Rifleshooter
Well-Known Member
So one of the many challenges I'm facing with the restoration of my 80 volare duster is that my speedometer is around 10 mph too slow.
Incorrect Speedometer
- Thread starter Rifleshooter
- Start date
mchartier105
Well-Known Member
You'll need to change your speedometer pinion gear to match the size of tires you're running, there's a chart online that tells you what tooth count you need based on the diameter of the rear tires you're running.
I've seen them range from around $20-$60 online.
I've seen them range from around $20-$60 online.
slant6billy
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Second that. You need to take some data on your car. What is the height of your rear wheels? As in Outside Diameter. If you can't get an accurate measurement, Tirerack works for plugging in the sidewall numbers to give you an average based on a rim width. You need the rearend differential ring & pinion ratio in you car. Old schoolers turn the yoke and count revolutions at the axle end. Or pop the cover off the diff and look for numbers on the ring. Finally pop your speedo gear out of the trans and see what you have. (Remember to note the eccentric location of the plastic housing- this is important) Now look at what number is embossed on the speedo gear. Once you have your numbers you can figure what is off- that is if it is not something wrong with the cluster all together.
Slant6billy is on the right track – but before you change speedometer gears (in transmission), there is two different items in play. Generally the two items are tied to each other and other times not – but you need to check first.
Your Odometer reading needs to be the first thing to correct, then retest to see of speedometer is off, or not.
What I would do is find a section of highway and drive at least 10 miles. More is better – but 10 miles is easy to divide by.
Either record your odometer reading (or take a cell phone picture) right at the mile marker.
Drive 10 miles and right at the mile marker, again, record your odometer reading.
This way, the tire size and differential gear ratio won’t be to much of a factor.
My example, I drove my ’77 wagon from Oklahoma City to Waco at the first of the year.
Along the way, I recorded:
39,642.3 At beginning of test
39,695.2 After traveling 50 miles.
53.9 miles accumulated in a 50 mile trip.
53.9 Miles times 2 = 107.8 miles traveled in 100 actual miles – or 7.8% difference.
My wagon came originally with F78-14 Firestone Super Belt Deluxe Champion tires (Wanted - 77 Volare rear leaf springs post #53 ).
Those tires are 26.5” tall and go on a 5.5” wheel.
The tires currently on car are not the correct size.
This car came with 2.9 gear ratio (either a 2.93 or 2.94) so speedometer gear should be a 29 according to the chart above.
According to the parts manual, F78-14 with 2.93 has a 29 tooth speedometer gear (black).
If a 2.94 ratio, then 30 tooth speedometer gear (yellow).
I know I have 2.9 but not sure which 2.9 (2.93 or 2.94) so it could be with either speedo gear.
Sense I’m recording more miles than actually going, I need to slow it down 7.8%
29 teeth - 7.8% = 26.74 (rounded to 27 (white))
30 teeth - 7.8% = 27.66 (rounded to 28 (blue))
So to get my odometer reading correctly, I need to have on hand a 27 (white) or 28 (blue) – depending on speedo gear I currently have.
To know what speedo gear I have, means I need to get under car. If you have rear of vehicle up high enough, you will not lose much ATF. Remove the speedometer clamp (7/16" bolt) then gently rock the cable assembly back and forth and unit will pop out of transmission.
The gear will be stamped what number it will be as well as the gears are colored plastic (red, orange, white, blue, etc.) - so if you can't read the number, at least get color.
With tire size, we can determine which gear you have.
One that is done, I need to retest to make sure odometer is reading correct.
Now I am able to test the speedometer reading (which I also know is not correct on my wagon).
- - - - - -
A speedometer uses a U shape piece of metal and a rotating magnet. Watching a video on internet might be easier than explaining how it works – but the way to adjust the speedometer is to lightly bend the tangs of the U-shaped piece of metal that goes around the rotating magnet inward to speed it up (or outward to slow it down). I do mean lightly bend, for thousandths of an inch makes a difference (0.001”).
Also, anytime you have a cable driven speedometer head removed, you also need to add light oil to a few key parts and to the cable, so speedometer needle doesn’t jump around.
I know where at on the ‘60’s speedometers but need to look at one of ours to tell you where at, on ours.
Calibrating a speedometer head (once odometer is correct) might be best left to a speedometer shop (if any are left out there) – for the area to work in is rather cramp.
