In the new CHEVY HI-PERF (MAR), page 78, there is an article about speedo gears, with good illustrations (sort of).

>ON PAGE 80, UNDER THE HEADING "SPEEDOMETER GEAR COMPATIBILITY", THERE IS SOME SERIOUS ERRONEOUS INFORMATION WHICH STATES THAT MUNCIES WITH RIGHT HAND SPEEDO GEARS HAVE REVERSE CUT TEETH ON THE DRIVEN GEARS< THIS IS ABSOLUTELY AND POSITIVELY INCORRECT! Then on page 81 the illustration shows 2 driven gears with opposite cut teeth, claiming the reverse cut is for Corvettes. NO! NO! NO! NO! NO! The chart for gears on page 80 lists part numbers for driven gears with 17-25 teeth. The part numbers and tooth counts are correct. I stock AT LEAST one of each--------THE TEETH ON ALL 10 OF THESE GEARS GO THE SAME DIRECTION!!! IT DOES NOT MATTER IF A SPEEDO DRIVEN GEAR COMES OUT THE LEFT OR RIGHT SIDE OF THE TAIL HOUSING (which they mistakenly call a Tail shaft), THE GEAR STILL TURNS THE SAME DIRECTION!!! IT DOESN'T MATTER IF IT IS A GTO, 442, CAMARO, CHEVELLE OR A CORVETTE!!! I guess the author of this article doesn't realize that ONLY 63-4 Muncies had the speedo on the left side of the TAIL HOUSING (and the PROPER term is extension housing), and 66-74 Muncies, without exception, were on the right side. PERIOD! The gear on the left side in the illustration on page 81 is correct. Maybe the gear on the right (reverse cut as they say) is for a Ford, Toyota or Chrysler, I have no clue. BUT IT AIN'T FOR THE GM MANUAL OR 350 TURBO TRANNYS. I don't know where or how CHP magazine got this info and I know for a fact they wouldn't intentionally steer us wrong. Everyone who reads this will have the correct info, but what about the people who don't read Team Chevelle?
In the table of gears for Muncie/T-350, the 17-22teeth gears are a smaller diameter to be used with a larger gear inside the tranny. The 22-25teeth are a tiny bit larger diameter to be used with a little smaller gear inside the tranny. MOST of the time these 17-25 gears can be used interchangeably.
All of this also applies for GM 3spds and the B-W Super T-10. EVEN THE RICHMOND 5SP IN MY CUTLASS! SAME-SAME!

What we really need, is for someone to tell us where or what that reverse cut gear is. Also, notice the spiral on the shaft, for oiling the speedo gear, goes the opposite direction.

I will be emailing this post to Chevy Hi-Performance.

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Tom Parsons

SIC-EM DZ...



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JR
70 396SS El Camino #'s Matching.
69 396SS Chevelle, project "Street Bruiser"
H-D Ultra Classic E-Glide
72 Chevy C20 Flatbed, $500 DRMO sale. Thanks Uncle Sam
I live to own toyz...

Thanks for the heads-up Tom.

Rick

Where would we be without ya DZ??Thanks for the "Right Stuff":d
Rick

Thanks for the warning on this article.It seems that many of these articles go to press without ANY proofreading.
However, I went to a local speedo shop for a driven gear and they mentioned the choice of right and left hand helix. So I returned with my old gear and they showed me 2 gears that were look-alikes except for the helix. They did not state what the applications were (mine was a plain old TH350)

Maybe Chevy High Performance should be informed of their errors so they can print a correction. The last thing we need is more erroneous information out there.

Could it be that Corvettes have a reverse-rotation speedometer? Those reverse helix driven gears must fit something. I wonder what.

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von '69 300 Dlx SS Murphy's Law is always in effect

Tom, you are awesome. Thanks for keepin us posted...

DZ I think a letter to the editor is in order.....

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Mike Reeh
Gold #34
San Diego, CA

Good thing I don't read Chevy magazines... http://www.chevelles.com/forum/tongue.gif

DZ- a 69 Chevelle with TH400 and factory 4:10 gears uses a 'speedometer adapter assembly' inline with the speedometer cable to allow the MPH to read correctly. If the adapter has only two gears it would reverse the direction of the cable. Could that be where the reverse direction gear is used?

Hey guys Tom did say he would send the post to CHP.Thanks Tom someone needs to keep them sraight...FRED

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<BLOCKQUOTE>quote:</font><HR>Originally posted by Fred Ont canada:
Hey guys Tom did say he would send the post to CHP.Thanks Tom someone needs to keep them straight...FRED
<HR></BLOCKQUOTE>
So cold up here fingers don't work...FRED


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Man DZ, I have to hand it top you, YOU RE THE MUNCIE(or any other manual tranny) MAN!!

I vote that you drive over to their office and slam a M-2(0,1,2) on the desk and show the author exaclty what he's not talking about!

" http://www.chevelles.com/forum/mad.gif What have you been smoking man! http://www.chevelles.com/forum/mad.gif"

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Francis Taracido Gold# 201 :)
sniper0666@aol.com
History shows again and again how nature points out the folly of man.
Oh No! You Know She's Got To Go!
Go Go Quadzilla! &lt;oo=+=oo&gt;
http://members.aol.com/sniper0666/page/intro.html

Von and All,
I have no clue what that reverse cut gear fits. Those speedo gear part numbers are the same for ANY and ALL Chev/GM tranys. When a Muncie (3sp, T-350, or whatever) was built, there was know way to know if it was going to the Corvette, Camaro or Buick assembly plant. So, as I say ALL speedo gears turn the same direction (just different speeds depending on the drive and driven speedo gear ratio). And all speedometer heads turn the same direction, therefore the speedo cable has to turn the same direction.

Joe,
If you hold one of those adapters in your hand and turn one end you will notice the other end turns the same direction (but different speed).

Over the years I have built Muncies out of everything, and the driven speedo gears still go the same direction (even ALL the GM internal speedo gears that slide onto the output shaft have teeth going the same direction).

And one last thing. If there was a reverse rotation speedo gear(s), it (they) would have to be in the parts books. They're not.

Beats the heck out of me!

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Tom Parsons

[This message has been edited by DZAUTO (edited 01-22-2000).]

Well, after seeing this post, I was curious because I have an M-20 out of a Corvette in my 70 Camaro. I also had the original TH350 that came with the Camaro. I knew the M-20 had the speedo on the RH side, so I pulled the gear out. It is PN 3987920, blue with 20 teeth according to the article. I also pulled the gear out of the TH350. It is on the left side. It is PN 3987921, red with 21 teeth. Both gears are the same direction.

Tom, that was a good catch!! You DA MAN!!!

I noticed some errors in their 10 bolt article last month, too, and e-mailed them about it. They need to do more research B4 printing this stuff.



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70 & 1/2 RS Camaro
SB406 & M20 4spd
9" Rear
70 Malibu
SB350 & TH400

Gold Member # 103
Driveline Technician

Since the article in Chevy Hi-Perf supposedly was based on info from Shannon Hudson of North Hollywood Speedometer, someone could probably get their number from directory assistance and call him to see what the reverse helix driven gears are for.

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von '69 300 Dlx SS Murphy's Law is always in effect

NOT ME! If he provided this info to CHP, he won't be happy with me contradicting him. I have been wrong before (many times) and probably will make more mistakes in the future. But as we have seen here on TC and in other areas, there are some people who WILL NOT budge 1in from their opinion. And when you try point something out to them, they just become more beligerant. I think sending my post by email to CHP was adequate.

P.S. I have posted a Part II to this subject.
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Tom Parsons

[This message has been edited by DZAUTO (edited 01-23-2000).]