Swapping TH400 to 700R4

[bucket]

I just mean 55-60 instead of 75-80 lol. Not 120.

Yeah, that's what I meant too

Except I'll run my th400 trucks down the highway at 70 mph. Unless they are tired and smokey, lol.

I could run my 700r4 Burb down the highway at 70 IF it was fairly level and there was a tailwind. But 65 was usually about the limit. I know most folks can do it just fine, but that's because the drivers have no idea how hot that fluid is getting. Ignorance is bliss... until it's trans rebuild time.

 

[Jrgunn5150]

That's weird, my Trailblazer and Sierra both have 4L60's. I have 4.56's in the Trailblazer and 33's, and 3.73's in the Sierra with 265's, or 31's, and either will run all day at 75-80 with the temps staying right around 190 F. I only see higher when towing or offroading.

Of course, they are both smaller, lighter, and more aerodynamic than a Squarebody Suburban, and 4.56 gear's in the TB help tremendously with keeping the converter locked, but I wonder if there is something else about a 4L60 that helps.

 

[bucket]

Gearing and aero are a large part of it. I was running 3.73's and 33's with my Burb. I think the 60E is also a little more reluctant to go out of lockup, which should help a bunch.

 

[Stepperado]

I felt pretty comfortable going with a rebuilt 700R from Monster Transmissions. From what I can tell they build a pretty good unit.

The PO also added a trans cooler to this truck and since it's a Camper Special, it has 4.11 gears. I really can't imagine trans temp would be a problem given these two factors. Thought?

And remember, I don't tow/haul anything.

But with all the controversy over how to switch from the 3 spd to the 4 spd, I'm afraid of buying all the parts and then finding out after I take the truck all a part that I do not have what I need to put it back together. I'm not getting the warm fuzzy I was looking for concerning this swap.

 

[foamypirate]

I felt pretty comfortable going with a rebuilt 700R from Monster Transmissions. From what I can tell they build a pretty good unit.

The PO also added a trans cooler to this truck and since it's a Camper Special, it has 4.11 gears. I really can't imagine trans temp would be a problem given these two factors. Thought?

And remember, I don't tow/haul anything.

But with all the controversy over how to switch from the 3 spd to the 4 spd, I'm afraid of buying all the parts and then finding out after I take the truck all a part that I do not have what I need to put it back together. I'm not getting the warm fuzzy I was looking for concerning this swap.

Ehh, not a fan of Monster transmissions. One of my best friends son bought the highest level they make in anticipation of a big block. He had it installed behind a stock TBI 350 in an 89' K1500. It died 1 month after the warranty period... Not the only horror story I've heard either.

 

[Jrgunn5150]

Yep, i learned how to rebuild automatic transmissions after buying a "Built" Monster 700r4 for my 87.

It lasted from Cleveland to Toledo, lost 2 and 4 gear's. When I arrived in Muskegon Mi a family friend tore it down, it did not have a 5 gear planet, did not have kolene steels or red alto clutches, and was a car case and pan.

Went with a TCI to get back home, and bought a book and an ASTG manual and have told everyone this story every time I hear or see the name MOnster.

 

[bucket]

Look at it this way, you're only going to gain 1 or 2 mpg with a 700r4 AND have a potential reliability issue. For the cost of the swap, you will have to drive the truck for a long time to break even. And that's if the trans even makes it that long.

I know we all fix stuff that ain't broke. It's just part of being a car guy. But it really doesn't make sense to fix what ain't broke if the new part is weaker than the old one.

 

[Jrgunn5150]

Look at it this way, you're only going to gain 1 or 2 mpg with a 700r4 AND have a potential reliability issue. For the cost of the swap, you will have to drive the truck for a long time to break even. And that's if the trans even makes it that long.

I know we all fix stuff that ain't broke. It's just part of being a car guy. But it really doesn't make sense to fix what ain't broke if the new part is weaker than the old one.

Agreed, Super Street Fighter TCI TH400 @ 1400 or 700R4 @2400. A no brainer, especially if your current TH400 is good.

 

[80goldenburb]

Look at it this way, you're only going to gain 1 or 2 mpg with a 700r4 AND have a potential reliability issue. For the cost of the swap, you will have to drive the truck for a long time to break even. And that's if the trans even makes it that long.