To summarize, there are two calibrations to speedometer assembly.
Calibrate (or confirm) Odometer first, then go on to speedometer calibration.
How to test Speedometer calibration – is a different topic.
BudW
Your Odometer reading needs to be the first thing to correct, then retest to see of speedometer is off, or not.
What I would do is find a section of highway and drive at least 10 miles. More is better – but 10 miles is easy to divide by.
Either record your odometer reading (or take a cell phone picture) right at the mile marker.
Drive 10 miles and right at the mile marker, again, record your odometer reading.
This way, the tire size and differential gear ratio won’t be to much of a factor.
My example, I drove my ’77 wagon from Oklahoma City to Waco at the first of the year.
Along the way, I recorded:
39,642.3 At beginning of test
39,695.2 After traveling 50 miles.
53.9 miles accumulated in a 50 mile trip.
53.9 Miles times 2 = 107.8 miles traveled in 100 actual miles – or 7.8% difference.
My wagon came originally with F78-14 Firestone Super Belt Deluxe Champion tires (Wanted - 77 Volare rear leaf springs post #53 ).
Those tires are 26.5” tall and go on a 5.5” wheel.
The tires currently on car are not the correct size.
This car came with 2.9 gear ratio (either a 2.93 or 2.94) so speedometer gear should be a 29 according to the chart above.
According to the parts manual, F78-14 with 2.93 has a 29 tooth speedometer gear (black).
If a 2.94 ratio, then 30 tooth speedometer gear (yellow).
I know I have 2.9 but not sure which 2.9 (2.93 or 2.94) so it could be with either speedo gear.
Sense I’m recording more miles than actually going, I need to slow it down 7.8%
29 teeth - 7.8% = 26.74 (rounded to 27 (white))
30 teeth - 7.8% = 27.66 (rounded to 28 (blue))
So to get my odometer reading correctly, I need to have on hand a 27 (white) or 28 (blue) – depending on speedo gear I currently have.
To know what speedo gear I have, means I need to get under car. If you have rear of vehicle up high enough, you will not lose much ATF. Remove the speedometer clamp (7/16" bolt) then gently rock the cable assembly back and forth and unit will pop out of transmission.
The gear will be stamped what number it will be as well as the gears are colored plastic (red, orange, white, blue, etc.) - so if you can't read the number, at least get color.
With tire size, we can determine which gear you have.
One that is done, I need to retest to make sure odometer is reading correct.
Now I am able to test the speedometer reading (which I also know is not correct on my wagon).
- - - - - -
A speedometer uses a U shape piece of metal and a rotating magnet. Watching a video on internet might be easier than explaining how it works – but the way to adjust the speedometer is to lightly bend the tangs of the U-shaped piece of metal that goes around the rotating magnet inward to speed it up (or outward to slow it down). I do mean lightly bend, for thousandths of an inch makes a difference (0.001”).
Also, anytime you have a cable driven speedometer head removed, you also need to add light oil to a few key parts and to the cable, so speedometer needle doesn’t jump around.
I know where at on the ‘60’s speedometers but need to look at one of ours to tell you where at, on ours.
Calibrating a speedometer head (once odometer is correct) might be best left to a speedometer shop (if any are left out there) – for the area to work in is rather cramp.
To summarize, there are two calibrations to speedometer assembly.
Calibrate (or confirm) Odometer first, then go on to speedometer calibration.
How to test Speedometer calibration – is a different topic.
BudW
Now to add another twist to this, in ‘75/76, Chrysler changed from a metal speedometer gear housing (in transmission) to a plastic one. Some newer cars got older gears/cables as stock on hand varied.
The pickups/vans still used the older speedo gears until they went to cable-less speedometers.
The plastic design is easier to work with on assembly line – but is harder to work on afterwards.
The older metal one has a screw on cable. You can remove transmission (or cable) fairly easy, by just unscrewing the large cable nut.
The newer plastic one has clips. You have to remove the speedometer gear housing to unclip the cable. Going back together – all you need to do is push the cable in and it snaps in place.
The older metal housing gears are more abundant and are even being made aftermarket. The newer plastic housing gears are not as easy to find.
The one thing that is holding me up on my wagon, is I’m going to change to the older metal housing and older cable style, first. Just need to replace with a new cable, first.
I have almost a complete selection of the older speedo gears at home – but only a few of the newer ones.
