Turbo 400 Time

[Burbinator]

I was reading the '700r4 or 400 turbo' thread. While there is a ton of great info from members in it, I just don't agree that the 700r4 is capable of holding up under extreme conditions. I understand that there are those of us who have the same 700R4 in their vehicle that it came with when it rolled off the assembly line - and I envy you. :D But a 700R4 for me has always been voodoo. I don't like 'em, and never did.

For instance, I just rebuilt a 700R4 with all new heavy duty parts - Transgo shift kit, 13 vane pump, heavy duty Red Eagle clutches and Kolene steels, larger servos, Beast shell... the works. I built everything to precise tolerances, and anything suspect was discarded. It lasted about 350 miles before it destroyed the sprag and a few other parts for no explainable reason. I hadn't even towed anything with it yet! So basically, I'm out $360 bucks for the rebuild kit and assorted parts, and about a week in personal labor - but that's a heck of a lot better than the $2500 some jokers want for a repop.

So now, I find myself staring at my Suburban across the yard again, waiting for another transmission. I laid my hands on a pair of Turbo 400s yesterday, and I'll get around to building one probably next month when I have the time and feel like, and hang an overdrive on the end after playing with the gear ratios. But until then, there's a problem. Yep. The modulator valve.

Those 6.2 diesels with a Turbo 400 had a vacuum valve up on the passenger side of the engine that worked with the vacuum pump to allow for proper shift points, and kickdown (in conjunction with the solenoid).

The kickdown solenoid isn't really a problem: B&M makes a solenoid that can handle that. The real problem is the vacuum valve. Anybody got a good part number or source for one?

[argo]

What about a cable operated modulator? I don't know if these are still available, but they used to be. I have an old copy of HP Books "The Turbo Hydramatic 350 Handbook" written by Ron Sessions. In it, they list a cable actuated modulator for the TH-250, TH-250C, TH-350, TH-350C, and TH-400. This would eliminate the (reportedly fussy) VRV from the equation.

[Burbinator]

Argo, that was brilliant. I had completely forgotten about those. People running blown BBCs in their street rods used to use those. I know at one time B&M used to make them, but had forgotten completely about them.

So I went and saw 'Mr. Love Buggy' (older fella that drives a vintage dune buggy - he sounds like the van in the Pixar movie "Cars" :D) and he tells me all about it since his buggy has a Turbo 400 in it. He says they are still around and can be had new, but you have to hunt for them now by calling directly to the manufacturer (gonna call B&M on Monday). He also told me that the trick to making them work is you gotta use a 700R4 cable on it since the correct cable that was made for it is no longer produced. Otherwise it'll leak a little and produce bad shift patterns.

So, I just gotta say thanks to ya Argo. And of course, thanks to Mr Love Buggy. :cool:

[Robyn]

I have a factory "vaccum" valve sitting on my desk at home.

Will post the ####'s for ya later tonight or tomorrow.

These were the standard OEM equipement for a TH 400 with the diesel.

The 700R can be made to run well but will never equal a 400 for sure.

A 400 with a shift kit and a cooler is almost indestructable.

A 700 even with all the good stuff is still a BOMB just waiting to go BOOOOOM.

Even the best clutch drum is still aluminum and even with the steel ring pressed over the splined hub area, the sucker can go away.

I have built a few and had good luck, but these trannies are always suspect.

Just way too flimsy inside.


Missy

[argo]

Robyn, would you be so kind as to read this thread I started and offer your opinion please? The thread can be found here: http://www.thedieselpageforums.com/tdpforum/showthread.php?t=37774

Thanks!

[Burbinator]

I agree with you completely, Robyn. I've never had anything but mediocre experience with a 700R4. A Turbo 400 is nigh indestructible, that's for sure. The biggest problem there is the heat.

