Parts and knowledge exist to make them really strong -- but it took some serious searching
GM's small four-speed automatic has been both cursed and blessed. Its 0.70:1 overdrive ratio in top gear is the primary reason for the 700R4's popularity, but the 3.06:1 First gear also helps both on the highway and in trail use. Cussing of the 700 is usually a direct result of breakage, or because the lockup torque converter is acting up.
A lot of things have to be right for a TH700R4 to work correctly and to hold up under trail use. Not much has to be wrong for the trans to either not function correctly, not at all, or self-destruct rapidly. Probably the most common cause of a 700 acting up--and consequent failure--is a maladjusted throttle valve cable. But for the tranny to work properly and last, there is much, much more that has to be done right, and with the proper parts for the application. It took 10 years of building and breaking 700s before the torture testing paid off and Team Ramco got everything right. Having successfully used a 700R4 behind a 589ci big-block, Flash feels that running a TH700 behind a 502 in your tow vehicle shouldn't be a problem.
It was never meant to be a very stout trans, but as we looked into the virtues of this four-speed juicebox in Four Wheeler's July '04 issue, we found that there are indeed several ways to make a 700R4 live, even in high-power applications. In the process, we kept digging deeper into the world of 700s and discovered several more things that can be done to the R4, as well as things that shouldn't be done. For example, Team Ramco's "Flashman" Sharrar says that they can be built to withstand up to 850 hp and 600 lb-ft of torque. In addition, we found that mixing parts from different transmissions seems to lead to all kinds of odd behavior, including weird shift points and gear selectability in general.
After spending many hours interrupting the normally efficient work flow of the crew at Team Ramco (a Yuma, Arizona, transmission shop) asking questions, taking photos and gathering information for this story, we learned that a 700R4 can be made stronger than we'd ever thought possible, and that doing so isn't exactly inexpensive. Basically, building a TH700 is similar to most things in life in that you get what you pay for--the good, trick parts don't come cheap.
Starting With the Correct Basics
Although relatively obvious, it's best to use a K-case (from a 4x4) rather than the weaker C-case of a 4x2 or car. All those good internal upgrades are irrelevant if the case breaks. To avoid potential problems, it's also a very good idea to use a virgin--or at least a stock rebuilt--core, and one free of internal cracks. Since there are a variety of cases, valvebodies, separator plates, and gaskets, it's easy to end up with a combination that doesn't function correctly. Not only do these components vary by year, but also there are specific parts for cars, hi-po cars, pickups, vans, utilities, and also for diesels. Mixing them doesn't necessarily produce a match.
Lastly, newer is better when dealing with 700R4s. Try getting an '85-or-later core, ideally one from the early '90s, as GM continually upgraded them over the years.
Pick Your Level of Strengh
There are lots of aftermarket high-performance parts and OE upgrades (including those from the later-model 4L60 and 4L60E transmissions) to choose from, but unless you're running a really healthy motor or punish your tranny on purpose, most likely not all of the available trick parts are necessary. Perhaps the main reason for not using all the good stuff is cost. Team Ramco charges $3,000 to $4,000, installed, for a completely built TH700R4. On the other hand, the resulting tranny is said to outlast a stocker by quite a bit. Normally, a stock 700R4 or 4L60 would survive maybe 30,000 miles of trail use and twice that on the highway, according to Flash, but you can expect triple that amount with the components shown in this story. Combined with the included two-year/24,000 mile warranty, having the trans built with the good stuff may not be all that expensive after all.