Turbo 350 vs TH 700r4

[HotRodPC]

I've thought about swapping out my TH350 in favor of the 700R4 because with the TH350 my RPMs are so high at highway speeds with only having the 3 speeds. At 70 mph I'm up in the 3000 RPM range and I'd rather been down around 2200 or 2300. I know that the swap is not just a straight swap as I'd have to fab a new mounting bracket and a shorter drive shaft but from I'm reading from you it'd take a lot more to give it the strength I'd want? I had not heard this before. I'd heard some bad things about the 4L60E but not too much about the 700R4's.

The 700r4 is junkier than the 4L60-E. The E has problems with solenoids and electrical computer issues, but can you really blame that on the trans? Not really. But the 700r4 was such a POS, every single year, improvements were made. Then about the time its becoming an OK trans, now we switch it up with a new set of problems going to -E models. But as far as the hard parts in a 4L60-E they have the better technology design changes in the strength area. Lucky for us, most of the 4L60-E parts are backwards compatible to many of the 700r4s, so you can update the 700r4 with the newer stuff in most cases, but not all. Where you want as far as a 700r4 build, is with an 88-92 700r4 case. (93 went to 4L60-E). So avoid the 82-86 700r4's when possible. The 87 is an OK unit too, but with the changes from 87-88, the 88-92 is preffered. Now many 4L60-E parts are NOT interchangeable in the 82-86 700r4. Just best to find a 88-92 and be on the safer side.

 

[HotRodPC]

There are pro's and con's to the 350 vs 700r4. IMO, the winning transmission would depend on what you're using the truck for. T350 is stronger of course, needs less done to it to handle some abuse. 700r4 has a deeper first gear which is great for taking off, or pulling something at take off. BUT, the 700r4 has a very wide ratio between first and second, so you can potentially get that fall off in the shift to 2nd, so racers usually wind up first gear real tight over their power band range, so that when they hit 2nd, they are still at the bottom of their power band range. No need to do that in a T350. Of course the obvious OD in 700r4, no explanation needed. But, for you nice cruising 77, yes you need a 700r4 and would be the practical proper choice if you drive it on the highway at 70mph. I myself like 700r4 because you can run alot lower rear end ratio, which is a torque gain for sure, and also takes strain off the 700r4 helping it last longer, so with the 700r4 you can have the best of both worlds. A low 3.73 or 4.10 rear end ratio, but yet have OD to compesate for it in the big end. But to have that, you need to have a 700r4 properly built to overcome many of its weaknesses where the T350 is bolt in and go and with a couple added stronger parts will handle alot of abuse.

 

[HotRodPC]

To convert your Old77 to a 700r4 is going to be alot less headache than you think. Good chance you might NOT have to cut your driveshaft. There is only 5/8 inch difference in the 700r4 and the Intermediate output shaft T350 which is what you should have in your truck now. The trans with the 9 inch tailshaft housing. The yokes are also the same for T350 and 700r4, so d-shaft might just bolt right in, no mods needed. The shift likage is in he exact same spot as is the cooling lines. You can likely also use the same brackets on the carb for your 700r4 TV cable that the T350 is using for the detent cable. The same trans mount too and crossmember, just have to move the crossmember a couple inches. The only other thing to addess would be the TConverter lock up. There are kits sold to fix that issure for about $40 or so.

 

[Old77]

Good thinking on starting a separate thread just for this! Might be helpful to also copy/paste your other posts over here, too, that you just posted with regards to needing or not needing a shorter driveshaft for the swap from TH350 to 700R4

I will definitely refer back to this thread when I actually do the swap!

 

[HotRodPC]

All GREAT info man!

When looking at a 700R4, what "era" tranny it is to determine that it's an 88-92 unit as opposed to the earlier units?

As said your prefferance will be the 88-92 model units. Easy to tell them apart, and then get dialed in on exactly the year model by the #'s on the side. I'll post some pics of the differences. For 1, the older models you don't want, have pressure taps on the passenger side of the transmission. If you see the pressure taps, you know you don't want it. Some also look for what they refer to as the rainbow on the passenger side of the case in the casting. I'll also posts pics of that. Then of course the best way to tell is by the #'s on the case itself.

