Transmission not responding on reverse

More than likely the reverse clutch is worn or the line pressure to the reverse circuit is not correct. The fact that this started as a lag and now no engagement means the clutch was slowly failing but has finally given out.

If servicing the unit did not help then unfortunately the next step is to remove the pan and look for metal.

https://www.2carpros.com/articles/how-to-service-an-automatic-transmission

If you did this and there was metal or debris in the pan then unfortunately we are going to need to disassemble the unit and inspect the reverse clutch and related drums. I would also suggest doing a line pressure check as shown below but I suspect that is fine if the forward gears are okay.

Please run through this and let me know what you find with this. Thanks

Okay. That is good info. That is burnt clutch material. Was the fluid dark and smell burnt?

If may not have because the reverse clutch is the least used gear so it may not have burnt the fluid before it failed.

Basically I suspect this clutch has been slipping for some time and it finally failed because all that dark substance was the remainder of the clutch material. This means it will need to be taken apart to confirm this is what is happening.

I am surprised there are no codes but that is not required.

Okay. That would be particles from the clutch discs. How much was there?

If it was a lot then that explains it.

However, the only other thing that normally causes the slow engagement and then no engagement is a pump issue.

So we should check the pressure and make sure it is correct in reverse. It could be a leak in the reverse circuit inside the unit.

Take a look at this info and let us know what you find. Thanks

Yes. The idea of the pressure test is the same but the way in which it is done (tools, access point, etc) are going to be different as well as the actual specs. However, they all operate the same way in that they create pressure and direct that to a clutch pack to apply the gear.

If you have a specific vehicle that you want to do it on, just start a post on that one and we can send the process. Thanks

Most all parts stores offer a set that would work. Unfortunately, AC sets will not work. I have never tried them, but I think the valve at the end of the line is different for the oil pressure vs the gas of the freon.

Here is a link to a common set:

https://www.harborfreight.com/engine-and-transmission-oil-pressure-test-kit-64872.html?cid=paid_bing|||64872&utm_source=bing&utm_medium=cpc&utm_campaign=&utm_content=&msclkid=565fa2d8c47313c1c19ac34e57f4b990