As an update, I found out why the sprag and pump went on that 700R4 with the 'goodie' parts I just built. Busted the case at the bellhousing, which I've seen time and again on these. And it was a K-case that was inspected for cracks prior to use in the rebuild, no less. Granted, I've been working and tweaking and massaging the motor to get as much as I can out of it with no turbo (should be around 200 hp now, or very close, and a noticeable increase in torque throughout the short power band as well). But that shouldn't have busted the case like it did. Then again, diesels are funny that way. Granted, I get my parts at discount. But I would at least like to get more than a buck per mile out of a fresh rebuild. :p

Anyway, please do hook us up with the part number for that vacuum switch. I want to experiment between that and the mechanical modulator and see which is more 'tweakable'. A good TCI or B&M vacuum modulator will allow for an adjustment in 2-4 mph increments. That's a very handy tuning tool to have at your disposal considering the narrow power band of a 6.2 diesel.

Thanks, Robyn! :)

[Jurek]

I have been running th 400 with deep aluminium pan, trans. cooler and gear vendors behind it for years /over 100k miles withouth any problems/.However never instaled any shift kit. You got me thinking. So question is :what kind of shift kit, who sell it and and how to installed/do I need to to take transmission apart/.Thanks . George.

[Burbinator]

Ideally, you should install a shift kit during overhaul with the transmission out of the vehicle and on the work bench. But, you can also install just about any of your choosing by dropping the pan and pulling the valve body while the transmission is still in the vehicle. I would suggest that if you have no experience in transmission work beyond changing the filter and fluid that you grab a good technical manual and read both the theory and overhaul sections prior to performing the job. You should do that even if you have a buddy who is experienced and will help you do the work.

There are a variety of shift kits available from different manufacturers but most are competition oriented, such as those offered by Hurst and TCI. Plus, those don't really do well in a stock transmission that hasn't had the pump or case modified, and heavy duty bands and extra clutches and plates installed (and hd drum, planetary gears, sprags, servos, et cetera). And by the time all of that has been done, you're looking at a rather expensive ($1500 bare minimum) transmission that's more adapted to racing than street or 4x4 use.

If you go for the hard, quick, race oriented shift, you'll probably break the transmission or something else in the drive line because the vehicle isn't a 1500 pound race car - if you have a Suburban like me, then its a 5 ton+ behemoth. On the other hand, if you're in loose medium such as sand, mud or snow, a cumbersome vehicle with a hard, snappy shift and no variance due to throttle pressure will bury you up to the frame in a heart beat because you lost traction and spun your tires. So really, you need a shift kit that is flexible enough to work with how you are playing with the throttle. That, by the way, is why a lot of us prefer a stick over an automatic. Personally, I think an automatic can be more difficult than a stick, if that automatic isn't set up right.

Anyway, I tend to go with Transgo shift kits. Granted, B&M has decent shift kits available, and the Transpak will let you calibrate your transmission for 'heavy duty and off road use'. But they just don't have the flexibility I like, and from my experience they tend to be hard on the transmission regardless of what the box says.

A Transgo kit, on the other hand, tends to strike a good balance between performance and endurance. You get a firm, moderately quick shift with no lag or sliding, and it gets harder and quicker the closer you get to WOT. That's exactly what you want for street and off road, and towing as well. A Transgo kit contains good documentation as well, and they offer a lot of nice little additional parts and pieces that solve a lot of different problem areas in many different makes of transmissions.

If it were me, I'd give Transgo a call and tell them what you want or need your vehicle to do. Give them your vehicle info, including year, engine, transfer case model, gears and tires you are running, and tell them you have a turbo 400, and ask which shift kit you should get. They'll hook you up.

And after you get that shift kit installed, grab an adjustable modulator valve. The stock repops are $10 bucks or less, and they have a single red stripe on them. Or, you can pay a little bit and get the B&M adjustable modulator valve. When you install a shift kit, it is going to alter your shift points a little. You can use that modulator to correct and enhance the shift kit by adjusting your shift points for max power and economy.

If you want to tune your shift points even more then you're looking at a governor calibration kit, which is going to run you about $40-$50, plus a little extra for a few quarts of trans fluid, and a day of juggling weights and springs, and test drives. Thankfully, a Turbo 400 governor is a lot easier to work with than a 350 or 700R4. A 400 governor cover is bolted on, while the 350's and 700's use a pressed in cover you have to pry out. But I'd only mess with the governor if I wanted to fine tune it to exact specs. Usually, an adjustable modulator is all the average enthusiast will want to mess with. B&M and TCI sell the governor kits, by the way.

