Builds Early Fj40 Rock Crawler Gets a Refresh (1 Viewer)

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Feb 21, 2012
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Snohomish, WA
 
Thanks for your input. Parts availability should not be too big of an issue because I am pretty positive any noises I hear are bearing related. Also nice to hear a press isn't essential. I did not find rebuilding my transfer case to be hard, so I am not too scared to dive into this trans. I'm really just looking for other things to trouble shoot before I tear it down.
Hopefully this weekend my dad will have some free time and can pop the transmission tunnel off and check the top cover situation. If that is not the issue, then at least I can get a head start on sourcing parts or getting some quotes from a shop to rebuild it. I still have a goal of being able to wheel it this summer but a busy schedule and lack of funds are making that quite the mission.
No problem. If you've got the time and patience, I'd recommend you take on the rebuild yourself. Paying a shop will be fairly cost prohibitive.

I will say that the bearings in the SM420 and SM465 are extremely robust and I've never personally seen a failed one assuming they have lubrication. HOWEVER I have seen a 1st/reverse gear with significant damage on the hub surface. It's not a syncro (because they're not synchronized on 1st/reverse) and I don't have my manual in front of me unfortunately. Essentially it's a hub "cone" and on the later year transmissions (which you think yo have) GM switched from bronze to some sort of aluminum compound which didn't hold up nearly as well. It can gall, seize and get very sticky. When I've rebuilt later year models, I've used the older assembly with the better bronze parts.

It's possible this could be your issue. I can send attach some parts of the damaged part later if you'd like. It's on my wall of shame
 
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Coarsegold
No problem. If you've got the time and patience, I'd recommend you take on the rebuild yourself. Paying a shop will be fairly cost prohibitive.

I will say that the bearings in the SM420 and SM465 are extremely robust and I've never personally seen a failed one assuming they have lubrication. HOWEVER I have seen a 1st/reverse gear with significant damage on the hub surface. It's not a syncro (because they're not synchronized on 1st/reverse) and I don't have my manual in front of me unfortunately. Essentially it's a hub "cone" and on the later year transmissions (which you think yo have) GM switched from bronze to some sort of aluminum compound which didn't hold up nearly as well. It can gall, seize and get very sticky. When I've rebuilt later year models, I've used the older assembly with the better bronze parts.

It's possible this could be your issue. I can send attach some parts of the damaged part later if you'd like. It's on my wall of shame
I have the patience for a rebuild, just not a lot of time unfortunately. 1st and Reverse is where I seem to have the issue of it really locking up so maybe that part is part of the issue that I am having. By locking up I mean to get it out of gear, I need to release clutch and inch forward to pop out of gear into neutral, or really slam the shifter back (Which I do not like to do obviously). I am really hoping its just an issue with my shift rails or top cover. If it is not I will gladly take on rebuilding this transmission myself. In the 5 years I've been driving, a transmission is the only thing I haven't had to rebuild so it makes sense to me that I might have to dive into this. I just write these off as learning experiences and luckily my parents aren't concerned about me lowering the property value by always having disassembled trucks laying around.
 
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So the transmission is on the ground, top cover off. The internals look very very clean. I can’t see any issues with the clutch either. What should I specifically be looking for inside this thing. Shift rails seem to be in decent shape. I do notice a good clunk when I move the reverse shift head. The gear appears to be interfering with something. I don’t know if that would cause the issues I’m having. I’m going to be tinkering and researching throughout the day. Hopefully something jumps out at me or someone can give me a good suggestion because I don’t want to blindly throw cash at this transmission.
 
Joined
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Oklahoma
So the transmission is on the ground, top cover off. The internals look very very clean. I can’t see any issues with the clutch either. What should I specifically be looking for inside this thing. Shift rails seem to be in decent shape. I do notice a good clunk when I move the reverse shift head. The gear appears to be interfering with something. I don’t know if that would cause the issues I’m having. I’m going to be tinkering and researching throughout the day. Hopefully something jumps out at me or someone can give me a good suggestion because I don’t want to blindly throw cash at this transmission.
Let me know what you find. I have a similar issue with my SM420 getting stuck in 2nd gear (3rd if you’re counting granny gear as 1st). I have to start pulling on the shifter a few seconds before I’m ready to shift to hopefully get it to “slot” it’s way out so when I depress the clutch it will come out of gear. If I don’t do that or if there’s a load on the transmission (going uphill) it’ll get stuck for sure.

Worst scenario I’ve had is trying to get onto the main road and it stuck in 2nd. Had to pull over and shift into low range and then convince it to work it’s way out.
 
Joined
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Coarsegold
No progress so far on the cruiser which is kind of depressing for me but it's not like I haven't been busy. Besides not having a shop or concrete to work on, the central California heat doesn't help motivate me to get outside and work. My next move is to get this trans back up into place and replace all of my clutch related hydraulics. Hopefully that cures my weird binding issues. I have very little experience with transmissions but the inside of this sm420 looks pretty mint. Along with advice on this forum, as well as some fb groups, my issue is most likely something with the mc/slave or a combo of the two.
I likely wont be able to work on the cruiser until mid August. Ill be doing a 10 day section hike on the John Muir Trail so that is taking up a few weekends. Hopefully the trans/clutch issue ends up being simple so I can get this thing moving and start doing some real work on it.
I scored a set of 37" km2's for cheap and some 17 inch pro comp wheels as well. This should help out the road manners. 60+ mph on 11 year old bias iroks can get a little crazy.
 