 

[89Suburban]

So my 700r4 trans is a piece of **** then? ***.

 

[HotRodPC]

You will notice in this ID chart, that the 82 and the 89 both have the 9 digit to identify them. Keep in mind, the 82 will have the pressure taps, the 89 will not, so that is how you tell the diffenece in an 82 and a 89 year model. The white arrow points to where you find that # to use the chart above.

 

[HotRodPC]

So my 700r4 trans is a piece of **** then? ***.

Why is yours a POS?? If its the stock 89 trans, that will be one of the better ones and most preffered. When its time for a build, you just need to do some mods to it to make it good.

 

[89Suburban]

Why is yours a POS?? If its the stock 89 trans, that will be one of the better ones and most preffered. When its time for a build, you just need to do some mods to it to make it good.

Oh, ok! I must say, the trans on this truck has been performing flawlessly and I tow a 2,000 lb boat 300 days out of the year, I am very pleased with it.

 

[89Suburban]

Also, Doesn't changing the trans fluid and filter lead to the beggining of cropping problems on high mileage trans?

 

[HotRodPC]

Here is a pic of the rainbow on a 700r4 that some will reffer to. This is what you want. The case with this rainbow in the case cast, is the more desireable unit to build. Also notice, NO PRESSURE TAPS.

 

[HotRodPC]

Also, Doesn't changing the trans fluid and filter lead to the beggining of cropping problems on high mileage trans?

Excellent point to bring up 89S. Don't ever fall for that . You should change your fluid and filter every 50K miles. Some will say more often, but they are usually trying to sell fluid and parts. If you tow alot or abuse your trans, you might wish to do it more often, say 35-40K. But, if you maintain your tranmission properly, YES you should change your fluid at those intervals no matter what the mileage is, even high mileage. In the event you have 120-140K and now you decide its time to change the fluid and filter, now you might have a problem. Because you may do is clean out gunk and junk out of the transmisison that has became a part of the transmisison and its tolerances. So now you clean the junk out, and your tolerances are much looser and you might start having problems. So the rule is. If you have always properly maintaned your trans, then continue to do so and you should get good life out of it. If you have NOT maintained your transmission and have let it go high mileage without maintaining it, then don't bother doing it now. Leave well enough alone and drive it until it quits. And btw, for all of those who have a slipping trans and think changing the fluid and filter will help, NO, don't waste your money on the new fluid and time for the job. The damage is done, its to late.

 

[crazy4offroad]

HRPC, I wish you werent so far away. I have a TH350 in the basement for my truck that I just know you could make it race ready. I wanted to rebuild it myself but I think it was water in the case and not sure what all might have been damaged, it mght be best to just turn it on for a core charge.

 

[HotRodPC]

HRPC, I wish you werent so far away. I have a TH350 in the basement for my truck that I just know you could make it race ready. I wanted to rebuild it myself but I think it was water in the case and not sure what all might have been damaged, it mght be best to just turn it on for a core charge.

Some of the hard parts may have become rusty depending on how deep the water was. I am building a T400 right now that sat outside and got water and mud in it. Its trying my patience badly. The servos are all stuck and rusted in it. The Center support bolt stripped out cuz it was rusty, corroded and seized. But its aprart now and I go pick up the case at the machine shop from being cleaned and I sure hope it came it out OK. Yep it might make a good core, then again it might even be OK to build. T350's are pretty easily had these days if people don't think they are gold since they aren't. I could sure build it though and make it last and handle some abuse. Do keep in mind, you want one that is NON LOCK UP. So if its got the 4 plug on the driver side, you want one that doesn't have that. The converter is stronger in the NON lock up model, and if you put the non lock up converter on the lock up trans, you literally explode the non lock up converter. No interchange there.

 

[HotRodPC]

How true this is, I dunno, I been told that the first 350C (C designates Lock Up Converter) used the same input shaft as Non LU T350 but it has a hole in to run fluid thru to the lock up mechanism in the converter, so that shaft woudl have a hole in. Otherwise, the Lock up shaft is differant and takes care of the guess work and unable to put a Non LU converter on the Lock Up trans. First Pic is NON LU, 2nd is 350C Lock Up.