I know we all fix stuff that ain't broke. It's just part of being a car guy. But it really doesn't make sense to fix what ain't broke if the new part is weaker than the old one.

only 1-2 mpg?? Not with taller ratios. My current burb has GAINED 7 mpg freeway driving. used to be 8 mpg @ 65 with th400. Now its 15 mpg @ 65 with 700r4. That OD gear makes that much of a difference when you don't have a steep towing gear out back and 31 inch or bigger wheels. My 700r4 is a non-rebuilt unit out of a '86 G20 van (MD8 case) and its holding fine so far. Bought it from a guy for 200 bucks. I use a digital temp gauge plumbed into the case pressure port and along with factory external cooler it doesn't get above 190 under normal driving. My "weaker part" is saving me money, my engines life and making the long trip more comfortable. GM should have made an OD version th400 in the 80's, but because they didn't we have to play the cards we are dealt with.

 

[bucket]

only 1-2 mpg?? Not with taller ratios. My current burb has GAINED 7 mpg freeway driving. used to be 8 mpg @ 65 with th400. Now its 15 mpg @ 65 with 700r4. That OD gear makes that much of a difference when you don't have a steep towing gear out back and 31 inch or bigger wheels. My 700r4 is a non-rebuilt unit out of a '86 G20 van (MD8 case) and its holding fine so far. Bought it from a guy for 200 bucks. I use a digital temp gauge plumbed into the case pressure port and along with factory external cooler it doesn't get above 190 under normal driving. My "weaker part" is saving me money, my engines life and making the long trip more comfortable. GM should have made an OD version th400 in the 80's, but because they didn't we have to play the cards we are dealt with.

Something else was causing your poor mileage before, the overdrive didn't gain you 7 mpg, guarantee it. Your current 15 mpg is what I could easily achieve with my C20 Burb that was a 454/th400 and ran 3.73 gears with 32" tires. 75 mph was still over 13 mpg and the truck could do it all day long without breaking a sweat.

And I don't know why you are so defensive of the 700R4 being a "weaker part". IT IS A WEAKER TRANSMISSION, plain and simple. It's not just my opinion, it's a well known FACT.

 

[HotRodPC]

IMO, if you want to go with an OD trans, just bite the bullet and go for the 4L80-E. Sure it costs more and will need a controller. By the time you throw the fortune at the 700r4 for upgrades, an OEM 4L80-E can be close to the same price. I personally wouldn't trust a used a 700r4, but I could trust a used a 4L80-E. Find someone you can trust or feel are shooting you straight and pick up a mid mileage used 4L80-E, buy a controller install it and be done.

 

[80goldenburb]

Something else was causing your poor mileage before, the overdrive didn't gain you 7 mpg, guarantee it.

I'm all ears, what could it be? Less mass to rotate compared to 400 trans?

Your current 15 mpg is what I could easily achieve with my C20 Burb that was a 454/th400 and ran 3.73 gears with 32" tires. 75 mph was still over 13 mpg and the truck could do it all day long without breaking a sweat.

my burb at 1:1 is revving 2600 rpm at 70 with 31.5 in tires. a big block revving higher than that gettin' above 10 mpg is, no offense, hard to believe.

And I don't know why you are so defensive of the 700R4 being a "weaker part". IT IS A WEAKER TRANSMISSION, plain and simple. It's not just my opinion, it's a well known FACT.

No hard feelings. i wasn't disagreeing with you. A 700 that is built right will last. Too bad so many "builders" out there don't build them RIGHT. My original response was to the fact that those who want overdrive shouldn't have to stick with a dinosaur that doesn't have enough gears all because GM was too lazy to make a vac mod or tv cabled version prior to 1991. There are more options in *2016*

IMO, if you want to go with an OD trans, just bite the bullet and go for the 4L80-E. Sure it costs more and will need a controller. By the time you throw the fortune at the 700r4 for upgrades, an OEM 4L80-E can be close to the same price. I personally wouldn't trust a used a 700r4, but I could trust a used a 4L80-E. Find someone you can trust or feel are shooting you straight and pick up a mid mileage used 4L80-E, buy a controller install it and be done.

4l80 cores are cheap too. All of em get snatched up off CL before I can get my hands one I would rather do the rossler box (at first) then manual valve body overhaul. ANYTHING is better than a damn computer guaranteed to malfunction at some point in time and leave you stranded.

