lets talk about TH400 to TH700R

[Fore Wheeler]

my brother in law has a motorhome with a 400 tranny in it, he was going to spend $2500 for a gear splitter for that tranny so he'd end up with over drive, my thought was to drop the 400 and put a 700 in with factory OD. this will bolt to the 454 that powers the big beast and if I'm correct the only differance will be the length, he may have to have his ds shortened. right?


also, does anyone have any idea how the linkage will differ? how the gear selector on the steering column can be changed to show od?


I'm thinking it should be a pretty straight forward swap with a better first gear and of course OD for limited money, for certain cheaper than the splitter he was looking at.

 

[PaulJ]

I've googled for this in the past and found some good information. Re-gearing the rear end is an option I would consider and maybe do the tranny too. The gear splitters are available as underdrive or overdrive and usually are used on tow vehicles where you're towing a big fifth wheel part of the time and running light the rest of the time. With a motorhome, it's always heavy so they usually don't use them. You don't want an early 700R4. They were significantly improved around '87 and around '93 they became electronically shifted so you would want something from in between those years.

 

[Fore Wheeler]

he's a motorhome geek like I'm a jeep freak, he frequents the motorhome forums like I do , when I mentioned the 700 tranny he was supurised that that may be an option cuz it's never been brought up on his motorhome forums, just the splitters. He's not the most mechanically inclined person, yet he can still turn a wrench.

good info on the years, I was sort of wondering that as well.

anyother info?

 

[Jerm S.]

I could be wrong but, I Think that the 700 was only a half ton tranny. I'm not sure if it would hold up to that much weight i think that they would over heat pretty bad. If you wanted the overdrive it would be a little more money but i would go for a 4L80E, out of a newer chev truck it is electronic but it would be worth it. They are just as strong as the 400 but with a factory od. And they are designed to go in to one ton trucks they have heat sink pans and huge cooler lines to get the heat out. You also have to rember that the worst enemy to any auto trans is heat, be sure to keep that in mind while you are thinking about it.

HTH

Jerm S.

 

[seanR]

The 4l80 won't work because it is a computer controled tranny. Go with the early 700R4s. If one is rebuilt by some one who knows what they are doing a 700 can be a bad @$$ tranny!

I had a 1/2 88 GMC back in the day that I got used. I had ALOT of troubles with the 700. I plowed snow and pulled skidsteers around with it (yea I should have had a 3/4 ton). Anyway, I took it to a guy in town who was recomended and he rebuilt the tranny with heavy duty parts and more clutches, I don't know much about the inards of one. It was trouble free after that.

Have your brother-in-law check that route.

 

[TRL WGN 1]

seanR is right. The 700 can be built to withstand quite a bit of abuse. We have a really good builder here who knows his stuff. He has been building the 700's for over 15 years with great success.
According to what I remember him telling me, he said that the older version is weaker, but can be upgraded, and the electronic version can be converted to mechanical, so it really isn't all the important which you get, if you are going to go through it anyways.
He also said that the weak point is the overdrive, because of the way it operates. I believe he said that the overdrive uses one of the other gear's clutches for operation. I do know that the 700 has a full throttle lock which keeps it from shifting into overdrive under full throttle, to protect that gear.
If you need to talk to someone who knows his stuff, I can get you the contact information for the guy I know.

 

[Matthew Currie]

I have a 700R on my 88 Chevy 3/4 ton truck, and like Sean R mine was totally cooked by snowplowing. I had it rebuilt, to the tune of about 1200 bucks, at UNDER 30K miles! It is supposedly upgraded, toughened, etc. and it certainly seems to work all right now, but.....

Before the rebuild, by the way, the transmission had 3 trivial bullshit recalls, all connected with its unnerving tendency to burst into flames when worked hard. The first was a new dipstick with a tight seal on the top to keep it from geysering hot fluid all over the engine. The second was a new overflow tube to keep it from spewing hot fluid all over the exhaust. The third was a new page to stick into the owner's manual, saying, in essence, "don't use overdrive for any cargo heavier than a feather pillow."

Even if it's an upgraded, well built model, I suspect that it will burn up if used in overdrive on a motorhome. You'd be fine if you keep it in third, but then why bother? The 400 isn't the most economical transmission out there, but it's made for the job.

I think, too, that when mine was rebuilt, one of the things the rebuilder did was to calibrate it so that it unlocks and goes into third a little more readily than it did before, and because of this, the economy isn't really much of an improvement over a 3-speed anyway. I get about the same mileage with a 350TBI and the 700 as I did on my '86 16 foot cube van with a 350 with 4-barrel Rochester carb and a 400 (12-ish). The only difference really is that the cube van had more guts.

 

[seanR]

Thanks for reminding me about my big burn spot at mile marker 160 on I-90!
That was the reason I had it rebuilt...ah the memories... Lukily I had a fire ext. right between the door and the seat. But yes DO NOT use OD if you have all of your golf clubs in the back of your pic up!