'Shimming' an A340- must read for all supercharged Yota's

[mastacox]

I am starting this thread as a place to discuss anything I've found in reading accross the internet on this particular topic. Perhaps when the information here has "matured" I will Wiki-ize it...

As most people with a supercharged 3.4l V-6 and Automatic tranny know, the added horsepower brought by forced induction and proper fuel delivery can lead to premature transmission failure, specifically in the 1-2 shift clutch packs. In the past, the "best" options to help combat this sort of failure have been to:

1) Add an aftermarket transmission cooler.

2) Have your transmission's valve body modified by a limited few trasmission shops on the east coast (either IPT or Level 10). Unfortunately, this modification is relatively expensive, costing as much as $1000 with shippping to the shops.

As of yet, I have not done the VB mod because of it's prohibitive cost, instead opting to stay out of the throttle near the 1st to 2nd gear shift region... a dangerous mistress, but acceptable when weighed against the current alternatives IMO.

But, in my and other people's search for an alternative to an upgraded valve body, it has come to my attention that there may indeed be an option, a process called "shimming the accumulators" commonly used by Toyota Supra fanatics pushing in the neighborhood of 400+ hp. This can have the effect on decreasing shift time, and limiting clutch burning in the transmission (coincidentally, the same thing a VB mod does). The transmission used in these cars is an A340e, a close relative of the Toyota Tacoma and 4Runner transmissions (the A340f and/or A340le).

Speedy of YT first mentioned this possibility, after some conversations with some Tacoma enthusiasts over at CustomTacos. Huge props to Speedy for bringing this possibility to light, and possibly bringing a new option to those who don't want the VB option to be the only possibility. I for one would much rather do my own tranny work for under $50 if the end result is the same. The main problem in the past has been that no one really knows what it is Level 10 or IPT do to the valve bodies to make them more effective. I personally suspect with a drill press and some higher rate springs, anyone could do the same mod in their garage... but, the companies did the research and they have the right to try and recoup their costs.

So, here are the links. The SupraForums thread is an especially informative read, although quite long at 14 pages. The Yotatech and Customtacos links are supplemental discussions related to adapting this shimming technique to a truck. I plan to shim my tranny in the next month or two, and see what the results are. I will take MANY pictures and prepare a detailed writeup of my trials and tribulations here.

Supra Forums Thread: "How to make an A340 last" by Raven97990
http://www.supraforums.com/forum/sho...d.php?t=267655

YT Thread: "Speedy's Supercharger Thread" by Speedy
http://www.yotatech.com/f2/speedys-s...9/index25.html

Customtacos Thread: "Tranny tech said don't do VB upgrade" by Speedy
http://www.customtacos.com/forum/showthread.php?t=97198

[MTL_4runner]

I saw that on CT about shimming the accumulator springs. I have long wondered about what "magic" was involved in the send your VB away upgrade because trannys really aren't that complicated at all (despite the spaghetti network of fluid passages in the VB). We know for a fact that stiffer springs were part of the mod (shimming would have a similar effect and allow you to use the same set of stock springs). Shimmming changes the spring rate slightly so no wonder different size shims have different effects on the crispness of shifts......it all looks very promising indeed and hopefully we'll eventually hammer out a formula like we did with the Tundra brake upgrade. Even a vehicle with a stock motor could benefit from a mod like this if you did alot of towing. I'm anxious to see more on this as it all progresses. I'm sure after tearing into my motor as far as I have that doing some tranny VB work would be a natural progression to make sure this thing lasts as long as possible. The best part is that as long as you don't permanently modify the VB, this mod will also be completely reversible if you want to sell the vehicle to a soccer mom at some later date.

[Cebby]

I'll be watching this intently since I have my trans out currently. Are there any close ups on the shims with dimensions?

[mastacox]

Are there any close ups on the shims with dimensions?

This is a little bit stickier as of this point, as it would appear that the thickness of shims used in the Supra's A340e are not as "effective" in a truck's tranny, so we have to go much thicker. Still, I have a pretty good idea of a good place to start, and results from 03TacoPre at CT as well QSVeilside and others will be flowing in en masse.

The shims used by the Supra guys are 20-21mm in diameter (no larger, otherwise might not fit) and 6-8mm in thickness. This works out to .787-.826" in diameter, and .236-.315" in thickness. According to the SupraForums reviews, 6mm is a significantly more positive shift, and 8 is borderline "neck-snapping." Usually, the Supra guys shim the 1-2 and 2-3 accumulators (usually a thicker shim on the 1-2 than the 2-3 as well), and leave the 3-4 accumulator alone.

Now 03TacoPre over at CT shimmed all three accumulators half an inch (.500) and said that the shifts were better but not as firm as he was hoping, and definitely not neck snapping. He has since said he would try a 5/8" or even 7/8" shim in the 1-2 accumulator for a better shift, but the 2-3 and 3-4 shifts are firm enough for his taste. Unfortunately, 03TacoPre's review is only marginally useful, because he has a 4cyl Taco. What we're really after is whether the tranny gets better shifts under full thorttle of a Charged/Fueled 3.4l...

