TH350 rebuild tech
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==Basic rebuild information== | ==Basic rebuild information== | ||
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'''NOTE:''' | '''NOTE:''' | ||
*This WIKI is not intended to be a replacement for an ATSG or factory tech manual. First time builders will likely need a tech manual. Recommended is Ron Sessions' book "TH350 Handbook" in the HP book series. It has good pictures, a lot of good info, but has some outdated info. Outstanding value for the money. | *This WIKI is not intended to be a replacement for an ATSG or factory tech manual. First time builders will likely need a tech manual. Recommended is Ron Sessions' book "TH350 Handbook" in the HP book series. It has good pictures, a lot of good info, but has some outdated info. Outstanding value for the money. | ||
*This is not a step-by step pictorial. That said, the following should help give a better understanding of the T-350 and possibly help when a question arises. | *This is not a step-by step pictorial. That said, the following should help give a better understanding of the T-350 and possibly help when a question arises. | ||
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===Exploded view=== | ===Exploded view=== | ||
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[[File:TH350 exploded.jpg|thumb|300px|center|]]<br style="clear:both"/> | [[File:TH350 exploded.jpg|thumb|300px|center|]]<br style="clear:both"/> | ||
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There was also a T-350'''C''' version that has a lockup torque converter (TCC). The case has a "C" cast into it, and there will be an electrical plug adjacent to the shifter shaft on the driver side of the tranny. Not to be confused with a TH350 non-lockup tranny with a screwed-in electrical connector on the ''passenger'' side of the case. This is a pressure switch that was used ~1972-'73 for the Transmission Controlled Spark (TCS) system. This disabled the distributor vacuum advance in all gears except high gear, and is a single wire switch threaded into a pressure port near where the cooler lines are located. In the case of this switch, you can either leave it in place, unused- or remove it and plug the port. There have been reports of some T-350 trannys having a temp sender in this area as well. | There was also a T-350'''C''' version that has a lockup torque converter (TCC). The case has a "C" cast into it, and there will be an electrical plug adjacent to the shifter shaft on the driver side of the tranny. Not to be confused with a TH350 non-lockup tranny with a screwed-in electrical connector on the ''passenger'' side of the case. This is a pressure switch that was used ~1972-'73 for the Transmission Controlled Spark (TCS) system. This disabled the distributor vacuum advance in all gears except high gear, and is a single wire switch threaded into a pressure port near where the cooler lines are located. In the case of this switch, you can either leave it in place, unused- or remove it and plug the port. There have been reports of some T-350 trannys having a temp sender in this area as well. | ||
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==Rebuilding the T-350== | ==Rebuilding the T-350== | ||
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===Bushings and thrust washers=== | ===Bushings and thrust washers=== | ||
A T-350 is known to be rough on bushings. Bushings are critical in that they allow the rotating parts to ride true on center, and for the lube to make it to the rear of the trans. | A T-350 is known to be rough on bushings. Bushings are critical in that they allow the rotating parts to ride true on center, and for the lube to make it to the rear of the trans. | ||
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===Case prep=== | ===Case prep=== | ||
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Once the case has been cleaned, all threads checked and/or repaired, and the rear case bushing installed you can start assembly. | Once the case has been cleaned, all threads checked and/or repaired, and the rear case bushing installed you can start assembly. | ||
===1-2 accumulator=== | ===1-2 accumulator=== | ||
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Photo shows accumulator cover, spring and piston (snap ring not shown). This is located on right side of trans case. Check the bore in the case for scratches or other damage if the spring was found broken. | Photo shows accumulator cover, spring and piston (snap ring not shown). This is located on right side of trans case. Check the bore in the case for scratches or other damage if the spring was found broken. | ||
[[file:T-350_acumilator01.jpg|frame|none|Accumulator cover, spring and piston with sealing rings.]] | [[file:T-350_acumilator01.jpg|frame|none|Accumulator cover, spring and piston with sealing rings.]] | ||
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=Transmission reassembly= | =Transmission reassembly= | ||
==Low-reverse piston install== | ==Low-reverse piston install== | ||
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The first item to go in the case will be the low/reverse apply piston. | The first item to go in the case will be the low/reverse apply piston. | ||
