Couple of "after autometer gauges installed" questions
#1
Racer
Thread Starter
Couple of "after autometer gauges installed" questions
Got all the gauges installed and they are working. However a couple are not working properly and I'm not sure how to go about correcting them.
- Speedometer: According to a radar device near my house it is reading about 9 - 10 miles off. Speedo says I'm going 55 and the radar says its 45. All equipment - rearend (3:08) tranny and wheels are original. I checked the trans gear when I installed a new speedo cable and it is the correct size for all my components. Any ideas?
- Fuel gauge: Says I have just over 1/2 tank but I stopped and filled it to the top. Is there a way to calibrate it?
- Oil Pressure: When driving it reads same as the original gauge did but when I stop at a light the original gauge drifted down to around 40 but this one bounces up to 100 and stays there. When I accelerate it moves back to the right pressure position but not while idling. Any ideas?
The rest are working find without any problems.
Thanks!!
- Speedometer: According to a radar device near my house it is reading about 9 - 10 miles off. Speedo says I'm going 55 and the radar says its 45. All equipment - rearend (3:08) tranny and wheels are original. I checked the trans gear when I installed a new speedo cable and it is the correct size for all my components. Any ideas?
- Fuel gauge: Says I have just over 1/2 tank but I stopped and filled it to the top. Is there a way to calibrate it?
- Oil Pressure: When driving it reads same as the original gauge did but when I stop at a light the original gauge drifted down to around 40 but this one bounces up to 100 and stays there. When I accelerate it moves back to the right pressure position but not while idling. Any ideas?
The rest are working find without any problems.
Thanks!!
#2
Racer
Member Since: Mar 2014
Location: Easton Massachusetts
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I have the Auto meter gauges with the speedometer and tach. but I have not had it on the road yet to test the tach and speedometer but here is something you may want to try. instead of relying on that radar device, if you have a smart phone, download a speedometer app. I have an Iphone and use the Speed Box App. Its VERY accurate and you can compare it to your speedometer while driving. It uses GPS to track your speed.
As for the fuel gauge, make sure you got one with the correct ohm sensor. You need the 0 - 90 ohm.
As for the fuel gauge, make sure you got one with the correct ohm sensor. You need the 0 - 90 ohm.
Last edited by Sacred Steel; 04-12-2015 at 05:16 PM.
#3
Racer
Thread Starter
Just in case someone else is doing this upgrade here is what I have found on the gauge problem.
- Oil: I talked to the guys at Auto Meter and found that the sending unit they furnish with their gauge is slightly different than the one that may be on your car. It requires that you remove the old one and use the one that came with the gauge.
Fuel: Funny that after all the research I did before I tackled this job not one person mentioned that when you purchase the fuel gauge you have to make certain that you get one for a GM car that the ohms match up. I purchased the wrong one without knowing that and now have to purchase another. The number for the Pro Comp gauge that will work on the C3's is #4314
Speedometer: It's done nothing but rain here all day today and says it going to the rest of the week so I don't know when I'll have a chance to check it again. I downloaded the app for my iphone6 and will check it with that. If its still off I may look into either a different driven gear or check into a "correcting ratio" drive joint.
- Oil: I talked to the guys at Auto Meter and found that the sending unit they furnish with their gauge is slightly different than the one that may be on your car. It requires that you remove the old one and use the one that came with the gauge.
Fuel: Funny that after all the research I did before I tackled this job not one person mentioned that when you purchase the fuel gauge you have to make certain that you get one for a GM car that the ohms match up. I purchased the wrong one without knowing that and now have to purchase another. The number for the Pro Comp gauge that will work on the C3's is #4314
Speedometer: It's done nothing but rain here all day today and says it going to the rest of the week so I don't know when I'll have a chance to check it again. I downloaded the app for my iphone6 and will check it with that. If its still off I may look into either a different driven gear or check into a "correcting ratio" drive joint.
#4
Racer
Thread Starter
Finally was able to head out for a decent drive today and check the gauges. All are working good with the exception of the Speedometer. I secured the app for my iphone that checks the mph and tested it against my speedo. It is off by, right at, 6 miles per hour. If the speedo says I'm doing 60 than I am actually doing 54. Is there a way to fix this? If I change the driven gear in the tranny how much difference will that make?
#5
Intermediate
If anyone is willing to share some pictures of their gauges, I would appreciate it. Looking to tackle this in the near future. Thanks in advance. How long of an event is it to complete them? Haven't decided what look suits me the best, so looking for options.
#6
Racer
Thread Starter
If you do a search on this site you can find tons of pics and instructions for this mod.
