Automatic Transmission Filter Replacement

[whh333]

I purchased a 1992 NSX with automatic transmission and 130,000 miles and incomplete service history. Looking through the Service Manual, I cannot see any procedure for replacing the filter, its only procedure is draining the fluid. I drained the fluid and it did not look or smell old. The magnetic plug showed little accumulation and the transmission is operating great. Before replacing the fluid, I wanted to replace the filter and a web search shows two filters for this year, one a typical flat metal housed filter



and a cannister filter like this



Does this transmission take either or both of these filters?

Also, I am not finding a source for automatic transmission pan gaskets, anyone know where these can be purchased?

Finally, I have replaced transmission filters before, but this does not look like typical pull the pan, see the filter and replace. There only seems to be a long, narrow pan where the shift linkage enters, is there a procedure for accessing and replacing the filter?



Thanks for any ideas!

 

[Honcho]

You need to remove the transmission and open up the case to reach the filter. Reference my post here:

Post in thread 'New NSX owner introduction'

28 October 2021

Yes. All I could afford atm

There is nothing wrong with an automatic NSX- it is still a NSX. You chose well. However, almost all U.S. autos have been neglected in maintenance. It's partially Acura's fault because they gave us incomplete guidance on the AT to keep it running long term. The NSX AT is a lot more similar to a modern DCT than a traditional automatic transmission in that it uses clutch packs to engage and disengage each gear. These clutch packs are basically stacks of thin metal discs that squeeze together. Like any clutch, the disc material wears out...

• Honcho

 

[whh333]

Wow, not only did Acura give incomplete guidance, they seem to have discouraged filter maintenance by making it inaccessible.

 

[Honcho]

Wow, not only did Acura give incomplete guidance, they seem to have discouraged filter maintenance by making it inaccessible.

Yeah, it's really frustrating. The AT can basically run forever if you change the filter every ~100k and keep the fluid clean (by changing it every 15k in between). But, for some reason, Acura decided it was better to just exchange the transmission for a new one whenever a customer's AT went boom. That worked until the car was discontinued in 2005.

The good news is that the shift solenoids and clutch packs are still available from Honda. My advice to any AT owner- especially those over 100k miles- is to buy all that stuff now and keep it on the shelf. Even if you catch it in time with a filter change and regular fluid changes thereafter, you've got piece of mind if the parts fail. Honda is not making any more of this stuff and once it's gone, it's gone.

Also, at this point I wouldn't trust Acura to have any idea how to service these AT units. As noted above, they didn't even let their dealer techs touch them when the car was in production. However, there is a bit of good new here too in that any halfway decent transmission shop that services Honda/Acura automatic transmissions should have no problem working on it. As long as you bring them the parts (they will probably have no clue about finding stuff for a NSX) and the pages from the service manual, they should be fine. After all, it's a transmission, not a space probe.

Clutch Packs (LOW and TOP):

ATM-4 Clutch (ﾛｰ･ﾄｯﾌﾟ) for Honda NSX frame E-NA1 - Auto parts - Amayama

www.amayama.com

Clutch Packs (L-H and 3rd):

ATM-4-1 Clutch (ﾛｰﾎｰﾙﾄﾞ･ｻｰﾄﾞ) for Honda NSX frame E-NA1 - Auto parts - Amayama

www.amayama.com

Clutch Pack (2nd):

Honda 22600-PR9-000 (22600PR9000) CLUTCH ASSY., SECOND

Honda 22600-PR9-000 (22600PR9000) CLUTCH ASSY., SECOND. New & genuine Japanese car parts. Fast shipping. Low prices. Request a quote from Amayama Trading Co. online.

www.amayama.com

Lock-Up Shift Solenoid:

Honda 28300-PR9-004 (28300PR9004) SOLENOID ASSY., LOCK UP

Honda 28300-PR9-004 (28300PR9004) SOLENOID ASSY., LOCK UP . New & genuine Japanese car parts. Fast shipping. Low prices. Request a quote from Amayama Trading Co. online.

www.amayama.com

Shift Solenoid:

Honda 28200-PR9-014 (28200PR9014) SOLENOID ASSY., SHIFT

Honda 28200-PR9-014 (28200PR9014) SOLENOID ASSY., SHIFT . New & genuine Japanese car parts. Fast shipping. Low prices. Request a quote from Amayama Trading Co. online.

www.amayama.com

Linear Shift Solenoid:

Honda 28250-PR9-004 (28250PR9004) SOLENOID ASSY., LINEAR

Honda 28250-PR9-004 (28250PR9004) SOLENOID ASSY., LINEAR. New & genuine Japanese car parts. Fast shipping. Low prices. Request a quote from Amayama Trading Co. online.

www.amayama.com

Filter & O-Ring:

Honda 25420-PR9-020 (25420PR9020) STRAINER, TRANSMISSION

Honda 25420-PR9-020 (25420PR9020) STRAINER, TRANSMISSION . New & genuine Japanese car parts. Fast shipping. Low prices. Request a quote from Amayama Trading Co. online.

www.amayama.com

Honda 91308-PW4-003 (91308PW4003) O-RING 21.8X1.9

Honda 91308-PW4-003 (91308PW4003) O-RING 21.8X1.9. New & genuine Japanese car parts. Fast shipping. Low prices. Request a quote from Amayama Trading Co. online.

www.amayama.com

 

[whh333]

@Honcho, many thanks for taking time to post these resources!

Would I buy the complete packs or would buying the clutch discs suffice? If I have to choose, it seems 1st and 2nd would be the high wear ones.

Also, I may be doing a timing belt, so dropping the engine/transmission could be in my future. How deep into the transmission would I have to go to get to the filter?

Thanks again.

 

[Honcho]

@Honcho, many thanks for taking time to post these resources!

Would I buy the complete packs or would buying the clutch discs suffice? If I have to choose, it seems 1st and 2nd would be the high wear ones.

Also, I may be doing a timing belt, so dropping the engine/transmission could be in my future. How deep into the transmission would I have to go to get to the filter?

Thanks again.

Clutch discs are all you really need as long as the metal plates still measure within spec. When they do this job in Japan (there are a lot more ATs there), they just replace the entire assembly.

The filter is doable, but you have to remove the left side cover and transmission housing to access it. Amazingly, Honda left us a comprehensive, step-by-step guide on completely overhauling the AT. I strongly recommend you read Section 14 of the 1997-2005 service manual and study it. The disassembly process starts at 14-120. Also worth doing are the shift solenoid screens- they have little gasket screens just like the VTEC spool valves on the engine. Clogging at these screens results in a loss of line pressure at the solenoids, which leads to slams shifts and eventual shattering of the clutch discs. They're only a few bucks and if your solenoids are still good, it buys you more time before replacement is needed.

Of course, by the time you've got the housing off for the filter, now you're into the "while you're in there" spiral. Is it worth replacing all of the $1 rubber o-rings on stuff like the accumulator pistons? Probably, but how deep into the trans do you want to go? Same with the axle seals. The main battle with the AT is fighting clutch dust and keeping it out of the very complex hydraulic circulation system. But now that these transmissions are approaching 30+ years old, you're also confronting the old, hardened rubber issue. If you have the trans out already for the TB/WP job, it might be worth dropping it off at a transmission shop with a copy of the service manual and all the replaceable parts, o-rings and seals neatly labeled. It's probably a couple hundred bucks worth of consumable parts (not including the clutch packs), but it resets your transmission to "zero."

Another thing you may want to consider is running the stall speed and line pressure tests on the transmission. It can tell you a lot about the health of the AT and amount of clutch dust accumulation. Again, Honda really did us a favor with the service manual. The procedure is on 14-104 and 106. If all of your line pressures are testing within spec, that means the clutch packs and torque converter are probably still in good shape, since they've never been slammed. In that case, you could just replace the filter and solenoid screens and call it a day. But, if the pressure is too low or on the borderline, it may be worthwhile to change out the clutch packs as well, since the test suggests they have been exposed to harsh shifting for a while.

 

[whh333]

Wow, great info, I have a transmission pressure test set, that seems the best place to start. The car is in surprising shape for 130,000 and after the first round of improvements, I can get a better idea of how it has been driven with a leak-down on the engine

 

[Honcho]

Wow, great info, I have a transmission pressure test set, that seems the best place to start. The car is in surprising shape for 130,000 and after the first round of improvements, I can get a better idea of how it has been driven with a leak-down on the engine

Yeah, I'd start with the stall speed tests and line pressure tests. I got my 92 AT with 137,000 miles and it still shifted very well. I found the service records and it turns out the previous owner changed his trans fluid every 2 years for 20 years, so he was flushing most of the clutch dust out of the transmission before it could accumulate. Even though the ATF has plenty of life left at that interval, it's the dirt you're really worried about. If your trans had regular fluid changes, I bet it will be great.