420A 1st gear hard to engage sometimes??

[Culon1997GS]

Hello everybody, my 1st gear sometimes won't engage, I try to shit into 1st and I'd feel like it doesn't want to go in, or I have to push it hard for it to go in, I changed my tranny fluid like 2 months ago, anyone has any idea what can be happening?

 

[BLACK'98DSM]

It may just be that the synchronizer is worn. This happened to me years ago before rebuilding transmission. It happens most when trying to engage the gear while slowing down, you'd want to completely stop for smoother engagement.

If it were an issue with the shifter cables/bushings then you'd be having this issue with more than one gear. A bent shift fork is possible but very rare and I don't think it's the case.

You can try using a thinner fluid so the synchronizer brake operates quickly but that places every aged bearing at risk of making noise or coming apart. The option I see best is tearing the trans open and replacing the synchronizer. Good news is that 1st & 2nd gear share a synchronizer, so by replacing it you will now have better operation for each shift. Bad news is that Mopar discontinued the OEM steel/fiber synchronizer so you have to use a full brass synchronizer. It isn't the worst thing ever, I have every synchro in my current transmission as brass. Each shift feels more mechanical though, they take some of the smoothness out of shifting that the fiber units offer. No biggie for a spirited driver but I'd prefer OE feel for a daily.

If you're interested in tearing apart multiple transmissions you may be able to piece together a full set of synchronizers in good shape (I usually keasure the inner liner thickness with a micrometer), but the time and effort isn't worth it when brass ones are dirt cheap and readily available.

If this issue pinches your nerves badly, I can help you tear the transmission open and fix it. If not, I'd say keep running it until more issues occur.

 

[Culon1997GS]

It may just be that the synchronizer is worn. This happened to me years ago before rebuilding transmission. It happens most when trying to engage the gear while slowing down, you'd want to completely stop for smoother engagement.

If it were an issue with the shifter cables/bushings then you'd be having this issue with more than one gear. A bent shift fork is possible but very rare and I don't think it's the case.

You can try using a thinner fluid so the synchronizer brake operates quickly but that places every aged bearing at risk of making noise or coming apart. The option I see best is tearing the trans open and replacing the synchronizer. Good news is that 1st & 2nd gear share a synchronizer, so by replacing it you will now have better operation for each shift. Bad news is that Mopar discontinued the OEM steel/fiber synchronizer so you have to use a full brass synchronizer. It isn't the worst thing ever, I have every synchro in my current transmission as brass. Each shift feels more mechanical though, they take some of the smoothness out of shifting that the fiber units offer. No biggie for a spirited driver but I'd prefer OE feel for a daily.

If you're interested in tearing apart multiple transmissions you may be able to piece together a full set of synchronizers in good shape (I usually keasure the inner liner thickness with a micrometer), but the time and effort isn't worth it when brass ones are dirt cheap and readily available.

If this issue pinches your nerves badly, I can help you tear the transmission open and fix it. If not, I'd say keep running it until more issues occur.

Yeah, I have to stop completely for it to go “smoothly” which sometimes it does go smooth, but rarely, I have to open my transmission anyways, my TOB is making noise, so I have to replace it, do you know where I can find the synchros? I’ll have to get used to them, bc my dsm is my daily

 

[BLACK'98DSM]

MANUAL / STANDARD TRANSMISSION - T350 NVT350 T355 NVT355 - Transmission Parts Distributors

T350 NVT350 T355 NVT355 TRANSMISSION PARTS & REBUILD KITS

www.transmissionpartsdistributors.com

 

[dwb]

Does it shift into first smoothly with the engine off? Does it creep forward while in gear, clutch pressed, and you rev the engine? If so, it's the clutch dragging, which if left like this will cause premature synchronizer failure.
In my experience (4g63t), a worn or broken synchronizer results in grinding/notchy shifting. You wouldn't notice it while stopped, but definitely while downshifting.

 

[BLACK'98DSM]

I'm yet to see a broken synchronizer. They are a high carbon steel and very tough. It's usually just that the fiber mesh inner liner (brake) wears down during high mileage use.

Also, replacing the throwout bearing does no require the transmission case to be opened up. You would only need to remove the transmission for that as it sits externally on the input shaft/clutch fork. Replacing the synchronizer actually requires the belhousing to be separated from the t-casing and for the 1-3 gear shaft to be pressed apart with at least 15 tons of force (hydraulic press). I have a transmission rebuild manual and can share pages from it if you'd like. Many OEM tools are "required" but most of them are discontinued. I fabricated replicas of some discontinued tools but other basic tools/contraptions can be used in their place, that's how I built the first transmission.

 

[luv2rallye]

How to test your syncros with engine and tranny still in car:

2G Transmission First and Second Gear Problems

I bought my car with a blown clutch, so after buying it I replaced the clutch. When I first drove it the car would not go into first gear from a standstill. I replaced the poppet balls and springs and I could get it into gear about 1/3 of the time from a standstill (I have to slam it in though)...

www.dsmtuners.com

 

[BLACK'98DSM]

That will work for every gear besides reverse. The reverse synchronizer only slows down the output shaft gearset, but the reverse idler gear engages via input shaft, so it will always grind if clutch is engaged. You'd be trying to mate a stationary gear with a spinning shaft, thus the grinding noise. The primary input shaft gear is part of the solid assembly, no bearing or synchronizer.

Also to note, the 3rd and reverse synchronizer are the same part. Usually when rebuilding the transmission you can use the reverse synchro for 3rd gear and install the brass for reverse. It isn't worn much. This way you still have an OE feel 3rd gear shift. That's only if you don't buy the full rebuild kit though.

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[dwb]

I'm yet to see a broken synchronizer. They are a high carbon steel and very tough.

Thanks for clarifying. I had no idea they were steel. I assumed (incorrectly) the F5MC1 used brass or bronze synchros like the W4A33.
Just for funsies, this is a broken 2nd gear synchro out my 91 AWD. It's the first revision that is made of brass (later rev is bronze).

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[Culon1997GS]

How to test your syncros with engine and tranny still in car:

2G Transmission First and Second Gear Problems

I bought my car with a blown clutch, so after buying it I replaced the clutch. When I first drove it the car would not go into first gear from a standstill. I replaced the poppet balls and springs and I could get it into gear about 1/3 of the time from a standstill (I have to slam it in though)...

www.dsmtuners.com

i did what he said on that thread "push the gear but not all the way in to see if it the engine slows down" 1st and 2nd didn't slowed down my engine.

 

[BLACK'98DSM]

That means, unfortunately, I was correct. The 1/2 synchronizer is worn. I have the full 34 page F5MC1/A578/NV-T350 transmission rebuild manual if you'd like pages of it. It's a meticulous job, especially if you have no experience with transmission internals. But I'm sure paying a shop to rebuild it would not be cheap. The link I already posted above is where to buy the brass synchronizer. At a minimum I'd also order the bearing and seal kit they offer. Usually the output shaft bearing and shift shaft seals are also deteriorated with the 1/2 synchronizer. Here's an exploded view so you have an idea of what you'd be getting into. Luckily the input shaft will not need to come apart unless you want to service 3-5 gears. And don't listen to anyone saying that the output shaft is not serviceable. The replacement assembly is $1200, but we've been servicing them for decades using the same rig as you would use to service the input shaft.

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