TH 350 shift issues

[ulm4lyf]

Sometimes, mine doesn't want to go into reverse right away if I haven't started it up for a few days. It is a 350/350. The trans fluid doesn't smell burnt at all, but I'm wondering if it would be detrimental to change the trans fluid filter. I just got the truck in July so I'm still doing maintenance/tune up things to it. Haven't got the chance to drive it much yet.

 

[Matt69olds]

Regardless of what people say, there is nothing wrong with changing fluid in a perfectly functional transmission. It’s just good preventative maintenance.

I doubt that will solve your problem. I doubt you even HAVE a problem to solve. After sitting a few days, the fluid in the torque converter naturally drains into the pan. Once the truck starts, it takes a few seconds to refill the converter.

The reason you notice the delayed engagement more in reverse is because of how the reverse gear is activated. To go forward, the forward clutch needs to apply. That’s it, one clutch comes on. However, for reverse the direct clutch AND the low reverse clutch has to be applied. It takes longer to fill 2 clutch packs.

Drop the pan, unless there are big chunks or lots of debris don’t worry about it. Replace the filter, stick a magnet to the inside of the pan (assuming there isn’t one already there) reinstall the pan and refill with fluid.

Assuming the trans works fine now, it will work fine with fresh fluid.

 

[Mlcdc1]

Still having shift issues with TH350 that won’t shift 2nd-3rd when it‘s warmed up, usually 15-20 minutes of driving. I added a trans cooler and new vacuum modulator with no change. i’m about ready to buy a new governor just to see if that fixes the problem. I’ve given up on the shop that did the rebuild 2000 miLes ago - they say no issues. Any suggestions?

 

[Matt69olds]

If it’s not making the 2-3 shift once it’s warmed up, why do they say no problem?? Seems to me that’s a pretty obvious concern.

With the engine cold, pull on the kickdown cable a few times. Pull it enough times you have a good idea of what it feels like. Next time it acts funny, pull the cable again, see if it feels differently. Maybe the cable is binding when it gets hot?

Inspect the vacuum modulator line, especially the rubber hose connections, and anyplace it’s near the exhaust. Maybe the hose is partially collapsing when it gets hot, restricting the vacuum signal?

Replace the vaccum modulator. I think the part number is MV100 at autozone, about 20 bucks. If I’m right on the part number, that one will be adjustable. You can move shift points 2-4 mph. Put it in the truck as is, see what happens. If it solves your problem then play around with shift points. Don’t turn the screw more than 4 turns either direction!!

It could also be a valve sticking in the valve body once it gets hot. If the shop flat out refuses to help anymore, you might try dropping the pan, and loosening all the valve body bolts, then retorquing them to 120 INCH POUNDS (not foot pounds!!) starting in the center and spiraling out.

If you still have the issue after all that, it’s time to remove the valve body. It’s pretty easy on a TH350, just messy especially if the trans has no drain plug.

 

[Mlcdc1]

thanks for the input. I’ve changed the vacuum modulator a couple of times and installed a new rigid line from the manifold to the modulator and measured the vacuum pressure at the manifold and the modulator and it read the same. I have not installed a vacuum gauge and driven it to see if there‘s a vacuum drop when it doesn’t shift. I might get try that before I drop the pan. If I get to the point of checking the valve body, maybe just Spend the money and get new?

 

[Matt69olds]

Since the last 350 trans was built in the early 80s, you’re probably not going to find a new one. The best you can probably hope for is a remanufactured valve body.

 

[Mlcdc1]

FYI - all the shift issues were corrected by installing a new governor. I torn the old one apart and it looks like when I had it at the the transmission shop they drill out the plastic gear to fit the retaining pin and there were some very small shavings that got down in the valve. I had checked the valve and it moved freely so moved onto other possible causes. Learned to be thorough in checking each possible problem/solution.