TH350 Issues

[Aura]

Recently I bought a 1983 GMC C10 (LWB) and I noticed that the shifting is very harsh and sudden. There is also this "winding down" noise I hear when slowing down and goes away once it has shifted at least once.

I have been driving it daily and the shifting is kind of getting annoying. No other issues with the truck except the shifting and that "winding" noise that I can't pinpoint where it's coming from.

Any ideas?

 

[Octane]

Sounds like whining,probably from the pump.Drive it till it all stops working is what I'd do.

 

[Aura]

Sounds like whining,probably from the pump.Drive it till it all stops working is what I'd do.

Yeah that's probably what's causing it but I haven't been able to find anybody else that describes the same "winding down" sound. I did find one person who described it the same way as me on some forum but no actual information in the replies.

There is also this braking feeling that I get when it starts to gradually slow down at any stop. It's kind of like when you put it into Drive 1,2 and drive and let off the gas. Everything on the truck is all original and I do expect some issues. My other trucks have 700R4's that are original to them and there are no issues whatsoever after 30+ years. While I do have a spare 700R4 to put in there I would like to keep it as original as possible.

 

[HotRodPC]

I wonder if you might not have a stuck governor and it's causing it to downshift early. So hard to guess with just a text explanation and not actually driving it.

 

[Aura]

I wonder if you might not have a stuck governor and it's causing it to downshift early. So hard to guess with just a text explanation and not actually driving it.

The sound I'm talking about is heard within the first 10 seconds after pulling out in the video I took. It can also be heard again when coming to the stop near the end of the video. Looking at other videos it does seem to fit that "whinning" sound but I wasn't sure how to describe it at first as I've never heard the sound before.

There is also a sound from Power Steering near the end as well but that's not related.

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[HotRodPC]

If it turns out to be the dreaded pump whine, it's short lived. If you don't want to rebuild the Th350, which I understand you want to keep it OEM as possible, so you'd want to keep that same core, otherwise may as well just put that good spare 700r4 in it since you've had such good luck with 700r4's unlike most people. The good news is, the 700r4 is a direct swap with the intermediate shaft Squarebody Th350 transmission. I think the crossmember bolts in a different place but that a minor issue. The same drive shaft length, same yoke, same cooling lines, use the same brackets for the detent cable on the Th350 for the TV cable on the 700r4. Just be sure to adjust that TV cable properly as its pressure regulation too and if it's wrong, you'll cook that 700r4 within a couple hundred miles or less depending on how far out of adjustment the cable is.

Then keep that Th350 and go through it someday to swap back in if you want to keep it OEM.

 

[Aura]

If it turns out to be the dreaded pump whine, it's short lived. If you don't want to rebuild the Th350, which I understand you want to keep it OEM as possible, so you'd want to keep that same core, otherwise may as well just put that good spare 700r4 in it since you've had such good luck with 700r4's unlike most people. The good news is, the 700r4 is a direct swap with the intermediate shaft Squarebody Th350 transmission. I think the crossmember bolts in a different place but that a minor issue. The same drive shaft length, same yoke, same cooling lines, use the same brackets for the detent cable on the Th350 for the TV cable on the 700r4. Just be sure to adjust that TV cable properly as its pressure regulation too and if it's wrong, you'll cook that 700r4 within a couple hundred miles or less depending on how far out of adjustment the cable is.

Then keep that Th350 and go through it someday to swap back in if you want to keep it OEM.

Actually I don't mind rebuilding the transmission if that is what needs to be done. I would prefer it to have a 700R4 in it mainly due to overdrive. It's not a absolute deal breaker switching out OEM parts that are beyond repair -- as long as it runs and drives then it's okay with me.

I've been reading up about it and noticed that a bad Torque Converter can make the similar sound. I'll be replacing that and the flywheel later to see if the sound goes away.

 

[HotRodPC]

Oh yeah, that's a Th350C with a lock up torque converter isn't it? It could very possibly even be the converter clutch making the whine noise. too.

 

[Matt69olds]

The hard quick shift sounds like someone installed a shift kit in the past. Does it’s shift at the normal expected speed, just hard? Does it shift hard into every gear?

Is the whining noise constant? Worse when the trans is cold? Does it whine in every gear? I have heard many 350 that have a faint whine in first gear, then stop when it makes the 1-2 shift. If that’s the concern your having, you have a planetary gearset of bearing making some noise. I’m might be the first symptom of impending failure, or it might last for years like hat.

Drop the oil pan for inspection and a filter change. Look at the valve body plate. If it’s a good anodized color, or black, chances are someone installed a shift kit if you want to get rid of the hard shift, your going to have to buy mother shift kit. You can’t make the holes in the plate smaller. Follow the instructions for the RV/towing calibration.

If there is a bunch of debris on the pan, chances are the whine is caused bypump or gearset wear. Start saving for that 700 swap

 

[Aura]

The hard quick shift sounds like someone installed a shift kit in the past. Does it’s shift at the normal expected speed, just hard? Does it shift hard into every gear?

Is the whining noise constant? Worse when the trans is cold? Does it whine in every gear? I have heard many 350 that have a faint whine in first gear, then stop when it makes the 1-2 shift. If that’s the concern your having, you have a planetary gearset of bearing making some noise. I’m might be the first symptom of impending failure, or it might last for years like hat.

Drop the oil pan for inspection and a filter change. Look at the valve body plate. If it’s a good anodized color, or black, chances are someone installed a shift kit if you want to get rid of the hard shift, your going to have to buy mother shift kit. You can’t make the holes in the plate smaller. Follow the instructions for the RV/towing calibration.

If there is a bunch of debris on the pan, chances are the whine is caused bypump or gearset wear. Start saving for that 700 swap

The shifts aren't as rough if I accelerate "normally" and they become more apparent when I try "floor it" from a complete stop. Not to say I'm always flooring it but in certain situations I do and the shifts are extremely rough and kicks in rather hard. Even on my other trucks, the 700R4 is smooth when trying to floor it compared to this 350. The whining sound can only be heard when accelerating from a stop and then goes away after it shifts once and won't be heard again until I am coming to a slow down -- in which the sound returns and I get the feeling of braking.

In the video I took above you can hear the sound for the first few seconds and completely disappear at 0:11 once it has shifted. The sound comes back at 1:06 when I'm coming to a slow and it's quite hard to hear that part. I have already put a decent amount of miles on it since I've had it and it seems like it's not giving up on me yet.

 

[Matt69olds]

For whatever reason, I can’t get your video to play.

Based on your description, the whine is almost definitely caused by a bearing or gearset issue. It’s something that only turns in first gear.

Once again, based on your description, the hard shift is almost certainly due to a shift kit. A firm part throttle shift that gets harder the more you stand on the “loud” pedal is a classic example.

If you want a softer shift, get the cheapest B&M shift kit. Follow the instructions for the towing calibration. That will give you a solid firm shift, one that won’t knock the dash out of the truck. Or just swap in the 700 your wanting anyway.