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

[tRustyK5]

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.

Not that I am a huge fan of the 700-R4, but every K5 and every 1/2 ton 'burb that came factory with the 6.2 got a 700-R4 behind it stock (except for the M1009's). It should have no trouble behind a 6.2 at all, and the correct TC is obviously avaialble.

Generally the 3/4 tons and one tons got the TH400 and most commonly had 4.10's. Adding a 700-R4 could gain 5-6 mpg which is quite a bit...

Rene

 

[u2slow]

I'll comment only because I have a C20 Burb with 6.2L/TH400.

The engine sucking up your trans fluid doesn't make sense to me. The engine doesn't create vacuum - the vaccum pump does. Sure your modulator could be bad, but you'd have trans fluid juicing out somewhere or (very unlikely) leaking through the vacuum pump filling up your crankcase

I lose fluid on my TH400 also... but between you, me, and my stained driveway, I know where its going I need to rework the edge of the trans pan with a ball-pein hammer and install a new gasket - or get a cast aluminum pan.

The modulator controls your shift points to some extent. If it were bad I would think you have driveability issues... either very early or very late shifts. (You can adjust shift behaviour normally with a small screwdriver)

The TH400 is a big heavy slushy monster. It is a huge thorn in the side of the relatively low power output of the 6.2L. Its why we get that nifty 11-14mpg instead of the ~20ish figures.

I have considered a TH700 swap at great length. The major holdback for me (besides the up-front TH700 cost) is the tv cable garbage. As finicky as the adjustment of that thing is (and new trans warranty at risk) I would need to find the OE tv-cable linkage for the injection pump.

4.10 was okay for getting groceries, but downright brutal for highway. In light of now running 3.21 ratio (4.10 originally), 3.42/3.54 seems like it would be a better balance.

On a side note, 33" tires fit on the rear without any mods, and that counters the 4.10s somewhat.

 

[big_truxx]

I dunno yet what ratio I gots. I am going to change the rear oil tomorrow morning and I will be able to find out. Just need to locate some RTV (know its around the farm somewhere... ) and I will be able to make my own gasket for that.

As for the trans fluid... I was 1st assuming that it was leaking out the pan somewhere due to the fact the whole bottom of the pan (on the outside for all you wise guys ) is coverered with the infamous grime (mixture of trans fluid & dirt). So After I change the engine oil & filter, trans fluid, filter & pan gasket as well as the rear oil I will know a lot more

 

[u2slow]

While you have the pan off, dimple the bolt holes slightly with a ball pein hammer. (Hammering from the seal-surface side.) This makes for a more even pressure against the seal when you put the pan back on.

I didn't find out about this trick until AFTER I changed the filter & oil. Sure enough it still leaks

 

[big_truxx]

While you have the pan off, dimple the bolt holes slightly with a ball pein hammer. (Hammering from the seal-surface side.) This makes for a more even pressure against the seal when you put the pan back on.

I didn't find out about this trick until AFTER I changed the filter & oil. Sure enough it still leaks

that would work great as far as I can see. I will try that tonight (if I get my second wind for the day) or in the morning(most likely to occur)

thanks

 

[big_truxx]

well found out I have 3.73's in the rearend. Now to afford a full tank of gas to check MPG's... here it is $2.46/gal... when off road is $1.85 about 15 min away... not sure what on road is since I didn't see any advertised prices earlier. maybe I should ge some cans and go w/ off road once I find out my MPG

 

[u2slow]

Now to afford a full tank of diesel to check MPG's...

fixed it for you.

Put some taller meats on the back and call it done.

 

[big_truxx]

fixed it for you.

Put some taller meats on the back and call it done.

um.... how about; NO!!! It's doggy w/ 3.73's now. and I am running the stock size 235/85/16's which equal 32" diameter as it is now... sooooooo.... yeah, no

 

[UD0MEILLD0U]

Why is someone saying a 4L80E? If he has a th400 then he wont have the proper electrical hookups for the E part of the 4L80E. 4 is the number of forward gears, L is for longituly (?) mounted meaning a rear wheel drive and 80 being the strength. The E portion means electronic! If your running a THM400 than you WILL NOT have the necessary computer hookups to run a 4L80E! The 700R4 will work but a mount at the throttle body/carb will be required for the T.V. cable. This cable controls Numerous functions including shift firmness as well as kickdown abilities and many others. You will also hafta figure out a way to get the torque converter lockup working (another electrical hookup) this is what locks ur torque converter in when in O/D. The THM400 got its name from its strength capable of handling 461 foot pounds of torque to the input shaft. The 350 is concidered the MEDIUM duty tranny of the THM's the 400 being the heavy duty! Keep the 400! A good rebuild (if necessary) and that tranny will outlast the vehicle (with propper services).