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Just how difficult is it to swap a th700 in place of a th400 in a burb?

Discussion in 'The Garage' started by big_truxx, Jun 7, 2005.

  1. big_truxx

    big_truxx 1/2 ton status

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    I think I had started to find out about this before but cannot recall. I was thinking I was told that I would have to either move the tranny mount or get the one from the th700 or something... :dunno: Also would need the driveshaft from the 700 burb. :dunno: any input would be much apreciated. I am starting to consider doing this sooner than I had anticipated since my th400 may be eating my tranny fluid :yikes:
     
  2. seschev3

    seschev3 1/2 ton status

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    Lets see. Crossmember, driveshafts, possible t-case adapter,dash shifter selector, and carb linkage. That is off the top of my head. Keep the donor vehicle close by, because there is always something that you miss or break during the swap. I took a 700r4 and 208 and swapped it into my 75' 3 years ago.
     
  3. Hossbaby50

    Hossbaby50 3/4 ton status

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    If you swap from a 700r4/208 to a 400/208 you won't need new driveshafts and you may not need the new tranny crossmember. That would be the easiest swap. You would need to swap the input gears on your 208 if you didn't get the 700R4 208 also. That is pretty easy though.

    Honestly I would not even think of swapping in a 700R4 especially to replace a Th400. The TH400 is a way stronger tranny. You don't have overdrive but that isn't the end of the world if your tranny will last alot longer and cost 1/2 as much to get rebuilt.

    A 700R4 will not last as long as a TH400 and will cost you twice as much to rebuild. It will not take the abuse that a TH400 will either.

    I have a TH400 sitting in my garage now just waiting on my 700R4 to die again. I don't know when it will die again but I know it will so I have a backup plan already in place for it.

    Harley
     
  4. big_truxx

    big_truxx 1/2 ton status

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    I appologize if I did not explain myself clearly which I do form time to time. I have an 89 burb 3/4 2wd and it has a 6.2/th400 combo. no xfer as it is a 2wd. And this is a family/errand/maybe trip type vehicle. not to be beat or offroaded or drag racing. :haha: That'd be amusing seeing a diesel burb try to drag race. :haha: so I am just looking to swap in a th700 for a better 1st gear and OD perhaps. I have no idea what I have for rear gears at this point cuz I haven't had the time to change the rear oil yet and see. It kinda drives like I got 3.08's though as it doesn't have a lot of acceleration. :dunno:
     
  5. mountain4x4

    mountain4x4 Registered Member

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    A stock 700 is an iffy proposition behind a diesel, and a good rebuild is expensive, but if you have the $, they are great trannys, lots of upgrades available. A 4l80e would be more reliable for your application, but even more $. I'm not sure youre going to get the shift points right with either of these trannys, though. It would suck to spend lots of $, and have the shift points not work out for a diesel application. A NV4500 would be ideal for your diesel, in all respects.
     
  6. big_truxx

    big_truxx 1/2 ton status

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    so for a 2wd swap I would need the th 700 xmember? Also I do not have a donor vehicle really. And I do at the same time. Ifwhen I can get around to doing this I will be most likely having parts shipped from someone who is parting a rig similar to mine w/ a 91 th700. And I do not have carb linkage so would both the 400 and 700 use the same setup on the 6.2? and just the shift selector for the dash? Nothing else in the shifting mechanism is needed right? My selector is currently stuck on 1 anyway :haha:
     
  7. big_truxx

    big_truxx 1/2 ton status

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    I do apreciate opinions. When was the 4l80 the actual designation replacing the 700? I thought it was in 88 when the body style of pickups changed. I would be looking at putting in a 91 4 spd auto OD whatever that designation is from a burb similar to mine. and also not beating it just driving on street. currently i seem not to accell rapidly but I have to see what I have for gears. I am putting trans fluid into my 400 but when I am right on to it it shifts real firm into 2nd so I do not seem to think the tranny is dying... But I know nothing about trannies.
     
  8. mountain4x4

    mountain4x4 Registered Member

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    You need to do more research into whether a OD Auto will work correctly with the 6.2. It may not. The 4l80e is more like a 400 w/OD. Really, the NV4500 is a better tranny for a diesel, installing a clutch is no big deal, and they shift real nice...
     
  9. google

    google 1/2 ton status

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    Does that hold true for a TH350 also???
     
  10. fatbob

    fatbob 1/2 ton status

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    eating my tranny fluid

    If your only problem with the th400 is that its eating tranny fluid, then check the vacuum line going to the modulator. If its wet inside, then the diaphram is ruptured and tranny fluid is being sucked into the engine and burned. It's a common problem and fairly cheap to replace the modulator. :grin:
     
  11. gambit420s

    gambit420s 1/2 ton status

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    700R4=4L60 mechanically controlled about the same as TH350 strengthwise (84-92?) avoid stock trannys before about 86-87 when they were upgraded
    4L60E electronically controlled needs computer (88->?)
    4L80E electronically controlled about the same as a THM400 strengthwise (90->?)

    i believe a 91 6.2 sub would have 4L80E w/ the stand alone computer, if not several companys sell computers, if it is a 700R4/4L60 you will prob need the throttle bracket and the detent cable(shift cable that runs from the throttle plate to the passenger side of the tranny)

    sorry dont own a diesel, maybe try the diesel forum?
     
  12. diesel4me

    diesel4me 1 ton status Premium Member

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    no upgrade here.....

