TH350 rebuild tech
(→Intermediate clutch clearance: add text, pdf link; minor clean up) |
(→Direct drum assembly: add text; minor clean up) |
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For racing and heavy towing use, you will want to machine the direct clutch piston down approximately 0.160" to allow for one extra friction and steel plate for a total of 5 frictions, and 5 steels in the directs. This can be accomplished on a brake lathe. | For racing and heavy towing use, you will want to machine the direct clutch piston down approximately 0.160" to allow for one extra friction and steel plate for a total of 5 frictions, and 5 steels in the directs. This can be accomplished on a brake lathe. | ||
| − | Stock measurement is | + | Stock measurement is 0.835", machining the piston to 0.685" to 0.720" will allow the use of 5 frictions using 0.070" steels. Ideally you would pre-assemble, and check clearance using a 4 clutch pack. Measure the additional thickness of the extra friction and steel, then cut the exact amount needed to leave you the exact clearance you desire. Rule of thumb for most auto transmission clutch pack clearance is 0.010" clearance per friction. So a 5 friction direct setup would work well with 0.050" to 0.070" clearance. It will work with less, but no less than 0.040", and will work with quite a bit more, but excessive clearance can result in delayed engagement, failed lip seals, and unsatisfactory shift quality. |
If the piston is too low, the bottom flat steel plate can drop below the grooves in the drum and bind up the piston. You can leave out center cushion seal if dual feed is used. | If the piston is too low, the bottom flat steel plate can drop below the grooves in the drum and bind up the piston. You can leave out center cushion seal if dual feed is used. | ||
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| − | Heavy duty applications should also get a heat treated intermediate sprag race. | + | Heavy duty applications should also get a heat treated intermediate sprag race. The heat treatment makes the race less brittle. A heat treated intermediate sprag race is darker colored than a stock part. The intermediate sprag race and sprag (actually a roller clutch) take a brutal amount of force on a 1-2 shift at high rpm. Even more so with harsher shift calibrations. It is the single weakest part of a TH350. This is not to say a TH350 is not tough; they can reliably handle power in the 600 HP or lb/ft range if properly assembled using the right parts. |
[[file:TH350intspragraces.jpg]] | [[file:TH350intspragraces.jpg]] | ||
| − | + | Several companies offer an even heavier duty direct drum/sprag assembly. It uses a 36 element sprag (similar to what is used in the TH400) and a machined drum; it will withstand more torque than a stock unit or one with just a hardened race. These units can cost $300.00 or more. | |
[[File:T-350_HD_drum_sprag.jpg|thumb|300px|left|TH350 direct clutch drum with 36 element sprag]] <br style="clear:both"/> | [[File:T-350_HD_drum_sprag.jpg|thumb|300px|left|TH350 direct clutch drum with 36 element sprag]] <br style="clear:both"/> | ||
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