Hard Shifting

[fmfdoc68]

I apologize in advance if this has been posted before, I searched, but to no avail. I've got a 68 F250 with the 360 and a c6 auto. The issue I'm having is that the trans is shifting really hard lately. I did have a leak around the radiator for the trans cooling lines, and was low on trans fluid. I replaced the fluid and fixed the leak, but the trans is really starting to shift harder. I didn't notice it from 1st to 2nd until yesterday, now even putting it into reverse is getting worrisome. Any ideas guys?

[Donnie]

The easy place to start is to check your complete vacuum system...a line off in the engine area, line to & including the modulator at the trans..
Are your shifts on time or later than usual? Both shift's, 1st to 2nd & 2nd to 3rd. are doing the same thing?
Does your engine idle seem to be too fast ? How much fluid did you have to add? check these & report..
How many miles on the trans? Guess if you don't know....Donnie

[fmfdoc68]

The easy place to start is to check your complete vacuum system...a line off in the engine area, line to & including the modulator at the trans..
Are your shifts on time or later than usual? Both shift's, 1st to 2nd & 2nd to 3rd. are doing the same thing?
Does your engine idle seem to be too fast ? How much fluid did you have to add? check these & report..
How many miles on the trans? Guess if you don't know....Donnie

All shifts are the same. I checked the vacuum line and the modulator and everything is hooked up. I didn't remove the line while the truck was running to ensure there is vacuum though. The idle speed is set pretty low, in fact, when the truck is warm, it seems to idle just above stall speed. The shifting seems to take place about where it should, I don't have to let off of the throttle to get it to shift.

I had to add about 2 quarts of fluid. As for miles on the trans, I couldn't even begin to guess. The truck reads 21,887, but my guess is that it has rolled probably several times. The trans looks like it's never been out of the truck, so i'm not sure.

[Donnie]

Hi, if your shifts are on time, and are not LATE & firm, JUST FIRM, you vacuum system is probably OK...There is a direct correlation between late & firm .....if your shifts are on time , just too firm, I would suspect hi pressure..You did say that even rev is too firm...There is a rev. boost valve in the valve body to increase the pressure in reverse.....I'm thinking you may have a valve sticking in the valve body or a broken spring...
Disconnect the modulator & plug the line so you don't have a vac leak....drive the truck, note the shift points & the shift feel,,report back
your shifts are going to be late & firm.....in fact you may not be able to get 3rd....if your engine is not strong , don't abuse it trying to get 3rd.
note how the 1 /2 shift feels.......is it harder than when the mod. is connected? or about the same.........Donnie