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Old 06-21-2017, 06:11 PM   #26
demian5
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Re: 454 + TH400 + 4.11 POSI = no freeway

Best thing I ever did for my 70 with 350/350 and 31" tires was a 3.07 rear end.
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Old 06-21-2017, 10:17 PM   #27
El Dorado Jim
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Re: 454 + TH400 + 4.11 POSI = no freeway

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Originally Posted by toolboxchev View Post
Put a 3.73 or 3.54 ring and pinion set in there. I would go with the 3.54 you have plenty of power to push those gears. Rather not to expensive either.
x2, cheapest way to go and the t-400 is an awesome transmission
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Old 06-22-2017, 06:55 AM   #28
Ken B
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Re: 454 + TH400 + 4.11 POSI = no freeway

Last summer I took my 70 Longhorn on a 12 hr. round trip. It has a 350 with a 4 speed and 4.10's. I never took it over 3k rpm's and generally kept it between 2600 and 2800 rpm's. At 2800 I'm running about 62 mph which is fine by me. I rarely take it on long trips but I'm not afraid to. I just have to mentally prepare myself that I'll be spending a lot of time in the slow lane.. First thing I would do if I were you is install a tach. The best advice I was ever given was 30 yrs ago by my father in law who built stock car engines.. He told me to keep it under 3k rpm's on the highway and I've never had a problem. I think your cheapest option is to find a complete rear end with some 3.08 gears.. If you have taller tires to put on there that will make a big difference as well.
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Old 06-22-2017, 08:14 AM   #29
Tom Vogel
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Re: 454 + TH400 + 4.11 POSI = no freeway

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My 69 C-20 has a Gear Vendor's OD unit in it.

TH400 an 4:10 R&P.

Make for some nice freeway cruising.

Just throwing that out there as another option.
^^^^^THIS.... This is the strongest, most fun, most awesome. Do some research on this. It's what I would do if I didn't have a five speed.
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Old 06-22-2017, 09:09 AM   #30
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Re: 454 + TH400 + 4.11 POSI = no freeway

My truck has a 4.11 which you rather need in WV (lots of hills!) but on the interstate it doesn't like going 65.

That was a bigger deal for me when I was younger but since 2006 I like to stay at 55 mph and in the slow lane. On a 200 mile trip it slows me down by 30 minutes but causes a 25% increase in fuel mileage in my daily drivers (Honda sedans). When I get my truck running I will stick with the 4.11 but may one day go to a 3.73. I wish my truck had overdrive but I have no desire to change it to an automatic.

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Old 06-22-2017, 10:06 AM   #31
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Re: 454 + TH400 + 4.11 POSI = no freeway

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My truck has a 4.11 which you rather need in WV (lots of hills!) but on the interstate it doesn't like going 65.

That was a bigger deal for me when I was younger but since 2006 I like to stay at 55 mph and in the slow lane. On a 200 mile trip it slows me down by 30 minutes but causes a 25% increase in fuel mileage in my daily drivers (Honda sedans). When I get my truck running I will stick with the 4.11 but may one day go to a 3.73. I wish my truck had overdrive but I have no desire to change it to an automatic.
I dunno. I think it depends on what kind of motor you've got. It's pretty hilly in my neck of the woods but I never feel myself wanting for more power. I have a 396 with a very mild cam, dual plane aftermarket intake, some basic aluminum heads.... it's not truly fast but it cruises up any long hill on the highway just fine with 3.07s. Sure does a lot better than my 5,500 lb pickup with a 5.3!
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Old 06-22-2017, 10:15 AM   #32
In The Ten Ring
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Re: 454 + TH400 + 4.11 POSI = no freeway

My dad told me that back in the 1960's a guy bought a new car with (I guess) a good sized engine. He had trouble driving in WV! My dad asked him what transmission he had, it was a 3.07.

The guy got rid of that car and got something with lower gearing. My 4.11 will pull hills in high gear but it only has a 250.....getting higher gearing really wouldn't work well for me unless I wanted to go down to first gear but then again, I drive like an old fogey anyway so low interstate speeds are fine with me.
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Old 06-23-2017, 04:50 PM   #33
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Re: 454 + TH400 + 4.11 POSI = no freeway

Thanks for all the responses guys. I think I'm going to get a 3.54 or 3.73 ring a pinion set on Summit Racing. I'm not entirely sure which one to get. I know I have a 12 bolt, but I realize that it says "series 4" or "series 3" on the descriptions.

Does it matter which one I get?

I'm assuming since I have 4.11 right now, chances are I have a Series 4? I noticed the tallest gear for a series 4 is 3.73. Can I still get series 3 gears to lower the ratio even further? Any brand recommendations out there?

https://www.summitracing.com/parts/rmg-12bt342

https://www.summitracing.com/parts/rmg-4902801
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Old 06-23-2017, 05:07 PM   #34
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Re: 454 + TH400 + 4.11 POSI = no freeway

Here's my truck. I'm in love

https://youtu.be/3wJhvIPABwI
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Old 06-23-2017, 05:29 PM   #35
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Re: 454 + TH400 + 4.11 POSI = no freeway

Nice!

