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420A transmission pops out of gear in 3rd

RJ_IS_BATMAN

Proven Member
103
18
May 7, 2020
Ontario, California
Hey Everyone,

Another issue to add to my wonderful DSM rebuild haha, So my transmission is now popping out in 3rd gear. If i put my hand on the shifter and hold it in 3rd gear it runs fine but if i try to put it in 3rd and let off the shifter knob it pops out of gear.

Is this a sign of the transmission going out?

Any assistance would be greatly appreciated! I can't thank everyone on here enough for helping me through the issues I've had with my dam
 

twicks69

Supporting Vendor
3,791
890
Mar 12, 2004
Milwaukee, Wisconsin
Well, only a few things it can be. Internally, your 3rd/4th shift fork plastic pads are worn off/damaged, your synchro lining is wiped out, or your 3rd/4th slider has excessive wear, your 3rd/4th hub and slider snapring is broken and will be killing 4th needle bearing soon. Reference pictures below.
20210206_130042.jpg20210205_085701.jpg20210205_085620.jpg

Externally, look at your shift cable bracketry, shift cable bushings, front/rear motor mount bushings.

As well, keep in mind, the NVT350/ A578/ F5MC1 transmission has brass synchros (some have a fiber lined middle cone) for 1st/2nd but then paper/fiber lined 3/4/5/R steel synchros so you NEED to use ATF+4.

I was just working on one last week for a customer that thought 80w90 was the recommended fluid. I can tell you every fiber synchro lining was killed. His also had wiped out 1st/2nd linings along with worn shift fork pads causing popout of several gears, and a broken 3rd/4th hub and slider snapring. It needed all new synchros, and then the wear and tear items like new shift forks (surprisingly still available from MOPAR, but not cheap) and then all new bearings. The 3/4 and 5/R hub and slider snapring is discontinued so you will have to do some searching for a snapring that will work from a different application. Dimensionally, the ID/OD of the evo 4-9 end shaft snapring is within spec but the overall snapring thickness is thinner than the 2G NT stuff so a shim would be needed or you would have to surface grind down the snaprings and double them up to fit the groove on the input shaft. Off the top of my head its around a 2.09mm snapring normally used and the Evo thickest option is like 1.68mm (MD748454). The snap ring sizing ranges from 1.36mm-1.68mm with limited options still available. There are several platforms that share this snapring between Mitsubishi and MOPAR (F5M51), but as you can see, modification would be required to use it. I haven't looked in to it too hard to find an alternative snapring solution because I work on so few of these transmissions in comparison to DSM/EVO and other platforms.
 
Last edited:

RJ_IS_BATMAN

Proven Member
103
18
May 7, 2020
Ontario, California
Well, only a few things it can be. Internally, your 3rd/4th shift fork plastic pads are worn off/damaged, your synchro lining is wiped out, or your 3rd/4th slider has excessive wear, your 3rd/4th hub and slider snapring is broken and will be killing 4th needle bearing soon. Reference pictures below.
View attachment 623110View attachment 623111View attachment 623112

Externally, look at your shift cable bracketry, shift cable bushings, front/rear motor mount bushings.

As well, keep in mind, the NVT350/ A578/ F5MC1 transmission has brass synchros (some have a fiber lined middle cone) for 1st/2nd but then paper/fiber lined 3/4/5/R steel synchros so you NEED to use ATF+4.

I was just working on one last week for a customer that thought 80w90 was the recommended fluid. I can tell you every fiber synchro lining was killed. His also had wiped out 1st/2nd linings along with worn shift fork pads causing popout of several gears, and a broken 3rd/4th hub and slider snapring. It needed all new synchros, and then the wear and tear items like new shift forks (surprisingly still available from MOPAR, but not cheap) and then all new bearings. The 3/4 and 5/R hub and slider snapring is discontinued so you will have to do some searching for a snapring that will work from a different application. Dimensionally, the ID/OD of the evo 4-9 end shaft snapring is within spec but the overall snapring thickness is thinner than the 2G NT stuff so a shim would be needed or you would have to surface grind down the snaprings and double them up to fit the groove on the input shaft. Off the top of my head its around a 2.09mm snapring normally used and the Evo thickest option is like 1.68mm (MD748454). The snap ring sizing ranges from 1.36mm-1.68mm with limited options still available. There are several platforms that share this snapring between Mitsubishi and MOPAR (F5M51), but as you can see, modification would be required to use it. I haven't looked in to it too hard to find an alternative snapring solution because I work on so few of these transmissions in comparison to DSM/EVO and other platforms.


