Th400 rebuild..
Thread Starter
Instructor
Joined: Aug 2014
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Th400 rebuild..
Here's an odd question for someone that has rebuilt turbo 400s... When your assembling the trans in front of the rear band some use a fretting ring before you install the center support. In the atsg manual it says if the lugs on the center support measure .327 you need to use one and if it measures .362 you don't use one. Upon a Google search I found a couple other forums where they say it's just used for assembly purpose and another website that says it is to keep the center support from chewing up the case.. Anyone here know if I can put it together without the fretting ring? When I took it apart there wasn't one there. From my measurement I would need to use one but I may be measuring wrong too. Any advice would help thanks
Racer
Joined: Dec 2007
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'69 and later needs to have a .040 snap ring installed before the center support goes in. If your center support measures .327 you need to use one.
If it didn't have one check the case for cracks around that area.
If you had a .362 thick center support you can't use a .040 snap ring because it won't fit. You would have to machine your center support down. GM used the .327 thick center support since mid '69.
If it didn't have one check the case for cracks around that area.
If you had a .362 thick center support you can't use a .040 snap ring because it won't fit. You would have to machine your center support down. GM used the .327 thick center support since mid '69.
Racer
Joined: Dec 2007
Posts: 416
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Thats casting flash. The most common problem in that area is the intermediate clutch snap ring blowing the lugs out of the case, and cracks around the center support bolt. You have to also realize that the two holes on either side of the bolt are fluid feed holes, these have to seal fairly well without any type of seal or gasket, make sure it's in good shape.
The .040 snap ring goes in place before the center support, it looks like it does nothing or isn't really needed but it has to be there. The .327 center support was made .327 to accommodate for the .040 snap ring.
It's significant enough that all '68 and older center supports either get replaced or machined thinner so the .040 snap ring can be used.
I've built a lot of th400's and they always get that snap ring.
The .040 snap ring goes in place before the center support, it looks like it does nothing or isn't really needed but it has to be there. The .327 center support was made .327 to accommodate for the .040 snap ring.
It's significant enough that all '68 and older center supports either get replaced or machined thinner so the .040 snap ring can be used.
I've built a lot of th400's and they always get that snap ring.
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Racer
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Le Mans Master
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From: near the thumb in the mitten
the bolt that that passes from case to center support is and should be an indicator of alignment. Center support should be "loaded" towards thrust side before bolt is torqued.
Thread Starter
Instructor
Joined: Aug 2014
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I was following the atsg manual the whole way.. I found a ring at the transmission shop nearby and it was only a couple dollars.. Got it all back together except the valve body.. Waiting for it to come in from summit. Thanks again for the help
Team Owner
Joined: Sep 2003
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This is going in a what? Year should do. Do you have the VSS from the 700R4 still or was this an M4+3 or maybe M6? Axle ratio and tire size of the old and the present? All of that information is needed to answer your question. Tail shaft housing is TH400 and not a TH375 with the smaller speedo drive hole? Hole is either approx. 1" or something just over 2".
Last edited by WVZR-1; Apr 22, 2015 at 05:36 PM.
Team Owner
Joined: Sep 2003
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I'd think the easiest and maybe least expensive way to accomplish it might be to use some truck stuff, 8655315 would be a rotor/reluctor wheel and 8655291 would be the VSS to match. You would need to use a DRA to convert it to match the cluster I'm quite sure because all of the TH400 electronic speedos had DRAC's. The only other way to do it would be use the cable driven housing and the correct gears for the tire/axle and the VSS meant to convert a cable drive to electronic BUT you would have to cannibalize a speedo-cable to seal the adapter/VSS.
The Painless part number for that I believe is a 60115 - they were intentioned for getting the signal to the ECM so it also could involve the use of a DRA to correct the signal that in an '84 the first stop is the speedo.
What is your Th400 out off? What is the casting number on the extension housing?
I asked earlier what size the hole in the extension and I asked if it might have been a TH375. You didn't answer that so all of this without knowing that could be wasted. Snapshots of the extension?
The Painless part number for that I believe is a 60115 - they were intentioned for getting the signal to the ECM so it also could involve the use of a DRA to correct the signal that in an '84 the first stop is the speedo.
What is your Th400 out off? What is the casting number on the extension housing?
I asked earlier what size the hole in the extension and I asked if it might have been a TH375. You didn't answer that so all of this without knowing that could be wasted. Snapshots of the extension?
Last edited by WVZR-1; Apr 22, 2015 at 07:12 PM.