C-4 Transbrake
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Senior User
Joined: Jan 2002
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From: Gloucester USA
C-4 Transbrake
we are building a drag mustang and when we rebuilt the c4, we put a transbrake in it.
the 1st time we ever got it moving in the driveway, after a while the tranny dumped all the fluid. would you believe that the instructions for the transbrake say "for a faster response drill a 1/16 hole in so+so area"... it didn't say, however, that not drilling this whole would cause the front pump seal to blow.
in the process of pulling out the tranny and fixing it. ain't that some *****
the 1st time we ever got it moving in the driveway, after a while the tranny dumped all the fluid. would you believe that the instructions for the transbrake say "for a faster response drill a 1/16 hole in so+so area"... it didn't say, however, that not drilling this whole would cause the front pump seal to blow.
in the process of pulling out the tranny and fixing it. ain't that some *****
Senior User
Joined: Jul 1999
Posts: 472
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From: USA
C-4 Transbrake
[updated:LAST EDITED ON 16-Feb-02 AT 11:16 PM (EST)]That seems wierd to me. Is the converter hub bushing OK?
All automotive transmisssions I have ever worked on have a bushing to support the converter hub. On one side of the bushing is T/C oil pressure (~50 psi or so), and on the other side is the front oil seal. To prevent pressure build-up from T/C pressure oil going past the bushing, a drain passage to sump is adjacent to the front seal. Oil lip seals can't handle more than just a couple psi of pressure. If too much oil flows past the bushing (worn or missing bushing), it could overwhelm the sump drain passage and blow out the front oil seal.
A couple years ago I repaired a Jasper-rebuilt C-6 where they mis-matched the case and pump castings. The ports were so misaligned that the gasket and square-ring blew out when it got hot (truck was stuck). So much oil leaked out of the bellhousing area that it appeared to be a blown front seal at first...
I'm curious where they wanted you to drill the 1/8" hole - probably was in the valve body to allow faster release of the front clutch pack. That clutch is only used for 3rd and Reverse on a normal transmission, but in this case it is applied also to "lock up" the transmission - providing the transbrake feature.
Art
All automotive transmisssions I have ever worked on have a bushing to support the converter hub. On one side of the bushing is T/C oil pressure (~50 psi or so), and on the other side is the front oil seal. To prevent pressure build-up from T/C pressure oil going past the bushing, a drain passage to sump is adjacent to the front seal. Oil lip seals can't handle more than just a couple psi of pressure. If too much oil flows past the bushing (worn or missing bushing), it could overwhelm the sump drain passage and blow out the front oil seal.
A couple years ago I repaired a Jasper-rebuilt C-6 where they mis-matched the case and pump castings. The ports were so misaligned that the gasket and square-ring blew out when it got hot (truck was stuck). So much oil leaked out of the bellhousing area that it appeared to be a blown front seal at first...
I'm curious where they wanted you to drill the 1/8" hole - probably was in the valve body to allow faster release of the front clutch pack. That clutch is only used for 3rd and Reverse on a normal transmission, but in this case it is applied also to "lock up" the transmission - providing the transbrake feature.
Art
5th Wheeling
Joined: Dec 2001
Posts: 47
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From: Gadsden
C-4 Transbrake
The extra hole needs to be drilled any time you run a trans brake. The trans brake works by applying reverse while you are already in low, locking the trans. When you hit the button the solenoid redirects fluid to the reverse piston. When you release it the fluid has to go somewhere. That's what the hole is for, just a place to dump the fluid. Without the hole it may have been forced back into the valve body, causing an extreme pressure spike. That may have blown the seal.
Later,
David Cole
Later,
David Cole
