700r4 swap - core and rebuilt or "new"?

[iacucv]

Ok so here's a topic on the 700r4 conversion I haven't seen and am currently arguing with myself about. If a guy doesn't already have a core, would it be better for a guy to find a junker trans and take it to a trans shop to have rebuilt, or order a new/rebuilt trans from many of the online suppliers?

If the online supplier route has any supporters, can anyone recommend a place that is knowledgable with hooking up to our 6.2 and can anticipate the turbo upgrade? Also could they use the output shaft that will make it a direct hook up to my np208?

I intend to do this swap in the next 6 months and know ill need the tv bracket etc but am undecided if I should get a core and have it rebuilt or go to a place I see that has them rated for 450tq 450hp for around 1k shipped and just round up a bracket. Opinions?

 

[Speddmon]

My own personal opinion...

Until you pay the extra money to have a "new" one refitted with a diesel governor and shift kit, you'll be money ahead to get a cheap core from CL or a junk yard and find a reputable shop to build it right. My core and rebuild cost about $900 total.

As to the output shaft, I understand you can get a 32 spline output shaft for the r4, but I also understand it is in the neighborhood of 5 bills for it. It is way cheaper to find a used civi np208 and pull the shaft from it.

 

[jw4x4]

Even with a turbo upgrade, I doubt the 6.2 could hurt the 700R4, provided it is kept cool. Excessive heat will cook any transmission.

 

[Recovry4x4]

Check with both on warranty too. The internet tranny folk may have a great warranty after you ship your tranny back if there are problems.

 

[iacucv]

Good points made here. Guess ill dig up a core and start making some calls. Thanks all.

 

[wayne pick]

Beleve me when I tell you, an on the cheap 700R4 swap is really not the way to go, and a stock rebuilt 700 will not last very long in these trucks. Although the 700 was in production in 1986, GM used the TH400 in 3/4 and 1 ton trucks for a reason. I spent nearly $1800.00 on an old core 700 that was swapped in by the previous owner, had it rebuilt and it lasted less than a year.

You will need an 89 or newer 4X4 core for a rebuild candidate. To do it right, just about all the internal components except the shafts will have to be upgraded. A $1000.00 700 swap will leave you dissapointed, beleve me. As far as adapting a 700 to your NP208 transfer case, it is far cheaper and easier to get a TH350 to NP208 adapter and a 27 spline 208 case, preferably out of a family truckster Suburban as they are rarely thrashed off road.

Recerch the 700R4 and it's problems. Here is a website that may be helpfull for rebuilding info.http://www.berrysweb.com/700-R4-Rebuild.htm Good luck.

 

[MarcusOReallyus]

The 700 rebuild info is at http://www.berrysweb.com/700-R4-Rebuild.htm

 

[iacucv]

Wayne, everyone else seems to rave about their 700r4 swap. Of course I intend to have it built up. The 1k trans I was looking at was rated for 450hp 450ft lb of torque, which would be well above even a turbo 6.2. I will look for the later K case core and let the trans shop I select know what the application will be and the numbers the engine will put out. I will have it built for the future turbo I plan to add. I have no problem swapping out the t case input shaft. Has to be much easier than swapping output shafts on jeep t cases. Dang AWD viscous coupler crap never lasts... Did you have your 700r built for the task, was it abused, did you use a trans cooler? Just wondering why you think yours failed so I can avoid the problem. Thanks.

 

[wayne pick]

The 700 rebuild info is at http://www.berrysweb.com/700-R4-Rebuild.htm

Thanks Marcus, I screwed up by not typing out the entire address. Good looking out brother.

 

[wayne pick]

Hea iacucv, The 700 I had rebuilt was old, an 82, and may not have been worthy of a rebuild in the first place, but the tranny guy that had been referred to me did it anyway. It was rebuilt with high end quality parts. A shift kit and a throttle valve upgrade kit was also installed, along with a master rebuild kit.

The old 700s had throttle valve sticking problems, and would not shift out of first gear due to clutch debris jamming the valve. The original sunshell was retained- mistake. the old 700 sunshells had poor welds on the hub and were prone to failure. The front and rear planitary gears, another weak point due to poor lubrication to the rear set, were not replaced-mistake.

Retained the original servo-mistake. A Corvette type servo will stiffen up the 2-3 shift and eliminate slipping. The original 7 vane pump was also retained. An upgrade to a 10 vane pump helps keep the converter filled when in OD at highway speeds. The trans wiring harness was replaced along with all the valve body switches. A non factor as the trans blew up anyway.


