700 vs 400 trans

AndyinCt. · 12-28-2008, 05:35 PM

My 87 4x4 3/4 ton currently has a TH400 auto. I have a 700 trans from a full size blazer. What are the pro's and cons of these transmissions? Are they the same length so if I do the swap I won't have tochange driveshafts? Is the 700 as durable? I would think the overdrive on the 700 would help fuel economy a bit. Thanks for your help.

heavychevy85 · 12-28-2008, 07:52 PM

i like the 700s alot better that the 400s the 400s are excelent in the big cars but i love the 700 for the rucks cuz its built a little beter and it has over drive and realy couldn't tell ya on the lenth

batty1214 · 12-28-2008, 08:13 PM

Im not sure on the lengths....... the 400 will handle a lot of abuse.... the 700r4 have over drive, and the 1st and 2 gears are quite low.. I believe that they are close to the same as the th400... but not as tough.. unless you are willing to build them.. but for everyday use, a 700 would be My personal choice of transmission.

gmctrucks · 12-30-2008, 03:15 AM

I have heard that the 700 has better gears in it for 4x4ing and so on.

csracing93 · 12-31-2008, 11:19 AM

The gear ratio for the 400 is 2.48/1.48/1.00
and the 700r4 is 3.06/1.63/1.00/0.70
does this help any?

batty1214 · 01-01-2009, 07:10 PM

cs racing has the numbers that I was looking for.......
the gears arent quite as low, but you gain one more gear... so highway you arent screaming at 70

hotrodpc · 04-16-2009, 01:36 PM

Quote:

Originally Posted by heavychevy85

i like the 700s alot better that the 400s the 400s are excelent in the big cars but i love the 700 for the rucks cuz its built a little beter and it has over drive and realy couldn't tell ya on the lenth

WOW. Someone said a 700r4 is built better than a 400??? Someone has misinformed this guy for sure. All of the rest of above is true. 700r4 does have OD and does have better ratios, but it WILL NOT, outlast, out perform, or take near the abuse a 400 can. Why? Becasue the 400 IS built better. You can build a 700r4 to be strong, but you can build a 400 to be even stonger in all cases. Turbo 350 is even stronger than a 700r4 IMO. In comparison, you can call the 700r4 an overdrive vesion of the T350C, and the 4L80-E as the overdrive version of the 400. The 4L80-E is the only transmisison that I would consider stronger than the 400 if talking about about an OD trans. And there are some parts that you can take from the 4L80-E and put into the T400 and make it even stronger. Mixing the old with the new makes a good trans. Not only does a 700r4 have its known weaknesses, it does NOT have a Center Support which makes a huge difference. So ther REAL question is. What are you doing with the truck, and then your question can be better answered. It may very well be the 700r4 is the right choice for you, and I can tell you some things that you MUST do to it, but, the 700r4 IS NOT better built by any stretch whatsoever.
PS- I know this is an older thread, but for those who find it, just needed to be properly informed.

samiam · 05-27-2009, 12:24 AM

if you need overdrive and cant afford an overdrive unit to bolt onto a 400, then get the 700, but know that heat kills them quickly. to make it last you must run a heavy duty radial rv cooler and if your fliud out line is a 1/4 inch tap it out to 3/8, if your in line is 3/8 tapp it out to 1/2 inch. i killed a 700 quickly havent killed a 400 yet. A buddy did what I suggested to you (his idea not mine) and he pulls a 12000 pound trailer all the time with no issues

semocoachworks · 05-27-2009, 07:30 PM

I had a th400 in my 84 3500 4x4 and pulled it to put in a 700r4. I had a heck of a time with the kickdown cable not staying adjusted, i would open it full throttle and push the thumb button down and it would be good for a while then all of a sudden, it would shift quickly into overdrive or stay in 1st forever. I replaced the cable and it seemed to have cured the problem. I will, however, be putting my th400 back in as soon as I get time. I tow quite a bit with this truck and it don't see the interstate very often so i really don't need overdrive. Just my 2 cents.

hotrodpc · 05-27-2009, 07:34 PM

Good Idea Semo. I am glad to see this thread getting some attention. It was older when I posted on it, but I wasn't going to leave it untouched when I seen someone said a 700r4 is better built than a T400. NOT. By chance did you notice any kind of gain in fuel mileage with the 700r4?

