Th400 transmission on a 6.2 k5 blazer m1009

[Sullivan Broadwell]

My transmission has been acting fine other than when I first drive it in the morning it takes some time for it to warm up but this evening I went to go back into a space and reverse just stopped working. I’m not entirely sure what’s wrong with it because I have no leaks and the reverse literally worked about 10 minutes before.

 

[87cr250r]

Check the fluid level.

Do you have a TH400 or 700R4?

 

[Sullivan Broadwell]

Check the fluid level.

Do you have a TH400 or 700R4?

Th400 and it’s full


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[87cr250r]

No reverse only doesn't seem to be that common or a problem. The TH400 transmission has a plastic accumulator piston in the valve body that fails. Usually this causes a loss of 2nd gear engine braking. Maybe a bad enough failure would cause a loss of transmission pressure?

 

[cucvrus]

This is the reverse band in the TH400. It is lined with clutch material. It will wear the lining out of the center. The lining is worn rapidly from working the transmission in reverse. I burn one out on a CUCV snowplow truck every 2-3 years. Not saying this is the issue. Just making the issue known that I experienced. I had them hesitate and slam into reverse. Ouch. That can hurt. I cracked the case on a few when the slamming took place during plowing. Change the fluid look for debris and make sure the O ring is on the pickup tube to the filter in the transmission housing. Good Luck. Report back.

 

[Sullivan Broadwell]

View attachment 884003
This is the reverse band in the TH400. It is lined with clutch material. It will wear the lining out of the center. The lining is worn rapidly from working the transmission in reverse. I burn one out on a CUCV snowplow truck every 2-3 years. Not saying this is the issue. Just making the issue known that I experienced. I had them hesitate and slam into reverse. Ouch. That can hurt. I cracked the case on a few when the slamming took place during plowing. Change the fluid look for debris and make sure the O ring is on the pickup tube to the filter in the transmission housing. Good Luck. Report back.

I will definitely check it out because lately it hasn’t been slamming into reverse but it does slam itself into first allot which could be something that’s causing the issue


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[cucvrus]

Get it fixed by a professional. I split a few cases from the slamming effect. Don't do a witch doctor/snake oil additive. Get it checked, repaired or rebuilt by a reputable shop. Make sure you also have them adjust the VCV so that it shifts properly. I see a few that shifted erratically after being overhauled and that is not good on internal parts either. At 35+ years I would not even spend the time replacing a defective TH400 transmission with a used one unless it has been professionally overhauled. That cost money yes, but money well spent. Sometimes money is the correct tool for the job. Most times you get what you pay for if you are a smart spender. Good Luck and Take Care.

 

[87cr250r]

If you can get your hands on a copy of this book you can rebuild your transmission.

How to Work with and Modify the Turbo Hydra-Matic 400 Transmission (Motorbooks Workshop): Sessions, Ron: 9780879382674: Amazon.com: Books

How to Work with and Modify the Turbo Hydra-Matic 400 Transmission (Motorbooks Workshop) [Sessions, Ron] on Amazon.com. *FREE* shipping on qualifying offers. How to Work with and Modify the Turbo Hydra-Matic 400 Transmission (Motorbooks Workshop)

www.amazon.com

Use the Hughes rebuild kits, they use OEM clutches.

 

[rtk]

Get it fixed by a professional. I split a few cases from the slamming effect. Don't do a witch doctor/snake oil additive. Get it checked, repaired or rebuilt by a reputable shop. Make sure you also have them adjust the VCV so that it shifts properly. I see a few that shifted erratically after being overhauled and that is not good on internal parts either. At 35+ years I would not even spend the time replacing a defective TH400 transmission with a used one unless it has been professionally overhauled. That cost money yes, but money well spent. Sometimes money is the correct tool for the job. Most times you get what you pay for if you are a smart spender. Good Luck and Take Care.

Yup , get it rebuilt , no reverse usually means low pressure in the trans , time for rebuild and as cucvrus said you only want to do the job once !!!