Author Topic: TH350 Problems  (Read 6354 times)

Offline uprising

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TH350 Problems
« on: November 19, 2019, 10:58:57 PM »
Good morning guys,
i have some troubles with my transmission. There is a leak somewhere at the transmission. The vacuumline, modulator and measurement tube looks ok. Maybe the seal between engine and transmission? If yes, which seal do i need? And how can i identify my modulator? At rockauto and   are different types (colours)? My actual installed modulator cant be really identified! Pretty durty and old.
Also the tranny reacts a little bit weird. If i set the reverse gear it takes 2-3s after the car is moving. Same for D. Any idea? Maybe the vacuum isnt working properly?


Offline Shifty

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Re: TH350 Problems
« Reply #1 on: November 20, 2019, 08:45:50 AM »
As for as the modulator, a simple adjustable unit solves any issues with selection, and make sure the old unit didn't kill the diaphragm, and has fluid in the line.   Make sure that the hose that plugs into it isn't cracked (on either end).   When is the last time it had a filter/fluid change?  Nice and red, or orange-ish-brown?
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

Offline uprising

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Re: TH350 Problems
« Reply #2 on: November 20, 2019, 12:08:28 PM »
The last fluid/filter change is 50km ago. It was clear but a little more orange and a little bit of wool was inside.
I found one at rockauto but there is something mentioned about red or blue... Dont know which one is the correct. What do you mean with diaphragm?
I think i will order a new line with the modulator and also the hose. Hope they can be ordered seperate.

Offline Shifty

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Re: TH350 Problems
« Reply #3 on: November 20, 2019, 01:13:18 PM »
The red one (at least in the two brands I sell) are the adjustable units, and there is a diaphragm between fluid and air....when they die, the fluid gets sucked into the engine.  There is an o-ring around the "stem" of the modulator that presses into the trans body that can leak fluid as well.  BTW:  A little hose should come with the modulator. 

Did you notice your issues since changing filter/fluid?
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

Offline uprising

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Re: TH350 Problems
« Reply #4 on: November 20, 2019, 11:26:08 PM »
Good morning,

ok. I will order one at Rockauto/ !
Nothing wet at the modulator. My fear is that there is a leakage between the transmission and engine.
This will be a jackpot... I will remove the cover next to the pan and will check.
Before i changed the fluid it was not so bad. A drop here and there but nothing critical!
Maybe there is to much fluid inside? Honestly i dont exactly knew how much i filled in. Filled in the same amount which flows out.

Which modulator should be ordered??
« Last Edit: November 21, 2019, 02:26:26 AM by uprising »

Offline Shifty

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Re: TH350 Problems
« Reply #5 on: November 21, 2019, 08:30:30 AM »
From that pic. I'd go with the first one, they are cheap as heck, and almost $50 for one is silly.   

I'd suggest:

https://www.summitracing.com/parts/atp-jx67/overview/
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

Offline uprising

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Re: TH350 Problems
« Reply #6 on: November 21, 2019, 11:16:23 AM »
Got it!
Stupid question: Is there a way to identify the year of the engine/transmission? My truck has another VIN! Dont know what happend in the past but the VIN is from a C20!

Any ideas about the weird handling from the transmission?

Offline Shifty

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Re: TH350 Problems
« Reply #7 on: November 21, 2019, 11:51:00 AM »
It's probably a leaky front seal, aka torque converter seal, or input shaft seal.  Fairly common problem. 

Are your wheels 8-lug or 5-lug? 
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

Offline uprising

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Re: TH350 Problems
« Reply #8 on: November 21, 2019, 02:11:20 PM »
Sry but what do you mean with lug? Never heard the word :)

Crazy thing is that the transmissions works great before the fluid and filter was changed. You set the gear r and i tooks latest 1s and the gear was in. Now it tales 2-3s. Is this a side effect of a leak?

Offline Shifty

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Re: TH350 Problems
« Reply #9 on: November 21, 2019, 04:26:31 PM »
Lugnuts, wheel studs, etc....my thinking (if you title is legit, and it probably is) is that at some point, it ended up with different badging, usually from fender replacement from a donor vehicle....

A half ton (C10) would have a five-lug wheel bolt pattern, whereas a C20 would be eight.
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)

Offline bd

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Re: TH350 Problems
« Reply #10 on: November 21, 2019, 05:04:38 PM »
...Honestly i dont exactly knew how much i filled in. Filled in the same amount which flows out.
...Crazy thing is that the transmissions works great before the fluid and filter was changed. You set the gear r and i tooks latest 1s and the gear was in. Now it tales 2-3s. Is this a side effect of a leak?

Check the transmission fluid level using the transmission dipstick with the truck on horizontal ground, the engine idling, and the transmission warmed up to operating temperature and shifted into Park.



...Before i changed the fluid it was not so bad. A drop here and there but nothing critical!...

There is a strong possibility that the leak is from the transmission oil pan caused by a distorted flange or damaged gasket that occurred during the fluid/filter change.  Did you replace the filter seal?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline uprising

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Re: TH350 Problems
« Reply #11 on: November 21, 2019, 11:03:51 PM »
@Shifty:

Aahhhh... Now i got it ;)
It has 5 Lugnuts. I think/hope they only changed the cabin and they forgot to change the plate. It has 4x4, so the wheelbase should be a k10. I dont think, they add 4x4 technic into a C20. Maybe i will find somewhere in the frame a different VIN. For some parts it is important to know the exact year. The VIN says it is 73 but i think it is 75. Is there a difference for the transmission seal from 73 to 75?

@bd
I measured the oil and it was good after the change but i will measure again after a short trip.
I used a new gasket for the pan and the screws arent fixed to heavy. Maybe i will order a new pan with a drain and a new gasket. Which gasket you prefer? With cork or rubber?

Offline MIKE S

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Re: TH350 Problems
« Reply #12 on: November 21, 2019, 11:40:58 PM »
Its very easy to not get the gasket between the filter and valve body lined up. I would bet its sucking air at that point since it was fine before.

Offline uprising

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Re: TH350 Problems
« Reply #13 on: November 22, 2019, 12:40:39 AM »
@mike
You mean that the vacuum is not correct caused to a wrong connected filter?
I think i have to renew the filter and gasket again.... dang it

Offline Shifty

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Re: TH350 Problems
« Reply #14 on: November 22, 2019, 08:43:22 AM »
Not Mike, but he's referring to the seal/gasket between the transmission filter and the valve body.  If it's not submerged, like during stopping, accelerating and cornering, it will suck air instead of fluid. 

As far as 73 and 75 TH350's, they will be the same.  The filters were available in both felt and a square screen style, but either work just fine.
87 V20 Standard Cab Longbed (current)

87 R30 3+3 Longbed (days of yore)