Hello all... I think I have figured this out by all the reading but please check.
- 1993, 5.7, auto, 2.59 gears, 2.85/40/17in tires, approx 25.5inches

I plan on changing rear gears to the 3.54 but concerned about screwing up my speedometer. From what I have read its a matter of changing the speedo gear in the tranny to a grey one 15 tooth. But then I also am reading about a new driven gear purple w/43 teeth as well as a new speedometer sensor. Do I need to change all of this to have a somewhat accurate speedometer? I am having the gears put in by a tranny shop but thought I would save a few bucks by doing this part myself.

Also... will this change in gear give me that much of an extra low end boost?

thanks

Rob

 

You do NOT want to do this after the gear change!

Your present set up with the 2.59 is likely 17/35.

I think the prefered would be 15/43. This would mean you need to swap the speed sensor to a 10456092. There are people who mention they invert your speed sensor now to accomodate the change in gear "pitch" but I've never done it with this style sensor.

You want this part of the work done along with the gear change in the rear. The drive-shaft needs removed to do the drive gear anyway! While the transmission shop is there you might consider having them do an extension housing bushing and the rear extension seal while they're right there. You might try to "negotiate" the gear swap to include the seal, bushing and transmission gears. My guess is that they would "accomodate you"!
The sensor is discontinued but in Canada there could be stock available. I'd ask at a dealer. If you need part #'s for the gears ask.

There will be "seat of pants" performance!!!

 

Removing the transmission extension housing is a pain with the differential in the car, doing so is required to replace the drive gear on the output shaft. It is very difficult to get clearance with the C beam in place but extremely easy while the differential is removed. Definitely do the speedometer gears while they have the rear end removed.
You will love the 3.54's

 

hate to hijack but if change my center section to 3.73's what do I need to change for the speedo to be correct. Going from 3.33's

 

Try this link

http://webpages.charter.net/khasting...peedocalc.html

 

Good info. thanks!

 

I found when trying that link you could end up really confused because while the math and the part #'s were correct it usually replied something similar to "use your current" which I had given it #'s that I already had the "original combination documented". It also would confuse someone attempting to marry the sensor to the gear combinations! It's interesting "for sure"! I wouldn't rely on it but maybe use it for reference/comparison. I like "my math"!!

Not near enough information! Is the speedo "correct" presently? Tire size? What transmission? Tire size? What is the tooth count on the drive/driven now? To absolutely give you "good information" all those need answered. If you're interested in just a "correct combination" these three can get the job done! Transmission? Tire size(If you've got the RPM [advertised revolutions per mile]? You've already supplied the 3.73!

 

You are correct that using the link can be a little confusing if you don't already know what is in the car.
As a general rule I have found the following to be true; the red 17 tooth drive gear (PN 8640517) is used on all cars manual and automatic with factory gears 3.07 or higher. Ratios lower than 3.07 (3.33, 3.45, 3.54, etc.) come with the gray 15 tooth drive gear (PN 8642620) since none of those ratios were available in A4 cars the gray drive gear is only found on manual trans cars unless it has previously been changed.
The recommended speed sensor application is to use (PN 10456091-black) for driven gears having less than 40 teeth (PN 10456092 -white) is suggested for all driven gears having 40 teeth or more)
As you are aware getting the drive gear right is the critical factor while you have the differential removed, the speed sensors or driven gears are easily changed at any time. The speed sensors have been discontinued so trying the 180 degree rotation using the black sensor may be the only option now, I have tried it out of curiosity and it does work though I'm not sure why it is necessary to rotate the sensor, the shaft for the driven gear does not seem to be eccentric from what I can tell.
The link should get you very close on the driven gear but if necessary pace the car with a vehicle known to have an accurate speedometer or use GPS, then change the easily accessible and inexpensive driven gear up or down one tooth at a time until you are on the money.
One exception is cars going lower than 3.73 (4.10 for example) since GM offers no suitable gears the only options I am aware of is to use an electronic converter such as the Dakota
http://www.dakotadigital.com/
or the very expensive gear sets available from Haibeck
http://www.zr1specialist.com/HAT%20W...on%20Gears.htm

 

Wow....yes I shall have the tranny shop do this. I had read, I think from Corvette Central of a module to can plug in somewhere that you can calibrate your speedo...it was @$150 and can calibrate to whatever gears. Have you heard of this thing?

thanks again

 

Like I mentioned "REFERENCE ONLY"!!! The sensor #'s you reference are also only '91 +. '90- use different! It's use is maybe interesting for "curiosity seekers" but "every result" needs to be "confirmed"!


It should only be used as a "last resort"! Again: "LAST RESORT" You certainly don't need it!!

 

The "module" you heard about is the same thing as the ones available from Dakota Digital, see the link in my earlier post. They are not "plug in" and the wiring can be tricky, as WVZR-1 indicated only use one as a last resort, the gears are easy to change, cheap and reliable just make sure you get the drive gear right while you have the rear end removed and the rest is easy.

 

I am pretty sure those are for 94-96 but not sure what model you are talking about so........

 

On my 1995 you change the setting in the computer.

 

Checked everything and you are right... at present I have the 17/35 w/ D8K - #10456091 for the speed sensor. I have located and ordered the 15/43 setup but having a heck of a time finding the D8L - #10456092 sensor. Stupid question... would there be much dif in speedometer accuracy if I got stuck using my sensor which is the next number down?

thanks

 

Looks like Ekler's may still have them, not even too pricey.

http://www.ecklers.com/product.asp?p...3&dept_id=1874

If they do not, when this was discussed in the past it was suggested the original sensor could be used by rotating it 180*, presumably to gain clearance for the larger diameter gear, you must pry the hold down retainer off to do this then reinstall.
I have no idea why rotating it is necessary, the bore for the driven gear shaft does not seem to be eccentric to the sensor itself at least by visual inspection. I do know I was able to use it that way when I installed 3.73 gears using a 15/45 combination, but I did eventually buy the correct sensor mostly for peace of mind.

 

I saw that one at Ecklers for the maunal tranny... when I did the cross check that they have http://www.ecklers.com/gm_reference.asp?PageNumber=25 the #10456092 comes up as a different one and disc.
I emailed transmissioncenter.net to see if they have anything. I will be having the tranny shop install when they do the gears but to save time I thought I would get everything ready. Shall see I guess.
thanks again

 

It should work, the sensors are the same for manual and automatic, the difference is that only the manual trans cars came with driven gears with more than 40 teeth, all other dimensions are the same.

Also found one here ( #55XX) but more money.

http://www.transmissioncenter.net/sp...0gear%20driven

 

Well... got the 3.54's put in the other day as well as the speedo parts. Everything is perfect....had to put in a full 75 litres of fuel so I could hook up better. I thought it went the hell before...wow... 20 mph in first (automatic) and punch it... you best hold on... what fun!!! Thanks everyone for your help!

Rob

 

It's good to see someone "come-back" and post results from a gear change and a "speedometer correction" that worked. I'm quite sure the mechanical calibration was a bit less expensive than the "ERA"!

The "SOP" is I'm sure worth the price of the install!

 

cool