C6 Guru Needed!

[FloridaPhil]

I just rebuilt my 1971 truck C6 and have run into a problem that I think is truck specific. My C6 has a 4 pinion rear planetary, no snap ring on the output shaft and a short tail housing with the big bearing. My shop manuals are all for passenger cars. Before disassembling the tranny I checked the end play and it was .030". After installing new seals, clutches, steels, thrust washers and gaskets, the drive train has grown by about the thickness of one thrust washer (.060"). I have verified that the tranny has been assembled correctly a dozen times. My original pump selective washer was .080". After the rebuild, the tranny locked up when the pump bolts were tightened up. I changed the pump selective washer to the .050" black washer and the everything turns by hand but I still have no end play. I am sure I have installed a thrust washer where I don't need it, causing the end play to be too narrow. I suspect the culprit is near the rear planetary. Does anyone have any experience with this issue? Thanks!

[Donnie]

Phil, did you change ANY hard parts ? Such as clutch drums, or planets ? If so, what did you change ? If not, I think that you are correct in your assumption... I would restack the parts outside the case, starting with a 1 gallon coffee or paint can---so you can set the pump in it & build a "tower" that is stable------add 1 piece at a time until you find your un-needed washer......make sure that the sun gear is in contact with the small torrington that is in the foreward clutch drum...there have been changes in that area.......Donnie

[FloridaPhil]

Thanks for the help. I believe you are correct. I think my extra washer is on the back of the front planet. My transmisson has two needle bearings both on the front planet. They are the three piece open style. One is on the top where it contacts the sun gear and the other is on the bottom. I also have a thrust washer on the bottom of the front planet. Might be the culprit.

[BobbyFord]

Copper-type thrust washer does not belong in contact with a torrington-type bearing.
This may help...> http://raceabilene.com/kelly/hotrod/ima ... /c6exp.gif

[FloridaPhil]

I have determined the extra washer is not in the tower section (assembled stack - sun gear to reverse high drum). Removing washers from this area does not affect the mesh depth of the input shell into the reverse high drum) nor does it affect the total length of the assembled tower itself. Everything seems fine in the tower with all clutches seated and needle bearings (front and rear of the forward planetary) in full contact. This only leaves 3 thrust bearings that could be causing the problem. One behind the reverse ring gear, one behind the rear planetary and one in front of the rear planetary. The large snap ring that holds the planetary in position fits perfectly into the groove in the reverse clutch hub, so I believe the thrust washer behind the rear planetary is OK in that position. My rear planetary is a four (4) pinion design not a three (3). My truck transmission has no small snap ring holding the output shaft. The shaft is held in position by the big bearing and the rear housing which is on the transmission at this time. This leaves the only possible culprit to be the thrust washer in front of the rear planetary. This washer would lay between the rear planetary itself and the input shell holding the sun gear. I removed this thrust washer and reinstalled the tower and the pump. I used the black (#1) selective washer behind the pump. With the pump bolts tight, I now have .020 end play. Yes, but there is no thrust washer between the input shell and the front of the rear planetary. There is a thin black shim under the sun gear itself, so the front of the planetary is not actually riding on the input shell. What do you think?

[BobbyFord]

There has to be a thrust washer between the sun gear/shell and the front of the rear planetary.

[Donnie]

Bobby is right, that thin black "shim" is the wear surface for the thrust washer to ride on. A washer is needed in this location.
Let me ask, WHAT FAILED in this unit that required you to rebuild it? Did you replace ANY hard parts, any at all? You had .080 end play on tear down, correct? that is excessive, what did you find worn to cause this much end play?
Have you had the back end apart yet...Do you have any end play in the rear section?....................

[FloridaPhil]

I purchased this transmission from a wrecking yard (1971 2WD F100), so I do not know how it worked. The end play before I took it apart was .030. I have replaced the thrust washers, clutches, steels, seals and gaskets. No hard parts. I have not upgraded anything. I measured all the thrust bearings and they are all .060" thick. There are two needle style bearings in this transmission, one in front of the front planetary and one behind the front planetary. The needle bearings are the open three piece type with a top shell, bearing and bottom shell. They are in the right postion. The tower goes together fine and the tabs mesh with about 1/8" overlap. This is a truck C6 with a 4 pinion rear planetary. The rear planetary has a thrust washer on the front and the rear. With all the thrust washers in place according to my exploded view and my shop manuals, I have zero end play with the thinnest #1 black plastic washer behind the pump. I thought I found the problem today, but it wasn't it. During the rebuild, I took out the large rear ball bearing in the tail housing for inspection. I thought that I had put it back in backwards and was driving the output shaft too far forward. This turned out not to be the case. I have the transmission apart again and am going to put the tower back in without the rear clutches, steels and one-way clutch to see if that's what's causing any problem. The one-way clutch race is definitely flush with the case and the bolts are torqued.