That being said here are some pics of the one I just finished. All in all it wasn't really difficult just have to be patient and take your time so you don't have to remove the dash more than once. Take pics on your phone so you know where stuff goes. I marked all the wires with tape just to be sure. The hardest pain of all was the lower dash on the driver's side. Some have completely removed the steering column but I didn't want to do that so I lowered it and wrestled with it.
If you have any questions as you go let me know and I will help with what I can.
Sorry! don't know why the pics are all sideways!
That being said here are some pics of the one I just finished. All in all it wasn't really difficult just have to be patient and take your time so you don't have to remove the dash more than once. Take pics on your phone so you know where stuff goes. I marked all the wires with tape just to be sure. The hardest pain of all was the lower dash on the driver's side. Some have completely removed the steering column but I didn't want to do that so I lowered it and wrestled with it.
If you have any questions as you go let me know and I will help with what I can.
Sorry! don't know why the pics are all sideways!
Last edited by BLDun; 04-21-2015 at 09:16 PM.
#8
Drifting
thegazman
Finally was able to head out for a decent drive today and check the gauges. All are working good with the exception of the Speedometer. I secured the app for my iphone that checks the mph and tested it against my speedo. It is off by, right at, 6 miles per hour. If the speedo says I'm doing 60 than I am actually doing 54. Is there a way to fix this? If I change the driven gear in the tranny how much difference will that make?
#9
Race Director
Not quite that much. A typical speedo driven gear has 16-25 teeth. So an example would be going from 20 to 21 teeth which would be 5%. 60 mph would then turn into 57 mph.
#10
Racer
Thread Starter
After a lot of searching there are multiple sites that will help calculate what size gear is needed. Here is the one I ended up using. Have to figure the percentage your speedo is off and then determine the new gear needed from there. According to this site each tooth represents a 2.5% movement - up or down depending on whether you add to the number or subtract. Mine turned out to be 6% off so I needed to move down a little more than two teeth so I opted for three. New gear only cost $8 and free shipping on ebay. This link will also help with the driven gear OD. Says there is more than one size on the GM and many shred gears because they don't pay attention the size needed.
http://chevellestuff.net/tech/speedo.htm
http://chevellestuff.net/tech/speedo.htm
#11
Drifting
thegazman
You still need to factor in the number of teeth on the drive gear as it will vary the ratio of the driven gear. Willcox is where read the 5 mph quote.
Last edited by thegazman; 04-22-2015 at 11:38 AM.
#12
Race Director
The drive gear is not relevant in this case. The drive gear only comes into play if you're at the end of the driven gear range and need further correction.
#13
Nam Labrat
Member Since: Sep 2013
Location: New Orleans Loo-z-anna
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There are two different charts for the two sizes of drive gears (FYI: Make sure you are using the correct model Automatic Transmission Chart if you have an Automatic/Correct Manual transmission chart if you have a manual). You have to choose a DRIVEN gear from the correct chart that corresponds to the DRIVE gear that is currently installed in your transmission. The driven gears are color coded to help you choose the one that will correct your problem.
My understanding is-----a new DRIVEN gear with less teeth than the original driven gear will cause the speedometer to read "faster" than it originally read.......and visa-versa.
Last edited by doorgunner; 04-22-2015 at 12:31 PM.
#14
Drifting
thegazman
Zwede..... Help me out here as I am not real smart. I looked it up and 7, 8, 9,10 tooth driven gears in a th350 will all handle a (for example 20 tooth driven gear). Will all those different drive gears turn the driven gear the same RPM? If they won't then the ratio is different.
#15
Race Director
Zwede..... Help me out here as I am not real smart. I looked it up and 7, 8, 9,10 tooth driven gears in a th350 will all handle a (for example 20 tooth driven gear). Will all those different drive gears turn the driven gear the same RPM? If they won't then the ratio is different.
6 tooth drive wheel: Rear gear ratios of 2.50-3.70.
7 tooth drive wheel: Rear gear ratios of 3.30-4.50.
8 tooth drive wheel: Rear gear ratios of 4.10-5.90.
The driven gear gets you the desired overall ratio within the range the drive gear has.
So if you had a 3.50 rear gear ratio you could use either a 6 tooth drive gear and X-tooth driven, OR a 7 tooth drive and Y-tooth driven (where Y > X).
Or to put it another way: You'd use the drive gear to make large adjustments and the driven gear for fine tuning. Only time you'd change the drive gear is if you change the rear gear ratio so much that you fall out of the range the drive gear can handle.
To further explain the "course/fine" part: If you go from a 6 to a 7 tooth drive gear your speedo changes 15%. A big jump. Going from a 40 to a 41 driven only changes it by 2.5%.
Last edited by zwede; 04-22-2015 at 08:11 PM.
#16
Racer
Member Since: Mar 2013
Location: Boca Raton Florida
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Here is my answer to wiring up the dash gauges…..I used stuff from radio shack and each dash piece comes out with one plug. Also my turn signal indicators are 12v LEDS mounted on the center cluster instead of at the speedo-tach area.