Its function is for oil to force it towards the front or bell housing side of the trans, applying the low/reverse clutches. This allows reverse when applied simultaneously with the direct (high gear) clutches, and allows manual low gear when applied with the forward clutches. Manual low gear creates engine braking on deceleration. The low/reverse clutches do not apply in automatic range 1st gear. The low sprag (low roller clutch actually) causes first gear when only the forward clutches are applied. | Its function is for oil to force it towards the front or bell housing side of the trans, applying the low/reverse clutches. This allows reverse when applied simultaneously with the direct (high gear) clutches, and allows manual low gear when applied with the forward clutches. Manual low gear creates engine braking on deceleration. The low/reverse clutches do not apply in automatic range 1st gear. The low sprag (low roller clutch actually) causes first gear when only the forward clutches are applied. | ||
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Then push it into the rear of the case evenly by hand, aligning it properly so it will seat (there is a "tang"). Look at the park pawl notch to help index it. | Then push it into the rear of the case evenly by hand, aligning it properly so it will seat (there is a "tang"). Look at the park pawl notch to help index it. | ||
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[[file:TH350caselowpiston.jpg|frame|none|Low-reverse piston installed into case.]] | [[file:TH350caselowpiston.jpg|frame|none|Low-reverse piston installed into case.]] | ||
Then install the return spring and retainer using the tool pictured. | Then install the return spring and retainer using the tool pictured. | ||
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[[file:TH350lowspringtool.jpg|frame|none| Tool used to compress the springs & retainer to install the retaining snap ring.]] | [[file:TH350lowspringtool.jpg|frame|none| Tool used to compress the springs & retainer to install the retaining snap ring.]] | ||
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Be sure you have the output ring gear to case bearing in the case. | Be sure you have the output ring gear to case bearing in the case. | ||
Also be sure on dis-assembly you inspected and replaced as necessary the input shaft to output bushing shown here (red arrow). | Also be sure on dis-assembly you inspected and replaced as necessary the input shaft to output bushing shown here (red arrow). | ||
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[[File:Input shaft to output bushing.jpg|frame|none|Check this bushing for wear, replace with new metal bushing or slip-in plastic insert.]] | [[File:Input shaft to output bushing.jpg|frame|none|Check this bushing for wear, replace with new metal bushing or slip-in plastic insert.]] | ||
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==Rear planetary unit install== | ==Rear planetary unit install== | ||
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Now you can install the low/reverse clutches, beginning with a steel, then a friction, alternating, ending with a friction. | Now you can install the low/reverse clutches, beginning with a steel, then a friction, alternating, ending with a friction. | ||
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[[file:TH350lowclutchesinstalled.jpg]] | [[file:TH350lowclutchesinstalled.jpg]] | ||
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'''Note here:''' | '''Note here:''' | ||
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Once it is pushed into place, install the snap ring, with the ends on each side of the spring or case-saver. | Once it is pushed into place, install the snap ring, with the ends on each side of the spring or case-saver. | ||
Now is the time to air check the low clutches. You do so by applying pressurized air to the passage at the rear pan area of the worm casting in the case. | Now is the time to air check the low clutches. You do so by applying pressurized air to the passage at the rear pan area of the worm casting in the case. | ||
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[[file:T-350_anti-rattle_spring.jpg|frame|none|Anti rattle (clunk) spring shown in correct location, use assembly grease to hold in place.]] | [[file:T-350_anti-rattle_spring.jpg|frame|none|Anti rattle (clunk) spring shown in correct location, use assembly grease to hold in place.]] | ||
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Next you install the 4-tang thrust washer into the large splines of the low sprag inner race (picture above), and then the sun shell and gear assembly. Before this step, for HD use, you would have wanted to install additional sun gear bushings, 2 on each end, and re-drilled the lube holes. | Next you install the 4-tang thrust washer into the large splines of the low sprag inner race (picture above), and then the sun shell and gear assembly. Before this step, for HD use, you would have wanted to install additional sun gear bushings, 2 on each end, and re-drilled the lube holes. | ||