QSVeilside (2000 2WD 4Runner Sport, what tranny does that turn out to?) will AFAIK be trying a 5/8" shim in his 1-2 accumulator, and 1/2" shims in 2-3 and 3-4. At this point, it is unclear whether the 3-4 accumulator even needs a shim, but some prefer the shifts to be similar in all of the gears. We should be getting some initial test reports back from Q within a week or two which will be critical, because he has a supercharger and fuel mods. Still, it could be we will have to take his experiences with a grain of salt because he has said the 1-2 shift is slipping badly under full throttle, hinting that tranny damage has already taken place.

I'm thinking I too will be going for a 5/8" shim in the 1-2 accumulator, and 1/2" in the 2-3 and 3-4; pending reviews from Q of course

Picture of a shim example and accumulator:
[img width=800 height=600]http://bedders.bulldoghome.com/photos/BDRES/bedders_bulldoghome_com/No.17.jpg[/img]

[mastacox]

I have long wondered about what "magic" was involved in the send your VB away upgrade because trannys really aren't that complicated at all (despite the spaghetti network of fluid passages in the VB). We know for a fact that stiffer springs were part of the mod (shimming would have a similar effect and allow you to use the same set of stock springs). Shimmming changes the spring rate slightly so no wonder different size shims have different effects on the crispness of shifts...

I have never believed that the VB mod is something that has to be done by a shop. One of my firends did a "VB mod" to his '01 cummins that involved drilling out some holes, and putting new springs in the unit. The kit was cheap and he did it in about 30 minutes taking his time (the tranny was already out). What they (IPT and L10) do to the VB is a mystery because they know as soon as the info is out, people would rather buy a "do-it-yourself shift kit" for $100 than send the VB off for $600-1000.

With this "discovery" we are one significant step closer to decoding the puzzle. Higher spring rate in the accumulator definitely decreases the shift time, so I'm quite sure that is one thing that's done. They use springs instead of shims, but the result is the same. As a matter of fact, if we knew exactly how far the accumulator springs were compressed while being used, it would be quite easy to figure out what spring rate spring would be required to equal a certain thickness of shim...

As for passages that need to be enlareged, that is a more difficult undertaking. I suspect they enlarge some passages to increase flow and pressure in specific parts of the tranny (such as the 1-2 shift pate). Some Supra guys are lucky enough to have a dial on their VB that achieves a similar result, but it is unclear which transmissions have it and which don't (03TacoPre's didn't, for example). I will be quite lucky if my transmission has one of the coveted "adjustable pressure" valve bodies (see pic below) because I will be able to increase tranny pressure (if it is not already at the max position) AND decrease shift times, giving me a VB mod for somewhere in the neighborhood of $50 including fluids.

Side note- Supra guys also increase the pressure in their A340e's by tightening the kickdown cable, or even locking it in the maximum position. While somewhat annoying at lower speeds due to the harder shifts, it is an effective solution.

The precious dial:
[img width=800 height=600]http://bedders.bulldoghome.com/photos/BDRES/bedders_bulldoghome_com/No.11.jpg[/img]

[Seanz0rz]

i wonder how this would perform without the SC. this may be a way of keeping the tranny from eating itself just out of normal and offroad use.

[MTL_4runner]

Usually, the Supra guys shim the 1-2 and 2-3 accumulators (usually a thicker shim on the 1-2 than the 2-3 as well), and leave the 3-4 accumulator alone.

That would make sense to shim the 1-2 side the most because the #2 clutch pack is usually the one that gets smoked under high torque (the lower the gear, the more torque is generated in the tranny and the faster the shift needs to be to keep from cooking the band clutches). So if the 1-2 shift isn't crisp, then your tranny is going to be absorbing that power as heat from friction. Rather than using shims what people really should try to find are stiffer springs. I'm sure there are places that make stiffer springs for these valve bodies because they often have interchangeable parts with other models.

Here's what your springs should look like:


Here's what comes back from the shop (3 new springs and one machined VB)


Here's a good thread with tons of internal tranny pics:
http://www.importperformancetrans.co...4a7e5cfc01c66a

Side note- Supra guys also increase the pressure in their A340e's by tightening the kickdown cable, or even locking it in the maximum position. While somewhat annoying at lower speeds due to the harder shifts, it is an effective solution.

The kickdown cable mod has been around for a while but it's really a band-aid fix.
You can definately tighten it, but I don't suggest locking it out at max.

Some Supra guys are lucky enough to have a dial on their VB that achieves a similar result, but it is unclear which transmissions have it and which don't (03TacoPre's didn't, for example). I will be quite lucky if my transmission has one of the coveted "adjustable pressure" valve bodies (see pic below) because I will be able to increase tranny pressure (if it is not already at the max position) AND decrease shift times, giving me a VB mod for somewhere in the neighborhood of $50 including fluids.

I hate to say it but don't hold your breath.....I have yet to see one on any of the A340 truck trannys.

[mastacox]

Rather than using shims what people really should try to find are stiffer springs. I'm sure there are places that make stiffer springs for these valve bodies because they often have interchangeable parts with other models.