#17
Drifting
thegazman
The drive gears each give a range for the driven gear. So a (made up) example:
6 tooth drive wheel: Rear gear ratios of 2.50-3.70.
7 tooth drive wheel: Rear gear ratios of 3.30-4.50.
8 tooth drive wheel: Rear gear ratios of 4.10-5.90.
The driven gear gets you the desired overall ratio within the range the drive gear has.
So if you had a 3.50 rear gear ratio you could use either a 6 tooth drive gear and X-tooth driven, OR a 7 tooth drive and Y-tooth driven (where Y > X).
Or to put it another way: You'd use the drive gear to make large adjustments and the driven gear for fine tuning. Only time you'd change the drive gear is if you change the rear gear ratio so much that you fall out of the range the drive gear can handle.
To further explain the "course/fine" part: If you go from a 6 to a 7 tooth drive gear your speedo changes 15%. A big jump. Going from a 40 to a 41 driven only changes it by 2.5%.
6 tooth drive wheel: Rear gear ratios of 2.50-3.70.
7 tooth drive wheel: Rear gear ratios of 3.30-4.50.
8 tooth drive wheel: Rear gear ratios of 4.10-5.90.
The driven gear gets you the desired overall ratio within the range the drive gear has.
So if you had a 3.50 rear gear ratio you could use either a 6 tooth drive gear and X-tooth driven, OR a 7 tooth drive and Y-tooth driven (where Y > X).
Or to put it another way: You'd use the drive gear to make large adjustments and the driven gear for fine tuning. Only time you'd change the drive gear is if you change the rear gear ratio so much that you fall out of the range the drive gear can handle.
To further explain the "course/fine" part: If you go from a 6 to a 7 tooth drive gear your speedo changes 15%. A big jump. Going from a 40 to a 41 driven only changes it by 2.5%.
Ken
#18
Race Director
One thing to think about when selecting speedo gears is that the speedo itself may be off, especially if it's the original one. The magnet in them slowly gets weaker over the decades and it will read low.
So to pick the right gear you should go by odometer rather than speed. What I do is use a GPS navigator (Garmin, TomTom or phone based all work fine) and drive about 10 miles. Then compare the distance as shown by GPS with the odometer. If they match the speedo gear is correct, even if the indicated speed is wrong.
Once I have the right speedo gear as verified by the odometer I calibrate the speedo. There's an adjustment on the spring that will compensate for the weakened magnet, at least up to a point. My '71 speedo so so de-magnetized it read 10 mph slow and the adjustment wasn't able to correct it. Although there are speedo rebuild services I opted to put a complete new speedo in it instead.
So to pick the right gear you should go by odometer rather than speed. What I do is use a GPS navigator (Garmin, TomTom or phone based all work fine) and drive about 10 miles. Then compare the distance as shown by GPS with the odometer. If they match the speedo gear is correct, even if the indicated speed is wrong.
Once I have the right speedo gear as verified by the odometer I calibrate the speedo. There's an adjustment on the spring that will compensate for the weakened magnet, at least up to a point. My '71 speedo so so de-magnetized it read 10 mph slow and the adjustment wasn't able to correct it. Although there are speedo rebuild services I opted to put a complete new speedo in it instead.
#19
Drifting
thegazman
One thing to think about when selecting speedo gears is that the speedo itself may be off, especially if it's the original one. The magnet in them slowly gets weaker over the decades and it will read low.
So to pick the right gear you should go by odometer rather than speed. What I do is use a GPS navigator (Garmin, TomTom or phone based all work fine) and drive about 10 miles. Then compare the distance as shown by GPS with the odometer. If they match the speedo gear is correct, even if the indicated speed is wrong.
Once I have the right speedo gear as verified by the odometer I calibrate the speedo. There's an adjustment on the spring that will compensate for the weakened magnet, at least up to a point. My '71 speedo so so de-magnetized it read 10 mph slow and the adjustment wasn't able to correct it. Although there are speedo rebuild services I opted to put a complete new speedo in it instead.
So to pick the right gear you should go by odometer rather than speed. What I do is use a GPS navigator (Garmin, TomTom or phone based all work fine) and drive about 10 miles. Then compare the distance as shown by GPS with the odometer. If they match the speedo gear is correct, even if the indicated speed is wrong.
Once I have the right speedo gear as verified by the odometer I calibrate the speedo. There's an adjustment on the spring that will compensate for the weakened magnet, at least up to a point. My '71 speedo so so de-magnetized it read 10 mph slow and the adjustment wasn't able to correct it. Although there are speedo rebuild services I opted to put a complete new speedo in it instead.