i believe my turbo 400 needs speedo gear replacement because the speedo registers higher speed than actual.i have replaced the cable but wonder what exactly has to come apart in/on tranny to correct this problem? is it a big job or a piece o' cake ??
Theres two gears. One were the speedo cable is coming out of, which is the easiest one to replace. The second one youll have to take the driveshaft out and unbolt the tailhousing of the transmission, the gear is on the output shaft of thetrans. Not a hard job at all.
thanks, sounds like fun,still need to figure correct gears, i know theres a post in here somewhere that explains math.
You may not need to replace the drive gear at all. It depends on you combination. We need to know the number of teeth on that drive gear. Easiest way to do that is remove the driven gear sleeve with the back of the car up high (less fluid loss). Pull the sleeve (one 1/2" bolt). Put the trans in neutral and rotate the driveshaft to count the teeth. Mark one tooth with something. Then slowly rotate the driveshaft and count. The gear is helical so go slow and get an accurate count, in fact do it several times. Usually, it is 16, 17, or 18 teeth. Then all you need is tire height (figured from tire size), and rear gear ratio. You can plug the numbers in here: http://www.tciauto.com/Products/TechInfo/speedo_gears.asp
Don't forget you need the correct speedo driven gear housing. Read my article for a full explanation: http://www.buickperformance.com/speedo.htm
ok finially got info need help to determine correct speedo gear . tire size p255 65r15,drive gear 19 teeth,speedo gear brown 39 teeth,3.73 rear, numbers on sleeve 36,37,38,39. tried using tci calculator but doing something wrong.
OK, you have a problem, and it's the speedo drive gear. With a 19 tooth drive gear, you would need a 51 tooth driven gear, and that doesn't exist, biggest is 45. If you change the drive gear to a 16 tooth gear, a 43 tooth driven gear will work. You will need the speedo sleeve that takes gears 40-45. Are you sure the tire size is 255/65-15? 255/60-15 is more common.
With your 28.1" tire, and 3.73:1 axle, you can't use a 19 tooth drive gear because there's no driven gear available to get you the right speedo reading. Looks like you'll need a 15 tooth drive gear and a 40 tooth driven gear. You'll also need the other gear housing (sleeve) that can handle the 40-45 tooth driven gears. Devon
Do you have a plastic or metal drive gear? The plastic ones go on with a clip and are easy to change, the metal ones are pressed on and require a puller. To change the gears requires that you drop the driveshaft and remove the extension housing.
yes the tire size is p255 65 r15. so i would need a 15 tooth drive gear,40 tooth driven gear,replace gear housing to 40-45 tooth. my existing tailhousing should be ok
i just looked up the parts on the tci site and noticed my existing drive gearis style c where as the 15 tooth is style b. is that another problem?
Crap, that's gonna be a problem. TCI actually lists style D as the only 15 tooth drive gear for the TH400, which is a steel press fit. Let me look into this a bit further. Devon
Looks like the clip is a different size. The hole in the output shaft of the transmission should be the same, you would need the clip. If TCI doesn't have it, a transmission shop should.
Try this place. They have a lot of speedometer parts and sell ratio adapters for about $62. Other places sell for well over $100. All you need to do is calculate what your ratio should be and then what you have with the gears currently in your trans. Let's say you are reading 100 mph when it should be 60 mph. You would then need a 60% reducer to get you correct. Just put the reducer between your trans and speedo cable and you are done. No gaskets/drive gears/driven gears/ or new housing. If you had to buy all that stuff, it would likely be more than the cost of the reducer not including your time. http://www.transmissioncenter.net/speedometer_calibration_______va.htm If you need more info on how to calculate, I can help. Good Luck, Scott
That link from Scott may be the ticket. Here's a quote: "We also have used TH400 plastic drive gears, call. Cost Used $8.00, 15 Tooth New $12.00" Devon
this is what i come with whadda tink? Code Product Quantity Price/Ea. Total 880028 GM Driven Speedometer Gear, 40-tooth black $17.08 $17.08 880043 GM Speedometer Gear Housing, 1.935" diameter for 40-45 tooth gears $32.72 $32.72 880018 GM Speedometer Drive Gear, 15-tooth grey $16.85 $16.85 880024 GM Speedometer Gear Clip, 5/16" $9.82 $9.82 Total: $76.47 2007 COMP Performance Group™. All Rights Reserved.
According to my calculations, you need about 76.5% of what you have now. They sell a reducer of about 26% which should work. Unless you have everything apart right now, you will need to remove the driveshaft, raise the trans off the mount and take the crossmember and tail housing off to get at the drive gear. Then have to fiddle with it in the trans housing. IMHO, a lot of work. The adapter screws onto the speedo sleeve in the trans and you just put the cable back on...................done. :TU: Again, apart one thing. Already together is another. Just my 2 cents Scott
