"Hypothetical" Question (Wink Wink)

[jjester6000]

Say I were to somehow come into ownership of an '86 Suburban C20 with a 454, th400, and 4:10 gears.

"Hypothetically" would a "hypothetical" Th700r4 survive behind a "hypothetically" stock "hypothetical" 454? The "hypothetical" Th400 is still good, but with the "hypothetical" 4:10 gears, the gas mileage is "hypothetical" ****. So I'd like to "hypothetically" swap the "hypothetical" Th400 for a "hypothetical" Th700r4.

Is this a good "hypothetical" idea? A "hypothetical" Gear Vendors Overdrive is out of the "hypothetical" range of my "hypothetical" wallet. Also I don't want to deal with a "hypothetically" complicated and "hypothetically" expensive "hypothetical" 4L80E swap.

Or should I just "hypothetically" swap the "hypothetical" 4:10 gears in the "hypothetical" 14 bolt rear end for some "hypothetical" highway gears.

"Hypothetically," I'd want to put a lot of highway miles on this truck, so the "hypothetical" current set up wouldn't "hypothetically" work.

What do you guys think about this "hypothetical" scenario?

 

[Rickf]

Gear vendors OD unit.

 

[Paladin]

Damn, I either need therapy or a "fattie" after reading this "Hypothetical" situation!!

 

[idahovette]

@jjester6000 , I'm kinda with @Paladin on this one?.....at least anyone who reads this thread should know how to spell hypothetical , now??

 

[Doppleganger]

Just say you're 'asking for a friend'. Same difference.

 

[Turbo4whl]

Having done this very same trans install years ago behind a BB I can say, yes it will last if you drive like it was made of glass. But you won't.

Well before there was anything so cool as a 4L80E I wanted the lower first gear of the 700R4 and overdrive. To make this happen I kept a spare trans in the garage. I got so good at swapping I could do it in an evening after work.

One of the early fails the band clutch would not hold tight enough on the drum. So upfit to the larger external piston apply and next it broke the mounting off the band.

Another failure was the reaction carrier. The two planet gear sets are on each side of it. Sheared that carrier in half. After several repairs and upfits to the original 700R4 the internal splines where the steels ride were so worn the case was junk.

And of course clutch disc failures added to the fail swaps. Better planet gear sets as they became available.

Bought a third 700R4 and added that to the rotation. Oh, at one point the rear slip yoke twisted and it would not slide in and out anymore.

So if you want to play, you got to pay. Boy, what a ride though!

 

[mcarlo86]

3.42 gears would probably work pretty well for what you are looking to do.

It is a BBC, so you have to be realistic about fuel economy. Swapping the gears is probably the most economical plan and it will get your cruising RPM’s down some and should improve the mileage some.

 

[Charlie]

 

[sirweesarunch]

https://www.google.com/search?q=bow...BAzYuNJgBAKABAbABBg&sclient=mobile-gws-wiz-hp

 

[Vbb199]

Hypothetically have a solid 700r4 built to run behind that hypothetical 454, and with a say, hypothetical 30ish or 31ish tire, on a hypothetical 3.42 ratio and you'd be good to go on hypothetical gas mileage on a hypothetical truck


Im running an actual 4.10 on my suburban, with a well built 700r4, on a healthy 300+ hp sbc, on a 31" tire, and its not screaming going down the road at hwy speeds (65-70 mph)

Even at 100 mph, its like, 28-3000 rpms

Gas mileage is like 14 mpg, but i have a terrible vacuum leak that causes excess fuel dumping its awaiting repair for.


I switched to 4.10 for towing, i would recommend a hypothetical 3.42 or 3.73 to you.

 

[Matt69olds]

I wouldn’t hesitate to run a well built 700 behind a mild big block. A well built 700 will have upgraded 3-4 clutch pack, upgraded input sprag, wide band, corvette or aftermarket equivalent servo, upgraded drive shell, pump and valve body updates, and careful assembly.

The upgraded parts are probably 400-500 (just a guesstimate) dollars more than stock replacement. I would think a 700 with those parts would live a long life at 450-500hp assuming it has the TV cable right.

If your big block is making more than 500hp, or plan to in the future, just bite the bullet for a 4L80. A good used junkyard 4L80 with a shift kit is far stronger than a 700 with every upgrade available would ever be.

Burn up or break a 700 a couple times, the repair bills will add up to far more that the cost of the better trans

 

[Turbo4whl]

I wouldn’t hesitate to run a well built 700 behind a mild big block. A well built 700 will have upgraded 3-4 clutch pack, upgraded input sprag, wide band, corvette or aftermarket equivalent servo, upgraded drive shell, pump and valve body updates, and careful assembly.

The upgraded parts are probably 400-500 (just a guesstimate) dollars more than stock replacement. I would think a 700 with those parts would live a long life at 450-500hp assuming it has the TV cable right.

If your big block is making more than 500hp, or plan to in the future, just bite the bullet for a 4L80. A good used junkyard 4L80 with a shift kit is far stronger than a 700 with every upgrade available would ever be.

Burn up or break a 700 a couple times, the repair bills will add up to far more that the cost of the better teams

Wow, I sure wish some of these upgraded parts were available when I was running my 700R4's.

I would like to think that I, and many others who were thrashing on early 700R4 transmissions created a market for these improvements.

 

[SquareRoot]

Hypothetical is ********. Real world that 700 won't survive for long unless you drive like your 80 years old. 4l80 or nv4500. You want a daily driver? LS swap or PF-4. Don't even ask about gas mileage. If you have to ask, you can't afford it. Carry on.

 

[SquareRoot]

Hypothetically have a solid 700r4 built to run behind that hypothetical 454, and with a say, hypothetical 30ish or 31ish tire, on a hypothetical 3.42 ratio and you'd be good to go on hypothetical gas mileage on a hypothetical truck


Im running an actual 4.10 on my suburban, with a well built 700r4, on a healthy 300+ hp sbc, on a 31" tire, and its not screaming going down the road at hwy speeds (65-70 mph)

Even at 100 mph, its like, 28-3000 rpms

Gas mileage is like 14 mpg, but i have a terrible vacuum leak that causes excess fuel dumping its awaiting repair for.


I switched to 4.10 for towing, i would recommend a hypothetical 3.42 or 3.73 to you.

100 mph in a burban.

 

[Vbb199]

100 mph in a burban.

I'll send a picture and tag you in it next time i do 100 with a screenshot of google map's "speedometer function"