Rakman
Newbie
Posts: 4
Loc: Southwest PA
Reg: 11-02-18
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08-05-22 06:01 AM - Post#2845487
Just had the 283 with the PG replaced with a crate 350 and a TH350 tranny. Noticed on the highway the my GPS is telling me I'm doing 60MPH, and my speedometer is telling me I'm doing 75mph.
I asked the guy who replace the tranny if he knew which Speedometer Drive Gear was on the TH350. He told me he just moved the Drive Gear from the PG to the TH350 but didn't notice how many teeth were on the gear.
Does anyone know which Speedometer Drive Gear would of been on the PG from the factory?
Obviously, I hoping to just replace the Driven Gear to get the speedometer closer to my actual speed.
Thanks in advance to anybody who may be able to answer my question. This forum has been a great resource through-out my restoration process.
-Rakmann
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junky
Valued Contributor
Posts: 3873
Loc: Northeast CT
Reg: 06-27-10
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08-05-22 06:22 AM - Post#2845488
In response to Rakman
I made a post about how to determine the correct gear in a post a few years ago. Should have all the information that you will need.
https://www.chevytalk.org/fusionbb/showtopic.php?t...
Never argue with an idiot. He'll drag you down to his level, then beat you with experience.
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55Brodie
Contributor
Posts: 405
Age: 70
Loc: Little River, SC
Reg: 12-26-15
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08-05-22 07:23 AM - Post#2845493
In response to Rakman
Your speedometer is reading 25% fast which means the driven speedometer gear will need 25% more teeth for correction. I think this will be impossible. I would try the TH350 gear and compare with the GPS and do the math again.
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 dgstarr
"5th Year" Silver Supporting Member
Posts: 339
Loc: Portland, OR
Reg: 04-16-13
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08-05-22 12:59 PM - Post#2845506
In response to Rakman
!963 pass with 3.08 or 3.36 axle: 8 teeth (1 27/32 OD X 39/64 thick) 3708144. This info name from GM parts manual.
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 docjns1
"2nd Year" Gold Supporting Member
Posts: 291
Loc: upstate NY
Reg: 11-12-19
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08-05-22 01:14 PM - Post#2845507
In response to dgstarr
1st thing coming to my mind is this...if final trans drive is straight out 1:1 (no o.d.), and the 'glide drive gear was used in the 350, and assuming you used the same driven gear that was in the car, there should be no change in the speedo.
350 drive gears were typically only a 7 or 8 tooth gear, most change was with the driven gear and/or use of an adapter where necessary. Junky's link to the previous thread is a good reference. I've attached a chart with some #s for you as well. As for the driven gear, 1 tooth would result in a 3-4 mph change on the speedo. You'd need to add 4 ( maybe 5) teeth to the driven gear to accomplish this so it 's all dependent on # of teeth you currently have
Steve
*********
'65 Impala SS, Crocus Yellow/blk
327 / 300 L74
M11 3 on the tree
12 bolt 3.31 open dif |
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docjns1
"2nd Year" Gold Supporting Member
Posts: 291
Loc: upstate NY
Reg: 11-12-19
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08-05-22 01:34 PM - Post#2845509
In response to docjns1
If you're changing the driven gear you're lucky in that the 1 27/32 drive gear equates to 1.84" in the chart I've provided. Since its a bit larger, the driven gears are just a bit smaller (see attached photo) to properly mesh. The 'smaller' gears are more readily available and easily identified as the last 2 digits of the part# is the # of teeth
Steve
*********
'65 Impala SS, Crocus Yellow/blk
327 / 300 L74
M11 3 on the tree
12 bolt 3.31 open dif |
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junky
Valued Contributor
Posts: 3873
Loc: Northeast CT
Reg: 06-27-10
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08-05-22 04:23 PM - Post#2845519
In response to docjns1
To use the larger gear on the left, you have to change the gear in the tail shaft. If you don't, then the plastic gear will get chewed up in 100 miles. I know, because that is what happened to one of my other cars.
Never argue with an idiot. He'll drag you down to his level, then beat you with experience.
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docjns1
"2nd Year" Gold Supporting Member
Posts: 291
Loc: upstate NY
Reg: 11-12-19
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08-06-22 09:53 AM - Post#2845536
In response to junky
thats correct, I had the opposite problem, smaller gear on output/main shaft requiring larger driven gear.
Online seller substituted the smaller one that hardly meshed as it was same # teeth then proceeded to argue about it...not worth the few $$ it cost, Speedo read about 30 and jumped around when I was actually doing about 50
Steve
*********
'65 Impala SS, Crocus Yellow/blk
327 / 300 L74
M11 3 on the tree
12 bolt 3.31 open dif |
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Rakman
Newbie
Posts: 4
Loc: Southwest PA
Reg: 11-02-18
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08-07-22 06:52 AM - Post#2845569
In response to Rakman
Gentelmen...I can't thank you enough for your information.
-Rakmann
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