Holding my SM465 in 3rd gear, am I about to blow it up?

[dccarpenter]

Ok,

So I converted my '84 c30 from a turbo400 to an sm465, it is in and running well except has the typical 3rd gear shift pop-out. I, like a fool, believed the guy I got it from when he said it was running perfectly and didn't rebuild it or even open it aside from flushing and refilling it before putting it in my truck. Now it's in there and pops out of 3rd gear, I know I need to replace the shift forks (and possibly another part or two on ). I need it to get around town for the next 2 or 3 weeks, it will stay in 3rd gear if I hold it in place, can I get away with this for that amount of time or am I likely to grenade this thing doing so and hence should I just let it lug in 4th gear? To clarify the driving is a 6mile ride to work and back, maybe a few parts runs, would be in 3rd maybe 5 times for 10-20 seconds.

Blazer's out of commission at the moment and the bus doesn't take me everywhere I need to go so not driving it isn't optional unfortunately.


Any help is greatly appreciated.

[grandfisher]

Having to hold it in 3rd is definitely an inconvenience, but it won't damage your transmission. Or maybe I should say, it's unlikely that it will damage your transmission. My brother's truck does the same thing. Been like that for a year. I've seen guys drive one for years like that. I couldn't stand it myself, but you should have no problems driving it like that for a while.

[dccarpenter]

Awesome, thanks a lot for the reply.

I've been googling this problem all evening since I got home and it looks like I'll be able to remove the trans hump, remove the top cover of the sm465 trans and replace the shift fork and shift rail springs and have a 80% chance of solving the problem without dropping the trans. Very very pumped about that.

I just put in a brand new flywheel and clutch and didn't feel like tearing the whole thing apart to rebuild the trans. I guess there's a slight chance there's a snap ring on the gear shaft itself that could be bad but I'll try the topmount fix first.

If anybody is reading this, the sm465 seems much louder than the turbo400 I had in before? Is this normal or do I need to give a closer look at my driveshaft/u-joints?

[oldgold70c10]

Originally Posted by dccarpenter

If anybody is reading this, the sm465 seems much louder than the turbo400 I had in before? Is this normal or do I need to give a closer look at my driveshaft/u-joints?

I had an SM465 in my burb before I converted to 700r4 and do not remember it making any noise at all, very quiet unit.

[Big Port Jimmy 6]

I had one with a bungee to hold it in 4th. Was like that for years. It was behind a 6.2 so it could have sang opera and you wouldn't have heard it. Jay

[cableguy0]

If its worn enough that its popping out of gear. Its probably noisey bearings in the transmission. mainly the head shaft bearing. It will make a ton of noise.

[dccarpenter]

Would that head shaft bearing contribute to it being louder in neutral than when in gear? If actually isn't horribly loud when moving outside of when it's revving. I think my driveshaft may be at a bit of an angle and some of the noise may be coming from there.
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[Wrenchbender Ret]

A bad front drive brg. will make noise when you let the clutch out in neatral & in the lower gears. 4 th gear will be much queiter. Sometimes the trans will sound noisey if the cover is rubbing it. If you cannot feel a good detent when you shift from neutral into a gear it indicates the spring in that rail is broken. If it is real noisey in 2nd. or 3rd. it indicates a snap ring on the countershaff is broken.

[dccarpenter]

I plan on replacing all the shift rail springs when I pull the top cover off to replace the forks so hopefully that will quiet things down some. As to that front bearing, how likely is that thing to grenade the transmission? If I can get the thing shifting into 3rd and staying and performing fine otherwise I suppose I can live with the noise for a few months until being in a position where I have another vehicle and can afford to pull the transmission.

[BIGBLU 72]

Mine doesnt pop outta any gears and is super smooth shift but it whines like a M22 in 1st,2nd and 3rd???

[Pyrotechnic]

My friend had one he pulled out of an 85 3/4 ton Suburban. It came with auto trans fluid in it! At first I thought it was previous owner error but I've been told it was factory fill to help increase gas mileage? He tried it with the ATF but it was noisy and rough shifting. Switching to regular gear oil made it quieter and it shifted much smoother.

[dccarpenter]

OK, quick update. I drained my transmission of the Coastal brand generic 80w90 gear oil I used when I installed the transmission and put in 1 quart of lucas transmission fix and 4 quarts of lucas 80w90 non synthetic gear oil.

It seems decidely quieter and a bit smoother. No more noise at all when I leave the transmission in neutral at a stoplight anymore. I'm feeling much better about this transmission not blowing up now, I think once I get the new 3/4 shift fork in and I'll be able to milk a year or two out of this thing.

[dccarpenter]

OK, quick update. I drained my transmission of the Coastal brand generic 80w90 gear oil I used when I installed the transmission and put in 1 quart of lucas transmission fix and 4 quarts of lucas 80w90 non synthetic gear oil.

It seems decidely quieter and a bit smoother. No more noise at all when I leave the transmission in neutral at a stoplight anymore. I'm feeling much better about this transmission not blowing up now, I think once I get the new 3/4 shift fork in and I'll be able to milk a year or two out of this thing.

[Harveybacon]

I have the same issue. Have been just holding third down for a couple years now. No trouble other than it progressively getting worse. Use to go 65 before would pop out, not soon as I put it in 3rd (around 35mph). Had reman'd tranny 6 years ago. I have been told it's just my drive shaft (bearings). I have checked my springs and forks and shifters, and all seems in order. I took it to Aamco today for free inspection, and we'll see what they say. But I too am hoping that I can fix it without dropping tranny.

[andyh1956]

i think you will find a broken / lose / missing snapper on the main shaft. this is a super common problem & there is a fixit kit that can be installed from the top side after the shift top is removed. call jackson powertrain at 601 932 3159 & john will fix u up!
andy

[Harveybacon]

Originally Posted by andyh1956

i think you will find a broken / lose / missing snapper on the main shaft. this is a super common problem & there is a fixit kit that can be installed from the top side after the shift top is removed. call jackson powertrain at 601 932 3159 & john will fix u up!
andy

OMG, thank you so much for that info! I took it to Aamco today (remanned it 5 yrs ago) and he straight told me the problem was IN the tranny. And swore that I had to pay 400 bucks for him to look at it. This is not the first tranny ppl I have taken it to. Transmission mechanics are a shame. I will NEVER have anybody else do work on my tranny again (after owning a 99 Mazda and rebuilding it twice), lol.

I'll be on the phone tomorrow. Thanks again!