Author Topic: tranny swap/ convertion  (Read 3089 times)

Offline 75??? franken-trunk

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tranny swap/ convertion
« on: October 12, 2007, 02:01:25 AM »
i was wondering if any one had info on a tranny swap from a 700r4 to a th350 or th400, due to the title having it say 75 when its not i have a 81-86 k10 short box with a 350 and as of now a 700r4. and for the mudding and lots of driving its a turd!!! the truck was parted together so i have a manual column and a Hurst shifter on the floor not for sure but i think i have a NP205 transfer case. so any info on driveshaft length and whats not please let me know  ;)         thax.........
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Offline Captkaos

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Re: tranny swap/ convertion
« Reply #1 on: October 12, 2007, 09:53:34 AM »
Changing the transmision from 700 to TH350/400 is going in the wrong direction in my opinion especially if you are doing a lot of driving.  I wouldn't blame the poor driving on the trans.  What is wrong with it?  Which one are you going with, the Th350 or Th400?

Offline Blazin

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Re: tranny swap/ convertion
« Reply #2 on: October 13, 2007, 08:45:04 AM »
I agree the turd thing could be gears, worn cam, carb issues, need a tune up, or a combo of these.
Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs

Offline 75??? franken-trunk

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Re: tranny swap/ convertion
« Reply #3 on: October 14, 2007, 12:54:56 AM »
well i agree with the save some gas part of a 700 but mine is on its last leg and i like to go mudding and whats not, oh and i had a 75 with a th350 and a 350 motor on its last leg and it would whale on this one i got now its all about the shift points and the 350 and 400 trannies can handle more power, i have a 383 stroker as of now with about 5000 miles on it and with 35" tires and a 4" lift in the mail... so how would i put ether one of those in would a th350 handle it, if so they are cheaper?
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Offline werewolfx13

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Re: tranny swap/ convertion
« Reply #4 on: October 14, 2007, 02:03:06 AM »
rebuild the 700r4..for like an extra $300 you can make it atleast as strong as a 350, if not stronger..should be good to ~450hp, plus you get a lower first gear for easier takeoffs, plus OD. a th350 is a good trans, and can be built to handle 450 hp as well, but unless you plan on sporting a wild 500+ hp motor, you really won't need the extra strength of a 400..
Chris
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'76 Chevy k20 LWB 6.5'x8' Flatbed
I know that you believe you understand what you think I said, but I'm not sure you realize that what you heard is not what I meant.

Offline Blazin

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Re: tranny swap/ convertion
« Reply #5 on: October 14, 2007, 08:08:59 AM »
For the money you would spend on getting the different trans to t case adapter, the shortening and lengthening of drive shafts. cross member mods etc. You would be ahead rebuilding the 700 R4. As stated before they can be built to be much more durable than the 3 speed autos. The output shaft on the 700 R4 might be a different size than a TH 350 or 400. Not sure but for some reason I am thinking there is a difference there. One is like 28 spline and the other 32 spline maybe? If this is the case you will need to change the input shaft on you t case, or get a t case to fit. Its not as simple as getting an adapter, and bolting it in. I would do some research before you just start ripping into it.
Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs

Offline 1976Scottsdale

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Re: tranny swap/ convertion
« Reply #6 on: October 14, 2007, 08:03:41 PM »
What are you building, a mud truck, a driver, or a weekend cruiser?  If you are not going to drive it a whole lot, then put in the th350 witha decent transfer case.  I will catch a lot of crap for this, but my 76 K20 is by far the best one I have had.  I installed a 305 H.O. that I built in my garage for like $350.00 and a rebuilt TH400 and NP203 case with rebuilt 3.73 gears and that thing runs great, lots of power, and gives me about 13-16 miles/gallon depending on how I drive.  BTW, it is full time 4x4... you would not believe how hard it was to find a set of those drive flanges for one of these trucks, let alone the dust caps.  I ended up removing a set from a Wagoneer(they fit in like a glove).  Get the TH400, beat it up, bang it up, it just won't die... but it does eat like 25 more horses that the TH350 or 700-R4.

