My 83 ss speedometer is almost excatly 20mph too slow anyone know what might be causing this? How about a way to fix it? I think i may get my gps out and see what it says as far as miles on the car and miles on the gps. if the miles are right then could i just pull the needle off and move it intil it it right then put it back on? BTW my ss has had a 350 swap but i dont know about the transmission yet if its stock or not. I do have aftermarket wheels and tires but i put that into a calculator and it said it should only rear like a few mph off. The guy i got it from said it had rearend work but is still stock, maybe someone changed the rear end gears, idk. Have any ideas?

 

there are a few things that will cause the speedo to be off. yes, oversize or undersize tires will cause the speedo to be off. the original tire size for your year monte is a 215/65r15. this overall diamter is 26". if a transmission has been changed your final drive may be off that will throw the speedo off. rear end ratio will cause the speedo off as well because this changes your final drive ratio. there is a formula that you can find out what final drive ratio you have with your transmission final drive, rear end ratio and your tire diameter. once you have gotten this figured out, you can find out exactly how much your speedo is off. if you go to your local speed shop, they can figure this out for you and may be even be able to recalibrate your speedo to match what you have.

 

well really, i dont think it matters why its off, it's off.
is it always off by 20mph? 20mph reading parked? or does it read 20 when youre going 30, and read 40 when youre 60?

20 off all the time, cluster problem... im not sure what to do with that, bend the needle or replace the cluster...or ask someone else.

if its off by a percentage of speed, off by more the faster you go, then you need to change your speedo gears. you need to know exactly how fast your car is going at a givin speedo reading, then determine the ratio or percentage u need to speed up the speedo by. next see what speedo gears you have, i'd count teeth and note color to double check. take the number of teeth on the driven gear multiplied by the ratio or percent off the speedo is, to find out how much smaller driven gear you need. if one small enough is not availible try a larger drive gear, or a combination of both to get the amount of change needed.

http://www.transmissioncenter.net/sp...n_______va.htm
i got parts for my 700r4 though those guys, they also have parts for some other transmissions, hopefully yours. and theres just general helpful info on speedo calibration there.

 

i was thinking the same thing as ls. if it is off when you are sitting still then it is defentaly the speedo it's self off.
Also do you hear any whining in the dash as your driving?
mos tof the older montes have this issue becuse the made the speedo cabel out of a metal then they put a plastic end on them so they would strip out and reem the indise of the plastic out. but they would make a ton of racket as they did it most of they time.

or when they did they swap out on the Tranny they put the wrong gear in to it. when i did my 78 i had this issue and i could not figure out fo rthe life of me why. we had changed all teh gears and found out that it was just so slow it would not turn the speedo. in your case you need ot changed it to correc tthe gearing. look at the color in the gear and also check the teeth. if you knwo a tranny shop in the area they have a book they can cross ref. this figure for you. and they might have the part laying around,

one more thing the tranny i had came out of the truck if you can figure out what yours came out of it might help you know more later with things also.

good luck

 

yea im sure its probaly the gears, i havent got my GPS out and monitored it though the change in speed but i had my dad match my speed when i bought the car and i was going 45 and he said he was going 65 then i slowed to 35 and he said i was doing about 55. But after looking at the trans a little i beieve i have a th350 now. and since the car came with the 200-4r to my understanding witch has an overdrive and now i have a th350 with no overdrive and i bet they didnt think to change the gear on the end of the speedometer cable, so ill pull it out and check it out for starters but i bet thats what it is. Thanks guys.

edit: actually now that i think of it all the gear ratios are off between the two trannies escept third with i think is 1:1 in both trannies, hopefully i can just get another driven gear and dont have to complety tear the rear part of the tranny apart. ill keep my fingers crossed

 

not doubting you but make sure you have the 350 in there.
Some of them will have that damed MEtric in them also and they lok the same for th emost part till you need to buy a part for them LOL then they come up and smack ya back in to the reality they are not the same LOL

but if it was changed it is most likey it is a 350 and then just make sure it is right.
Good luck. at least they are not hard ot get to they sit ont he side of the tranny and in the open.

 

hmm well just by looking at the pan it looks like a 350 tranny, so idk, i put my gps on the dash board and drove around and watched how much it was off. When the speedo said 15, i was really going 25; when it said 25 i was doing 40; when it said 35 i was doing 50; when it said 45 i was doing 52; when it said 55 i was doing 74; and when it said i was doing 65 i was doing 87. also i pulled the speedo gear out and the drvin one (the one on the cable) is brown and has 18 teeth and the drive gear (the one in the tranny) is yellow and has 6 teeth. so see what you guys can make of that mess. thanks

 

ok the color of thsoe corasbond with the number of teeth and also the gearing needed to make the rear end and the tranny have the right speed being sent to the speedo.

So just for Exampel.
I took a white one ou tof my 78 and it had 20 teeth i belive it was.
the one i replaced it with was a dark pupril and had a diffretn count on it.
the one in the tranny as long as it is in good shape should be good to go it is just a mater of figureing out the right combo for your car and rear end and also the tranny.
you might take the gear in your hand and go to the nearest tranny rebuild shop. and talk with them and ask if they can give you a idea on how to speed up the speedo.
i would think if you need to speed it up if you take teeth out it would casue it to be faster as it would spin faster or go around more times in the smae time as the one you have now.

to make it slower you would have to get one with more teeth to make it slow down.

Thsi ight be backwards now tha ti think of it but ya ge tthe idea.
im sure they mostlikey know it pretty well or have a book they can serch it up in.
offer to do the leg work if they will jus tpoint you in the right direction some of the small non name brand shops will help you out this way.
Good luck

 

ok kool ill have to do some more research. btw the yellow gear i counted 6 teeth on is wrong i counted it wrong, but the colors are right yellow in the tranny and brown 18 tooth on the end of the cable. what rear end rear ratio do the old montes come with? thanks


edit: the tire size i have is 255/60/15 so that accounts for 4% of it being off.

 

the rear end ratio depended on a bunch of stuff. SO with that said
make life easy on you. do a serch for G.M. Vin code DEcoder on line threw Googel. and then enter your VIN#. it shoudl tell you wha thte car had stock then you can go to the car and find out what you have in it. you siad tha the tranny was changed so you can get the numbers on it and figure out what it came out of.

once you figure out wha thte rear is out of and the tranny . then you can get the gearing for those cars and check the speedo gears agains them to find out wha tyou should have and what you have now and replace the correct one.

you sa they are the right ones. if this is the case then one of them is slippign or the speedo is off on the car also.

stupid question is the need in the 0mph. position when you turn the car off? or when you come to a stop dose it return to the pin or 0 location?