As for 700s they can be built (if the right HD parts are used) for around 1k. Hard to believe, yes but i've seen it. Low on ends for now, I just won't tow anything heavy than 4k, just to be safe

 

[HotRodPC]

Because I build transmissions, I'm one of the few that will agree a 700r4 CAN BE built to hold up better than an OEM unit with aftermarket redesigned hard parts. However, by the time you bought all the needed hard parts, you've spent a fortune to where an OEM built 4L80-E will hold up even better than all the upgrades you can throw at a 700r4. Mainly due to an aluminum vane pump. Noway a million dollars in upgrades will you overcome the aluminum pump vs cast iron crescent pump. Nor throwing $800 at hardened input and output shafts, you'll never get past the fact the 4L80-E shaft are bigger and stronger in diameter and splines. You'll also never get past the much stronger center support, however there is an expensive upgraded aftermarket bolt in center support upgrade for the 700r4 with a stronger sprag now.

I get it though. I might be building a 700r4 soon to put behind my stock OEM 454. I have a feeling I'll be consolidating my 2 projects to 1. I want my K10/K20 project more than anything and don't have funds or time for 2 trucks, so my good running 454 and wiring harness out of my C20 is likely going to be used on K10/K20 project that is set up for 700r4/NP208. I have no intention of moving crossmembers, cutting or lengthening driveshafts so someday if I ever get my clutch conversion done to that truck my A833 trans will bolt right in since all the shafts and crossmembers use the same locations.

 

[bucket]

I'm all ears, what could it be? Less mass to rotate compared to 400 trans?




my burb at 1:1 is revving 2600 rpm at 70 with 31.5 in tires. a big block revving higher than that gettin' above 10 mpg is, no offense, hard to believe.



No hard feelings. i wasn't disagreeing with you. A 700 that is built right will last. Too bad so many "builders" out there don't build them RIGHT. My original response was to the fact that those who want overdrive shouldn't have to stick with a dinosaur that doesn't have enough gears all because GM was too lazy to make a vac mod or tv cabled version prior to 1991. There are more options in *2016*




4l80 cores are cheap too. All of em get snatched up off CL before I can get my hands one I would rather do the rossler box (at first) then manual valve body overhaul. ANYTHING is better than a damn computer guaranteed to malfunction at some point in time and leave you stranded.

As for 700s they can be built (if the right HD parts are used) for around 1k. Hard to believe, yes but i've seen it. Low on ends for now, I just won't tow anything heavy than 4k, just to be safe

I have no idea why your mileage was so poor before the overdrive, maybe your combo just didn't like the tall gears and that rpm?

I don't know what my rpm was going down the highway, there was no tach. Besides the smog pumps (yes, pumps) I removed, it was bone stock right down to the factory duals and super quiet mufflers. It was smooth sailing at literally any speed. Mixed city/highway driving got me 8.5 in the winter and around 10 mpg in the summer. Driving 70-75 down south and through the Smokies got me 12-13 mpg. Level highway at 65-70 got 15 mpg. 70-75 was obviously less. I no longer own that Burb (sure do miss it too), but another member here owns it now.

And I know a 700r4 can be built to hold up, but finding someone that knows what they are doing is tough. And in a 4x4 application (like the one that started this thread), there's basically no MPG increase at all. I've run two Burbs with the same engine, same gears and same tire size- one with a stock TH400 and one with a built right 700r4. The MPG from the two Burbs was the same. My other Burb (th400) with a carb and steeper gears also gets comparable mpg.

 

[mtnbiker727]

I don't know a whole lot about transmissions, but the transmission guy I spoke to about a 700r4 said that he takes 700r4's out of trucks and puts TH350s in them because they're so much tougher.


One thing that surprised me reading this thread is that if I'm cruising at 70 mph in my TH350 equipped C10, I could be overheating my tranny. They recently increased the speed limit between my place and my parents' from 65 to 70 on a 10+ mile stretch that pulls a pretty big hill. I only have idiot lights in my truck, so I have no idea what temp I'm running at.... the truck will do 85 mph with no trouble, but I don't sustain that speed for more than a few seconds at a time....


So my question is: Should I not sustain or exceed 70 mph pulling that hill, or anytime for that matter?

I should also note that my truck is my toy, which gets ~1,000 miles per year, but the transmission has 194,000 miles on it.