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Transmission Swap

bullit70

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bullit70 Enthusiast

bullit70

Posted
Posted

Hello again, I have a question on what is needed to do a trany swap. The K2500 has the th400 3 speed witch is a good transmission but i want an over drive. I have been able to find TH700-R4s all over the place for cheep and a good rebuild kit is also cheep and the np241c bolts up to them with an adapter but even then it is doable. What do I need to and how hard is it to do the swap? Also the steering collum is set up for the 3 speed would i have to change this as well?

 

thanks guys.

davzog Enthusiast

davzog

Posted
Posted

I think that this is probably a bigger deal that it might initially appear to be....a guy in our car clud converted his 79 Vette from a TH350 to a 700R4 a couple of years ago and had lots of issues. As I recall, almost nothing lines up, brackets had to be fabricated and he had to have a custom made drive shaft.....or had is shortened...I forget.

 

I also suspect that the shift linkage will be all different, regardless of the display ont he dash.....the attachment to the tranny will not work from the TH to the 700R4, I don't think....don't remember exactly.

 

Anyway, his Vette was and still is a daily driver...he did the swap to save gas with the overdrive.....last he said, it will take about 300,000 miles in gas savings (which were not all that much anyway) to pay for the swap....ugh!!

 

ANyway, maybe the swap on a truck is a bunch eaasier....let's hope so....good luck!!

bullit70 Enthusiast

bullit70

Posted
  • Author
Posted
I think that this is probably a bigger deal that it might initially appear to be....a guy in our car clud converted his 79 Vette from a TH350 to a 700R4 a couple of years ago and had lots of issues. As I recall, almost nothing lines up, brackets had to be fabricated and he had to have a custom made drive shaft.....or had is shortened...I forget.

 

I also suspect that the shift linkage will be all different, regardless of the display ont he dash.....the attachment to the tranny will not work from the TH to the 700R4, I don't think....don't remember exactly.

 

Anyway, his Vette was and still is a daily driver...he did the swap to save gas with the overdrive.....last he said, it will take about 300,000 miles in gas savings (which were not all that much anyway) to pay for the swap....ugh!!

 

ANyway, maybe the swap on a truck is a bunch eaasier....let's hope so....good luck!!

 

Well with that said would the swap be worth the MPG increase or should i just live with the 3 speed? also what do you think the MPG is right now? i have been lookingfor the specs but so far i have not been able to find it. it is just the 350 TBI with a TH400 3 speed 4x4 i am thinking it is going to be about 10 MPG but i don't know if that is going to be the on the highway or the city. thanks again.

davzog Enthusiast

davzog

Posted
Posted

There are no EPA mileage specs for 3/4 ton or bigger trucks....they are all considered work vehicles are do not fall under the same laws as 1/2 ton trucks or cars....

 

If you are getting 10 mpg now the tranny swap would not get you much more than 12 mpg or so....my son's 8.1 get 9-10 with the Allison and I get 12-13 with a 4 speed overdrive....

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