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Shown here. | Shown here. | ||
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[[file:TH350sungearbushings.jpg|frame|none|Double bushings installed. You MUST drill oil holes in bushings.]] | [[file:TH350sungearbushings.jpg|frame|none|Double bushings installed. You MUST drill oil holes in bushings.]] | ||
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Install the input planet next, pictured below with thrust washer installed. | Install the input planet next, pictured below with thrust washer installed. | ||
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[[file:T-350_front_planet.jpg|frame|none|Front planet with thrust washer in place.]] | [[file:T-350_front_planet.jpg|frame|none|Front planet with thrust washer in place.]] | ||
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Then install the 3-tang thrust washer onto the top ring gear. | Then install the 3-tang thrust washer onto the top ring gear. | ||
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[[file:3_tang_whr_t-350.jpg|frame|none|Front ring gear with 3 tang thrust washer in place.]] | [[file:3_tang_whr_t-350.jpg|frame|none|Front ring gear with 3 tang thrust washer in place.]] | ||
==Direct drum assembly== | ==Direct drum assembly== | ||
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. | ||
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Stock measurement is 0.835", I cut them to 0.700". 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 on most auto trans friction clearances is ~0.010" clearance per friction. So a 5 friction direct setup would work great with 0.050" to 0.070" clearance. It will work with less, I wouldn't go less than 0.040", and will work with quite a bit more, but excessive clearance can result in delayed engagement, busted lip seals, and unsatisfactory shift quality. | Stock measurement is 0.835", I cut them to 0.700". 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 on most auto trans friction clearances is ~0.010" clearance per friction. So a 5 friction direct setup would work great with 0.050" to 0.070" clearance. It will work with less, I wouldn't go less than 0.040", and will work with quite a bit more, but excessive clearance can result in delayed engagement, busted lip seals, and unsatisfactory shift quality. | ||
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An even heavier duty direct drum/sprag assembly is available. It uses a 36 element sprag and a machined drum, it will withstand more torque than a stock unit or one w/just a hardened race. These units can cost upwards of $300.00. | An even heavier duty direct drum/sprag assembly is available. It uses a 36 element sprag and a machined drum, it will withstand more torque than a stock unit or one w/just a hardened race. These units can cost upwards of $300.00. | ||
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[[File:ATI direct drum and sprag.jpg|thumb|300px|left|ATI TH350 direct clutch drum with HD 36 element sprag]] <br style="clear:both"/> | [[File:ATI direct drum and sprag.jpg|thumb|300px|left|ATI TH350 direct clutch drum with HD 36 element sprag]] <br style="clear:both"/> | ||
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Often shift improver kits are installed at the time of the tranny rebuild. Various manufacturers make shift improver kits, Trans Go has a good reputation. | Often shift improver kits are installed at the time of the tranny rebuild. Various manufacturers make shift improver kits, Trans Go has a good reputation. | ||
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| + | ===Reference manuals=== | ||
| + | [[File:Sessions- ATSG-Haynes manuals.jpg|thumb|600px|left|Left to right: [http://www.amazon.com/Turbo-Hydra-Matic-350-Handbook-Sessions/dp/0895860511 Turbo Hydra-Matic 350 Handbook] by Ron Sessions; [http://www.northernautoparts.com/ProductModelDetail.cfm?ProductModelId=786 ATSG manual] p/n 44400; Haynes [http://www.amazon.com/gp/product/1563924234/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=0895860511&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0J4A1QHT1Y8B032P3Z6P GM Automatic Transmission Overhaul] manual, p/n 10360.]] <br style="clear:both"/> | ||
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| + | The Sessions and ATSG manuals are the preferred texts. | ||
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| + | ==Governor modifications== | ||
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| + | [[File:B&M Governor recalibration kit.jpg|thumb|300px|left|B&M Governor recalibration kit.]] <br style="clear:both"/> | ||
==Shift point changes== | ==Shift point changes== | ||
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<Blockquote> From this point we work with governor weights, springs, and shift valve springs.</Blockquote> | <Blockquote> From this point we work with governor weights, springs, and shift valve springs.</Blockquote> | ||
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[[Category:Transmission]] | [[Category:Transmission]] | ||
[[Category:Good articles]] | [[Category:Good articles]] | ||
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