Offline VileZambonie

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Re: tranny swap/ convertion
« Reply #7 on: October 14, 2007, 08:18:10 PM »
Rebuild your 700R4 and get yourself a good set of final drive gears
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Offline Blazin

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Re: tranny swap/ convertion
« Reply #8 on: October 14, 2007, 09:24:14 PM »
I have nothing against the TH 350 or 400. My 55 has a TH 400 in it. It still works but its getting slow between 2nd and 3rd. I will be replacing it with a 700 R4 if I stay with an auto, or a Borg Warner T10. I have a low milage T10 and a brand new rebuilt 700 with less than 300 miles on it. So it s toss up. My Blazer has a Built TH 350 in it, came out of a C10 with a HO 305, went into my 74 Malibu with a mild 454, came out of that, cut an inch or so off the output shaft and in my Blazer it went. Have done allot of wheelin and it still shifts hard and firm. I have a buddy that builds auto transmissions, they are all good if they are built right.
Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs

Offline 75??? franken-trunk

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Re: tranny swap/ convertion
« Reply #9 on: October 15, 2007, 06:14:10 AM »
What are you building, a mud truck, a driver, or a weekend cruiser?  If you are not going to drive it a whole lot, then put in the th350 witha decent transfer case.  I will catch a lot of crap for this, but my 76 K20 is by far the best one I have had.  I installed a 305 H.O. that I built in my garage for like $350.00 and a rebuilt TH400 and NP203 case with rebuilt 3.73 gears and that thing runs great, lots of power, and gives me about 13-16 miles/gallon depending on how I drive.  BTW, it is full time 4x4... you would not believe how hard it was to find a set of those drive flanges for one of these trucks, let alone the dust caps.  I ended up removing a set from a Wagoneer(they fit in like a glove).  Get the TH400, beat it up, bang it up, it just won't die... but it does eat like 25 more horses that the TH350 or 700-R4.
What are you building, a mud truck, a driver, or a weekend cruiser?  If you are not going to drive it a whole lot, then put in the th350 witha decent transfer case.  I will catch a lot of crap for this, but my 76 K20 is by far the best one I have had.  I installed a 305 H.O. that I built in my garage for like $350.00 and a rebuilt TH400 and NP203 case with rebuilt 3.73 gears and that thing runs great, lots of power, and gives me about 13-16 miles/gallon depending on how I drive.  BTW, it is full time 4x4... you would not believe how hard it was to find a set of those drive flanges for one of these trucks, let alone the dust caps.  I ended up removing a set from a Wagoneer(they fit in like a glove).  Get the TH400, beat it up, bang it up, it just won't die... but it does eat like 25 more horses that the TH350 or 700-R4.


im building a daily driver that i use for work to deliver pizzas on weekends i like to go beat on her a little on the trails and mud pits and i plan on a 4" lift and 35"s so strong and reliable is what i want if a 700r4 can handle all that driveing and calm relaxing 4x4ing without the heat getting it and then it takes a dump i'll build mine but if i fork out the money and it take a dump anyways thats a problem... so what should i g0 for
« Last Edit: October 15, 2007, 10:35:26 AM by Captkaos »
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Offline Blazin

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Re: tranny swap/ convertion
« Reply #10 on: October 15, 2007, 06:46:51 AM »
Your truck, we can't make the decision for you. I think you have allot of good input here to make an educated choice. Either way you will be forking out money. rebuild your 700, or rebuild a TH 350 or 400, they both cost about the same to rebuild. Plus spend money on other parts to make it fit in your truck. You mention heat, a 26,000 GVW cooler is only about $40 to $50. It goes in line with your stock cooler, not stand alone. A deeper pane more fluid will help too. Install a trans temp gage so you can keep an eye on it. It doesn't matter which trans you have. if you wail it to the point of getting it to hot its going to wreck it.
 A rebuild kit is between $150 and $200, a torque converter is around a $100, cooler about $50, deeper pan around $30 to $50, a good shift improver fluid flow kit about $100 maybe a bit less. you might spend $100 or more on misc. stuff too. Get in good with someone that can rebuild them might do it for short money and 6 months worth of Fri. night pizzas? Only draw back there is probably no warranty!
Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs

Offline Captkaos

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Re: tranny swap/ convertion
« Reply #11 on: October 15, 2007, 10:38:29 AM »
If you search around the majority of offroaders are swapping TO the 700 not the other way around.  If you are going to be driving it daily, keep it in Drive for a day, that is what it would be like if had a 3 speed.  Gas mileage is going to suffer.

Offline Blazin

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Re: tranny swap/ convertion
« Reply #12 on: October 15, 2007, 02:43:04 PM »
I agree don't use overdrive unless your on the highway at or above 50 MPH for extended period.
Some people are like Slinkies. Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs