727 loud clunk going into third gear.

[ling102]

I have a 1967 Coronet RT. 440 with a 727. I had the trans rebuilt with a hemi 2500 stall torque converter.
The 1st to second shift seems ok, however, when the trans shifts into 3rd under normal acceleration, there is a loud clunk.
If I am accelerating quickly, it seems to shift ok. Is my problem with the torque converter or transmission itself or ??? Thanks guys.

 

[Bad Sport]

First thing I would check is U joints, then the rearend for any excessive play.

Under normal acceleration by the time you hit third there is minimal torque being applied, so it may be as simple as a worn part.

You don't hear it under hard acceleration because when you hit third you are still applying that torque into the shift to third..

Do you have any clunk going from drive to reverse?

 

[Evan Frucht]

That does not sound like your torque converter. But then again I'm not an expert on trans stuff at all.

Does it have a shift kit ?

How long ago was it rebuilt?

Does it have a sure grip?

Maybe check the driveshaft as well make sure everything is tight and in good shape.

 

[66383]

What kind of valve body?

 

[ling102]

I have less than 100 miles on the rebuild. It does have a suregrip, the ujoints are good.

 

[ling102]

I will be going to a manual valve body soon. My concern is will the problem still exist?

 

[Evan Frucht]

I have less than 100 miles on the rebuild. It does have a suregrip, the ujoints are good.

Bring it back to the trans shop and tell them you don't like the way it's acting and ask them to check it out . It may just be a matter of simple adjustment

Maybe the shift points needs to be raised
slightly. At what speed does it shift into 3rd and make that clunk?

My trans was giving me slightly too harsh 3 shift recently (this was after having it rebuilt by a reputable shop a couple months ago)

So the other day what I did is increase the throttle pressure at the trans by adjusting the kick down rod for slightly more travel (about a1/16" to 1/8") and that brought my 3rd shift point higher and it made the third shift quicker and smoother. Much better now.

I thought the rod was going fully back because it was kicking down and generally working fine, but now it's great and better than before. Instant kickdown without any delay and better acceleration and shifting. Shifts into 3rd at 35 or 40mph now which is probabaly as good as it'll get as I cant adjust it any further. It was shifting into 3rd at roughly 25 mph before.

 

[JG71B]

Bring it back to the trans shop and tell them you don't like the way it's acting and ask them to check it out . It may just be a matter of simple adjustment

Maybe the shift points needs to be raised
slightly. At what speed does it shift into 3rd and make that clunk?

Agree, after all, there is only 100 miles on it. Very possible a simple adjustment

 

[Dipstick]

Could be a severe case of overlap, front clutch is engaging before the band has released. Can be cured with an orifice restrictor in the case to slow down the clutch application.

 

[dvw]

Many 727 will overlap at light throttle. It will do it with a manual VB. Not really a big deal. It can be tailored by restricticting the high clutch feed orifice. This requires removing the valve body.
Doug

 

[ling102]

Thank you everyone for the replies.