Hard, notchy shifting when warmed up

[seattlestiva]

Hey All - Has anyone else encountered a weird issue where , when cold the car shifts like butter, but after about 30-40 minutes of city driving, the shifting gets incredibly notchy and sticky. Once cooled down, it shifts great. FYI -'88 5 spd.
Had fluid changed a month ago (Redline MTX). No difference.

[JoDan]

Wow... that's like the complete opposite I'm used to.... good luck

[Festy46]

It sounds like your oil may be breaking down. When the transmission starts to act up, stop and get out feel the round "nose" of the transmission under the starter for any hot spots. You may have a bearing preload problem that is generating a lot of heat. I know all (or most) of the guys on here use automatic transmission fluid in a manual transmission, but I never do. I use only full synthetic gear oil.

[JohnGunn]

It sounds like your oil may be breaking down. When the transmission starts to act up, stop and get out feel the round "nose" of the transmission under the starter for any hot spots. You may have a bearing preload problem that is generating a lot of heat. I know all (or most) of the guys on here use automatic transmission fluid in a manual transmission, but I never do. I use only full synthetic gear oil.

I enthusiastically support Festy46's decision to use gear oil in our manual transmission. The original factory fill was probably not the ATF you buy off the shelf at AutoZone.

Before you do anything to your transmission read this thread You'll never put ATF in another Mazda manual transmission.

I found Penzoil Synchromesh Manual Transmission Fluid saved what I thought was a hopeless transmission. I plan to give Red Line MTL, not "MTX", a try in the near future and will report my experience on the above referenced thread. In the mean time, I would strongly suggest you spend $16 on a couple of quarts of Penzoil. You might want to rinse the transmission with some cheap ATF first, especially if you see any glitter suspended in the old fluid. If you do this, I predict you'll never look back.

[JohnGunn]

seattlestiva, the fact that you have left your thread and those of us who responded hanging, suggests that you may not have bothered to read the thread I referred you to. It is long, so I'll make it easy for you.

Here is the part that directly applies to the condition you describe.

"For Ford's plan of never having to change the fluid in these manual transmissions to work, they must have thought that there would be absolutely no wear of the synchronizers in the process of shifting. I'm sure they must have tested that and found it to be plausible. But I can assure you that they did not come to that belief while testing with ATF. That original fill would have had to be something better, much better than that.

For Ford's plan to work, the synchronizing of the gears would have to be accomplished without any metal-to-metal contact. When I was putting pressure on the synchronizers to make them shift, that pressure was necessary to get them to come up to speed. At that point, there was surely little if any of the relatively thin ATF left to separate the metal parts, hence all those shiny bits.

The feeling I now have is that there is a cushion of oil between the parts and that they, nevertheless, have enough friction to bring them quickly up to sychronizing speed."

And how does this pertain to your transmission shifting smoothly when cold but harshly when warm? I'll give you a hint. It has to do with the low viscosity of ATF when cold and the even lower viscosity when warm.