12-28-2008, 05:35 PM	#1
AndyinCt. Full Member Join Date: Jun 2008 Posts: 12	700 vs 400 trans My 87 4x4 3/4 ton currently has a TH400 auto. I have a 700 trans from a full size blazer. What are the pro's and cons of these transmissions? Are they the same length so if I do the swap I won't have tochange driveshafts? Is the 700 as durable? I would think the overdrive on the 700 would help fuel economy a bit. Thanks for your help.

05-27-2009, 07:34 PM	#10
hotrodpc Senior Member Join Date: Jul 2008 Location: OKC, OK Posts: 3,149	Good Idea Semo. I am glad to see this thread getting some attention. It was older when I posted on it, but I wasn't going to leave it untouched when I seen someone said a 700r4 is better built than a T400. NOT. By chance did you notice any kind of gain in fuel mileage with the 700r4? __________________ *Winners NEVER Quit , Quitters NEVER Win !!!*

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12-28-2008, 07:52 PM	#2
heavychevy85 Senior Member Join Date: May 2008 Location: Muncy, PA Posts: 290	i like the 700s alot better that the 400s the 400s are excelent in the big cars but i love the 700 for the rucks cuz its built a little beter and it has over drive and realy couldn't tell ya on the lenth

12-28-2008, 08:13 PM	#3
batty1214 Senior Member Join Date: Nov 2008 Location: Vernal Utah Posts: 1,135	Im not sure on the lengths....... the 400 will handle a lot of abuse.... the 700r4 have over drive, and the 1st and 2 gears are quite low.. I believe that they are close to the same as the th400... but not as tough.. unless you are willing to build them.. but for everyday use, a 700 would be My personal choice of transmission.

12-30-2008, 03:15 AM	#4
gmctrucks Senior Member Join Date: Nov 2006 Location: Houston,Texas Posts: 4,033	I have heard that the 700 has better gears in it for 4x4ing and so on.

12-31-2008, 11:19 AM	#5
csracing93 Full Member Join Date: Nov 2008 Location: Warren, Ohio Posts: 34	The gear ratio for the 400 is 2.48/1.48/1.00 and the 700r4 is 3.06/1.63/1.00/0.70 does this help any?

01-01-2009, 07:10 PM	#6
batty1214 Senior Member Join Date: Nov 2008 Location: Vernal Utah Posts: 1,135	cs racing has the numbers that I was looking for....... the gears arent quite as low, but you gain one more gear... so highway you arent screaming at 70

05-27-2009, 12:24 AM	#8
samiam Full Member Join Date: Jan 2009 Location: yuba city California Posts: 21	if you need overdrive and cant afford an overdrive unit to bolt onto a 400, then get the 700, but know that heat kills them quickly. to make it last you must run a heavy duty radial rv cooler and if your fliud out line is a 1/4 inch tap it out to 3/8, if your in line is 3/8 tapp it out to 1/2 inch. i killed a 700 quickly havent killed a 400 yet. A buddy did what I suggested to you (his idea not mine) and he pulls a 12000 pound trailer all the time with no issues

05-27-2009, 07:30 PM	#9
semocoachworks Senior Member Join Date: May 2009 Location: rapid city, sd Posts: 428	I had a th400 in my 84 3500 4x4 and pulled it to put in a 700r4. I had a heck of a time with the kickdown cable not staying adjusted, i would open it full throttle and push the thumb button down and it would be good for a while then all of a sudden, it would shift quickly into overdrive or stay in 1st forever. I replaced the cable and it seemed to have cured the problem. I will, however, be putting my th400 back in as soon as I get time. I tow quite a bit with this truck and it don't see the interstate very often so i really don't need overdrive. Just my 2 cents.