Secret Manufacture's 4EAT Error?

[Trevor]

Relative History

The 4EAT transmission was developed by Mazda and Nissan, and was a replacement for the Ford LC transmission, adding a fourth gear, overdrive and electronic control.

The current manufacturer JATCO, was formed in 1999 after Nissan separated its transmission section into an independent company. Since then, JATCO has been supplying, Nissan, Mazda, Ford, Subaru. BMW, Volkswagen, MG/Rover, Hyundai, Jaguar, Daimler-Chrysler.

Recent Discovery

During 1990, Nissan registered a US patent, which covers an automatic transmission pressure regulating valve, with filtered flow to a pressure feedback chamber. The quite specific title, immediately drew my attention, as it directly ties in with the SVX 4EAT transmission, notably developed by Nissan.

The patent abstract, describes what is in fact a proposed production alteration to an original design, involving a modification required in order to correct a fault. The registration of this patent confirms the fact that Nissan were very conscious of an existing problem, which involves the blockage of a small strainer incorporated within the valve body.

Patent application requires that this is made and granted before the item involved is marketed, so that it is unlikely that the upgrade involved, was incorporated in early transmissions fitted to the SVX. The strainer at issue, is shown within the several coloured flow diagrams, as well as valve body illustrations, included in section three of the SVX manuals and filters fluid delivered by the pilot valve. The illustrations show no evidence of the strainer being incorporated in the SVX transmission, even though many other small details are represented.

Any gradual blockage of the strainer directly reduces line pressure accordingly. The invention covers an improvement, whereby there is a means of compensation for any restriction in flow through the filter. Feedback within the pilot valve, previously obtained from a point before the filter, is sourced after the filter. In this way the filter is included within the feedback loop, so that any build up of restriction is offset.

It would appear that this upgrade involves considerable alterations to the valve body passages, and therefore would incur substantial costs in making alterations within an existing production schedule. Did Subaru have access to this patented upgrade, at a time when Nissan supplied transmissions? Were special commercial considerations, obligations or circumstances involved? Was the patented upgrade incorporated within all or even any, production SVX transmissions?

As far as I can ascertain, no bulletin has ever been issued by Subaru covering an applicable upgrade, or alternatively an instruction advising the necessity to strip down the valve body and clean the strainer at regular maintenance intervals. Was there a cover up?

If the upgrade is not incorporated, as the strainer becomes progressively fouled, there will be a slow deterioration in line pressure. This may not become detectable, until on going damage finally results in friction surfaces failing. This could constitute an important undisclosed reason for premature transmission failure. With this in mind, I have installed a permanent dash mounted pressure gauge in my SVX, to keep a precautionary eye on line pressure.

Now required is a member with hands on experience, who can investigate the valve body, in order to ascertain and physically verify the facts. This is vital information of special interest here, and if properly sorted, understood and applied, could save members a lot of money.

[svxfiles]

Trevor, Great find!
I have to pull the valve body out of "Christine" as soon as I get a moment
I will say that when I installed LAN's reworked valve body in my Claret the flow was SOO much better that the trans,
(always filled with BG Products full synthetics)
dropped to the of causing my TC lockup not to happen at about 55°f ambiant!
Since my Claret has become a mostly warm weather car its not an issue.
If it were I'd remove the HUGE external trans cooler.




No, there is no such thing as too many mods!


Don't tell Di!

[Trevor]

Originally Posted by svxfiles

Trevor, Great find!
I have to pull the valve body out of "Christine" as soon as I get a moment
I will say that when I installed LAN's reworked valve body in my Claret the flow was SOO much better that the trans,
(always filled with BG Products full synthetics)
dropped to the of causing my TC lockup not to happen at about 55°f ambiant!
Since my Claret has become a mostly warm weather car its not an issue.
If it were I'd remove the HUGE external trans cooler.




No, there is no such thing as too many mods!


Don't tell Di!

Good one. Do you have a manual with a diagram of the valve body flow paths etc. as this would enable me to explain further details ?

In order to access the small strainer/filter you will have to split the valve body. In order to confirm whether or not the modification has been included, it will be necessary to trace a short flow path involving the pilot valve.

You could become a knight in shining armour.

[sowise]

Couldn't we possibly get replacement valve bodies from the Nissans with 4EATs or atleast recommend it as a potential improvement? Wonder if the Nissans were released with this mod if that would be something LAN would be interested in getting them for his valve body mods. Wasn't the Xterra one of the 4EAT we could swap with?

[Trevor]

Originally Posted by sowise

Couldn't we possibly get replacement valve bodies from the Nissans with 4EATs or atleast recommend it as a potential improvement? Wonder if the Nissans were released with this mod if that would be something LAN would be interested in getting them for his valve body mods. Wasn't the Xterra one of the 4EAT we could swap with?

Hopefully LAN will chime in here and advise if he has noticed blocked strainers, and or variations in the valve bodies between different models. As I understand it, he deals with Subarus other than the SVX.

[Hondasucks]

Can't speak for the 4EAT since I've never really had one apart, but I tore apart a 3AT (the three speed non-electronic trans) from an 82 GL, and it had "3N71B" cast into the valve body, which is what Nissan referred to their 3 speed automatic (which was also used in Ford Couriers, Nissan/Datsun pickups, Mazda pickups/cars, and RX7s among other things), I have never had the internals laid out side-by-side to compare though.

[Trevor]

Originally Posted by Hondasucks

Can't speak for the 4EAT since I've never really had one apart, but I tore apart a 3AT (the three speed non-electronic trans) from an 82 GL, and it had "3N71B" cast into the valve body, which is what Nissan referred to their 3 speed automatic (which was also used in Ford Couriers, Nissan/Datsun pickups, Mazda pickups/cars, and RX7s among other things), I have never had the internals laid out side-by-side to compare though.

Thanks for your interest. Let us hope that someone has the required hands on experience to provide further information.