I am not a transmission guy by any strech, I have gotten the above information through searching hundreds of pages regarding the 700s problems. I do know however, the importance of upgrading this transmission to make it reliable through my unpleasant experience. As far as your question about cooling, I run a Derale 16 pass fan driven cooler and an external spin on filter. I do not know why my trans blew up, I have not had the time to dissesemble it. I know something big let go. I think it was the rear planitary. There was trans oil pumping out of the trans and into transfer case.


I finally bit the bullet and got a Monster trans super duty 700R4. When i ordered it, they asked specific questions about HP, torque rating, and if it is turbocharged. If you have an 89-92 core, most if not all the hard parts I mentioned above that are prone to failure have been upgraded already, so a good heavy duty rebuild will do you well. Good luck.

 

[Speddmon]

Wayne,

I'm not saying that it was the issue with your trans that blew up, but is the pic in your avatar the truck at question? If so, pushing a plow around with a 700R4, not quite build heavy enough, and also in a 1 ton truck probably had something to do with the lack of longevity.

 

[wayne pick]

Thats the truck. I've had that truck as my avatar since I joined SS, I change the photo every once and a while. You have probably seen it with and without the plow rig on it as I take the rig off it in spring. I found it odd that you stated that the truck being a 1 ton may have been a factor in it's failure. 95% of the 700R4 threads-swaps here are in regards to the 1 tons. Your M1028 that you swapped a 700R4 in is a 1 ton correct? I did push snow with the rebuilt trans that failed.

The three or four times it snowed here were light powdery storms of 6in or less, so I doubt that was a factor. The truck handles the 7-1/2' fisher plow like it's not even there. As you can see in my avatar, the SECM body was replaced with a flat bed, so the truck has lost approx 900 lbs. I do not load the truck with any weight when plowing, it doesn't need it. I bought this truck with the 700 trans already installed. I did not do the swap, and it was pretty much toast when I got it. I babied this truck since the first day I got it so it was never abused and other than the trans issue, it is in almost prestine condition.

The TC lock up controller was disconnected, and it had the wrong TV cable-too long, was installed by whomever. From what I understand, it was driven like this pryor to me owning it for an extended period of time. There are do's and don'ts when it comes to these transmissions, those are two don'ts.

It is common knowledge that just rebuilding or throwing a shift kit in an early 700 is pointless. Mine was an 82, the first year of production. I had my new Monster trans built for my aplication, so I don't expect to have any future problems. As I stated above, I am no expert. I did do extensive research on the 700 though. True, there are members here that "rave" about their 700 swaps. Only time will tell how great the swap turned out.

 

[Speddmon]

I mentioned the truck being a 1 ton, because to the best of my knowledge, GM never intended this transmission to be in a vehicle that heavy duty. I do realize that they were installed in some full size suburbans with the 6.2 but even at that I'm willing to bet there is still a significant weight difference betwen the burbs and the trucks. I may be wrong but I think Kenny (Recovry4x4) said one time he had a diesel burb with an r4 that tipped the scales at around 5200 or 5400 or somewhere in that neighborhood. I used to have a '95 Ram 2500 4x4 gasser that weighed 5400#, and it was no where nearly as heavy as my 1028/1031 is.

And I'm also sure you never abused the truck, but a plow on a pick-up wreaks havoc on the drive-trane even if used moderatly and properly.

I'm only speculating but I agree with you about the poorly done rebuild, and if the wrong tv cable was on the truck and it wasn't shifting properly. Combined with the weight issues and plow, all of those factors combined were probably the death of your last transmission. With the rebuild you did and the upgrades to the cooling you made, I'm sure you will get much better results from this one.

 

[wayne pick]

Hea speddmon, Thanks for the feedback. Your right, the 700R4 was never ment to be in any 3/4 or 1 ton trucks. Thats why I stress the importance of really building these trans for the task at hand. I've heard guy's on other sites say their 700s will withstand 450+HP, mabey so in a 3400# Corvette, not in a 7000# M1031. Weight is more the issue than horse power and torque.

www.thedieselpageforum.com/tdpforum of which I am also a member, states that the harmonics of the 6.2 engine takes it's toll on the 700R4, and that far higher HP small and big block engines have less of an effect on them. I found that pretty interesting when I first read it. There are also many threads regarding the building of these transmissions in that forum.

