Turbo 350 speedo help. - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Transmission - Rearend
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 11-23-2009, 10:39 AM
BigRoy1978's Avatar
Registered User
 
Last photo:
Join Date: Nov 2009
Location: Hugoton, KS
Age: 25
Posts: 338
Wiki Edits: 0

Thanks: 4
Thanked 0 Times in 0 Posts
Turbo 350 speedo help.

Got a 78 T/A, pontiac 400, turbo 350 with 3.73 gears and 28" tall tires, my problem. What in the world speedo gears do i use?!!? It has a 30-something tooth driven gear in it now, but the drive on is worn out so ill replace both the drive and driven gears. Just need some help finding out which two i need, and possibly the part numbers for them. Before it was right on with 2.56 gears, but the gear wore out just before i changed to the 3.73's, so i dont have anything to compare to. thanks for any help!

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 11-23-2009, 06:54 PM
M&M CUSTOM's Avatar
Hotrodders.com Moderator
 
Last wiki edit: Transmission identification
Last journal entry: 1988 Suburban, the project continues.
Last photo:
Join Date: Mar 2003
Location: Northwest Pennsylvania.
Age: 43
Posts: 2,231
Wiki Edits: 9

Thanks: 0
Thanked 1 Time in 1 Post
A 9 tooth drive and 24 tooth driven gears will get you the 2.66 speedometer gear ratio you need according to the di-it-yourself math equation calculator on Transmissioncenter.net's website for speedometer gear parts. BUT the 24 tooth gear isn't available for the TH-350 from them, drive gears are available in 7, 8, 9, or 10 tooth, and driven gears are available in 17, 18, 19, 20, 21, & 22 tooth count gears. LINK HERE.

Their linked online calculator can be found HERE.
The linked calculator says you can use a combination of a 7 tooth drive and 19 tooth driven, OR 8 tooth drive and 21 tooth driven gears.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 11-23-2009, 11:24 PM
BigRoy1978's Avatar
Registered User
 
Last photo:
Join Date: Nov 2009
Location: Hugoton, KS
Age: 25
Posts: 338
Wiki Edits: 0

Thanks: 4
Thanked 0 Times in 0 Posts
forgot to mention, it has the large driven gear, about an inch and a half across, not the smaller one.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 11-25-2009, 03:42 AM
Registered User
 
Last wiki edit: Transmission identification
Join Date: Mar 2008
Location: Terra
Posts: 704
Wiki Edits: 85

Thanks: 1
Thanked 26 Times in 24 Posts
Quote:
Originally Posted by BigRoy1978
Got a 78 T/A, pontiac 400, turbo 350 with 3.73 gears and 28" tall tires, my problem. What in the world speedo gears do i use?!!? It has a 30-something tooth driven gear in it now, but the drive on is worn out so ill replace both the drive and driven gears. Just need some help finding out which two i need, and possibly the part numbers for them. Before it was right on with 2.56 gears, but the gear wore out just before i changed to the 3.73's, so i dont have anything to compare to. thanks for any help!
You changed your ratio in the rear end by 46% [(3.73/2.56) - 1] so change your speedo gears by 46% and they will be correct.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 12-07-2009, 09:41 PM
Member
 
Last photo:
Join Date: May 2003
Location: Shreveport LA
Age: 65
Posts: 5,103
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
http://novaresource.org/speedo.htm has the formula you need and the available gear combinations for both sizes of driven gear.
Reply With Quote Quick reply to this message

Recent Transmission - Rearend posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may 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
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Turbo vs Supercharger - Write up!! FastChevyTruck Engine 107 02-16-2011 01:18 PM
SBC Motor and a Turbo 350..Will it work? 31fordcoupe Engine 2 10-06-2009 11:40 AM
200R4 vs 350 Turbo knothead Transmission - Rearend 9 01-14-2008 12:19 PM
newer sbc 350 to older turbo 350 yragat Transmission - Rearend 8 10-20-2007 08:52 PM
350 turbo or 400 turbo? nd500 Transmission - Rearend 2 02-21-2003 09:25 PM


All times are GMT -6. The time now is 01:37 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.