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Old 02-12-2019, 08:45 PM   #1
jamie72
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over drive in a 71

whats the best route in putting an over drive in my 71 k20,i think the 410s and 33 will too low in a daily driver.
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Old 02-12-2019, 09:24 PM   #2
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Re: over drive in a 71

I have a 700R4 in both of my trucks. Big difference with overdrive and a lock up converter.
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Old 02-12-2019, 09:35 PM   #3
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Re: over drive in a 71

you have auto or manual trans?
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Old 02-12-2019, 10:16 PM   #4
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Re: over drive in a 71

play with this . you can change speeds at the bottom click the window and put in what you want .
http://www.grimmjeeper.com/gears.html

th350/400 - 4.10 - 33" tire @ 70mph = 3087 rpm
700r4 ----- 4.10 - 33" tire @ 70mph = 2046 rpm

sm465 4speed - 4.10 - 33" tire @ 70mph = 2922 rpm
nv4500 5speed - 4.10 - 33" tire @ 70mph = 2192 rpm

hope this helps you a bit .

try and find your engines best vacuum reading cruising and match the rpm with what you find to your new range and this will help you stay in the power curve sweet spot . if to high or low its no good as your maxed or at the bottom fighting to get to the sweet spot .
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Old 02-13-2019, 05:36 AM   #5
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Re: over drive in a 71

Quote:
Originally Posted by mongocanfly View Post
you have auto or manual trans?
auto.
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Old 02-13-2019, 05:38 AM   #6
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Re: over drive in a 71

Quote:
Originally Posted by mongocanfly View Post
you have auto or manual trans?
most of the tranny guys around here don`t recommend them as they say they are weak and it takes a lot of $$ to build them up to hold??
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Old 02-13-2019, 12:15 PM   #7
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Re: over drive in a 71

4L80e and move the engine forward to install it
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Old 02-13-2019, 01:01 PM   #8
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Re: over drive in a 71

I am partial to this OD, HA!


http://67-72chevytrucks.com/vboard/s...d.php?t=750764
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Old 02-13-2019, 01:26 PM   #9
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Re: over drive in a 71

Alright already, I'll try to be helpful this time. This chart shows a TH350 or TH400 (3 speed) 1:1 ratio with the convertor locked and the effects of tire size and final drive ratio on engine RPM (add a couple hundred RPM if the convertor is unlocked). Most manual five speeds have the 1:1 ratio at 4th gear (like the NV4500) and then 5th gear is the OD ratio usually somewhere around .7:1 or .73 or even a little closer to 4th like .8:1. You can use this chart to find your engine RPM at 1:1 (3rd gear for auto or 4th gear for manual) then take that RPM and multiply it by .7 or .73 or .8 or whatever OD your new trans has. That's easy enough right? Sorry for the resolution but it is the only picture I have of this. I think a 700R4 has OD in 4th (it still has 1:1 in 3rd) but I do not know what ratio it is maybe close to .73 or so. Maybe someone else can add that.
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Old 02-13-2019, 01:43 PM   #10
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Re: over drive in a 71

Sorry I think this chart was written at 60 MPH, I can't find it for sure now. Makes sense when compared to sweetK30 numbers.
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Old 02-13-2019, 02:17 PM   #11
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Re: over drive in a 71

Ok, I found my old post from 2013 and the chart was written at 65MPH but I think that may be wrong compared to sweetK30s numbers above. Maybe sweetK30 can shed some light on where his numbers be comin' from. Also the chart is divided into three categories. The rpm highlighted in black are
optimum for the tire size and ratio combination. These will most closely
give you the best overall drivability. If you're looking for a ratio that
will give better fuel economy for highway driving at the expense of some
acceleration and overall performance, choose a ratio in the yellow shaded
area. If you're looking for a ratio that will improve acceleration and
towing power at the expense of some fuel economy, choose a ratio in the blue
shaded area.
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Old 02-13-2019, 02:25 PM   #12
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Re: over drive in a 71

Quote:
Originally Posted by Orange Crate View Post
Alright already, I'll try to be helpful this time. This chart shows a TH350 or TH400 (3 speed) 1:1 ratio with the convertor locked and the effects of tire size and final drive ratio on engine RPM (add a couple hundred RPM if the convertor is unlocked). Most manual five speeds have the 1:1 ratio at 4th gear (like the NV4500) and then 5th gear is the OD ratio usually somewhere around .7:1 or .73 or even a little closer to 4th like .8:1. You can use this chart to find your engine RPM at 1:1 (3rd gear for auto or 4th gear for manual) then take that RPM and multiply it by .7 or .73 or .8 or whatever OD your new trans has. That's easy enough right? Sorry for the resolution but it is the only picture I have of this. I think a 700R4 has OD in 4th (it still has 1:1 in 3rd) but I do not know what ratio it is maybe close to .73 or so. Maybe someone else can add that.

how do you lockup the convertor on a non lockup trans ? ? ?

convertor unlocked is a little over 200rpm extra from all i have read.