[FloridaPhil]

I've been working on this project for a week and I've learned more about a C6 than I ever wanted to know. After assembling and disassembling the tranny at least 20 times and checking everything over and over, I believe I've found the problem. My manuals show two thrust washers (#7 & #8) between the rear planetary and the input shell. #7 is a standard copper .060" thick thrust washer and #8 is a black steel disc mounted under the sungear. I've inventoried and measured every washer comparing and matching the washers in my rebuild kit. I have come to the conclusion that this transmission did not have a copper style thrust washer #7, it only has the steel washer #8 riding on the rear planetary. The wear pattern on my planetary seems to back up this theory. I think this has to do with the fact that my transmission is a truck tranny with a 4 pinion rear planetary and the big bearing holding the output shaft in position. Now, with #7 removed and the original .078" selective thrust washer behind the pump I have .018" end play.

[BobbyFord]

The copper thrust washer on the front of the rear planetary assembly MUST be there and if you run it without it you will be pulling your transmission back apart very soon.

[FloridaPhil]

OK.. I give up. I guess I'm off to the transmission shop.

[Donnie]

Phil, just an afterthought, it has been a long time since I have been where U are.......BUT, if your planet has a captive bearing in it, does the sun gear reach the bearing to provide a contact surface to ride on . IF there is a bearing there, a thrust washer is not needed....just trying to recall...................Donnie

[FloridaPhil]

The front planet has two needle bearings. They are the open type with a top and bottom shell separate from the bearing itself. The bottom needle bearing sits in the forward clutch drum race. The top shell faces up where it's center projection fits into the rear of the planet. The bottom shell has a rounded edge on the bottom and the round edge is facing down. With the front planet in place, I can reach in with a small curved screwdriver and feel that the planet is sitting flat on the needle bearing. There also is a thrust bearing behind the planet. To see if the thrust bearing on the bottom of the planet was the problem, I removed the thrust bearing on the bottom of the planet and it had no affect on the planet height or the mesh of the reverse high drum and the sun gear shell. There is also a captive needle bearing sitting under the three gears at the front of the planet. The top shell of that needle bearing fits into the sun gear. The sungear shell and the reverse high drum seem to mesh with the right amount of overlap. The tabs of the sungear shell are about midway into the slots of the reverse high drum. I've compared the way it looks to many pictures and I believe the problem is outside of the assembled tower. The one-way clutch race at the back of the transmission is flush with the case and the bolts are torqued. The output shaft is not keeping the ring gear or the reverse clutch hub from seating. This only leaves the two bearings on either side of the rear planet. All the clutches are engauged fully and solid. You can't remove the thrust washer on the back of the rear planet or on the back of the reverse ring gear because it would create too much slop under the snap ring that's holding the rear planetary into the reverse clutch hub. That only leaves the thrust washer in front of the rear planet. If I reinstall the thrust washer on the front of the planet, the transmission has zero free play with the thinest selective thrust washer (black plastic .050") behind the pump. I could take .015" off the black plastic washer under the pump and make it work, but I'm usure if this is the right thing to do.

[FloridaPhil]

I am very appreciative of all the help I received with this post. I suspect my junk yard C6 has some mismatched parts or that I have some kind of a mind block going on. Anyway, I'm moving on and will buy a rebuilt unit from a local supplier. I have a new respect for automatic transmission repair people. As well as being somewhat complicated, the parts in those things are heavy has heck. I never had a work out at the gym as good as I had pulling those parts around. I'm moving on the different subjects. Thanks again!

[Donnie]

This does not sound correct...look closely for witness marks..The sungear shell and the reverse high drum seem to mesh with the right amount of overlap. The tabs of the sungear shell are about midway into the slots of the reverse high drum.

in this area.. there should be more than half way contact here. half way is not enough..... sorry, my paste went into the wrong area.....Donnie