Steel Th400 Speedometer Drive Gear Gm Part Number UPDATED
Steel Th400 Speedometer Drive Gear Gm Part Number
Manual Speedometer Gears
* Charts from Chevrolet Parts & Accessories Catalog - circa 1972
The post-obit information is reprinted with the permission of Mr. Fred Aldrich, a.one thousand.a. The Chevelle Engineer. Information presented are the same from his popular website with only minor changes to spelling and overall format. Mr. Aldrich passed away in 2011 and graciously allowed me to use some data from this website before his passing.
Speedometer Gear Selection
Many of you have changed tire size or axle ratio on your Chevelle and now the speedometer reads likewise high or depression. While this can be corrected with an aftermarket ratio adapter, I like to change the speedometer driven gear at the rear of the transmission to correct for error. If yous want a "correct" car, this is the way to go.
Determining Speedometer Fault
Checking the accuracy of your speedometer is easy. Await for a stretch of interstate highway with mile markers. Utilise a finish lookout (or a lookout with a sweep second hand) to determine the time to travel ane mile with your speedometer indicating exactly 60 MPH.
Now find your actual MPH using this formula.
Bodily MPH = 3600/Time - Time in seconds to travel one mile at exactly 60 MPH. Example: It takes 69.2sec. to go a mile, so 3600/69.2sec. = 52 MPH bodily. The speedometer is indicating 8 mph too loftier.
Percent Error = MPH error/bodily MPH - 8/52 = 15.4% high
Correcting Error
TH400, TH350BOP, 700R4: Speedo driven gears take from 34 to 45 teeth. Each tooth added lowers the speedometer reading most 2.v%. Each tooth removed raises the speedometer reading nearly two.5%. In our case, we want to lower the speedometer reading from 60mph indicated to 52mph indicated. We need to add teeth to lower the reading by spinning the speedometer cable slower. Remember, one tooth = 2.5% so nosotros need to add about six teeth. (fifteen.4%/2.5% = 6.2 teeth)
Thursday 350C, Powerglide and Muncie 4 Speed: Speedo driven gears accept from 17 to 25 teeth. Each tooth added lowers the speedometer reading most 5%. Each tooth removed raises the speedometer reading about 5%. In our example, we are reading 15.4% loftier so we would need to add teeth to spin the speedometer cable slower. Recollect, ane tooth equals 5% so nosotros need to add together most iii teeth. (15.4%/5% = 3.1 teeth)
At this point, pull the speedometer gear out of your transmission tail housing past removing the small bolt and clamp that retains the speedometer gear sleeve and pulling on the speedometer cable. Then count the teeth, subtract or add to the number of teeth and select a new gear from the appropriate chart below based on your manual. Utilise color only as a cantankerous check. Plastic gears immersed in transmission fluid for many years will be stained and off-color. You often encounter the speedometer driven gear referred to equally the "pencil" gear and the speedometer drive gear the "circle" gear.
TH400, TH350 BOP, 700R4: Let's say that, in our example, we find a white gear with 36 teeth. Adding half-dozen teeth to correct a speedometer reading fifteen% high gives usa a 42 teeth. We need to buy a 42 tooth (green) 1362049 gear.
TH350C, Powerglide & Muncie 4 Speed: Let'due south say that, in our case, we find a brown gear with 18 teeth. Adding three teeth to correct a speedometer reading 15% high gives the states a 21 teeth. We need to buy a 21 tooth (red) 3987921 gear.
The GM TH350C, 4-speed and Powerglide transmissions all use the 345215 sleeve merely they used iii different bulldoze gear diameters, one.92", ane.84" & ane.76". The charts show which drive & driven gears are compatible. If you utilise incompatible gears, they volition destroy themselves and maybe fill your manual with plastic fries.
If you observe that your "correct" gear falls between two molar counts as information technology does in well-nigh cases, information technology's normally all-time to option the smaller gear so your speedometer will read slightly high. As I recall, GM practice was to selection speedometer gears and then that the speedometer would read between 60 and 63 MPH at a true 60 MPH.
Virtually of these parts are still available from GM so run across your local dealer. They'll have the best prices and you lot'll discover virtually very cooperative if yous know which function numbers you lot demand. Almost won't exist very helpful, nonetheless, if yous ask them to solve your problem. Takes a lot of attempt and chance on their part as they're not usually very familiar with the 60'south and 70'southward products and, of course, yous'll want them to have the parts back if they're the wrong stuff and then they'll exist stuck with parts they'll probably never sell. Prices and availability shown are those at https://www.partszoneonline.com/index.php on 8/1/2004. Your local dealers volition probably not match these prices.
Big 8 tooth drive gear - 1.84" - GM #3708144 (27 molar spline) or GM #3978758 (32 molar spline)
Pocket-size 6 tooth bulldoze gear - one.76" - GM #3708145
To aid make up one's mind the driven gear needed for either bulldoze gear based on rear gear ratio and tire diameter, try hither.
