I recently put the 4.11's in the GS, of course, I now have speedo issues. Unfortunately, I can't use my buddies power programmer due to him adjusting the fans recently so it's "married" his car. What do I need to do, drop the driveshaft and go into the tail end of the tranny? Part #'s would be great. Simple? or PITA? Thanks.........CP

 

Unless your car is different then my 84, you don't have to drop anything. Get a 10 mm wrench and remove the bolt that holds the clip in place. Its located by the left tail of the transmission. Place a container under the area where you are working because it will rain fluid. After the initial surge of fluid, you'll be okay. Can't help with part number. This is one of the easiest jobs you'll ever perform on your car.

 

On auto's 3.75 is the steepest you can go and still correct the speedo using factory speedo gears. Nothing aftermarket that I am aware of. I hope the stick cars are different. Have no clue though.

 

Since your GS is not an auto, the only way to correct the speedo is by re-programming. Expect to pay around $200 for this little service at a Vette shop.
This is what the local shops told me when I inquired about a gear change.
Sorry.

Larry
code5coupe

 

- You have to program the ECM for your new gear set. You can also do some minor tuning while your at it (re-program the fans, adjust timing, adjust a/f ratio, etc....)

 

Change your, probably green, 42 tooth, driven gear for a light blue, 45 tooth, driven gear, GM part number 25513052. That should do it.

RACE ON!!!

 

WRONG!!!!!!!!!!!!!!!!!

A 4.10 axle ratio with a 15 tooth drive gear would require a 48 tooth gear with a 315 tire! There is NOT one available from GM. With out a change of the DRIVE gear speedometer correction is NOT done with a DRIVEN only change. DRM and Lingenfelter might still offer the package but it was pricey $145 comes to mind. An electonic ratio adapter is about the only "practical" solution.

People struggle with some of these Dakota and Abbott. The real fix I believe might be a Terf branded adapter.

 

315 is the section width of the tire in millimeters. By itself, it has no bearing on speedometer calibration, which is a function of the tire effective rolling circumference, of which tire width plays no part.


Wrong again, gear grease breath. C4s were made with no less than 7 different rear axle ratios. There have never been any more than 2 different drive gear tooth counts available, 15 and 17 teeth. How do you imagine GM managed 7 gear ratios on 2 driven gear tooth counts, if "speedometer correction is NOT done with a DRIVEN only change"?


Admittedly the 15/45 tooth combination is not perfect, but it will get you within about 5%. If $145.00 from DRM and/or Lingenfeler seems "Pricey", what do you consider $160.00 to $200.00 for a black box? Lets see here... on one hand it's a $10.00 plastic driven gear. On the other hand it's $145.00 to $200.00. Whatever is one to do???

RACE ON!!!

 

P/N: OBDII (96-97) "Saver Package" Programming
Price: $75

http://madz28.com/9697.php

 

I believe I got this off the forum long ago. Haibeck Automotive Technology (ZR1 guy in Illinois). I think $110-$120 for the nylon gears, since they are custom made/CNC'd. He will know the accuracy percentage. Call 630-458-8427 (CST).

 

I've never heard that one!!

 

I just asked and she said: "It aint so"!

BTW I'm still waiting your call!

I'm pretty comfortable with my "statements" since everything was directed to "one" car and a specific ratio change! A GS with 315 tires.
** I believe the error with the 45 is closer to 10%

I didn't even consider the OBD2 "factor" here and if it can be done with programming it would have likely been the "only" recommended procedure.

I did a ZF cable drive conversion for a "young fellow" with a ZF in an '85 Monte Carlo with 3.73's recently. He had no speedo for some time. The chassis dyno said I passed the test and "the Judge" approved also! He had been told he needed an electronic to cable drive box ($150 plus install). I accomplished his with an old style sleeve and gear combination. His cable actually ended up being long enough. He was done with less than $50 in new parts. The 5.7 and ZF "black label" in his car with the 3.73 gear is an interesting car to drive.

 

Thanks for the support! Here's a link to his site with the information and pricing! The information "confirms" my calculations with the change to a 13 drive etc! Ole "grease gear breath" I guess didn't do to bad here! Be sure to see my reply to Sam(65Coop) ..... I asked and she said "It isn't so"!!!

http://www.zr1specialist.com/HAT%20W...on%20Gears.htm

Still if with an OBD2 and a ZF the calibration can be done with programming I believe it would be the way to "fly"!

 

How nice for you that YOU are comfortable. How about backing up some of your incorrect statements?

Let's see you justify, "would require a 48 tooth gear with a 315 tire" that the section width, stock or otherwise affect the speeometer reading.

After spouting, "With out a change of the DRIVE gear speedometer correction is NOT done with a DRIVEN only change.", how do explain GM using only two different drive gear tooth counts with seven different rear axle ratios?

I never suggested that there weren't other ways to correct the speedometer. I popped up with a simple, inexpensive solution and you come back with WRONG and cite nonsense as to why I'm wrong. It's great that you are comfortable, I for one am happy for you. Now make the rest of us comfortable, namely me, with some justifications for your challenged statements.

RACE ON!!!

 

How nice for you that YOU are comfortable. You cannot declare someone WRONG and not back up the challenge to your statements. How about some enlightenment?

In light of your declaration, "would require a 48 tooth gear with a 315 tire", let's see you justify, that the section width, stock or otherwise, alone, affects the speeometer reading.

