73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: hondarider188 on July 02, 2014, 02:46:16 pm
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i know that's this has been asked a lot about, but i have had a hard time finding the answers that i need and have become confused on some things. lets start out by first saying that my truck is a 1983 k10 that originally came with a 305 engine and 700r4 combo also 3.73 gears, but about 4-5 years ago the last owner swapped in a 350 engine and a th350 trans when the 700r4 burned out. and that is still whats currently in the truck. The first issue that i have is whether the 700r4 is what i want. where i live in utah i am surrounded by high mountain ranges that i drive constantly with grades that are typically 8-10%. with the th350 it does ok but is constantly jumping between 2-3 gear and makes it hard going up the mountains, and then when i'm on the highway the rpms at 65 are around 3,000. i think that with the 700r4 and the extra gear with OD will really help alot with staying in a gear up the mountain and lower rpms on highway. can someone agree with this or am i wrong in my thinking.
the next thing is i have found a couple of transmission around here one is an 1988 for $100 or a 1991 for $250. would the 1991 be worth the extra money or is it all the same. the next issue that i run into is mounting the 208 transfer case to the 700r4, will it bolt right in or do i need an adapter plate. also i read that the shaft on the th350 is 27 spline and the 700r4 is 30 spline but im not sure what shaft that is or what to do about it. last is the drive shaft, so what i need to know here is how do i know the one i have now will work? Thanks in advance
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I'm replying to this old thread after finding it through the search function as is often "recommended" but found out there were no replys. I hate that because my circumstances are literally the exact same as the OP. He seemed to ask all the big questions and I hoped all the answers could be found in one place. Can someone with experience in this swap chime in or possibly provide a resource that has all the info in one place or document?
I need clairity on the tranny length and spline subjects as well as the TV cable/carb bracket mods. My 85 k10 is long wheel base and originally had the 305/700r4/NP208 set up but now have a crate 350/TH350/NP208. I'm assuming relocation of the tranny crossmember is no issue since I should have the original holes from the factory set up. I'll probably order a rebuilt 700r4 from a reputable builder and want to order it with the right configuration to bolt up to the transfer case. Again, even a link to a one stop shop of the job would be great if no one wants to do all the typing.
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The 700R4 will be a direct swap. You will need the crossmember or to move your existing crossmember. You will need the appropriate driveshafts. The TV cable and bracket. All of these items can be sourced from a donor, junk yard craigslist etc or of course aftermarket has an array of options for you. If someone changed the shift indicator you will probably want the correct one in there as well.
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Thanks for chiming in. When you say it's a direct fit, is that housing length and spline count? Seems like I've read that the main case of the 700r4 being longer than the TH350?
So I only need to relocate the tranny cross member and the 700 will bolt right up to the NP208 in its present location?
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Made it through 50 threads in searching and and the majority of discussions are in 2wd applications. Trying to determine if the whole topic of driveshaft length modifications is a moot point in a 4wd application due to hooking up to the NP208 transfer case. Are there still any fitting issues between the motor and transfer case besides the cross member if going from TH350 to 700r4?
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the 700r4 is a 27 output shaft and so is the th350. you can swap the transfer case and adapters between them no problem. as long as the output shaft is the same length.
the 700 is about 1¾" longer than the th350 so all you will be doing is pushing the tcase back 1¾" this shouldnt be a issue with the front shaft and the rear shaft but it might be more of an issue for the rear shaft
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Ok. I've got 5.5" rear blocks so the drive shaft was pulled out a little. This may just place it back closer to its original position.
Do the transmission cooling lines bolt right up between both transmissions? Isn't there also an issue bolting up the speedo cable?
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the front shaft might be too short then. cant help with the cooling lines but make sure you flush the cooler. the speedo should be in the t case since youre reusing the 208 it shouldnt be a problem
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Thanks a lot. I appreciate the info