After 5 spd conversion, speedo reads 10mph lower, why?

[winstontj]

The tranny should have nothing to do wth the reading. It is the diff that makes the difference. Your speedo is geared to the final drive ratio.

If you didn't change the diff ratio, you should be OK !

If using a speedo geared for a 3.64, but your final drive is 4.10, you will indicate too high. The other way around, you would indicate too low.

The diffrence is about 12 percent ( pretty notable )

Slavs

EXACTLY! Speedo (in the dash) is geared for a specific diff. The gearbox has NOTHING TO DO WITH IT. There is simply a little wheel that turns the speedo cable proportionally to the driveshaft. Whether you have a 3,4,5,6speed gearbox, dogleg, catleg, etc. speedo gear spins relative to the driveshaft revolution.

Did you change the diff or the speedo or is this simply a 5-speed upgrade in an existing car that was accurate before hand?

Are you using the correct automatic speedometer cable? It could be possible that your speedo cable is too short and is binding somewhere. That would not be good at all but it could throw things off. Just a guess but I'd start there - or if you changed your diff... time to send a speedo (and $120) to VDO!

[dubois]

The tranny should have nothing to do wth the reading. It is the diff that makes the difference. Your speedo is geared to the final drive ratio.

If you didn't change the diff ratio, you should be OK !

If using a speedo geared for a 3.64, but your final drive is 4.10, you will indicate too high. The other way around, you would indicate too low.

The diffrence is about 12 percent ( pretty notable )

Slavs

that's what I think too. The gears on the speedo should match the gears on the final drive, and I didn't change either! I just replaced the tranny, and it is a 5 spd overdrive (I wish I was wrong and was a CR but is not, trust me on that one).

The only thing that I have left to check is the connection to the speedo and the replacement cable itself (I had an ASSisstant do that part of the job) I'll post an update when I find the problem. I don't think a speedo can go bad overnight! I guess I have to tear in to the back on the inst. panel and check things out. Just what I had planned to do today! Great!

[winstontj]

I guess I have to tear in to the back on the inst. panel and check things out. Just what I had planned to do today! Great!

I never had a lower trim panel under the driver's side of the car so it was easy. You can reach up under there (you probably know how) and check with one hand. OR because the auto cable is that much longer you can unscrew the two fasteners and pull the cluster out into the car with everything attached.

Should be a 5-minute job unless you find something.

[Guest Anonymous]

Are the speedo gears in the various trannys all the same. I have been lucky where speedometer always seemed close to accurate. Never had to go further.

Recall being warned by an acquaintance that I should have the correct corresponding plastic speedometer gear. Was unable to confirm this.

[jimk]

Daily posts to this board tout the efficiency and intelligence instilled in this car but the posts on this subject have injected lots of complications that don't exist.

BMW didn't want to get involved with having different transmission parts for various final drive ratios for a car order on the assembly line. Also if later, the final drive ratio is changed, you don't have to dig into the trans. ---End of Trans discussion in this problem.

It's the U.S. way where the speedo gear is changed when the diff ratio is changed.

So BMW calibrated the speedos for the turns per mile of the speedo cable (which is 1 speedo cable turn to 2.5 driveshaft turns (1:2.5). Same ratio for the 02 as the 320. (The driveshaft turns per mile is also the 60mph engine rpm while in direct drive gear, usually 4th gear.) And that's why we change the different speedo when the final drive ratio changes. (To keep simple in the discussion, then for the number on the speedo, just take the 60mph rpm, 4th gear and divide by 2.5 and you got the number on the back of the speedo). Somebody correct me if the ratio is not 2.5 because I am away from my references.

So if there was no change of final drive ratio, there should be no change of speedo calibration.

[winstontj]

Are the speedo gears in the various trannys all the same. I have been lucky where speedometer always seemed close to accurate. Never had to go further.

Recall being warned by an acquaintance that I should have the correct corresponding plastic speedometer gear. Was unable to confirm this.

If you look at the end of the speedo that goes into the gearbox it's litterally a little square wire and it's the same between the e21's, 2002's and all other cable driven speedos (AFAIK). It'll either fit in and work, or not fit at all IMO. Sorry that's not more of a definate answer. I know that a manual trans 02 cable, a manual 4 & 5spd e21 cable, and an auto 02 cable are all interchangable on the 2002 & e21 4, 5 & CR gearboxes if that helps.

[Guest Anonymous]

As noted in my original post, I never explored to possibility of different plastic gears, etc. because, in my case, never saw the need.

As an afterthought, and from memory, I'm sure I collected a couple of these "white plastic gears" and it may have been from automatics or from big 6 cylinders models upon which I fiddled.

JimK, is your information correct about the 6cylinder model as well, in other words, they used the same gears too? (Same gears for all 6cylinder models?) Just wondering. Would prefer dispelling myths rather than perpetuate them.

Thank you.

[jimk]

JimK, is your information correct about the 6cylinder model as well, in other words, they used the same gears too? (Same gears for all 6cylinder models?) Just wondering. Would prefer dispelling myths rather than perpetuate them.

Thank you.

I have no info on the 6cyl models, but this is the case with the 02s. Try checking for the Real OEM PNs for Tran worm gear on the output shaft for various models to see if it is the same.

[InkaSteve]

Daily posts to this board tout the efficiency and intelligence instilled in this car but the posts on this subject have injected lots of complications that don't exist.

BMW didn't want to get involved with having different transmission parts for various final drive ratios for a car order on the assembly line. Also if later, the final drive ratio is changed, you don't have to dig into the trans. ---End of Trans discussion in this problem.

It's the U.S. way where the speedo gear is changed when the diff ratio is changed.

So BMW calibrated the speedos for the turns per mile of the speedo cable (which is 1 speedo cable turn to 2.5 driveshaft turns (1:2.5). Same ratio for the 02 as the 320. (The driveshaft turns per mile is also the 60mph engine rpm while in direct drive gear, usually 4th gear.) And that's why we change the different speedo when the final drive ratio changes. (To keep simple in the discussion, then for the number on the speedo, just take the 60mph rpm, 4th gear and divide by 2.5 and you got the number on the back of the speedo). Somebody correct me if the ratio is not 2.5 because I am away from my references.

So if there was no change of final drive ratio, there should be no change of speedo calibration.

First...my apologies to all for my part in contributing to the misinformation in this thread. Comes from engaging my keyboard before clearly thinking through the problem. However, it sure got me thinking and digging for the truth.

My conclusions: everything I have read confirms Jim's post. Unlike American cars, 02's adjust for different diffs by using different speedos. There was an excellent thread in November discussing the markings on the back of the Speedo and what Diff. they match up with. http://www.bmw2002faq.com/component/option,com_forum/Itemid,57/page,viewtopic/t,282485/highlight,speedometer/

One area not discussed is the odometer reading....If it is reading correct, then we have the correct speedo (which is likely), but the speed readout is faulty and needs repair.

At this point, I will step away from my keyboard and let more knowledgable FAQ'ers take it from here. It has been enlightening and the new search function really works well...try it.

[_z_]

Maybe we should create a FAQ for this

Especially since so many people swap out difs and such -- it must be pretty common issue. A lot of people probably running around with their spedo's not reading right and don't even notice it

[Guest]

3421912

are just as big and she is the same color Hah

[Guest Anonymous]

Huh?

[InkaSteve]

Huh?

Rob is referring to his Inka touring and it's tailights.....It looks like mine #3410837

[ingraham]

That factoid comes from another make or model. The 2002 speedo/odo gears accomodating the diff ratio are metal.