..." i wait your help regards Enzo
Hello Thanks for repley I don't know, sensor was new But speedometer works fine. Only o someter works so fast. I think both works with same sensor Where is put, the sensor? Same one, have other idea? Regards Enzo
I thought that this was to do with miles & kilometres getting mixed up. But the maths doesn't work. Has this problem always been there? Anything else happen when you started noticing it? Is the change consistent or variable?
Now there's something in the back of my memory that later senders (308 injection etc) give double reading - but I don't know which figures they double
Hello thanks for answers i buy car las week, and travel 600 km, to my house. And i think problem is consistent.- the car is 208 gt4, is made only for Italian market, and speedometer and odometer ar in km/h.- Is carbs car, not inyection.- I just think for alternating current and as many cycles, double the engine speed odometer command. - But up to two I used DC, unless for example the reading taking both coil and double the speed it odometer engine. - But strikes me that the speedometer works fine. - Any other ideas on how I can troubleshoot or verify what the problem is? greetings and thanks
How can check out pu current? Whith tester. Can you tell values of out put current in alternador? How can i check dioses works? Regards Enzo
Hey that's awesome.... Now, all you have to do is figure out what the electrical problem is, then invert it ---- so that you can make the odometer register only 1/2 the actual miles traveled. Then sell the "kit" to every owner with a Ferrari from that era ---- and you will make a fortune !
Enzo have you considered that you might just have a defective odometer and clock and maybe the rest of your electrical system is fine?
Are you sure it is an electronic speedometer? I have seen evidence that a few GT4s were equipped with mechanical units
The odo is pulse driven (similar to a stepper motor), the displayed distance does not depend on the supply voltage but only on the incoming pulses. The Speedo also relies on the incoming pulses but is calibrated independently of the odo. The only situation i could think of where an unmodified early 308 speedo would display double the odo distance would be when paired with the later speedo sensor, which is mounted on the bottom of the gearbox (the correct speedo sensor for this odo is mounted from the top). If you have access to a square wave generator you could test the odo on the workbench, happy to explain the procedure if you want to try this.
Hello thanks alhbln how can i check if, right conect or is wrong?? I think is possible, when you said: "The only situation i could think of where an unmodified early 308 speedo would display double the odo distance would be when paired with the later speedo sensor, which is mounted on the bottom of the gearbox (the correct speedo sensor for this odo is mounted from the top)." as I can tell is well connected odometer sensor? or speedometer sensor is not influencing the odometer sensor? i want check all possible in the car, i am tecnic, but not works in this area.- i not "have access to a square wave generator you could test the odo on the workbench" (i live in very small city).- have you any idea how I can check or repair odometer operation, perhaps with some diode or resistor that limits the pulses in half?? regards Enzo
I have a function generator I no longer use as the sine wave distortion is too high for my needs, but the square wave would be fine for this. You are welcome to it if you want to pay for shipping.
Enzo, there are two types of Speedometer sensors, the early type (which is the correct one for your car) is mounted on the top of the gearbox and looks like this: http://www.ferrarichat.com/forum/attachments/308-328/1746771d1375016205-308-early-speedo-drive-sensor-repair-speedometer-sensor-finished.jpg The later type (which would be the wrong one for your GT4) is mounted from the bottom of the gear box. I am not even sure that this later type can be mounted on a standard GT4 gearbox but the symptoms of using this newer sensor type with your Speedo would lead to the double amount of pulses, e.g. double odo distance. Niels very kind offer to send you his old function generator for the shipping cost would make it easy to diagnose if the Speedo is in good working order: The testing procedure for checking the ODO calibration of a km/h Speedo: Reset the ODO trip counter to zero Wire function generator "ground" to the Speedos ground input (black wire) Wire a +12V source/battery to the Speedo (minus to black wire, plus to green wire) Set the function generator to "square wave" with an amplitude of 6-8V Set the function generator frequency to 68 Hz Connect the function generator "output" to the Speedos sensor input (red/black wire) for exactly 60 seconds After 60 seconds, the odo should have run for exactly one kilometer (red dial on the right side moves one full turn). While the test runs, the Speedo needle will display a speed of 60 km/h if calibrated correctly. Good luck, Adrian
Hello thanks for information. I have scare to ship And reship speedometer internacional , And loos in post or través. I m looking anyone, have machine to check The sensor of speedometer And oso meter is The same? Regards
You don't need to ship your speedometer, Niels offered to send you his function generator so you can do the test on your own. The sensor for the Speedometer and Odo is the same.