The older gears are (to me) just far easier to work with – even for simple things like transmission removal and so forth.
BudW
The pickups/vans still used the older speedo gears until they went to cable-less speedometers.
The plastic design is easier to work with on assembly line – but is harder to work on afterwards.
The older metal one has a screw on cable. You can remove transmission (or cable) fairly easy, by just unscrewing the large cable nut.
The newer plastic one has clips. You have to remove the speedometer gear housing to unclip the cable. Going back together – all you need to do is push the cable in and it snaps in place.
The older metal housing gears are more abundant and are even being made aftermarket. The newer plastic housing gears are not as easy to find.
The one thing that is holding me up on my wagon, is I’m going to change to the older metal housing and older cable style, first. Just need to replace with a new cable, first.
I have almost a complete selection of the older speedo gears at home – but only a few of the newer ones.
The older gears are (to me) just far easier to work with – even for simple things like transmission removal and so forth.
BudW
Aspen500
Well-Known Member
The biggest trouble when using the plastic housing is actually finding a speedometer drive gear. They are not easy to come by and to find one with the correct number of teeth can sometimes be like,,,,,well,,,,,,,pulling teeth.
If you are unaware, the gears from the plastic housing and metal housings do not interchange.
Side note: My take on why they went to plastic is,,,,,,it's most likely cheaper. Isn't that always the way?
If you are unaware, the gears from the plastic housing and metal housings do not interchange.
Side note: My take on why they went to plastic is,,,,,,it's most likely cheaper. Isn't that always the way?
Correct.
The gears, the housing and the speedo cable (lower end, if have cruise) are all different, at that '75/76 date cutoff - except for pickups/vans which used older style for some time later.
I think they changed for cost and ease of assembly when car is being built - IDK.
I do remember seeing some '77's with older metal speedo housing - so there were some part supply issues.
My '77 wagon has plastic (built November 11, '76 at 11:10am (11/11/76 at 11:10).
Aspen500
Well-Known Member
True. I suppose it's easier and quicker to push lock the cable in vs. screwing on the nut. Same reason as new cars where everything is quick-connect (A/C, fuel, coolant lines, trans cooler lines, etc). I say quick-CONNECT because sometimes they sure as bleep aren't quick DISconnect, especially the metal ones that have corroded after a few years.............GRRRRRRRRRRR.
Rifleshooter
Well-Known Member
I understand everything youre talking about Bud, my only question however is how to i end up finding what rear gear i have without having to take off the diff cover. My diff currently has tiny metal shavings in it and id prefer not having to change it out just yet as it is one of the later things on my list of things to fix or replace.
I have all of Chrysler part books from late fifty’s to 2012 – except for ’80 and ’81, so I can’t look at them to find out.
You had a choice of gear ratio's in '82 of 2.2, 2.7 or 2.9.
By '84, you could get any gear ratio you wanted, just as long as it was an 2.2! (or 2.9 for police)
According to the ’80 sales brochure, the standard tire size is P195/75R14 (26.30”).
Optional tire sizes are P205/75R14 (26.93”) and FR70-14 (26.40”)
Standard gear ratio for /6 is 3.2 (California 2.9).
I removed an 8¼” differential from a ’80 Volare wagon a few months back and it had a 2.4 in it (318 automatic).
My ’79 parts book shows:
7¼” (which is what I suspect you have) 2.4 (2.45 or 2.47), 2.7 (2.71 or 2.76) or 3.2 (3.21 or 3.23).
8¼” choices are 2.4 (2.45 or 2.47), 2.7 (2.71 or 2.76), 2.9 (2.93 or 2.94), 3.2 (3.21 or 3.23) or 3.5 (3.54 or 3.55).
Note: if you have fine metal in differential fluid, I would highly encourage you to change fluid out and get that metal debris out – for when you do get a chance to overhaul the differential, the potential for part damage to gears and axle shafts will be much less (unless you have no intention of re-using existing differential).
With inspection cover off, and with rear tires off of the ground, rotate the ring gear around and you will find the gear ratio, date of manufacture and part number stamped on outer gear edge.
This picture was taken from eBay, for a NOS gear set of 3.23 for ’70 (or ’71) 7¼”. This gear set might fit our member’s cars and might be worth picking up (I would want to make sure it fits first – but I suspect it will).
Gear ratio in red circle, blue arrow is part number and white line is date of manufacture.
