The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > Info Center > FAQ Truck Tech > Engine and Drivetrain

Web 67-72chevytrucks.com


 
 
Thread Tools Display Modes
Old 01-06-2009, 08:30 AM   #1
Bruce88
Registered User
 
Bruce88's Avatar
 
Join Date: Oct 2008
Location: Everett, WA
Posts: 326
Speedometer calibration with a 700R4 Trans

Speedometer calibration with a 700R4 Trans

The concept for most transmissions is the same getting the right drive gear to the right driven gear so the speedometer reads the correct speed. Other transmissions use different gears, housings, and retainers even the electric transmitter models. So this “how to” will only deal with the 700R4 mechanical speedometer set up (a popular transmission swap for the 67 – 72 Chevy trucks)

I’ve borrowed a few part pictures from PATC Raptor Transmissions web site to help in visualizing the process. I’ve used them for parts and found good service and reasonable prices http://www.transmissioncenter.net/sp...n_______va.htm . There are many places you can find the parts including the junk yard.

The most expensive part to acquire or find is the “Driven Gear Housing” there are two different ones depending on what gears are used. Driven Gear Housings run approximitly $35.00 used to $70.00 new.

When ever you’re working on an automatic transmission I recommend using new O-rings and seals lubed with trans fluid and always make sure that the sealing surfaces are clean with no damage before assembly. (New seals are cheep insurance to prevent leaks later on)

Hear is a picture of some of the parts that you will be dealing with

Name:  Speedo-Cal-1.jpg
Views: 26839
Size:  71.8 KB

There are a few things that you will need to know before you start gathering your parts.
1 Tire Diameter – I will be using 27 inch tire diameter for my installation
2 Differential gear ratio – I will be using 3.42 ratio for my installation
3 Drive gear teeth – I will be using a Gray 15 tooth drive gear (note my
transmission came with a Red 17 tooth drive gear)

You may not have to change the drive gear as I am, all the driven gears work with the color coded drive gears shown above. I already had a driven gear housing that works with the 34 to 39 driven gears and it was cheaper to replace the drive gear and new seals than get the other housing. After putting in tire diameter, differential gear ratio and drive gear teeth that you have in the calculator, you might not be able to find a driven gear tooth count that will work with your drive gear. If this is the case you can try deferent drive gears in the calculator until you find one that works.

Hear is a picture of the drivers side of the transmission and the driven gear housing removed to find out what drive gear is installed.

Name:  Speedo-Cal-2.jpg
Views: 28182
Size:  74.7 KB

There are many speedometer calibration programs that can be found on the web. They all work in a similar manner. You plug in the information you gathered and it calculates what your driven gear should be. I took some screen shots of the calculator that I used http://www.bgsoflex.com/speedo1.html shown below.

Name:  Screen-shot-speedo-cal.gif
Views: 14983
Size:  39.5 KB

After you have gathered all the parts that you need its time for the installation.

If you need to change the drive gear you will need to remove the drive shaft then the transmission rear housing. On some 700R4 transmissions you will find a cylinder/cup with seals just behind the drive gear it will slip off the shaft so that you can change the drive gear. When reassembling reinstall the cylinder/cup if so equipped.

Hear are some pictures showing changing the drive gear

Name:  Speedo-Cal-3.jpg
Views: 21472
Size:  96.6 KB

Now to the final steps installing the driven gear and housing. I think the picture below will cover all the information required

Name:  Speedo-Cal-4.jpg
Views: 20986
Size:  60.0 KB

If anyone sees where clarification or additional information is needed please feel free to contribute.
__________________
My Build Thread: http://67-72chevytrucks.com/vboard/s...d.php?t=318544
Bruce88 is offline  
Old 02-01-2009, 04:03 PM   #2
68SHORTBOX
Registered User
 
68SHORTBOX's Avatar
 
Join Date: Jul 2006
Location: El Cajon Ca
Posts: 84
Re: Speedometer calibration with a 700R4 Trans

The torque for the tail shaft housing bolts is 26 ft lbs. Very nice write up and a great link.

Last edited by 68SHORTBOX; 02-01-2009 at 04:03 PM.
68SHORTBOX is offline  
Old 02-07-2009, 03:19 AM   #3
67ChevyRedneck
Hittin E-Z Street on Mud Tires
 
67ChevyRedneck's Avatar
 
Join Date: Nov 2004
Location: Greenville, SC
Posts: 21,490
Re: Speedometer calibration with a 700R4 Trans

Quote:
Originally Posted by woodridge View Post
Good thread. I didn't know about the speedo rpm's.
I didn't either. So 1,000 if for all 67-72 stock speedos? Where did you find that info?
__________________
Jesse James
1967 C10 SWB Stepside: 350/700R4/3.73
1965 Ford Mustang: 289/T5-5spd/3.25 Trac-Loc
1967 Pontiac Firebird: Project Rusty Chicken!
2015 Silverado Double Cab 5.3L Z71
2011 Mustang V6 ~ Wife's ride
American Born, Country by the Grace of God
1967 CST Shop Truck Rebuild!
My 1967 C-10 Build Thread
My Vintage Air A/C Install
Project "On a Dime"
Trying my hand at Home Renovation!
1965 Mustang Modifications!
67ChevyRedneck is offline  
Old 02-08-2009, 12:28 AM   #4
Bruce88
Registered User
 