Hello Nielsk In my bad english, i not understand your offer. I search in my little cita And not find generator. I realy happey , with your offer, And realy apreciate. Yes i can pay shipping cost . If you give, your paypal acount, i will send monee. My Mail is [email protected] And adress is Enzo A. Rodríguez Diéguez Rivadavia 645 - Santa Rosa La Pampa - Argentina - CP 6300 THANKS And Regards Enzo
Hello I read some thread, about speedometer problem. And i m not aire if i can check my sensor with generator, but if possible i will try. You are a gurú of speedometers, Inside sensor, you know same parts y can measure or control with multimeter?? I read this thread Hi Gang, Sorry this is so long but I hope it has some useful info. I have a 1978 308 GTS with a Veglia Borletti speedometer. When I first purchased the car, the speedo worked but the odo did not so I set out to find out why. I dismantled the unit by first pulling the whole instrument cluster out (lots of threads on how to do this). Ive got to hand it to the Italians for the ease of removal here. I did not have to remove the steering wheel, I just maneuvered the entire unit forward and then down and to the right, and it comes right out. Just three big connectors to unplug. The speedometer is easily removed from the cluster with two thumbscrews. This makes me think that they actually knew how often this thing would need to be repaired. Once the unit is separated from the cluster, you rotate the outer steel band like a large screw and it pops off with a plastic ring and front window. Look for the gap in the ring flange and get this threaded on the outside rim of the plastic housing. This step while seeming simple is important so that you dont scratch anything. Set these pieces aside. There are three screws on the rear that come out but more importantly, you must gently (I mean gently this is old dry plastic) pry the plastic plug that is the strain relief for the three wires going in to the instrument part of the speedo. This piece comes straight out away from the housing. The three wires are +12V (Green), Ground (Black), Sender (Red) Signal. Once the little plug comes out, put your hand on the front of the unit and gently ease the speedo unit out the front of the housing into your hand while feeding the three wires into the back. Try not to smudge up the front face of the speedo. You should now see the speedometer and odometer in all of its naked glory. Now I can only speak for this specific unit but I bet they didnt change it too significantly for a number of years. Here is how it works. There are two sections to the unit and they are functionally separate. The speedo needle is attached to a DArsonval meter. This is simply a moving coil over a permanent magnet. When the coil gets a certain current, the meter moves up. The sender unit puts out a certain number of +12V pulses based on the rotation of the rear axle. There is about 530 ohms to ground and then the signal is fed into the SAY115Y Integrated circuit. This darned chip is obsolete. My Canadian friend, Gerrit, actually got the U.S. version of the datasheet and sent it my way Thanks Gerrit! Anyway, the pulses are integrated into a current that is supplied by an on-chip current source. This current directly drives the meter. So, the faster you go, the faster the pulses are generated and the higher the needle goes. The duty cycle or shape of the pulses is not important, just that they are periodic. The SAY has a pulse re-shaper that makes sure the needle is integrating the same shaped pulse. There is a variable resistor on the board which will move the needle up and down for the same pulse rate. This is the calibration potentiometer. There is also a small screw that holds a fixed adjustment for how hard the spring on the needle wants to drive it back down. I will get to this later during calibration. The odo section consists of a whole bunch of plastic gears to increment miles in tenths. There is the main odo section and the resettable mile counter section both driven by the same initial gears. The mile counter section is reset with a mechanical linkage to the front of the instrument panel. When you turn this little knob, a cable turns inside which turns the plastic gears, resetting the counter to all zeros. Of course, this does not affect the main odometer mileage. This entire little two-part mechanical counter is driven by a worm gear that is driven