Here's what your springs should look like...

Given the specs, you can find ANY spring here:

http://www.centuryspring.com

When I take my VB apart, I may do some basic measurements of the springs (rate, free length, coil dia, working compression, etc.) and from that I may be able to estimate the specs of the replacement springs...

[MTL_4runner]

It looks like 3 items are being addressed for the the VB upgrade.

Here was the original comments on what was involved:

As many Toyota and Jeep owners know, the AW4 / Toyota 340, A340, and A341E series of transmissions are generally very well made and demonstrate excellent durability in unmodified applications. The framework is present for an extremely strong transmission that is to be used in a high performance or extreme duty application.

The problem is that the original calibration is engineered for driver comfort rather than ultimate component strength. The soft, sliding shifts that are part of the original design are not appropriate for increased horsepower applications, towing, off road use, racing, etc.

These calibration inadequacies quickly manifest themselves as extremely poor shift quality, and more often than not, severe damage to the gearbox is soon to follow. One of the most common symptoms of this is the engine stuttering or hitting the rev limiter during a full throttle upshift.

Without going into too much technical detail, the factory shortcomings can be addressed through modification and recalibration of the control valve assembly, a.k.a. the valve body.

The valve body is a component that is comprised of valves, solenoids, an orifice separator plate and an intricate series of passages- it is the most complex component in the most complex part of your vehicle- the automatic transmission.

The function of the valve body is to act as the "brain" of the automatic transmission- it directs hydraulic pressure to the appropriate clutches and bands at the right time to initiate upshifts, down shifts, selection of reverse, converter clutch application, etc. As well as controlling shift timing and shift quality, it is also responsible for directing hydraulic pressure to the cooler and the lubrication circuit.

As you can imagine, the transmission's operational characteristics can be drastically altered and also customized to the given application through modifications to this component.

Because there are no commercially available shift kits for these transmissions, we began working on valve body modifications that were appropriate for Supras, Jeeps with the AW4 transmission, Toyota Tundra, Tacoma and 4Runner, and also Lexus SUV’s and rear drive passenger cars- especially those that needed to handle the additional power that accompanies the installation of a supercharger, turbo or nitrous oxide injection.

At the risk of oversimplification, there are a few things that are done in concert to create much more favorable operation of the gearbox.

First part
The first thing that needs to be done is to increase the hydraulic operating pressure of the transmission- this pressure is known as "line pressure". All hydraulic functions of the transmission are based on this pressure- what is especially of concern for these purposes is the clamping force which is applied to the clutches and bands to get them to hold against engine torque.

In simple terms, increased engine output is complemented by increased line pressure and increased "clamp" on the clutches- this can be likened to a performance clutch with a heavier pressure plate spring in a manual transmission equipped vehicle.

The idea is to raise this pressure only slightly at light throttle but increase it by 30-40% at full throttle- where it is really needed. The effects of this are shifts that are not overly uncomfortable at lower throttle openings, while at heavier throttle, firm shifts with much shorter clutch application time and increased clamping force can be achieved.

An additional benefit of this is increased flow through the transmission’s cooler and lube system.

Second part
Secondly, hydraulic pressure is normally routed through an orifice in a metal "separator plate" that resides between the two halves of the valve body before it gets to its intended destination. By altering these orifices, we can increase the volume of hydraulic oil that is used to apply the various clutches and bands.

Third part
The final part of modification is the alteration of the accumulator circuits. These are hydraulic circuits that are parallel to the components that are used for shifting. Their function is to absorb or "accumulate" some of the hydraulic pressure that is intended to apply a clutch pack or band. By limiting the action of what is essentially a "shock absorber" for each shift, we are able to further reduce clutch lock up time and shift lag at wide open throttle.

The end result is that shift time is reduced by 30 to 80%, depending on the amount of acceptable shift feel and the intended application. The clamping force that is required to apply the clutches and bands is increased by 30 to 40% at full throttle. Flow through the cooler and lube circuit is increased and the converter clutch application time is also reduced.

Transmission and valve body upgrades are not only for American made vehicles anymore. Increased performance and more efficient shifting is now available for vehicles of almost every manufacturer thanks to the few companies that are willing to do the research and development work required for this rapidly growing segment of the automotive aftermarket.

So now it's just a question of understanding the fluid circuits and modifying as necessary.

[mastacox]

- Update -

QSVeilSide successfully modified his transmission by shimming the accumulators. He used a 5/8" shim in the 1-2, and 1/2" in 2-3 and 3-O. However, in retrospect he said that he thinks a 7/8" shim in the 1-2 and 1/2" in the 2-3 would be ideal, with nothing in the 3-O accumulator. Shimming the 3-O accumulator can make downshifts somewhat harsh, and makes shifting into reverse irregular.

Interestingly, he also found the "pressure aduster" on his valve body, however it looks different than the Supra A340e adjuster, and also appears to be in the maximum position. So, might be a no-go there... I plan to tighten my kickdown cable a bit more when I go for this modification.