TH350 woes

[RedRoad]

History: Rebuilt buy a supposed quality shop less than 2 years ago, less than 6000 miles since. Here is what they said they did

TH350 Performance Package includes

Alto Red Eagle Clutch Plates
Kolene Steels
Alto Red Eagle Band
Teflon Rings
High Endurance Gaskets, Seals and Bushings
TransGo Reprogramming Kit

I added a trans cooler and have run a temp gauge since new and never been hotter than 190*. Royal Purple synthetic since new, cast B&M 3 quart sump.

Today I went to the store which is only a mile a way, no problems or weird noises. Got back started the truck, shifted into reverse no problem, then to drive again no problem. Drove out of the lot and noticed it wasnt shifting to 2nd or 3rd. Pulled over and went through the detents put it back into drive and took off, same thing. Got home checked the linkage and everything looked good, a bit loose but no binding or anything. Now no other gears including reverse except 1st.

Anyone have any idea what might be going on?

Did I mention I HATE automatics!!!!

[bd blk 12v]

Did you check fluid level and for burnt smell or material?

[60case]

pull out the governor and check if the plastic gear is worn out

[TBONE1964]

The first and easiest thing to do is to make sure the vacuum modulator has a good source of vacuum from the engine. If it does not, the transmission will not shift correctly.

Hope this helps,
Tom

[RedRoad]

Fluid level fine, but the purple stuff stinks. Doesnt smell burnt but not what I am used to with regular ATF.

Ill check the hose and modulator tomorrow.

Thanks for the replies

[leddzepp]

Originally Posted by TBONE1964

The first and easiest thing to do is to make sure the vacuum modulator has a good source of vacuum from the engine. If it does not, the transmission will not shift correctly.

Hope this helps,
Tom

X2. I had the same issue a while back and it turned out to be a cracked vacuum line.

[kwmech]

It's the vac line, burnt fluid will give indications of slipping before going out

[RedRoad]

Never driven an auto that was slipping, whats it supposed to feel like? I have a low stall converter in it ~1500 rpm, shifts felt firm as far as I know. Is it similar to a oil soaked disk on a manual?

[RedRoad]

Been thinking about this more, I can see how a vacuum leak would cause problems with up/down shift but why no reverse?

[Bigdav160]

Third and reverse out means the direct clutch is out.

[67 chevelle]

Originally Posted by TBONE1964

The first and easiest thing to do is to make sure the vacuum modulator has a good source of vacuum from the engine. If it does not, the transmission will not shift correctly.

Hope this helps,
Tom

x3

[Bigdav160]

Modulator/Governor have nothing to do with reverse.

[Oldblue68chevy]

Pull the pan check for for metal shavings or pieces. I had a TH350 do a very similar thing it blew apart the low/reverse sprag. The weird part was it happened backing out of a parking spot not doing a burnout or racing. Had to drive home in 1st gear. Keep us posted what you find.

[Gromit]

I'd vote for OldBlueChevy's diagnosis on this one.

Notice that the two sprags are not in the rebuild kits but should be IMO..

The low/reverse one costs about $22 - and not all that hard to replace except for pulling the trans..

If he is right definitely wouldn't be good to spin the trans until you know - risk is that all those sprag pieces may go to the cooler, torque converter & rest of the trans.

Here is a photo of the sprag or roller clutch..

[RedRoad]

Replaced modulator and inspected governor today, vacuum lines are fine and plastic gear was in good shape weights worked as they should and the valve moved freely and was free of debris. Disconnected linkage to rule that out and attempted to shift directly but no dice. Today it felt different in park, kind of felt like it had a trans break and would lurch forward when shifted in whats supposed to be reverse. Didnt get to drain the fluid and drop the pan as the 1 year old only gives me an hour max to work on stuff. Ill try again tomorrow but not expecting any easy fix.

Thanks all for the recommendations, Ill take pics of the carnage tomorrow.

Now looking for Z bar and engine stud to convert this **** box to SM465

[Bigdav160]

The problem with the above hypothesis is the low roller is used for (only) first gear, not reverse.