ALSO, with known tire size and speedometer gear – one can reverse engineer what gear ratio you have.
Honestly, tire size and gear ratio doesn’t matter a lot, as long as you know what percentage the odometer is off and you know what speedo gear you currently have, is.
BudW
You had a choice of gear ratio's in '82 of 2.2, 2.7 or 2.9.
By '84, you could get any gear ratio you wanted, just as long as it was an 2.2! (or 2.9 for police)
According to the ’80 sales brochure, the standard tire size is P195/75R14 (26.30”).
Optional tire sizes are P205/75R14 (26.93”) and FR70-14 (26.40”)
Standard gear ratio for /6 is 3.2 (California 2.9).
I removed an 8¼” differential from a ’80 Volare wagon a few months back and it had a 2.4 in it (318 automatic).
My ’79 parts book shows:
7¼” (which is what I suspect you have) 2.4 (2.45 or 2.47), 2.7 (2.71 or 2.76) or 3.2 (3.21 or 3.23).
8¼” choices are 2.4 (2.45 or 2.47), 2.7 (2.71 or 2.76), 2.9 (2.93 or 2.94), 3.2 (3.21 or 3.23) or 3.5 (3.54 or 3.55).
Note: if you have fine metal in differential fluid, I would highly encourage you to change fluid out and get that metal debris out – for when you do get a chance to overhaul the differential, the potential for part damage to gears and axle shafts will be much less (unless you have no intention of re-using existing differential).
With inspection cover off, and with rear tires off of the ground, rotate the ring gear around and you will find the gear ratio, date of manufacture and part number stamped on outer gear edge.
This picture was taken from eBay, for a NOS gear set of 3.23 for ’70 (or ’71) 7¼”. This gear set might fit our member’s cars and might be worth picking up (I would want to make sure it fits first – but I suspect it will).
Gear ratio in red circle, blue arrow is part number and white line is date of manufacture.
ALSO, with known tire size and speedometer gear – one can reverse engineer what gear ratio you have.
Honestly, tire size and gear ratio doesn’t matter a lot, as long as you know what percentage the odometer is off and you know what speedo gear you currently have, is.
BudW
Rifleshooter
Well-Known Member
If I remember correctly from when I replaced the clutch disk on my duster, I ended up counting 34 teeth on a green speedometer gear. If that helps any.
slant6billy
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When my Speedometer was off (It read 80 when the car was only doing 30). So my stock 24 tooth had to go and the 41 went in. I really wanted a 43. However at different speeds the spread was variable- As in at lower speeds it was less a variant. As the car accelerates, the spread got greater. Like I mentioned and Bud did above. Do some trials at different speeds and distance. Get a GPS or a pace vehicle with a known good speedo. Definitely get your diff some service with new fluid and inspect it for bearing damage and damage or wear. Trust me, don't risk da rear!
You are going to get dirty to get the info.
You are going to get dirty to get the info.
Green is correct color for 34 speedo gear.
They also made the 22, 31 and 39 tooth gears in Green as well (no rhyme or reason on colors).
Depending on Original Equipment (OE) tire size, that would point to a 3.2 ratio differential (one of the good ratios).
Now we need to drive the car for X miles (more the better) so we can get an accurate percentage on odometer reading.
BudW
They also made the 22, 31 and 39 tooth gears in Green as well (no rhyme or reason on colors).
Depending on Original Equipment (OE) tire size, that would point to a 3.2 ratio differential (one of the good ratios).
Now we need to drive the car for X miles (more the better) so we can get an accurate percentage on odometer reading.
BudW
Dr Lebaron
Well-Known Member
Marty has these
4028925
4028926
4028927
4028928
4028930
4028934
4028935
4028937
last two digits are the # of teeth
75.00 each plus shipping
www.arizonaparts.com
4028925
4028926
4028927
4028928
4028930
4028934
4028935
4028937
last two digits are the # of teeth
75.00 each plus shipping
www.arizonaparts.com
Rifleshooter
Well-Known Member
Well going off of the chart toward the top of thus page I'd say I'll most likely need a 28 tooth gear, but before I give a define answer I'll need to find out what rear gear I have for sure
shadango
Well-Known Member
So if one had the metal housing from any other (and older) 904 trans, they could swap it in for a plastic one?
jasperjacko
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You'll have to change The cable as it has a diferent end. My car has cruise, so I put an older style screw on cable from the cruise unit to the transmission.