After spouting, "With out a change of the DRIVE gear speedometer correction is NOT done with a DRIVEN only change.", how do explain GM using only two different drive gear tooth counts with seven different rear axle ratios?

I never suggested that there weren't other ways to correct the speedometer. I popped up with a simple, inexpensive solution and you come back with WRONG and cite nonsense as to why I'm wrong. It's great that you are comfortable, I for one am happy for you. Now make the rest of us comfortable, namely me, with some justifications for your challenged statements.

RACE ON!!!

 

CFI-EFI,

It's a GS Coupe (assumed) Factory tire (assumed) 31535/17 ! 315 is merely a reference to the "tire"! Tire roll-out (revolutions per mile) on a 31535/17 is something at 785.
Formula: drive gear (15) X ratio (4.11) X tire roll out (785) / revolutions per mile used to calibrate the head (1000)= driven gear (48.3) That's how I did it and I believe it to be pretty accurate. Here's a link that pretty much confirms it! Some divide by 1001, I know not why! A cushion maybe! ATI uses this I believe. Since this is a digital "read" and electronic the 1000 could be replaced by maybe pulses and change the calculation a bit, but you asked "comfortable" and I am with that #!

http://www.bgsoflex.com/speedo1.html

There was "no nonsense" cited and my reference to "drive and driven replacement" was pointed to "this application"! The use of the two gears you mention for manual trans C4 applications is correct but all axle ratios and tire sizes "fit" the available desired drive/driven combinations that could be compiled with GM existing parts. Through about 3.75 axle, driven (only) changes will generally do when using tire diameters used in production or "similar" diameters. Get wild with "tire" diameter and it "all" changes again!
Your reference "about 5%" I believe is flawed by almost 2 times. The error is something I'd say nearer 9+%.

I didn't see "GS348" anywhere stipulate "inexpensive" or just a WAG!

He did ask simple or PITA!
1. If it can be done with programming "simple", the expense seems resonable.
2. If it needed to be done with gears, depending upon one's skills "simple"!
3. An electronic box, if your one to play with the rear gears "frequently" and there are those, maybe it's the better buy. Again the cost "reasonable" depending on one's "skills"!

If it were a job one needed to "hire out" regardless of the method the price other than programming "escalates"!

Everything I stated was regarding this "one single" axle ratio change on this car with some "assumed" factory equipment (3.45 gear, 31535/17 tire)

There was never an intention to "attack you"! Perhaps I shouldn't have SHOUTED!!!!

NUFF said! I'll close with your "RACE ON"!

 

Guys --- all the debate is nice, and typically what you need for an older C4, but HIS SPEEDO CAN AND SHOULD BE DONE WITH PROGRAMMING. I speak the voice of experience (I have 17x9.5f / 17x11r wheels, 315/35/17 tire, 96 Coupe, 4.10 gears)

okay?

Now you can continue the debate

 

I pretty much convinced myself that it was "programable" after checking your profile and saw the LT4 and the 4.10. I had planned on just leaving it alone and "should have" but then the "throw a gear at it" came in to play! The rest is "before your eyes"! I never considered the OBD2 and I had done a couple ZF's recently one problem with a speedsensor with the wrong "pitch" ('90), and the other a mechanical change over, a Chevelle I mentioned in an earlier post.

I "LEARNED" that's cool It was a "tough" lesson!!!!!!!!!

 

That was a nice dance. Even a veteran politician would have been impressed. You circled the subjects and bounced off of all sides without directly addressing the questions. I will make some comments and then ask a couple of pointed questions and we'll see if you can deal with a direct question or two, on the subject.Still no reference as to how the section width of the tire affects the speedometer calibration, as alluded to in the statement, "...would require a 48 tooth gear with a 315 tire'


Not by your own numbers. Check it out: Meanwhile, in another attempt to cloud the issues, I did NOT ask for "comfortable". You said that you were and I said that I was happy for you. I am not now, nor have I ever questioned your formula. I merely questioned your accusation that I was wrong in all my statements. I admitted to an approximate 5% error with the 45 tooth driven gear. You say it is more like 10%. Assuming your formula is correct and that even though you say, "With out a change of the DRIVE gear speedometer correction is NOT done with a DRIVEN only change.", and setting THIS faux pas aside, your 15/48 combination yields a speedo gear ratio of 3.20:1. The 15/45 tooth count is a 3.00:1 ratio. .20/3.20 = .0625 or an error of 6 1/4% from your "perfect" number. That looks like it's a lot closer to 5% than it is to 10%.


You made no allowances for any particular application, and if you had, it wouldn't matter. You simply stated. "With out a change of the DRIVE gear speedometer correction is NOT done with a DRIVEN only change.". With C4s alone having 7 available rear axle ratios and only 2 different drive gear tooth counts, that is the definition of nonsense.


Did you see in my initial answer that I was "guessing"? Did I state that it was the only, or cheapest, way to go?

Here are two simple, straight forward, questions, based on your declarations.

1.) In light of your statement, "...would require a 48 tooth gear with a 315 tire!", please explain how section width, alone, will affect a speedometer reading.

2.) In light of your statement, "With out a change of the DRIVE gear speedometer correction is NOT done with a DRIVEN only change.", how do you explain GM using no less than 7 gear ratios with only 2 drive gear tooth counts?

You can step up the the plate and defend your statements or you can dance some more.

That ought to be clear and easy enough.

RACE ON!!!