Loud noise when I apply reverse... changing crossheads

For some time now I have been experiencing a loud noise when engaging the reverse of my Jeep Wagonner Limited (automatic gearbox), it is a sound like metal hitting another or like a gear that does not fit correctly, but believe me There have been times when the noise has been quite loud. Based on that, we have been trying to detect where such noise comes from and the truth is it has been a quite complex task. At first we thought it was the transfer, but the noise did not seem to come from there but from the rear transmission or the crossheads.

In a previous maintenance, my mechanic had already mentioned to me that the universal joints were quite deteriorated and that it was necessary to change them, I am referring to the rear universal joints, but by not considering this as an emergency I gave the matter quite a long time. At the time, maintenance was done on the transmission, in fact, we replaced the planetary gears and satellites since what I had had a lot of wear, but it really wasn't the solution, after a couple of days I heard the knock again. I must clarify that this knock is not heard every time I apply the reverse, in fact, I would say it is 50%, but it is a percentage more than enough to activate the alarms.

There was a time when I was able to reduce the number of times I heard this noise and that was by regulating the minimum to about 500 RPM, but it was very low for this vehicle and that caused me problems since it very often went off when I released the throttle. throttle. Now, while it is true that this helped me, the fact that the minimum is maintained at 800 or 900 RPM as appropriate should not generate that loud noise.

So we decided to replace the crossheads to determine if that was the problem. I was able to buy one for $10 (Alloy brand) and another for $5 (Mocar brand), why two different ones? Well, where I bought the first there was only one, but fortunately I got the second one at a better price.

We dismantle the cardan to remove the previous crossheads and replace them with the new ones to which we apply a good amount of grease.

It was recently yesterday that we carried out this work and the initial tests have been successful, at the moment the noise cannot be heard, but I will not be calm until at least a week passes without that exasperating knock that makes me feel that the gearbox is suffering and that It could cause more expensive damage, but I don't know, I'm not an expert on the subject.

Now, according to your experience, what could cause a loud noise like the one I explained at the beginning of the post every time I apply reverse? Believe me, your opinion will help me a lot to pay attention to other parts of the truck that may not be we have checked. Greetings to all!