by a step motor. The step motor is a single-phase unipolar drive type. This means that it needs a single energized pulse to bump it a step. The SAY115Y contains a divide-by-64 circuit. So, while the input pulses from the sender are happily converted to current to drive the speedo needle, they are also being divided down such that two out of every 64 pulses will step the motor. The motor gets stepped twice because it steps each on the high part of the dived clock and the low part. The IC has two darlington transistor pair outputs that are designed to drive motor coils. The designers chose to connect one of these to a little PNP transistor acting as an amplifier to provide the +12V drive to the motor. The other output was connected directly to the motor for the Ground drive. This is the one that shorted to ground (inside the SAY IC) in my speedo. I used the remaining signal that was still driving the PNP transistor and placed a small NPN transistor to provide the Ground or low side drive to the motor. This is shown as the dotted line circuit in the schematic. It seems to work fine and does not get warm. The Speedo and odo are separate but do run through the same IC and use the same sender signal. One can be busted and the other working. If this is the case, your sender is probably fine because neither can work without those pulses. When speedos are reading high, they could simply need to be adjusted for wear or spring tension or the IC is failing. When the odo is not working, the stepper is probably ok (I dont think these itty bitty parts can take out the coils in the stepper) but your drive circuit has failed. This type of failure is not that unusual for electronics driving inductive loads like a motor. I reverse engineered the schematic and it is attached. Yes, I spent a couple of hours with a meter and a bright light (to see through the board to the copper). I hope this helps you guys. I wouldnt work on one of these unless you understand electronics because you can break something pretty easily. Gerrit tells me that he is designing a board replacement (you can look him up on Fchat). If Gerrti does this, the board should only have a few connections and should be pretty easy to install. Practical Facts: 1) The sender rotates 2 times for each revolution of the axle. This was measured by removing the sender, jacking up the back end, putting a little flag with a toothpick on the spindle sticking out of the axle and rotating the wheel one complete revolution. 2) The sender puts out 4 cycles per rotation, therefore the sender puts out 8 cycles for each rotation of the axle. This was measured by connecting the sender up to +12V, using a 560 ohm resistor from the sender output to ground (pulldown). The resultant signal is a square wave with about 6 V peak to peak. This was checked on an oscilloscope. 3) Doing the math yields 109.8 cycles per second at 60mph for a 24.5 inch tire diameter. (((5280 ft/mi. * 12 in./ft. * 60 mi/hr.)/3600 s/hr.)/(Pi * 24.5in.)) * 8 cycles/rev.= 109.8 Hz 4) The odometer contains a divide by 64 circuit in the SAY115Y. 5) The odometer requires exactly 200 steps of the step motor to increment 1 full mile. 6) The odometer steps the motor on EACH half cycle. I point this out because up until now, every thing was based on a single cycle causing a single event vs. in this step, a single cycle causes two events. 7) Doing the math for 60mph yields: ((200 steps/mi. / 2 steps/cycle) * 64 divider)/60 seconds/minute = 106.7 Hz Note: What the odo requires as an input is a better use to calibrate the unit vs. the calculation based on wheel size. This is because the tire diameter is a squishy variable. 8) If oversized wheels are used, the stock odo will not read correctly without some sort of circuit addition i.e. there is no adjustment for it. The speedo, however, can probably be compensated by the variable resistor. Easy sender checker - Connect a +9V battery plus side to the green wire of the sender. Connect the minus side to the housing of the sender. Connect a 560 ohm resistor from the red wire on the sender to the housing (minus). The resistor is in a pulldown configuration. Connect a voltmeter negative lead oto the sender housing (minus) and the positive lead to the red wire of the sender. Rotate the sender and you should see the voltage change from 0.5-1V (Low) to 5-6V (High). I dont know if this works on all senders but it works fine on