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Old 03-01-2013, 09:46 AM
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T-350 Intermediate clutch stack clearance

Getting ready to finish my transmission build up for my street car. Running a small block under 450hp, 6,500 rpms max. I placed the intermediate clutch packs in place with trust washers and bearings. Total endplay of .025, looks good to me. Measured intermediate stack clearance at .109 and which I am not happy with. Spec should be .040 - .100, I would like it to be closer to .060. So here is where I am at. I had the intermediate piston machined to .970 (was at 1.184) as instructed by several top places. My motor trans manual gives a spec for a 3 stack clutch piston measuring .992 and now I am wonder why machining down an extra .022 was required? That extra .022 in my stack would have been nice. So now I am looking to taking up extra clearance.

Looking at the idea of putting a low/reverse scraped off friction disk behind the piston seems dumb. This method creates a shim that measures at .032, which would be nice to tighten up the clearances. But the idea of raising the intermediate piston out .032 from it's bore sounds like a bad fix. I would rather install thicker steels or machine a thicker piston down to achieve the clearance I am after. So my question is, can anyone confirm measurements of a standard 2 disk and 3 disk intermediate piston? I have also noticed that there seems to be a few different variations of this piston with the return spring retaininer (some have seats in the piston and some have 20 or 30 springs). Can anyone clear this up?

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Old 03-01-2013, 09:53 AM
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what trans
2004r/th350/th400/???????
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Old 03-01-2013, 10:02 AM
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Th350

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Originally Posted by jimsmonte80 View Post
Getting ready to finish my transmission build up for my street car. Running a small block under 450hp, 6,500 rpms max. I placed the intermediate clutch packs in place with trust washers and bearings. Total endplay of .025, looks good to me. Measured intermediate stack clearance at .109 and which I am not happy with. Spec should be .040 - .100, I would like it to be closer to .060. So here is where I am at. I had the intermediate piston machined to .970 (was at 1.184) as instructed by several top places. My motor trans manual gives a spec for a 3 stack clutch piston measuring .992 and now I am wonder why machining down an extra .022 was required? That extra .022 in my stack would have been nice. So now I am looking to taking up extra clearance.

Looking at the idea of putting a low/reverse scraped off friction disk behind the piston seems dumb. This method creates a shim that measures at .032, which would be nice to tighten up the clearances. But the idea of raising the intermediate piston out .032 from it's bore sounds like a bad fix. I would rather install thicker steels or machine a thicker piston down to achieve the clearance I am after. So my question is, can anyone confirm measurements of a standard 2 disk and 3 disk intermediate piston? I have also noticed that there seems to be a few different variations of this piston with the return spring retaininer (some have seats in the piston and some have 20 or 30 springs). Can anyone clear this up?
There's nothing wrong w/shimming using the scraped friction like you mentioned. You can also use thicker steels.

Forgot to add the clearance you are shooting for is 0.050" to 0.070".
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Old 03-01-2013, 10:10 AM
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Sorry, I got wrapped up with discussion, I forgot to mention it is a TH-350. I would really like to research the option on a thicker piston before shimming, I just need to conform thickness of the piston. Thanks for the reply.
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Old 03-01-2013, 11:16 AM
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There are only 2 int. pistons for the 350.The 6 cyl. which took 2 int. clutches,and the 8 cyl.,which took 3 int. clutches. All 6cyl pistons were 1 set thickness [no variation] and the 8 cyl piston was 1 set thickness [no variation].Unless you are machining a 6 cyl. piston to 8 cyl. specs,to make it a 3 clutch 8 cyl piston,there is no reason in the world to ever machine an 8 cyl. piston.The int. clutches in the 350 are one of the trouble free areas in that trans,street OR strip..I would get another 8 cyl. piston and put it in.Make sure its stacked correctly, with the wavy ring going on top of the last steel.If you are eliminating the wavy and replacing it with another flat steel,be sure you are using a hardened sprag race[Beware with that set-up...it shifts HARD].You can get .010 thicker steels to put in it if you insist on tightening up the clearance.
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Old 03-01-2013, 11:55 AM
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Quote:
Originally Posted by jimsmonte80 View Post
Sorry, I got wrapped up with discussion, I forgot to mention it is a TH-350. I would really like to research the option on a thicker piston before shimming, I just need to conform thickness of the piston. Thanks for the reply.
Can't help w/the thickness of the piston. But there are intermediate steels in 0.068", 0.078" and 0.089" available (page #40) to get you in the range you want if you cannot find another V8 piston.
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Old 03-01-2013, 12:57 PM
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Oh,and to answer your earlier question...with the early 350's you had to manually place the loose springs into all of the pistons bosses,then the retainer.The later 350's had the springs attached to their respective retainers,and the bosses were removed in the piston,leaving just a smooth surface.So in the int. piston,if its a smooth surface where the springs go,then it takes the retainer with the springs attached to it.Late retainers will work in the early trans,but not visa-versa.
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Old 03-01-2013, 01:53 PM
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This was all some damn good info. Thank you all. I still can't figure out why B&M specs have you machine the piston to .970, this leave too much clearance even with 3 frictions installed. I understand that this extra clearance does not have an issue with durability, but it does give a slow 1-2 shift. So here is my solution. I am getting another intermediate piston (without spring bosses so I can reuse my same spring retainer) that measures 1.175 (6 cyl.) and maching it down to a spec that will leave me with .060 of clutch stack clearance. Anyone in the market for a .970 machined intermediate piston? I know this one would work, I just want it to work better.
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Old 03-01-2013, 09:10 PM
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t/350

heres what i do.just add 1 extra steal plate ditch that machined piston,you can also add a aditional steel to the reverse pack.been doing it for 35 t yrs
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Old 03-01-2013, 09:48 PM
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I also was thinking about adding an extra steel to take up clearance. I could also use thicker steels as well. I do have an awesome machinist who can do the work cheap. I might just have this larger piston machined down to give me about .060 clearance. When all is finished. I even seen a trick with taking 2 frictions and removing the material off of each side and placing them together as in one thick friction. I still don't understand why b&m has the piston machined down to .970, that is just too much.
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Old 03-01-2013, 10:15 PM
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B&M's recommendation for a 0.970" piston requires the use of the wavy 'cushion' plate. Did you include that in the stack?
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Old 03-02-2013, 06:32 AM
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Yes, I included the wavy cushion spring in the stack. Pretty sure it is discouraged from removing the cushion spring, which can cause too much shock to the intermediate sprag.
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Old 03-02-2013, 06:51 AM
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I generally use at least one thicker flat steel to tighten up the clearance even on a factory 3 friction apply piston
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Old 03-02-2013, 07:07 AM
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I would think by putting an extra steel in the stack to tighten it up is a much better idea, shimming the piston I feel is a bad idea. GM has specs on piston sizes, 1.184 for 2 frictions and .992 for 3 frictions, all with the wavy cushion spring. Not sure why B&M is taking off an extra .022. I might have to just call and ask.
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Old 03-02-2013, 11:43 AM
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I generally use at least one thicker flat steel to tighten up the clearance even on a factory 3 friction apply piston
To clarify, I add thicker steel plates to replace the original steel plates. I do not "add" an additional flat plate.

OE plates are about .070 thick. The thicker plates are .082 -.085 or so in thickness
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