Reverse input drum
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From: Dade City, Fl.
Reverse input drum Checking the drum after I installed the piston with new seals and stacked with new steels and clutches. How much air should escape past the seals? I was using about 40 psi. I couldn't feel any air ,but I could head what sounded like air going past the seals. Did I cut the seals on installation? Also I only have .030 clearance on the clutch stack up. What do I need to do to get to the .045-.070" Help!
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GM went with a "feed bleed" system starting with the 1987 700R4's and it is still used today. This was to cushion the clutch apply of the piston to make things smoother. The piston has an air bleed in it. You need 125psi. or more to make reverse work correctly. When in the vehicle it never sees less than 150psi. DO NOT restrict the hole in the piston as recommended by TransGo as it can create a problem. Are you using the oem Belville steel on top of the aluminum piston or a waved steel? If it is the waved, move it so that the waved steel sits in a different position over the hole in the piston, so there might be less of a leak between the steel and piston when air testing it.
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Joined: Jan 2018
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From: Dade City, Fl.
It has the Belleville spring. It is also a new reverse input drum. I used the "feeler gauge "method to install the piston into the drum. I didn't have to fight very much to get the piston to seat in the drum. Do you think I could have messed up the seal and it is holding the piston up some? I'm confused
Any doubt, take it apart and check it.
Whether you messed up the seal or not shouldn't be a matter of anyone guessing.
This is the problem with amature rebuilds (no offense) someone can take something apart and put it back together, replace parts, etc. But no amature knows whats normal and whats not.
Sure, air leaks out of the drum. It's relying on the belville plate to flatten out and cover the air bleed hole. Thats not a precision seal by any means, but thats how they all are and they were designed that way.
How much air should you hear leaking, unfortunately no one can answer that unless they are standing next to you. The seals should not leak at all.
I guess you could try stacking it upside down so a flat steel is against the piston. But the seal is still a steel plate against an aluminum piston with no gasket or anything. The question is still whats normal.
Whether you messed up the seal or not shouldn't be a matter of anyone guessing.
This is the problem with amature rebuilds (no offense) someone can take something apart and put it back together, replace parts, etc. But no amature knows whats normal and whats not.
Sure, air leaks out of the drum. It's relying on the belville plate to flatten out and cover the air bleed hole. Thats not a precision seal by any means, but thats how they all are and they were designed that way.
How much air should you hear leaking, unfortunately no one can answer that unless they are standing next to you. The seals should not leak at all.
I guess you could try stacking it upside down so a flat steel is against the piston. But the seal is still a steel plate against an aluminum piston with no gasket or anything. The question is still whats normal.
If it helps here is one out of a core I have. I first was going to put new seals on a different drum but I didn't have the inner seal.
Then I was going to test this as usual - on the pump. But the sealing rings were blasting air, not even sure why, they looked good.
This is at 105 psi. At the beginning of the air test you can see fluid in the drum being blown around by air coming out of the bleed hole.
Then I was going to test this as usual - on the pump. But the sealing rings were blasting air, not even sure why, they looked good.
This is at 105 psi. At the beginning of the air test you can see fluid in the drum being blown around by air coming out of the bleed hole.
I made another video just to see how much air was leaking out of my air chuck or the bleed hole.
This video has some tape over the bleed hole and the clutch stack in almost upside down, just so theres a flat steel over the hole.
Only the first application is accurate, you can see it hold air until I pull the air chuck out. I had problems getting it to seal after that. If you want to see how the clutch is stacked it's shown at the end.
This video has some tape over the bleed hole and the clutch stack in almost upside down, just so theres a flat steel over the hole.
Only the first application is accurate, you can see it hold air until I pull the air chuck out. I had problems getting it to seal after that. If you want to see how the clutch is stacked it's shown at the end.
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From: Dade City, Fl.
Much thanks Jay! I figured I would have to take the drum apart to see why there is so little clearance. I might even put all the new parts into the old drum and check the stack up clearance if I don't find anything when I disassemble the new one. Thanks again for the info and videos !
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From: Dade City, Fl.
I had a little time today so I took the drum apart again. The seals look fine so I put it back together and measured again. Still not .040"
I measured the height of the belleville spring and got .179" I'm wondering if I should buy a new belleville spring or go with the wavy washer set up from Alto.
I measured the height of the belleville spring and got .179" I'm wondering if I should buy a new belleville spring or go with the wavy washer set up from Alto.
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You will have to check the clutch clearance. If too much or little, changing the pressure plates is one way to fix it. The stack up I use is the waved steel from the 1982 - 1986 setup, 4 early Borg Warner clutches (.080" thick instead of the late BW clutches .070" thick) and 4 turbulator steels. If you use the Alto setup it will come with their version of a waved steel and a .090" thick steel plate to replace the Bellville setup. You could flip over the Bellville steel you have now, and this will change the clearance somewhat and see if this helps with your problem.