Weird issue with th350c

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GBodyVillain

Not-quite-so-new-guy
Jan 4, 2021
28
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3
Hi, I've recently had the th350c in my elky rebuilt and everything has been fantastic with it until the rooster comb providing the detents for the gears came loose. It would cause the roller to contact it at a weird angle and woudl throw off the detents so that the shifter would always detent between gears and not actually engage. I ended up taking the pan off, finding the issue and removed the rooster comb and reinstalled it to get it properly seated again. Removing it cause some fluid to come out wich I thought nothing of. I torqued the rooster comb back down properly and then I ran the car and let it idle in each gear for about a minute each. The very next morning after doing this I've been having an issue where when the car is started cold and driven when the thermostat hasn't opened yet (unrelated but gives a frame of time of how long the car has to run before this issue doesn't pop up) I would drive about a quarter mile to half a mile or so and when I get to my first stop, the transmission would lurch forward like it does when I first put it into drive. I've had issues where I would come to a start to make a right hand turn and when I go to take off, the engine would rev up and then the gear would engage and do so pretty hard since obviously the engine speed is up. If I drive for about 10 minutes and everyhthing is up to temperature It won't do this again until the transmission is completely cooled down to ambient temperature. I can't figure out what the hell is going on and what to do about it. Before the transmission was rebuilt I drove it for about 3 years and have never once had this issue. I've tried searching on this forum and have so far come up with nothing. I've tried googling and have also come up with absolutely nothing. Anyone here ever come across this problem before? Thanks for any input anyone can provide. For now I've been allowing adequate time for everything to get up to temperature before taking off down the road to avoid the transmission slamming itself into gear if I try to stop and go quickly. P.S. it doesn't seem to matter if I stay in 1st, get up to second or even 3rd. It always happens when I approach and/or come to a stop and everything isn't up to temperature.
 

ELCAM

Royal Smart Person
Jun 19, 2021
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Sounds like it is low on fluid. Pump is starved at first and there is no line pressure, when it quits cavitating and gets enough fluid the line pressure comes up and it slams into gear with the off idle RPMs. As it gets hot and clearances close up there is more fluid available in the pan and it stops doing it.
 
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GBodyVillain

Not-quite-so-new-guy
Jan 4, 2021
28
16
3
Sorry, that's something I forgot to include. When the car is running and I check the fluid level, its actually slightly over the indicated area that it's suppose to be when running. Around an 1/8 of an inch above the indicator on the stick if that.
 

ELCAM

Royal Smart Person
Jun 19, 2021
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One thing that comes to mind is that a 200-4R filter was used in place of the 350 filter when rebuilt. The 2004R will fit but the pick up holes are on the top of the filter and the 350 is on the bottom of the filter.

Try adding half a quart and see what happens, if it doesn't help you can drain it out.
 
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timo22

G-Body Guru
Sep 10, 2012
550
1,072
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St. Louis,Mo
Is the transmission shifting later than usual? I have seen this when the vacuum modulator isnt getting vacuum causing hard late downshifts. Make sure you are getting vacuum to the modulator.

timo22
 
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GBodyVillain

Not-quite-so-new-guy
Jan 4, 2021
28
16
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No the modulator is operating properly. I added half a quart and the reshift was extremely soft coming to a stop. added the rest of the quart and it went away. Level is way over the indicator on the dipstick tube. I bought this dipstick and tube and itwas listed as specifically for a th350. I'm trying to look through my purchase history to see exactly what brand it was so I can avoid it in the future. Going to buy another and just be done with the issue. Also looking at just dropping the pan and replacing the gasket as it seems to be weeping a bit and I'll find out what's going on with the filter. I thought on it some more and when I dropped the pan to fix the rooster comb I remember seeing the paper filter and noted to my friend how much different it was from the upward facing screen ones I would normally use. If that's the case then the fluid level was really low and all the more reason to replace the dipstick. Thanks for the help guys, I was so sure I wasn't low on fluid. Glad I took another look at that angle after posting here.
 

ELCAM

Royal Smart Person
Jun 19, 2021
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If I remember correctly you can put a straight edge across the pan mating surface and use it to draw a line on the dipstick and that will be the full line. Good way to make sure the stick matches the application.
 
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78Delta88

Royal Smart Person
Supporting Member
May 23, 2022
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SW Arizona
This is older post, but if question comes up again.

With your pan off and the dip stick installed, Mark the stick 1/4 above mating surface is what l was always told.

I 've had some say 1/2 inch but I always used at the mating line plus 1/4 to 3/8 inch.

I wouldn't run each gear range a minute in idle, as a test. It's not going to tell you much.

With car on level ground and foot on brake shift from park to reverse. It should engage less than a second.

Now with foot on brake shift to neutral keep foot on brake, count to 20.

Keep foot on brake and shift from neutral to drive, it should engage less than a second.

Engagement should be firm not harsh. Of course if running modded or shift kit engagement might be firmer.
 
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