The 700R4 swap itself is easy. I think croatiankidd had one of the few in depth build threads here at SS for the internal hard parts needed for a pretty much bullet proof 700R4. BTW, after installing my new trans, I found a new never used HD 4x4 TH400 on flea bay. One of nine that has been in a Brooklyn NY warehouse for thirty years for $450.00. If this 700 fails, it's back to stock and 55 MPH for me and my 1031.

 

[Recovry4x4]

My burb tips the scales at 6200#. Just because of weight I have to run a heavy truck tag. It started life as a half ton but the axles were upgraded to 3/4 ton just to get the 4.10 gears. It does have a factory installed 6.2 and 700R4. I have put an additional 100,000 miles on it since I've had it and it had 154,00 when I got it. I don't know if it ever had tranny problems before but it hasn't for the last 100,000. I often mention the fact that the 6.2 doesn't have the power to hurt a 700R4. Many bring up the weight of the vehicle and the fact that it's a 1 ton truck. There have been millions of these 700R4 put in full size trucks with the higher HP 350 and subsequent 3.42 gears. This makes me also consider that the 4.56 gears give the 700R4 a little easier time with things vs a 5000# truck trying to get underway pushing 3.42 gears. The 4.10 gears helped quite a bit with my burb. Others mileage may vary but my experience with all of the 6.2 700 trucks I've owned was very positive.

Oh, the burb has seen its fair share of towing as well. I try not to exceed 4000# but I have towed 6000# with it.

 

[Speddmon]

Kenny, thanks for the correction, I was off by a few pounds!

I agree with you fully, the gearing of these trucks will definitely make it easier on the transmission. The guy that rebuild mine only gave me two pieces of advice when I told him what it was going into...make sure the TV cable is adjusted properly from the get-go. One time of getting any run-up at a shift and you've already started to wear the clutches, so if you need to do an adjustment, do it immediately don't wait until you get it back to the garage. And cooling is essential. The better the cooling the longer things should last.

 

[DieselBob]

My 89 V1500 Jimmy had the TBI 350/700R4 combo in it and I had 350K+ on it when I sold it and the second owner put another 40K on it before junking the truck from rust. I used to pull a 6800# travel trailer with it on a fairly regular basis and never had a transmission issue. I did install a second cooler rated for 18K as soon as I purchased the truck and flushed the original fluid around 15 ~ 20K miles to get the break in crap out. After that I changed the fluid every 50K miles give or take a little. Just used regular fluid no synthetic's. Your millage may very.

 

[MarcusOReallyus]

And cooling is essential. The better the cooling the longer things should last.

On another forum, someone said that TOO cool is bad, too. He's a trans rebuilder by trade. He recommended adding an external cooler inline with, and BEFORE the radiator heat exchanger. That way, you shed any excess transmission heat BEFORE dumping it into the radiator, but if it's too cool, the radiator heat exchanger can bring it back up to the correct temperature.

This was the first time I'd heard that you can get too cool with a trans. I guess it makes sense that there's an optimal temperature. We all know things don't work as well at 50 below...


What do you folks think about it?

 

[wayne pick]

Kenny, thanks for the correction, I was off by a few pounds!

I agree with you fully, the gearing of these trucks will definitely make it easier on the transmission. The guy that rebuild mine only gave me two pieces of advice when I told him what it was going into...make sure the TV cable is adjusted properly from the get-go. One time of getting any run-up at a shift and you've already started to wear the clutches, so if you need to do an adjustment, do it immediately don't wait until you get it back to the garage. And cooling is essential. The better the cooling the longer things should last.

An improperly adjusted TV cable will cause what you call run-up, or flair. It's usually the 2-3 shift. The throttle valve controls shift points through line pressure. The right way to adjust the TV cable is to do it with a line pressure test, not just the mechanical tension adjustment for the IP linkage. I will dig up the proceadure and post it if anyone is interested. Even with a proper TV cable adjustment, most older 700s have low line pressure and will flair the 2-3 shift. The only way to remedy this is to install a HD corvette servo. It increases the line pressure and makes firmer shifts in all gears. It may make the 1-2 shift harsh, but it eliminates 2-3 flair and makes the 2-3 shift much firmer and more positive.

 

[cliffyp]

Yes, line pressure is very important. You can err on the high side but definitely don't want low pressure. This is out of the manual I used when I built my 700r4 and its how I fine tuned my TV cable. It's very easy to rig up a test pressure gauge to get things right.