I have been having some issues with my shit cables breaking on this car, When i purchased the vehicle the previous owner had removed the shift cables as they had torn around the area that has the rubber boot on it. I found a replacement pair in the junkyard and these too gave up after less then 200 miles. I replaced then a 2nd time with another pair of shift cables and these have been working fine except for the occasional issue where the shift retaining clip has popped out and i have to put it back in again.

As for the Rear motor mount i discovered about 3 weeks ago that the car didn't even have the motor mount installed in the rear, The motor mount bushing was there but the bracket was cracked where it connected to the trans and was just there without being bolted down. I found a replacement and installed it but didn't change out the mount.

Im going to change out the motor mount bushing, inspect the shift cables and also drain and replace the transmission fluid with ATF + 4 and see if this helps. If worse comes to worse i guess ill pickup a tranny from Miller Imports as i see they have a few available.
 

XC92

Proven Member
685
93
Jul 22, 2020
Queens, New_York
Well, only a few things it can be. Internally, your 3rd/4th shift fork plastic pads are worn off/damaged, your synchro lining is wiped out, or your 3rd/4th slider has excessive wear, your 3rd/4th hub and slider snapring is broken and will be killing 4th needle bearing soon. Reference pictures below.
View attachment 623110View attachment 623111View attachment 623112

Externally, look at your shift cable bracketry, shift cable bushings, front/rear motor mount bushings.

As well, keep in mind, the NVT350/ A578/ F5MC1 transmission has brass synchros (some have a fiber lined middle cone) for 1st/2nd but then paper/fiber lined 3/4/5/R steel synchros so you NEED to use ATF+4.

I was just working on one last week for a customer that thought 80w90 was the recommended fluid. I can tell you every fiber synchro lining was killed. His also had wiped out 1st/2nd linings along with worn shift fork pads causing popout of several gears, and a broken 3rd/4th hub and slider snapring. It needed all new synchros, and then the wear and tear items like new shift forks (surprisingly still available from MOPAR, but not cheap) and then all new bearings. The 3/4 and 5/R hub and slider snapring is discontinued so you will have to do some searching for a snapring that will work from a different application. Dimensionally, the ID/OD of the evo 4-9 end shaft snapring is within spec but the overall snapring thickness is thinner than the 2G NT stuff so a shim would be needed or you would have to surface grind down the snaprings and double them up to fit the groove on the input shaft. Off the top of my head its around a 2.09mm snapring normally used and the Evo thickest option is like 1.68mm (MD748454). The snap ring sizing ranges from 1.36mm-1.68mm with limited options still available. There are several platforms that share this snapring between Mitsubishi and MOPAR (F5M51), but as you can see, modification would be required to use it. I haven't looked in to it too hard to find an alternative snapring solution because I work on so few of these transmissions in comparison to DSM/EVO and other platforms.

I know this is for a 420A and not a DSM, and you're just giving an illustrative example about yet another situation, but using 80W90 gear oil can ruin all these parts? Or was it GL-5, which I know is bad for brass and other soft parts because of sulfur additives? Or is this problem specific to a 420A trans and shouldn't concern DSM trans?

I put EP90 GL-4 in my 1G DSM AWD trans after I drained it, to have something in there for the relatively little amount of driving I needed to do (to replace dry rotted tires, get it inspected and fill it with gas) before dropping it again to fix a similar popping out of gear issue, and hope this isn't going to do further damage.
 

twicks69

Supporting Vendor
3,791
890
Mar 12, 2004
Milwaukee, Wisconsin
This is specific to the 420a transmission only. The F5M33 and W5M33 transmission uses GL-4 and GL-5 based 80w90 style fluids in stock form. The linings of the New Venture T350 (NVT350)/ A578 / F5MC1 transmission are completely different for friction material which is more like that of an automatic transmission friction lining.
 

XC92

Proven Member
685
93
Jul 22, 2020
Queens, New_York
This is specific to the 420a transmission only. The F5M33 and W5M33 transmission uses GL-4 and GL-5 based 80w90 style fluids in stock form. The linings of the New Venture T350 (NVT350)/ A578 / F5MC1 transmission are completely different for friction material which is more like that of an automatic transmission friction lining.

