700r4 behind a mild 454

[USSkoval]

I currently have a mostly stock tbi 350 in my burb with about 145K on it. There is about 3K on the built 700r4. The truck has good power for doing about anything as long as it's under about 50 mph. I want to swap in a tbi 454, but am not sure if the tranny will hold or not. After searching, some people say yes, and some say no. Who has actually ran this combo and how did it turn out?
The truck sees daily driving duty, long trips on the highway and in mountain/hilly terrain, and occasional towing of cars and trucks (sometimes long distance). Currently, when loaded down, the convertor spends much of it's time unlocked and I don't want to kill the new tranny. If there were more power, there would be less throttle which should mean less downshifting and convertor cycling. Current gearing is not ideal, but overall works out decent. Will I be OK sticking with the 700r4?

 

[shaun89]

i think it depends on how built the 700 is, find out some info about what they did to the tranny when they built it. if it is built pretty strong and with the right gearing in sure it will be fine. but if the tranny is just a couple of steps above stock...i would say no.

 

[chevyuser74]

how built is your 700r4? also gearing is key for it.

 

[shaun89]

do u hear an echo? haha just playin

 

[chevyuser74]

ya i know i typed it then posted it then noticed yours lol

 

[USSkoval]

I had it built by a local trustworthy shop that knows their stuff. Some things I remember (I'm certainly not a tranny guy) are: HD convertor with furnace brazed fins, beast sunshell, "z-pack"? or something that involved more clutches, and there likely was some other stuff. There is also a shift kit with firm shifts, the 1-2 has good kick to it. Right now I'm running 3.73's and 305/70/16. Future plans call for 4.56's and a 35 or 36 tire. Also, the tranny is still the '88 model which I gather is stronger than the earlier units.

 

[shaun89]

from the sounds of it, i would say it will be fine with 4.56s and 35s, but try and call the guy and get more info if u can, or even just ask him what u want to do with it and im sure he can tell u a lot more about it then most people on here, seeing that he seems like a tranny guru.

 

[4X4HIGH]

Sounds like the trans is built good enough to live behind a BBC. Keep in mind that you'll have to do something about a provision for the TV cable hookup on the 454 TBI unit.

 

[Blue85]

I know that combo was in Stephen Watson's truck "Wally" for a while. Maybe it still is? It was good enough for TTC.

 

[nocoasthardcore]

Depending on what shift kit is in this might be irrelevant, but, what is knows as the 'Corvette Servo' mod. Helps with that goofy 'I'm a 700r4 and I can't seem to decide when down shifting is a good idea' trait. External cooler and a deep pan for more fluid capacity is a good idea bbc or not.

 

[USSkoval]

There is already a cooler on the truck, but the pan is still stock. Every once in a while, only when the conditions are just right, the tranny will hunt between two gears. It's only done it three or four times, and I just give it a little more gas to make it quit.

Looking back at the paperwork, there was also a 2-4 kevlar band, pump stator, rear planet assembly, sun gear assembly, and 1-2 accum spring installed. I also noticed I have a 2 year/24,000 mile warrantee, I didn't realize it was that long.

 

[bigblock72]

The trans will be fine during regular driving as long as the TV cable is set up properly. The 454 throttle body DOES NOT have TV provisions and will have to be modified to work. Towing will get you into trouble especially when you get over 10k gross combined. The 454 has enough torque to slip the 3-4 clutch at part throttle, it doesn't take much slippage to kill the 3-4 clutch. The Z-pack clutch tolerates slippage better than most but it still has it's limits. A billet 4th servo, a deep trans pan and type F fluid will help but you'll need to be nice to it.

The short answer is yes the trans will live with the big block as long as you keep the trailer light.

 

[USSkoval]

OK, so the 3-4 clutch won't be an issue if I don't tow a heavy load in overdrive, right? Also, is the billet 4th servo the same (but better) as a corvette servo? And can it be installed without tearing the whole tranny apart?

 

[4X4HIGH]

Not sure on the billet servo being any better than the vette servo but it is easy to change from the outside passenger side of the trans.

 

[bigblock72]

The Corvette servo is second apply only it doesn't have anything to do with 4th apply. A billet 2nd servo does have more apply area then a corvette but probably not enough to justify the cost. The servo can be changed fairly easily, it's best to drop the pan so you can make sure the apply pin engages the band properly.

Not towing in OD helps but you're still using the 3-4 clutch in third and again it's not too hard to slip even in drive with over 400 ft lbs and some weight. Keep the fluid cool (install a temp gauge) and run type F fluid and I think it'll be ok.

 

[Blue85]

Depending on what shift kit is in this might be irrelevant, but, what is knows as the 'Corvette Servo' mod. Helps with that goofy 'I'm a 700r4 and I can't seem to decide when down shifting is a good idea' trait.

The servo has nothing to do with the "decision" to shift. That is all handled in the valve body. There are mods to make it more decisive - in particular a replacement valve to keep it in OD to higher throttle positions (is this from B&M?). Some shift kits deal with this, some just try to make it shift firmer. The biggest things are to have the right gears for your tires and set the TV cable right.

The "servo" consists of two independant pistons, each with the same function of applying the band to the drum (they work through the same pin). You can run the larger 4th apply piston (i.e. Billet Servo) without any valve body modifications because the 3-4 shift is just application of the band. It will slow this shift down slightly because more fluid is required to push the pin. It's changing (or not changing) the 1-2 apply piston that causes problems. Again, the larger apply area gives more force, but inherently applies more slowly. This can lead to a bind in the 2-3 shift where the 3-4 clutch is grabbing before the band has released (this is actually 4th gear for an instant). I don't know of any way to predict whether or not this will be a problem other than talk to a guru who has built tons of 700s.

My point is just that servo mods should generally match valve body mods, but some people get lucky.

It is generally advised to tow in 3rd. The biggest problem with OD in the 700 is that the fluid flow is reduced which hinders cooling. That being said, a tranny that is not slipping with the TC locked doesn't make a lot of heat unless it is shifting a lot.

 

[Hossbaby50]

The 700R4 is not the optimum trans for a BBC but it can/has been done. Just be smart. Keep it cool and don't tow anything in OD. Also with 305's and 3.73's make sure you are in the right gear, don't let it hunt 3 & 4 on the highway. Get lower gears if you plan to keep running a 700R4. 4.56's and 35's is ok but if you plan on 35's and think or know you want to go to bigger tires and keep the 700R4 then get 4.88's or 5.13's.

My 700R4 loved it when I had 4.56's and 32" tires. When I had 35" and 37" tires and 4.56's it didn't love me as much. Now I have a Th400.

Harley

 

[rancid]

4l80e

 

[USSkoval]

4l80e

Yes, that is the ultimate goal, but I just recently dropped a bunch of cash on this 700r4. The original plan was to replace the 350 with a 400sb and call it done, but then I decided to stick my 400 in my Blazer. If the 700 will last for 2 or 3 years behind a 454, then that's the route I would like to take.

 

[kennyw]

I would tell you to fix your gearing problems first or even the low power 350 is gonna kill the 700R4. What gears and tires do you have now?