700R4 swap killing me

[scorchingeng]

So I'm doing a 700R4 swap from a TH350 right now. It's amazing how many cost over-runs there are. I didn't expect to have to buy TWO new custom shafts instead of one. $275 a piece... ouch. (oh, I have a 4x4 k10 with NP205.)

Ok, I do have a question here though, not just here to complain.


Can anyone educate me a little on torque converter lockup? What is it and how do I know of mine is setup for non-electronic TC lockup? I really don't even understand what it actually DOES exactly.

Thanks in advance for posts.

[weircc]

looks like your new welcome to the site im sure someone will chime in soon

[nightmare]

This is a good article to read: Diagnosing Torque Converter Lock-Up Problem

[treveiger]

Lol been there with upgrades, for a heads up the to do list NEVER ends. Welcome to the forum .
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[Longhorn Man]

to over simplify this...
a converter is basicly two fans submerged in tranny fluid. To give you a visual, picture two of those 20 inch window box fans facing each other. One plugged in and turned on high, the second one is turned off.
The first one is the one that is driven by the engine, the second one is the one that drives the tranny, and the air blowing through, is your dextron II fluid.
When the drive (engine) fan is blowing through the driven (trans) fan, the driven fan will start to turn too. Once it is turning, that is the same as your truck cruising slowly through the parking lot. When you hit your brakes and come to a stop while in gear, the driven fan can come to a stop, and the drive fan can keep on going.
Now if you are picturing this, then you can see the 2 fans never going the same speed. The driven fan will always go a tick slower. In most light duty cars and trucks, 200 RPM is the typical slip. So if the engine is running at 2500 RPM, then trans will (at best) get 2300 RPM.
Now imagine these two fans spinning at this RPM, and a mechanical linkage suddenly connects the two fans together. It 'locks up' the two, so they now spin the same speed.
This, is the simplified way that a lock up converter works.

[dukcaln]

well worth it when its all done...... going to do it soon too.... have my eye on one

[MusicMan70]

Thanks Longhorn...I see it all clearly now. Yes that makes great sense to me now...Much appreciated.

[Mike Bradbury]

Longhorn, that has got to be the best description of the TC I have heard. I know how they work but have always struggled to find the words to explain it to others. I don't have that problem anymore, thanks


Scorch,
Why would you have to replace both shafts, the rear should not be affected by the length of the 700r4?

Oh nevermind I just read you have a 4x4

[treveiger]

That's a awesome explanation
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[mac]

I liked the mpg increase (14 to 17.7) after I did a T400 to 700R4 swap. Made it well worth the trouble.

[va72longhorn]

Im sitting here in astonishment. For 49 years, Ive never trully understood how a converter works and now in 5 minutes I can explain to someone else! Ive thought of doing the same on my Longhorn in order to add an overdrive, but it was my understanding that the OD is still the same 1:1 output that the Turbo 400 is ? Is that not correct? This 4:56 rear is killing me.

[JORGIE95961]

Originally Posted by longhorn man

to over simplify this...
A converter is basicly two fans submerged in tranny fluid. To give you a visual, picture two of those 20 inch window box fans facing each other. One plugged in and turned on high, the second one is turned off.
The first one is the one that is driven by the engine, the second one is the one that drives the tranny, and the air blowing through, is your dextron ii fluid.
When the drive (engine) fan is blowing through the driven (trans) fan, the driven fan will start to turn too. Once it is turning, that is the same as your truck cruising slowly through the parking lot. When you hit your brakes and come to a stop while in gear, the driven fan can come to a stop, and the drive fan can keep on going.
Now if you are picturing this, then you can see the 2 fans never going the same speed. The driven fan will always go a tick slower. In most light duty cars and trucks, 200 rpm is the typical slip. So if the engine is running at 2500 rpm, then trans will (at best) get 2300 rpm.
Now imagine these two fans spinning at this rpm, and a mechanical linkage suddenly connects the two fans together. It 'locks up' the two, so they now spin the same speed.
This, is the simplified way that a lock up converter works.

that was awesome

[Mike Bradbury]

Originally Posted by va72longhorn

Im sitting here in astonishment. For 49 years, Ive never trully understood how a converter works and now in 5 minutes I can explain to someone else! Ive thought of doing the same on my Longhorn in order to add an overdrive, but it was my understanding that the OD is still the same 1:1 output that the Turbo 400 is ? Is that not correct? This 4:56 rear is killing me.