[berg]

not trying to throw this off topic but a turbo 400 does not have an overdrive.... so then what a 4l60 or 80? Then you got to worry about a controller.
So why is the turbo 400 desired when you hit max rpm and you have to stay in the right lane.

[Burbinator]

Oh no. I don't think you're off topic at all. Its true that a Turbo 400 doesn't have an overdrive - in stock form. But you can turn a 3-speed Turbo 400 into a 6-speed with an overdrive unit (from GearVendor) and the only mod you'd have to perform is to slightly shorten and re-balance your rear drive shaft. That, and install a few other odds and ends that control the GV unit, which you can program to be fully automatic in function, or control manually. Granted, you can do the same with a 700R4 and get even more gears. But I had to consider the following.

First, I just snapped the case of a rebuilt 700R4 like a pencil at the bell housing. It was a K case transmission inspected for cracks and flaws, with all new, heavy duty, quality parts. That's not the first time I've seen that happen with a 700R4. Now, opinions vary and people have differing experiences with these transmissions and therefore you have the camp that likes them, and the camp that doesn't. I don't like them, and my experiences with them (street, serious racing, 4-wheeling, towing) has led me to believe that from an engineering point of view the 700R4 is simply a poorly designed transmission, inside and out.

The Turbo 400, on the other hand, was a superior design from the start, and it was intended to be so. You can say it was actually 'over engineered'. Even in stock trim, the TH 400 can withstand a heck of a lot of horsepower and torque due to superior internal and case design. Its a marvelous transmission, and its been around for over 40 years with little to no change - its still in use today as the 3L80. Now, let us set aside the overdrive and slightly better first gear advantage of the 700R4 - which can be overcome with a gear change in the TH 400 and augmented with the use of the GV, or by the GV alone. Now we have two equal transmissions to compare.

In order to get a 700R4 to even come near a TH 400 (let alone withstand the torque even a mildly massaged diesel is capable of producing) you'd have to:
debur the 700R4's case,
drill several oil passages to remove residual restrictions left over from the machining process,
upgrade to a steel Beast shell (stock is aluminum),
replace the planetary gears (more gears, better material),
rework the entire front pump assembly and install a 13-vane pump,
upgrade the sprags
upgrade the servos and accumulators (forget that Corvette servo crap, you need Sonnax parts) to improve band function and holding power,
rework the shuttle valves in the valve body to keep the transmission from slide-dropping into various gears and generally having what can only be described as a rather flaccid shift feel,
install a quality, heavy duty rebuild kit, with Borg Warner or (preferably for me) Alto Red Eagle parts
upgrade to a severe duty torque converter and switch (which if you don't know somebody, is going to burn you for about twice the amount of a stock hd converter, and they ain't cheap to begin with).After you do all that, then you can add your shift kit. And then you'll have something close to what you get with a TH 400 in stock form. That's just too much money to invest in a transmission with that many inherent flaws. And here's the icing on this cake of sorrow: the 700R4 has a very temperamental TV cable that controls the line pressure; if you mis-adjust it even a little transmission failure is assured within a month or less depending on driving habits.

Why did I build the 700R4 I just destroyed, then? Because I had most of the parts in the list just sitting on shelves in the back of my shop from when I was a lot younger and used to race, and it was only a few hundred more for the TC and rebuild kit. I didn't want to go with a GV unit yet, and thought the 700R4 would hold until I'd finished what I was doing with the rest of the drive train and motor. And it would have lasted a while, too. But the case failed on me. It can't handle the torque and horsepower the engine is putting out, which is going up. A Turbo 400, however, will handle the torque it is putting out now, and with a better drum and planetary gear assembly, it'll be able to withstand what I'm going to get out that motor before I even consider hanging a turbo on it.