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No pics worth posting but updates on the 40.

I took quite the break from working on the 40 as I had a big hiking trip coming up. I've spent my life in the outdoors and camping but never backpacked before this. I went a lot bigger than your average first timer. I met up with some friends who were doing the John Muir Trail and hiked about 100 miles with them. Immediately after returning, I spent a weekend in August trying to figure out my binding issue that I have been fighting. I replaced all the hydraulics and nothing changed. Then the next realization was that on steep inclines my drive line could possibly be binding just enough to restrict movement. Not the case either. With a new clutch, master cylinder, and a slave cylinder, my binding issue has to be somewhere in the transmission or transfer case.

I lean towards transmission because there is for sure bearing noise when in neutral with the engine spinning the goes away when the clutch pedal is depressed. The transfer case remains a variable though because I did reuse the old input gear during my rebuild last summer and there were a few small chips. I'm thinking those small gear chips may have become big chips and under load they are causing a bind. I ended up deciding my next move needs to be trans and transfer case tear down to figure out whats not spinning. Took it out and set it on a bench so I could save some funds. Well then the Creek Fire started. Luckily my family is not in direct danger but the pre evac warnings came within a few miles of the house so I ran home to help prep a bit in case the fire made a run. Part of the prep was getting the cruiser mobile to limp it out just in case.

My next move is to just save up and throw some cash at this setup. I do not want to find a new trans because I'm not ready to re do all of the associated mounts that come with a trans swap. I thought about finding a new sm420 but even that I am not interested in as I have no idea how this one off adapter is set up and I'd rather rebuild my existing trans than swap parts to a used one or NOS.

I want to do t/c and trans at same time. I want this all done at once and I want it done right so I am not taking this out again in a year. I am leaning towards going with the Orion case because stock 3 speed gear sets are hard to find and pricey. The other thing I like about the Orion is I will have the gearing that I learned to love in my dual cased pickup.
 
Joined
Jan 9, 2004
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It used to be that when an sm420 wore out you could replace it for $100.00 I love sm420's so I have collected a few. I have had a couple wear out over the years and just retired them. Given the age of that transmission you could potentially throw a bunch of money into it and not get any good results. I don't think it matters how the one off adapter is setup, it is a fairly easy to connect an sm420 to a 3 spd. case. If it was me, I'd find another one and throw it in.
 
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It used to be that when an sm420 wore out you could replace it for $100.00 I love sm420's so I have collected a few. I have had a couple wear out over the years and just retired them. Given the age of that transmission you could potentially throw a bunch of money into it and not get any good results. I don't think it matters how the one off adapter is setup, it is a fairly easy to connect an sm420 to a 3 spd. case. If it was me, I'd find another one and throw it in.
I've been considering swapping in another one but for a few bucks more it seems I can just get mine professionally rebuilt which might be the route I end up going with. If a killer deal comes along I will probably snag a used one though.
 
Joined
Mar 12, 2005
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How much more work is it to swap in a 465? They seem to be much more plentiful and all around a better transmission? Excuse any ignorance..
 
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How much more work is it to swap in a 465? They seem to be much more plentiful and all around a better transmission? Excuse any ignorance..
To be honest I don't know and that was going to be part of my research today. I do know it is a bit longer and a new adapter would be longer than my current one, which would force me to re do my driveshafts as well as all of my mounts. I really did not have any issue driving the sm420 around so I don't have a huge desire to upgrade. Even if I did find a great deal on a 465, I'd have to get new adapters, re do my mounts, etc... In my quick search on craigslist I already found a few 465's in my area which shows this could be a decent option. Right now I am just in the research stage of all of this until the wildfire smoke goes away and working outside isn't as miserable.
 
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Personally, I like sm420's better. The adapter setup is very close to the same on both, with the exception of the output shaft.The sm465 needs to be drilled out and tapped for a bolt to retain the input gear of the t-case. The sm420 is tapped from the factory. Not that big of a deal, I just find the 420 is a bit smaller a bit lighter and a bit better #1 gear ratio. They are both very tough trannies.
 
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Personally, I like sm420's better. The adapter setup is very close to the same on both, with the exception of the output shaft.The sm465 needs to be drilled out and tapped for a bolt to retain the input gear of the t-case. The sm420 is tapped from the factory. Not that big of a deal, I just find the 420 is a bit smaller a bit lighter and a bit better #1 gear ratio. They are both very tough trannies.
I am heavily leaning towards keeping the sm420 that I currently have. Local shops have given me good quotes on a rebuild and the idea of having a fresh 420 for not much more than a craigslist find is appealing.
 
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Jan 9, 2004
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The point I was making about re-building is the fact that they are so old, when components wear out to the point that the transmission starts to jam up, there could be parts inside that are worn beyond repair. The cost to replace these parts will outweigh the cost of a used one that shifts correctly, not to mention mixing old and new parts in a gearbox is sometimes questionable. I think most of the old timers who know that transmission well are mostly dead. That being said, I hope you have good luck rebuilding and your transmission works well afterward.
 

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