No 700 has a lower 1st gear and then higher in all the rest than the 400. plus over drive. the final drive is .70

[va72longhorn]

oh ok, so would you have an idea as to the amount of RPM's it would lower my 402 to at highway speeds? The last I remember, it was screaming at about 3200 rpm's at 60 mph. The overdrive is actually an electronic activation, isnt it?

[truckster]

Originally Posted by va72longhorn

oh ok, so would you have an idea as to the amount of RPM's it would lower my 402 to at highway speeds? The last I remember, it was screaming at about 3200 rpm's at 60 mph. The overdrive is actually an electronic activation, isnt it?

If your engine is turning 3200 with a 1:1 final drive and you replace it with a final drive ratio of 1:.7 the engine should be turning at 2240 (3200 X .7), but you should also lower it by a couple of hundred with the torque convertor locked.

[va72longhorn]

Kewl !! Anyone know of a reason that I would nt go this route?

[mpotts64]

I replaced the 350 in the brown truck with a 700. It has a new, stock, 283, 700 miles on it and i have absolutely no top end on o/d. I do not know the rear end gears but I do have newer style 17" tires, 32" tall. It does ok if you keep it in 3rd but when it shifts to o/d, forget it, about 70, maybe 75, mph on interstate is top speed. I am also getting about 13/14 mpg. I am going to put a shorter set of tires on it and find out what is in the rear end. The 700 was rebuilt with heavier and more bands, a corvette shift kit, hydraulic lockup, and other stuff done by a professional tranny guy. I am not unhappy with the transmission, just need to find out why I have no top end. It could well be I have way too much tire, wrong gears, and not enough motor.

[dmack91]

"It could well be I have way too much tire, wrong gears, and not enough motor."

Probably a combination of all three. Can't blame the trans for no roll-on power at speed, that probably starts with the 283 just not having the torque to overcome the resistance of a heavy, non-aerodynamic truck at highway speeds.

Not bashing, just an observation. Trying to find that fine line between economy, power, and performance is always elusive. Sacrifices in one area are generally needed to see gains in another.

[mpotts64]

oh I agree with you 100% dmack, and it is a good transmission, but the o/d definitely illuminates other problems I guess is the only point I was really trying to make earlier, I am not unhappy for the doing the swap, and it was an easy swap, I think I had to have 1" cut off the drive shaft was the only mod I had to do, otherwise went well, now time to look at the two ends of the truck, gears and motor, but, first gonna start with shorter tires and see what that does

[rpmgroup]

Longhorn; great description of how the convertor works. mpotts64; following this thread and hope you find your gear ratios.

[brad_man_72]

yikes 2 new shafts. The one that needed to be shorter should have been shortened and ballanced. Then the one that needed to be longer should have been retubed and ballanced.... If all of the pieces were in good shape.

[Longhorn Man]

mpotts64... you probably have too much gear. I'm willing to ber you'll find a 3.07 gear out back. I always advise against a 3.07 and overdrive in a truck with an old school engine. I've only seen one or two people say that it worked, and MANY who say it does not work. Once your RPMs drop too low, then your engine is strugling to keep the speed, and then you end up pushing on the throttle more just to maintain your cruise speed, and that kills any MPG gains you would have seen.

I am glad everyone likes my oversimplification. I'll spend years trying to figure something out to a way I can understand it, and then I come up with something that makes it seem so simple, yet still be acurate.

[mpotts64]

thank you longhorn and rpm, I do appreciate it, I need to get in that rear end and find out, I have another rear end out of a 67 lwb that had 3 ott, need to check that one as well, again, thanks to all for your help

[dave69]

Originally Posted by Longhorn Man

mpotts64... you probably have too much gear. I'm willing to ber you'll find a 3.07 gear out back. I always advise against a 3.07 and overdrive in a truck with an old school engine. I've only seen one or two people say that it worked, and MANY who say it does not work. Once your RPMs drop too low, then your engine is strugling to keep the speed, and then you end up pushing on the throttle more just to maintain your cruise speed, and that kills any MPG gains you would have seen.

I am glad everyone likes my oversimplification. I'll spend years trying to figure something out to a way I can understand it, and then I come up with something that makes it seem so simple, yet still be acurate.

I have a question about what year 700R trany to look for, I did a engine swap last fall to a 96 Vette LT4 and kept my TH 350 and would like to go to OD. I have a 69 C 10 daily driver and never skips a beat rear gear is a 3:07. There is nothing wrong with my trany and now with the LT4 do you think I should go to over drive? Thanks Dave

[Steve Hafner]

. . . .

Here's a list of final ratios:

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