this one. When you reinstall your sender, make sure you get the small shaft on the sender into the cup receiver shaft sticking up from the axle. If you miss, the little coupler will miss the axle turning and you will think your sender is faulty. If you jack the back end up and get on your back looking up, you can see these two mate before screwing the sender down. Calibration I thought I could nail this thing and really tune it in tight but I cannot. The design of this unit is such that there is no way to get it perfect, just close. Since the odometer is pulse driven and essentially fixed all the way back to the wheel, I thought would start there. The calculations show that the odometer needs to have a 106.7 Hz frequency to simulate 60mph. A frequency generator with +12 amplitude was connected to the red input wire (sender input). The green wire into the speedo was connected to +12V and the black wire to ground. The generator was set up to output a 50% duty cycle at first. The setting of the odo was recorded with the starting time and the unit was left to run for 5 minutes. At this frequency, there was exactly 5 miles shown on the odo. Step one complete. There is no adjustment for this, just verification. The speedo jumped up to about 55mph. The variable resistor was adjusted to bring it up to 60mph at 106.7 Hz. Doubling the frequency and halving the frequency should have yielded 120mph and 30mph respectively, but it did not. This is where the second adjustment comes in. There is a small screw on the underside of the meter portion of the speedo. When loose, a plastic arm can slide to the left or right by a couple of centimeters. This arm simply winds the little resistance spring on the meter up or down providing more or less tension to resist the magnetic field that is positioning the needle. Since 60mph worked but the others did not, I would call this somewhat of a linearity adjustment. It also serves to pull the needle to peg at zero when the car is stopped, otherwise it floats a few miles above zero. Anyway, I messed with this in many positions and could get close but not perfect. I could get one or maybe two of the three readings to match the input frequency but not all three. I decided that I wanted the best accuracy below 85mph and concentrated on making 30mph and 60mph work. Because of this, when I put 213.4 Hz into the meter (double the 106.7 to get 120mph simulation), I got 114mph. This is the best I could do. It is interesting to me that all this talk of high speeds can be off by as much as 5-10 percent or more! So, my speedo/odo works now and only so-so accurate. I dont want to worry about it anymore. Its getting to be time to drive. -RJay P.S. If anyone wants the schematic and layout for the board, please PM me because it is too big for the site. Attached Images From http://www.ferrarichat.com/forum/technical-q/101159-308-speedo-odo-sender-system-fix.html I think, if speedometer works good, And odometer works with same sígnal, maybe problem is is in current go to the little motor of the odometer . What you think?? Problem is in sensor? Or in odometer motor?? From where come current to this motor?? Pardon if i ask same wrong question. I understand only , a little of electronic Thanks , Regards Enzo Adrián (too) Rodriguez Dieguez
You can measure some of the parts in the sensor with a multimeter, but to find out if the sensor is really ok you need an oscilloscope (sensor repair: http://www.ferrarichat.com/forum/308-328/416720-308-early-speedo-drive-sensor-repair.html). -> To find out if the speedo sensor or the speedometer itself is the problem, i recommend to do the test with the function generator (http://www.ferrarichat.com/forum/142723810-post19.html). This test will help you understand if the speedo sensor is broken or wrong, or if the Speedometer itself is defect. Both the speedo sensor and the speedometer can be repaired, but first we need to understand what part is actually broken, so it's best if you first do the test as above. good luck, Adrian
There are also 2 types of chips, SAY115Y and SAY115X. I once repaired a speedo that had an SAY115X in it, same symptoms as here. I would expect if the sensor was outputting 8 pulses per wheel rotation that the speedometer section would also be out. Standard for this chip is 4 pulse per wheel rev. for SAY115Y. Use a magnifying glass to check the part number on the chip in the speedometer ... Gerrit