Thanks, and didn't mean to "hijack". Your post just gave me a brief scare, which you just alleviated. But since you just brought it up, isn't GL-5 a big no-no on either the F5M33 or W5M33, since both use brass synchros?
 

twicks69

Supporting Vendor
3,791
890
Mar 12, 2004
Milwaukee, Wisconsin
Thanks, and didn't mean to "hijack". Your post just gave me a brief scare, which you just alleviated. But since you just brought it up, isn't GL-5 a big no-no on either the F5M33 or W5M33, since both use brass synchros?
Almost every fluid on the market nowadays is GL-5. For the stock power level 4G63T cars on a F5M33 or W5M33 transmission, the OEM spec is Eneos Multigear GL3/4/5 85w90 dino oil. I typically have customers run Redline 75w85NS (no slip version) or Redline MT-85 (GL-4), and Redline 75W140NS for higher power levels and warmer climate driving.

The NVT350 / A578 / F5MC1 CAN take other oil that works with the paper fiber lined synchros, such as Mobil 1 Racing 4T 15w30 engine oil, or if the transmission is rebuilt with ALL BRASS SYNCHROS, then you can run a higher viscosity fluid like the turbo stuff. There are only a few rebuild kits that use full brass synchros for 3/4/5/R out there. I know that All State Gear rebuild kits come with fiber synchros, but I believe that Cobra Transmission kits are full brass, but you would have to confirm that the BK414WS kit that uses full brass synchros and not steel rings with fiber linings.
Link to synchro I am talking about - https://cobratransmission.com/a578-synchro-ring-551158426-1
 

XC92

Proven Member
685
93
Jul 22, 2020
Queens, New_York
Hmm. I was just going according to Jack's Trans which says not to use GL-5 or anything with sulfur in the trans, because it will mess up the brass parts. I thought that GL-5 was not really backwards-compatible with GL-4 because it has sulfur additives. This is not true?
 

twicks69

Supporting Vendor
3,791
890
Mar 12, 2004
Milwaukee, Wisconsin
Again, this thread is regarding 2G NT 420a NVT350 / A578 / F5MC1 transmissions, not the 4G63T F5M33 / W5M33 transmissions.

The ones I mentioned are non-Sulphur additive non-corrosive gear oils above (again, for use in the F5M33 / W5M33 transmissions)
https://www.redlineoil.com/75w90-ns-gl-5-gear-oil
https://www.redlineoil.com/75w140-ns-gl-5-gear-oil
https://www.redlineoil.com/mt-85-75w85-gl-4-gear-oil

If you want what was sold by Mitsubishi the last 30 years, buy that. It is cheap dino 75w85 Diamond gear lube (Eneos multi-gear non-synthetic) and is a rip off. MZ320197

For the 2G NT 420a NVT350 / A578 / F5MC1 transmissions, there are a few things that they can use with the paper fiber synchros.
04874465 - MOPAR manual transaxle oil for NVT350 (factory recommended for NVT350)

Diamond SPIII ATF - MZ320200 (factory recommended for NVT350)
AMSOIL - Manual Synchromesh Transmission Fluid (5W30) (used for years by owners with no problems)
Redline - D4 ATF (used also for years with no problems)
 

XC92

Proven Member
685
93
Jul 22, 2020
Queens, New_York
Yeah, I got the Mitsu oil for the trans. Haven't used it yet but since it's already paid for and I'm running a stock setup I might as well use it. Should be fine. I did get the Redline MT-85 75W85 GL-4 for the t-case and 75W90GL-5 for the rear diff.

So, enough about DSM trans in this thread. Thanks for the answers.
 

RJ_IS_BATMAN

Proven Member
103
18
May 7, 2020
Ontario, California
So, i decided to go through the linkage, check fluid levels etc and found the issue.

My bell housing has a huge hole and crack in it causing the transmission to leak fluid thus causing then 3rd gear to pop out.

So im debating if i should just get a bellhousing from the junkyard or just ditch this transmission and look for a replacement.
 

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twicks69

Supporting Vendor
3,791
890
Mar 12, 2004
Milwaukee, Wisconsin
Dude. Just replace the entire trans.
 
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