Bruce88's Avatar
 
Join Date: Oct 2008
Location: Everett, WA
Posts: 326
Re: Speedometer calibration with a 700R4 Trans

Quote:
Originally Posted by 67ChevyRedneck View Post
I didn't either. So 1,000 if for all 67-72 stock speedos? Where did you find that info?
I wish I had a answer for you and a manual to point to that has the specification data but there is none that I have available to me. I can say that by using the 1000 revolutions per mile in your calculations your speedometer will read correctly for a 67-72 Chevy truck. Most cars and trucks from 1965 and up use the 1000 revolutions per mile on mechanical speedometers.
__________________
My Build Thread: http://67-72chevytrucks.com/vboard/s...d.php?t=318544
Bruce88 is offline  
Old 02-16-2009, 12:20 PM   #5
nightmare
Senior Member
 
nightmare's Avatar
 
Join Date: May 2002
Location: houston, tx
Posts: 1,663
Re: Speedometer calibration with a 700R4 Trans

Quote:
Originally Posted by 67ChevyRedneck View Post
I didn't either. So 1,000 if for all 67-72 stock speedos? Where did you find that info?
Quote:
Originally Posted by Bruce88 View Post
I wish I had a answer for you and a manual to point to that has the specification data but there is none that I have available to me. I can say that by using the 1000 revolutions per mile in your calculations your speedometer will read correctly for a 67-72 Chevy truck. Most cars and trucks from 1965 and up use the 1000 revolutions per mile on mechanical speedometers.
IIRC, they are stamped in ink on the backside of the speedo.
__________________
Mike

2001 Dakota R/T - Silver CC - 1 of 1671 •360 w/46RE •392 limited slip
1969 Chevy C/10 - Blue LWB •350 w/ 700R4 •3.73 posi •PS PB A/C - SOLD

Using your turn signal is not "giving information to the enemy"

67-72 FAQ

Quote:
Originally Posted by GMCMAX View Post
My lugnuts require more torque than your honda makes!
nightmare is offline  
Old 03-11-2009, 11:31 AM   #6
nightmare
Senior Member
 
nightmare's Avatar
 
Join Date: May 2002
Location: houston, tx
Posts: 1,663
Re: Speedometer calibration with a 700R4 Trans

I didn't see any part number's listed, so I found some that should be posted too:
Attached Images
 
__________________
Mike

2001 Dakota R/T - Silver CC - 1 of 1671 •360 w/46RE •392 limited slip
1969 Chevy C/10 - Blue LWB •350 w/ 700R4 •3.73 posi •PS PB A/C - SOLD

Using your turn signal is not "giving information to the enemy"

67-72 FAQ

Quote:
Originally Posted by GMCMAX View Post
My lugnuts require more torque than your honda makes!
nightmare is offline  
Old 05-04-2009, 02:02 PM   #7
sleepertruck72
theetileguy
 
sleepertruck72's Avatar
 
Join Date: Nov 2007
Location: Turlock California 95380
Posts: 2,070
Re: Speedometer calibration with a 700R4 Trans

I need to do that, but my tranny is in the truck already. Does it need to drained of tranny fluid ? Ive been driving it that way for awhile now, so I could live with it I guess.

GREAT write up by the way !!!
__________________
72 C20 Longbed
72 C10 Shortie

Last edited by sleepertruck72; 05-04-2009 at 02:03 PM.
sleepertruck72 is offline  
Old 05-04-2009, 03:20 PM   #8
6772owner
Gearhead
 
6772owner's Avatar
 
Join Date: Jan 2008
Location: Colorado
Posts: 1,192
Re: Speedometer calibration with a 700R4 Trans

If you have to change the drive gear (on the tailshaft) you have to remove the tailshaft housing so its best to drain it in my opinion. I have changed the driven gear several times without draining the trans, I just jack the rear up to put the fluid towards the front of the trans. You can also pitch it a little to the passenger side, this will give you minimal fluid lose, just top off the trans when finished.
__________________
2000 Buick LeSabre, My D/D
2008 GMC Sierra 1500, Ext cab/6.5, 4wd, 4.8l, mods to come!
2013 Ford Edge Limited AWD, AEM Filter, LED lighting - (Sold)
2015 Ford Fusion SE, Ecoboost - Wife's D/D
2012 Malibu 1LT, Taupe Grey Metallic - (Sold)
1994 GMC Sierra C2500, XC/LB, 454, 2" Rear Shackles, Roll Pan, HD Wheels, Tinted Windows - (Sold)
Project C10 (my 72' C10 w/96' LT1, 700R4, bagged F&R, 18's (for now), Short/Fleet) -- SOLD!
Build Thread: http://67-72chevytrucks.com/vboard/s...d.php?t=313644
2003 Chevy Avalanche 1500 Z71 (Flowmaster Muffler, Predator, S&B CAI, 285/50/20's, Kenwood DVD) -- SOLD!
1967 K10 Stepside (Torch Red, 350/350, 33'' M/T's, Cowl Hood) -- SOLD!
1995 Camaro Z28 (True Black, M6, T-top, K&N FIPK, STS, 52mm TB, 1.5" Drop, STB, SFC's 17" ZR1's) -- SOLD
6772owner is offline  
 

Bookmarks

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 04:28 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.
Copyright 1997-2013 67-72chevytrucks.com