[Steve25]

Thanks for the pics.

That shaft spline looks mostly "normal" for the short spline end.

Look carefully at the splines in the forward drum.
Look from the front to rear.
I bet the splines in there are "shorter" than they should be,
allowing the input shaft to move toward the rear and then contacting the output shaft.
I've seen that before on units that got driven hard.

That forward drum hub where the washer sits looks kinda chewed up.
I'd seriously consider replacing that drum.

Will do. The other two shafts, a PA hardened shaft sits flush and a stock C5 shaft only sticks out .010 I do have another forward drum if needed. It was "rebuilt" before I got it so who knows what they did to it before I got a hold of it and did things to it.

Now the next question is this what was causing the actual original reverse problem that I was having. Don't know yet. Seems like it is always something. 😀

 

[galaxiex]

Will do. The other two shafts, a PA hardened shaft sits flush and a stock C5 shaft only sticks out .010 I do have another forward drum if needed. It was "rebuilt" before I got it so who knows what they did to it before I got a hold of it and did things to it.

Now the next question is this what was causing the actual original reverse problem that I was having. Don't know yet. Seems like it is always something. 😀

That chewed up input shaft and the likely matching damage on the output shaft would have created significant metal particles.
Ford valve bodies are NOT very tolerant of trash and metal particles in the oil.
Sticky valves come to mind, but you said a different VB didn't fix it.

Maybe??? the in and output shafts were "binding" against each other somehow?

Regardless, I would strip the entire unit down and super clean EVERYTHING.

And don't forget the cooler!
Coolers can trap an incredible amount of trash and metal particles that comes out later and ruins all your hard work.

A magnet in the pan to collect metal is never a bad idea.

 

[Steve25]

Will do. The other two shafts, a PA hardened shaft sits flush and a stock C5 shaft only sticks out .010 I do have another forward drum if needed. It was "rebuilt" before I got it so who knows what they did to it before I got a hold of it and did things to it.

Now the next question is this what was causing the actual original reverse problem that I was having. Don't know yet. Seems like it is always something. 😀

Will do. The other two shafts, a PA hardened shaft sits flush and a stock C5 shaft only sticks out .010 I do have another forward drum if needed. It was "rebuilt" before I got it so who knows what they did to it before I got a hold of it and did things to it.

Now the next question is this what was causing the actual original reverse problem that I was having. Don't know yet. Seems like it is always something. 😀

View attachment 175170

Thanks for the pics.

That shaft spline looks mostly "normal" for the short spline end.

Look carefully at the splines in the forward drum.
Look from the front to rear.
I bet the splines in there are "shorter" than they should be,
allowing the input shaft to move toward the rear and then contacting the output shaft.
I've seen that before on units that got driven hard.

That forward drum hub where the washer sits looks kinda chewed up.
I'd seriously consider replacing that drum.

Ok I found another much better forward clutch drum and I agree with your assessment. It looks like there was some minor wear right before the splines. Also it looks like the thrust washer spun on the face as shown in the photograph. I am not sure how that could happen. It must have happened before the earlier rebuild.
I am still going to use the C5 shaft as it looks ok and scrap the other shaft.
I was going to use the PA Hardened shaft, but it fits loose in the pump bushings. It is a new shaft. The pump bushings are new. Must be a little undersized. The C5 shaft fits really nice and turns smooth in the pump bushings.
I do appreciate all the help. It is easy to overlook things that others see.

 

[Steve25]

That chewed up input shaft and the likely matching damage on the output shaft would have created significant metal particles.
Ford valve bodies are NOT very tolerant of trash and metal particles in the oil.
Sticky valves come to mind, but you said a different VB didn't fix it.

Maybe??? the in and output shafts were "binding" against each other somehow?

Regardless, I would strip the entire unit down and super clean EVERYTHING.

And don't forget the cooler!
Coolers can trap an incredible amount of trash and metal particles that comes out later and ruins all your hard work.

A magnet in the pan to collect metal is never a bad idea.

The pan was very clean, but the two magnetic drain plugs did have some metal particles on them. I have a spin on oil filter in the cooler lines before the trans cooler. Yeah, the shaft grinding thing was really strange. It is a new one on me. The two shafts are close together may be a 1/4 inch or so. If things get out of whack, I could see some grinding might happen, and did happen.

I have a theory, may not be correct, but the way I understand it is that under load in forward gears the gear train is forced to the back to the number 9 thrust washer. I would guess the output shaft also. So going forward no problem with input output shaft spacing. Same in neutral and park. But in reverse the gear train is forced toward the front and may be the output shaft also.
This puts the load on the brass stator support selective thrust washer. and also brings the output shaft closer to the input shaft.
Normally not a problem unless the input shaft is sticking out of the forward clutch drum too far as what happened here, and the shafts come together. the input shaft is going one way and the output shaft is going the other way. I would think that if this happened the output shaft would just push the input shaft back without any grinding.
But if the driven member in the torque converter is pushing against the input shaft with enough force, the two counter rotating shafts start the grinding process and cause the transmission to bind up in reverse. The more throttle you give it the harder the driven member pushes against the input shaft causing even more friction between the input shaft and the output shaft making the bind up even worse. Now only full throttle has enough force to overcome the bind up and the car then more less goes backwards.
This may not be correct, but it is just a guess based on what I have experienced.
Feel free to correct me as I always learn something new every day.

 

[Steve25]

The pan was very clean, but the two magnetic drain plugs did have some metal particles on them. I have a spin on oil filter in the cooler lines before the trans cooler. Yeah, the shaft grinding thing was really strange. It is a new one on me. The two shafts are close together may be a 1/4 inch or so. If things get out of whack, I could see some grinding might happen, and did happen.

I have a theory, may not be correct, but the way I understand it is that under load in forward gears the gear train is forced to the back to the number 9 thrust washer. I would guess the output shaft also. So going forward no problem with input output shaft spacing. Same in neutral and park. But in reverse the gear train is forced toward the front and may be the output shaft also.
This puts the load on the brass stator support selective thrust washer. and also brings the output shaft closer to the input shaft.
Normally not a problem unless the input shaft is sticking out of the forward clutch drum too far as what happened here, and the shafts come together. the input shaft is going one way and the output shaft is going the other way. I would think that if this happened the output shaft would just push the input shaft back without any grinding.
But if the driven member in the torque converter is pushing against the input shaft with enough force, the two counter rotating shafts start the grinding process and cause the transmission to bind up in reverse. The more throttle you give it the harder the driven member pushes against the input shaft causing even more friction between the input shaft and the output shaft making the bind up even worse. Now only full throttle has enough force to overcome the bind up and the car then more less goes backwards.
This may not be correct, but it is just a guess based on what I have experienced.
Feel free to correct me as I always learn something new every day.

 

[Steve25]

In this picture you can see how close the input shaft is to the output shaft. I would guess about 1/4 inch or so. I would think that things would not have to be much out of kilter to make them touch/grind together.
Also, the picture shows that the input shaft does not (or should not) extend beyond the face of the forward clutch.
Something else I have noticed is that in this 1964 picture the input shaft is apparently kept from moving farther into the drum by a lip on the face of the drum. The input shaft can't move any farther. See how long the splines are? There is nothing on the other face of the drum to keep the input shaft from moving any farther.
Later drums don't have this lip. They use the drum to stop the input shaft from moving any farther when the splines stop, and the full size of the shaft contacts the drum.

Maybe this explains my problem of the input shaft sticking out too far. I may have had an early input shaft in a late model drum. This also may explain why the splines measure longer on this shaft than the other shafts I have even though the overall shaft length is the same. It is starting to look like an early input shaft in a late model drum was the cause of the problem.
Any comments appreciated.

 

[Steve25]

My C4 works fine now. However, the problem with reverse was not easy to locate. When I found the input shaft sticking way out of the forward clutch drum and grinding into the output shaft, I thought I had solved the problem.
Re assembling the C4 using a C5 input shaft that fit like it should and using a different forward clutch drum in resulted in no improvement in reverse. Same problem as before. After using some words, I can't repeat here, I pulled and dissembled the C4, (again) then using a magnifying glass, inspected every part. Then I found the problem.
The forward clutch hub and ring gear, when in reverse only, was pushing up against the forward clutch upper pressure plate causing the forward clutch plates to press together and lock up the transmission.
It was clear to see the contact point between the two where they were rubbing together. I put a shim under the number three thrust washer to make some space between the two. This solved the problem. If I had access to a machine shop, I would have turned down the upper pressure plate as shown in the above picture. But I don't.

Looking at the above picture from 1964, it shows the forward clutch upper pressure plate machined down at about a 45 deg angle on one side inner diameter. This is the very same location where mine was rubbing the forward clutch and ring gear. It looks like a known problem all the way back to 1964.
I have not seen a forward upper clutch plate like this before. Maybe I just never noticed before. But an upper forward clutch upper pressure plate like shown in the above picture, if used would have solved the reverse problem. May be some mix and matching of early and late parts happened somewhere along the many rebuilds this transmission must have gone through.
Anyway, it works fine now. Thanks for the help.

 

[Steve25]

 

[Steve25]

In my post above, I said upper picture, but it is actually the lower picture. I did not know where the picture was going to be. This picture shows a 45 deg angle on both parts. However, the forward upper pressure plate I have has no 45 deg angle and the two parts make contact.
From the picture, it would seem that the part on the top would contact first, as it looks closer, but that did not seem to be the case. The machine work shown here on the forward upper pressure plate making a 45 deg angle was done for a reason. In 1964 anyway.

 

[gregaust]

Hmmm that is a very interesting issue ...
On every one I assemble i ensure input shaft does not protrude past the #3 thrust washer. Then you know there is clearance to the output shaft usually .

Although on quite a few now I clean up the output in the lathe and cut a small recess.

 

[Steve25]

 

[Steve25]

Point of contact with forward clutch upper pressure plate with no 45 deg angle.

 

[gregaust]

Not seen that before . Will do some measuring on next I do