Transmission not shifting fourth or overdrive gears

JWR2009

MEMBER
1998 CHEVROLET BLAZER
4.3L
V6
4WD
190,000 MILES

I purchased the vehicle listed above with problems with transmission not going after a few minutes. Pulled the pan changed fluid and filter. Shifted and ran fine for 2 months then acted up again so changed shift solenoids and flushed changed fluid and filter again. Now it will get to 70 MPH and acts like no fourth or overdrive is there no slippage or noise. Is there anything else I could do other than pull and rebuild? Valve body or any parts I can change before pulling to see if that helps. Parts in pictures are the ones I'm about to buy to rebuild. Anything I missed please let me know.

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Tuesday, December 28th, 2021 AT 5:43 PM

5 Replies

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi,

First, I attached a pic below showing the fluid flow for the fourth gear/TCC engagement. I nearly went blind looking and trying to follow it. LOL

Here is what I've found: The 3-4 shift valve is not directly controlled by a shift solenoid. The PCM controls the shift by energizing the solenoids (on) which redirects fluid to achieve fourth and ultimately overdrive.

So, if it is staying in third, there is a chance the valve body is corroded internally, or it could be related to an electrical issue.

With that, have you checked to see if there are any diagnostic trouble codes stored? Was the pressure control solenoid also replaced? Was the TCC solenoid replaced?

Also, since there is no slippage, at this point I don't see the need to replace the clutches. I feel it is either electrical or in the valve body.

Let me know.

Joe

See pic below. Also, sorry but it will drive your eyes crazy after a while.

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Tuesday, December 28th, 2021 AT 7:57 PM

JWR2009

MEMBER
45 POSTS

I bought a used valve body before I even checked the old one, I am thinking I made a mistake when I did but I only replaced the shift solenoids nothing else but only did that after the problem started 2 weeks ago. The fluid was nasty and shiny, so I was afraid I burnt the clutches. But I guess tomorrow I'll take it all apart and make sure everything is clear. I don't know much about sensors in the pan. Do you have a list of them that could explain what they are and what they do? Someone said the temperature switch could be bad and it won't allow it to go into fourth or overdrive. Thanks for any help.

Also, no codes for transmission only codes on vehicle is pump motor open and wheel speed sensor that has been on since I bought it 3 months ago.

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Tuesday, December 28th, 2021 AT 8:21 PM

JACOBANDNICKOLAS

MECHANIC
110,176 POSTS

Hi,

I attached all I have related to the valve body and solenoid valves. As far as the temperature sensor, it would have set a code (P0712 or P0713). If the transmission was hot for an extended period, a P0208 will likely be set.

The automatic trans fluid temperature (TFT) sensor is part of the automatic transmission fluid pressure (TFP) manual valve position switch assembly. See pic 5.

Let me know if this helps. Also, pic 5 shows the sensor/solenoid locations a little better.

If I can help, let me know.

Take care,

Joe

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Tuesday, December 28th, 2021 AT 9:05 PM

JWR2009

MEMBER
45 POSTS

Thank you. I'll see how much everything cost for solenoids and electrical and replace that first if all else fails that automatically means I have to rebuild.

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Tuesday, December 28th, 2021 AT 9:38 PM

JACOBANDNICKOLAS