But again, it all goes back to what you like, and what you want to do with your rig. If you're not going to tow anything heavier than a very small trailer with, say, a riding lawnmower on it across flat interstate, and stay in town and not do much off roading, then a 700R4 behind a stock or mildly upgraded 6.2 is just fine. Mind the big hills, though. A 6.2 is notorious for being underpowered and some have problems cresting even a speed bump - without towing anything. Plus, you have to consider that you can't tow anything with a 700R4 in overdrive. The transmission wasn't designed for that. You have to tow in drive, or, once again, you'll eat the transmission. And that's true of a stock and a built 700R4.

A TH 400, on the other hand, doesn't have any of these problems, and it far outshines a 700R4 with respect to durability, longevity, and flexibility. And with a GV behind it, you'll get better gearing and as a result equal and probably better fuel economy - whether you're towing or not, going through the mountains or not, or have made motor/gearing mods or not. So taking this into consideration, and planning ahead for the fact that the motor is eventually going to be producing about twice what the factory horsepower and torque ratings are, a TH 400 is pretty much a necessity for me. It just turns out that, in light of what I just did to that newly rebuilt 700R4, it became a necessity sooner as opposed to later.

[arveetek]

I absolutely LOVED my 700R4 I had in my '81 project truck.

In 1996, I converted my '81 C20 from a 305/TH350 combo to a 6.2L/700R4. The 6.2L was mostly stock, but freshly rebuilt. The 700R4 was a '90 model, which I purchased used from a salvage yard.

That tranny survived behind the stock 6.2L, then I added a turbo, then I completely tore the engine down and bored it .040" over, installed low-comp pistons, bigger pump, etc etc. The tranny was still going strong with over 120K miles put on by me. I don't know how many miles were on it when I bought it.

The only problem I ever had with the 700 was with the torque converter. It was mostly my fault, because I kept trying to tow in overdrive. This resulted in ruining the clutch facings and then the TC would no longer lock up. By the third TC, I had one custom built.

I wasn't easy on this 700 either. I towed a 5th wheel RV many miles, including a trip to South Carolina, Florida, and another trip to Colorado.

The tranny finally gave up after I sold the truck last year. The new owner told me that the rear seal popped out, causing the fluid to leak out, and then he cooked it.

So, my 700 lasted for over 13 years and over 120K miles, with additional unknown miles before that.

I think it's just like anything, sometimes you get a good one, sometimes you get a bad one. A lot of people think the 6.2L's are junk too. But I like 'em.

Casey

[Robyn]

By 1990 the 700R had been through a metric buttload of upgrades and redesigns.

Having purchased your 700 from the bone yard, the little critter may well have had a few other things done to it, such as a shift kit and some other mods along its life too.


The 4L60 of today is still basically the same gear box as the 700R except that it is electronically controled.

One of the worst spots in a 700R is the TV circuit (manages the line pressures) If this system is not absolutely right these trannies will self destruct quickly.

My biggest dislike for the 700R is that it is so small inside. All the clutches are tiny compared to even a TH 350.

The input drum is the area that contains the bulk of the clutches and it is aluminum with an aluminum spline where the input shaft connects.

This is another weak spot.

The late 700 is the only one to fool with as the early ones had very small input shafts and other serious faults.

"K" case is the magic word here Large K cast into the bell nousing up near the top.


I am actually considering a TH400 for my Blazer/6.2 project.
With the 3.73 gearing in the diffs and the 33" tires it will place the RPM right in the sweet spot for the 6.2 .

The only caviat is that the 400 does not have that lovely deep 1st gear.

The 3.06 low gear is great for getting up and rolling.

The Military rigs (CUCV) all had TH 400 trannies.

If you dont mind spending some $$$$$ on the 700R it can be a really good little box.

The 400 can be slopped together with just about any assortment of good stock parts plus a shift kit and come out kicking butt.

Now if there was a way to do a lockup converter on the 400 that would be sweet.

The 4L80 is nice, but the need for a computer to run the beast takes its toll on the pocket book for sure.


Best of luck however you go


Missy