-klb
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Old 06-23-2017, 05:53 PM   #36
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Re: 454 + TH400 + 4.11 POSI = no freeway

You can get series3 gears if you get a series3 carrier. As mentioned before.
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Old 06-23-2017, 06:29 PM   #37
Hayden Buck
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Re: 454 + TH400 + 4.11 POSI = no freeway

I have a chevy 350 with a thr400 trans in it and run it at 7 with 100 percent octane and it seems to run great as long as I don't run less than 100 octane. It gets 16 mpg with the trans kit I have in it
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Old 06-23-2017, 06:41 PM   #38
Phorbes
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Re: 454 + TH400 + 4.11 POSI = no freeway

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Originally Posted by ElKotze View Post
You can get series3 gears if you get a series3 carrier. As mentioned before.
So the ring and pinion set would set me back a couple hundred, but to switch out the carrier it would be an additional $500-600.

Does that sound right?

I'm almost certain it's a series 4 right now so the tallest gears I could get with that series is 3.73 correct?
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Old 06-23-2017, 06:46 PM   #39
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So the ring and pinion set would set me back a couple hundred, but to switch out the carrier it would be an additional $500-600.

Does that sound right?

I'm almost certain it's a series 4 right now so the tallest gears I could get with that series is 3.73 correct?
I think that's right I would have to check tho.
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Old 06-23-2017, 11:08 PM   #40
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Re: 454 + TH400 + 4.11 POSI = no freeway

3:73 is the highest gears you can install in your 4 series carrier unless someone used a thick gear set in a 3 series posi carrier which is unlikely. If your going to change gears then get the 3:42 set, it's enough of a difference that you will be happy with the change, the 3:73 is not enough of a change...only about 10 percent
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Old 06-23-2017, 11:12 PM   #41
Hayden Buck
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Re: 454 + TH400 + 4.11 POSI = no freeway

Yes that's correct sorry it took me so long I had to fix my truck I have a race on July 1
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Old 06-23-2017, 11:12 PM   #42
Hayden Buck
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Re: 454 + TH400 + 4.11 POSI = no freeway

I have a 4.10 gear on mine so it has a thicker gear
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Old 06-23-2017, 11:30 PM   #43
Hayden Buck
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Re: 454 + TH400 + 4.11 POSI = no freeway

I have a 4.10 gear on mine so it has a thicker gear
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Old 06-24-2017, 12:23 AM   #44
Marine-58
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Re: 454 + TH400 + 4.11 POSI = no freeway

If you want to see your engine rpm with different gears, you can go to google and look up

Engine rpm calculator. There are a lot of them out there. Enter your trans ratio, rear end gearing and tire diameter. I have a th400 which is a final drive ratio of 1:1, rear end of 3.55 and tires 31 inches. That calculates to about 2700 rpm at 70mph. Exactly what the tach says. This may help you decide on the ratio you want.
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Old 06-24-2017, 12:26 AM   #45
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Re: 454 + TH400 + 4.11 POSI = no freeway

Ok
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Old 06-24-2017, 01:52 AM   #46
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Re: 454 + TH400 + 4.11 POSI = no freeway

I used to have the same problem. I have a '72 c10 that is currently running a 454ci powering 295/50r15's on the back end, and used to have a TH400 in it - the transmission bit the dust, so instead of rebuilding it, I got it swapped out for a 700R4 with overdrive, and man...that made a HUGE difference. I can now launch off the line faster because of the shorter gear ratios, AND I can cruise on the highway at a reasonable RPM!
Now I just need posi lol....ARB air-lockers, here we come XD
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Old 06-24-2017, 03:42 AM   #47
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Re: 454 + TH400 + 4.11 POSI = no freeway

The bigger issue I see is your sloppy shifting TH400. Find out if its an issue, or if you're just used to modern transmissions. Biggest mistakes I see on this board are people who replace and modify what they want to, and not what they need to, or what's more practical and efficient. It would suck to swap rear gears, then your transmission goes out and needs a rebuild. That money could get you really far into an overdrive where you'll benefit from a few added mpgs AND keep the low gearing if you wanted.
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Old 06-24-2017, 05:59 AM   #48
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Re: 454 + TH400 + 4.11 POSI = no freeway

I drive 60. Could go faster like I used to, but guess I'm used to O/D these days and now it feels hard on the truck. Perspective... back when no one had O/D it didn't bother anyone, and the speed limit was 70. In the '90s I remember buttoning up my '71 Custom Camper after doing the timing chain and no-lead head job, hoping in it, and driving at 75-80 down I-95 to Myrtle Beach, SC. I ran that truck another ten years (original 350) and now have the engine on a stand ready to drop in something else. O/D was out there yet automakers ignored it. Vehicles were built to drive on the 70 mph freeways in 67-72. They can run all day long and it doesn't hurt them. Then came the improvement of O/D, which lowers RPM at a given speed to reduce wear on engine and that is what we are used to. Unfortunately, the tense general public took to using O/D impulsively to drive faster and now earlier stuff seems too slow. They are wearing their engines the same as with no O/D. You also see these people driving across parking lots at 30-40 mph and passing on the double yellow line when following someone obeying the speed limit. Just happened yesterday. The front car was doing 40 in a 30 through this cluster of old houses along the road. Dumb and thoughtless.

Running 50-60 series rear tires doesn't help the situation either. If your trans is good, I'd go with a Gear Vendor set-up. I'm all over the place in my '72 K2500 w/4.10s and think how nice O/D would be. I get 70 mph out of my '95 Suburban with same gears/tires at same rpm my '72 is doing 60. The truck is all original in nice shape, it costs a lot to go O/D, and in the meantime I just enjoy it in the RH lane. I only drive the Suburban 70 when I'm in a hurry. It really likes 65 and I get 2-3 more MPG
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Last edited by special-K; 06-24-2017 at 06:21 AM.
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