| 350C, Powerglide & Muncie 4 Speed Speedometer Driven Gears | |||||
| Function Number | Teeth | Color | Sleeve | Price | Drive Gear OD |
| 3987917 | 17 | Purple | 345215 | $3.61 | 1.84" |
| 3987918 | 18 | Brown | 345215 | $three.01 | i.84" |
| 3987919 | 19 | Natural | 345215 | $3.01 | one.84" |
| 3987920 | twenty | Blue | 345215 | $3.01 | 1.84" |
| 3860329 | 20 | Steel | 345215 | one.92" | |
| 3987921 | 21 | Red | 345215 | $3.01 | one.84" |
| 3987922 | 22 | Silver | 345215 | $3.01 | 1.84" |
| 3860341 | eighteen | Brownish | 345215 | 1.76" | |
| 3860342 | 19 | Natural | 345215 | 1.76" | |
| 3860343 | 20 | Bluish | 345215 | 1.76" | |
| 3860344 | 21 | Reddish | 345215 | 1.76" | |
| 3860345 | 22 | Green | 345215 | $3.01 | 1.76" |
| 3860346 | 23 | Black | 345215 | $3.61 | one.76" |
| 3860347 | 24 | Yellowish | 345215 | $iii.61 | i.76" |
| 3860348 | 25 | Orangish | 345215 | $3.61 | 1.76" |
| THM350BOC, THM400 & 700R4 Speedometer Driven Gears | |||||
| Part Number | Teeth | Colour | THM400 Sleeve | 700R4,350BOP Sleeve | Price |
| 9774413 | 34 | Lt. Light-green | 1362294 | 25512340 | $three.61 |
| 9780628 | 35 | Orangish | 1362294 | 25512340 | $3.61 |
| 1359270 | 36 | White | 1362294 | 25512340 | $three.61 |
| 1359271 | 37 | Scarlet | 1362294 | 25512340 | $3.61 |
| 1359272 | 38 | Blue | 1362294 | 25512340 | $3.61 |
| 1359273 | 39 | Brownish | 1362294 | 25512340 | $3.61 |
| 1362048 | 40 | Black | 1362293 | 25512339 | $3.61 |
| 1362195 | 41 | Yellow | 1362293 | 25512339 | $3.61 |
| 1362049 | 42 | Dark-green | 1362293 | 25512339 | $3.61 |
| 1362196 | 43 | Imperial | 1362293 | 25512339 | $3.61 |
| 9780470 | 44 | Dk. Greyness | 1362293 | 25512339 | $three.61 |
| 9775187 | 45 | Lt Blue | 1362293 | 25512339 | $three.61 |
| 200-4R Speedometer Driven Gears | ||||
| Part Number | Teeth | Colour | Sleeve | Price |
| 25502669 | 26 | Chocolate-brown | 25519848 | $3.61 |
| 410731 | 27 | Black | 25519848 | $3.61 |
| 416765 | 28 | Yellowish | 25519848 | $3.61 |
| 403999 | 29 | Light-green | 25519848 | $3.61 |
| 561035 | 30 | Blue | 25519848 | $3.61 |
| 403417 | 31 | White | 25519848 | $3.61 |
Speedometer Sleeves
GM calls the part that mounts the speedometer driven gear to the transmission a Sleeve - Speedo Driven Gear. The THM400, TH350BOC & 700R4 uses 2 sizes which have care of the different diameters of the diverse driven gears. They are marked with the driven gear tooth numbers they will accept. In our TH400 example, our white gear used a PN 1362294 sleeve so we have to buy a new sleeve (PN 1362293) to friction match our new 42 tooth green gear.
The charts beneath bear witness all the drive gear information I've been able to collect. If no cost is shown, the function is no longer available from GM.
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*** These gears are available at: https://world wide web.transmissioncenter.net/speedometer_calibration_______va.htm
@@ These gears are available at: http://www.dandltransmission.com/muncie.html
Off The Nautical chart or Can't Buy The Correct Gear?
Ah, back where we started. We'll have to use a ratio adapter and perhaps a speedometer gear alter as well to tune in the speedometer. GM used #3932220 ratio adapter on many Chevelles. This part has a ratio of 0.7333/one and retails for almost $75 list from your friendly GM dealer. The effect of this adapter is the same as lowering the number of teeth on the speedometer driven gear by 26.7%. For example, if you lot needed a 48 tooth gear for your THM400, none is available but yous can use this adapter with a 35 tooth gear to get the same result.
These adapters were used by GM for high (numerically like iv.eleven or 4.56) axle ratios where the "right" gear was larger than the largest available. The adapter screws on the speedometer connector on the transmission and the speedometer cable attaches to the adapter.
Another GM ratio adapter is #368022 at $117 listing. It has a ratio of 0.9444/one and lowers the speedometer output by 5.6%. *** to a higher place too offers several ratio adapters.
By The Numbers
If you lot are into formulas, you can calculate the correct gear every bit follows:
- Get your tire rev/mile from your tire manufacturer. Try www.BFGoodrichTires.com or gauge it from your Rear Tire Diameter.
Rev/Mile=20168/Rear Tire Bore (in inches)
- Count the teeth on the speedometer drive gear, the ane mounted on the manual output shaft
- Determine your beam ratio
- Compute the right number of teeth on the driven gear with this formula.
N(driven) = N(drive) x (Beam Ratio) x (Rev per Mile) /1001
Primary here is that a correctly calibrated GM mechanical speedometer turns exactly 1001 revolutions in 1 mile. That'due south 1001 rpm at 60mph.
New info on THM400 Drive Gears added thank you to Charlie Brecheisen at Fletchs.com
July 17, 2006
Note: As noted at the start of the page, Mr. Aldrich passed abroad in 2011 and graciously allowed me to use some data from this website before his passing. Data presented here are assumed to exist correct but no guarantees are implied.
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Steel Th400 Speedometer Drive Gear Gm Part Number UPDATED
Posted by: jeffreynowelpleady.blogspot.com
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