my no's were from the link i provided in my post above . its a SUPER calculator that lets you pick from a list of trans options / t-case options / or enter your own and enter axle and tire dia or by size . then you can edit the results in the rpm's or mph box's by clicking and changing them .
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Old 02-13-2019, 04:51 PM   #13
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Re: over drive in a 71

Quote:
Originally Posted by sweetk30 View Post
how do you lockup the convertor on a non lockup trans ? ? ?
I said I would "try" to be helpful, I didn't say I actually "would" be helpful!
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Old 02-13-2019, 06:35 PM   #14
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Re: over drive in a 71

Quote:
Originally Posted by Orange Crate View Post
I said I would "try" to be helpful, I didn't say I actually "would" be helpful!
please its all good . we cool .
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Old 02-14-2019, 05:37 AM   #15
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Re: over drive in a 71

thanks guys, appresite all the help
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Old 02-14-2019, 12:23 PM   #16
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Re: over drive in a 71

Quote:
Originally Posted by sweetk30 View Post
how do you lockup the convertor on a non lockup trans ? ? ?
GM actually had a TH350C that had a lock-up converter.
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Old 02-14-2019, 12:45 PM   #17
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Re: over drive in a 71

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Originally Posted by renegade6 View Post
GM actually had a TH350C that had a lock-up converter.
oh i know . only ever had my hands on just 1 and it was in a parts truck . do you remember the twin pitch convertor th400 i think it was ?
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Old 02-14-2019, 02:18 PM   #18
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Re: over drive in a 71

For OD with an auto trans, you are looking at a 200R4, 700R4, 4L60E, or 4L80E.

A 700R4 is what would had come in a truck 82-92. They are hydraulic. A 200R4 is a weaker version, but they can be built up.

A4L60E / 4L80E is what would had come in a truck 93-??. They are very similar to the 700R4, except that they are electronic controlled. 4L60Es are considered to be weak, 4L80Es are considered to be bullet proof. If you go with either of these, you will need a standalone TCM to control the transmission.

My years may be 1 or 2 off...

To me, having a TCM kind of goes against the point of having an old truck, but that's up to you.

Trying to gauge how well a transmission will hold up can be difficult. One person may call the transmission a hand grenade, while others have had them last over 200K. If your mostly on the street and cruising, it will last longer. If your towing, off roading, or racing, you may opt for something stronger. Look around at write up, what others have done, how different setups have held up.
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Old 02-14-2019, 05:07 PM   #19
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Re: over drive in a 71

I have a sm465 manual trans in mine with 4:10 's. I am going to put a Gear Vendor overdrive in mine, I already have it, just need to buy the adapter
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Old 02-19-2019, 06:48 PM   #20
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Re: over drive in a 71

Wait, was some one offering beer???
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Old 02-19-2019, 07:27 PM   #21
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Re: over drive in a 71

Quote:
They are hydraulic [shifted]. A 200R4 is a weaker version, but they can be built up.
No 4x4 versions of the 200-4R although you could go with the divorced transfer case option.
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Old 02-19-2019, 08:47 PM   #22
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Re: over drive in a 71

700r4 is not the strongest trans, but it's fine for your stock-ish big block. You should talk to a competent trans guy...a few upgrades make them handle some power fine. I have quite a few built, they're usually about $900-1300 with upgrades plus converter, crossmember, dipstick, fluids, cable, etc. Never had any trans builder complain about them or not warranty them and I've never lost one. Last one I did is currently behind a pretty rowdy cammed 5.3L, it does the job well and fries tires at will. Good cores are getting harder to find though, I snatch them up whenever I can. Passed on a few 4x4 versions and picked up a couple of 2wd's recently.
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Old 02-23-2019, 07:29 PM   #23
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Re: over drive in a 71

For a good recommendation, tell us what you do with the truck, and how you drive. Do you prefer an auto, or roll your own gears?
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Old 02-25-2019, 07:04 PM   #24
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Re: over drive in a 71

its going to be a daily driver, and tow 3500lbs about 2-3 times a yr. i`d be fine with a stick, but ineed to go auto so if need be the wife can drive it.
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Old 03-01-2019, 02:02 AM   #25
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Re: over drive in a 71

Quote:
Originally Posted by jamie72 View Post
its going to be a daily driver, and tow 3500lbs about 2-3 times a yr. i`d be fine with a stick, but ineed to go auto so if need be the wife can drive it.
Precisely the reason I run an NV4500...the thought of my wife driving the Brick!

Kidding aside, we have an 04 Yukon XL Denali 6.0 urban assault grocery getter with a 4L65E. I think the car is 7 or 8k lbs and we tow a 4500# boat and have our 4 kids, wife's stuff and boat stuff. Never weighed it but its heavier than the truck when loaded and towing. I had a transmission built by TransStar a few years back with a couple of better parts on Clinebarger's recommendation. This transmission has been awesome. Id probably run it behind the old 396 that I had in the truck.

The 454 that i have now is a different story. Id feel a little weird not having a 4L80 behind that. It makes a more torque than the LQ9 in the Denali and way more than the 396 ever could.

I think that stand alone controllers and harnesses can be had for either electronic transmissions as well.

You've got a few choices which is good.
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