    I'd fix the TH400 !!...dont swap the best GM tranny for the weakest one with a poor reputaion for durability just to gain 3 mpg!...the 700R4 for a diesel has a different stall speed converter and govenor than a gas tranny...and I bet they die much faster behind a diesel than a gas engine--.they dont like a lot of torque in stock form...most 6.2 trucks I see in the junkyards are there due to a blown 700R4 tranny,and the owners balked at fixing the truck after getting an estimate.. :frown1:

    In my estimation swapping a 700R4 in place of a TH400 would be like having a date with Jennifer Anniston,and breaking it so you could go out with Rosie O'Donnell instead... :screwy: :1zhelp: :eek: :tongue1: ..

    .Check the modulator as suggested!!--they are cheap,about 15 bucks-the only leak that would cause me to ditch my TH400 would be a cracked case!..other than that I'd never trade it for an overdrive tranny...you will gain nothing except a backache from all the work,and a headache when the 700R4 and everything else you had to swap in to make it fit starts acting up... :crazy:
     
  13. big_truxx

    big_truxx 1/2 ton status

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    where is the modulator and what does it look like?
     
  14. fatbob

    fatbob 1/2 ton status

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    Look for a vacuum line comming from the intake down to the right side of the tranny. It's usually a metal line with a short peice of rubber hose at each end.
    One end connects to a tee or elbow on the back of the intake, and the other end connects to the modulator at the back of the tranny. I think its on the passenger side under the lines that go to the tranny cooler. :thumb:
     
  15. seschev3

    seschev3 1/2 ton status

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    Not sure on a 2wd as far as the x-member, but it will need to be moved back because the 700r4 is longer. Also forgot about the torque converter. Diesel has a different stall speed and may be different between the 400 and 700. The linkage setup for the tv cable is normally specific for 700's and very important to set the tv cable correctly. Having the 400 rebuilt or fixed may be a better option. I have to pull my 700 this weekend for the 4th time for some fixes. I have $2500 into it to make it bulletproof and still having issues with only 13000 miles on it. This time it is the front seal that needs to be replaced. Last time I blew up a double lined torque converter and sent bits of kevlar through the tranny. I never had issues like this in my 78 with a th400.
     
  16. big_truxx

    big_truxx 1/2 ton status

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    so basically what everyone is trying to tell me is even for just a grocery getter that doesn't get beat on I still need the th400 as far as reliablity is concerned? :doah: And I had sourced an auto OD from a 91 diesel burb too :( but if what everyone says is true I will end up w/ a costly rebuild no matter what style of driving I have... :dunno:
     
  17. big_truxx

    big_truxx 1/2 ton status

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    I did try to check the modulator.... dunno if it is wet inside or not... kinda all oily ya know what I'm talking about when one has an oil leak for a while and all the dirt coagulates with the oil and forms nice oily gunk. :haha: that stuff is all over the bottom of the tranny. I am thinking perhaps need to replace the screen inside the th400 (or whatever that things is or is called as I know next to nothing about trannies) and put all new fluid in it and have a brandy new pan gasket w/ a healthy amount of RTV to seal it real good anbd check for leaks then. Of course I should get some brake cleaner 1st just before taking it all apart and blast all the grime away so I can tell better if there is a leak or not :waytogo: :D
     
  18. diesel4me

    diesel4me 1 ton status Premium Member

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    heres how..

    Best way to check the modulator is to remove it(one bolt and a fork looking clip hold it in--just like a distributor!)..tip the vacuum hose side down--if ATF drips out onto the ground(or your shoes)--its junk!..--Or put a peice of twine or string in the vacuum hose spout and into the "can" and see if it comes out with pink tranny fluid on it,if you'd rather not remove it--(removing it is a better test--you might not see ATF on the twine,but it still might be in there!
    .you could test it with a vacuum pump,and see how long it holds vacuum,but the pump costs more than 2 modulators....

    I'd just drop the pan,put in a new filter after blasting it all clean with brakecleaner and an air hose,and put in fresh ATF and a new modulator--it will cost about 40 bucks for everything..but I'd skip the RTV on a tranny pan gasket--it usually gets in the tranny and can wreak havok!...I usually put them on dry--WIX filters kits have the best gaskets with the smaller bolt holes,so they "hold" themselves in place by screwing a few pan bolts in it....

    I had a TH400 in my 69 GTO years ago--I beat that tranny bad!..I did more burnouts in 1 day than most guys did in a year--I rocked from drive to reverse when I got stuck in snow covered feild for nearly an hour,until it whined like a power steering pump does when its empty!---the next day I changed the fluid--it looked like maxwell house coffee grounds from a percolator!( the pan was FULL!)--I expected the tranny to croak shortly thereafter--but it not only didn't sound like a siren anymore,I drove that car 50,000 more miles and the friend I sold it too had it 2 years with no tranny woes!...THAT TH400 sold me!--now they are the only automatic I'd rather have if possible....had decent luck with TH350's too,but they are a bit weaker..

    Its too much cost and work to change the whole drivetrain just to install a 700R4 tranny--that money would have rebuilt your TH400,maybe twice!--AND paid for all the gas it will "waste" not being an overdrive...I'd keep it! :crazy:
     
  19. big_truxx

    big_truxx 1/2 ton status

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    that's cool for sure. But I will not even be attempting any burnouts w/ my burb :haha: Just grocery getting or the equivilent driving. Nothing hard. I have an 85 shorty 2wd that some day will be my hotrod :D This weekend I will try to scrape up the $$ to replace trans filter & fluid & gasket along with the engine oil & filter.
     
  20. Pookster

    Pookster 1/2 ton status

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    I personally like the 700r4's as a light duty tranny, especially if you do a lot of highway miles. If your 400 is fine, keep the 400. The only real difference is that you really have to limit your highway crusing speed unless your engine is screaming away. Most owners have replaced/upgraded the tranny anyways, my subs previous owners was miticulous about receipts. (heck, he even had the original brochure and manual).
     

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