TH350 rebuild tech
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==Overview== | ==Overview== | ||
| − | + | The GM Turbo Hydra-Matic 350 transmission (aka "TH350", "Turbo 350", THM350, "T-350", etc.) was used between 1968-'86 in RWD and 4WD GM domestic vehicles. The TH350 was still produced many years beyond 1986 for export sales. It is a relatively rugged, compact transmission that lends itself to a wide variety of applications and modifications. | |
| − | The GM Turbo Hydra-Matic 350 transmission (aka " | + | |
==Basic rebuild information== | ==Basic rebuild information== | ||
{{Note1}} | {{Note1}} | ||
| − | *This | + | *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, [http://www.amazon.com/Turbo-Hydra-Matic-350-Handbook-Sessions/dp/0895860511 '''''Turbo Hydra-Matic 350 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 It has good pictures, a lot of good info, but has some outdated info.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 tutorial. That said, the following should help give a better understanding of the TH350 and possibly help when a question arises. | |
| − | *This is not a step-by step tutorial. That said, the following should help give a better understanding of the | + | |
*The following info draws heavily from an original Hotrodders forum thread by jakeshoe, titled [http://www.hotrodders.com/forum/th350-rebuild-tech-145361.html ''TH350 Rebuild Tech'']. | *The following info draws heavily from an original Hotrodders forum thread by jakeshoe, titled [http://www.hotrodders.com/forum/th350-rebuild-tech-145361.html ''TH350 Rebuild Tech'']. | ||
| − | ==Variations of the | + | ==Variations of the TH350 family== |
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There is also a TH350C and TH250C version that has a lockup torque converter (TCC). Look for the end of the input shaft to have a smooth polished end with O-ring on it. 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. | There is also a TH350C and TH250C version that has a lockup torque converter (TCC). Look for the end of the input shaft to have a smooth polished end with O-ring on it. 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. | ||
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Hughes, TCI and Boss Hog make TH350C torque converters. | Hughes, TCI and Boss Hog make TH350C torque converters. | ||
| − | =Rebuilding the | + | ==Rebuilding the TH350== |
===Bushings and thrust washers=== | ===Bushings and thrust washers=== | ||
| − | A | + | A TH350 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. |
| − | Be prepared to replace almost ALL the bushings in a | + | Be prepared to replace almost ALL the bushings in a TH350. Might as well order a bushing kit, as well as a thrust washer kit. It is also recommended to get two additional sun gear bushings individually. |
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| + | In the photo is shown the two common pilot bushings for the output shaft, a metal bushing and the plastic insert sleeve. The plastic sleeve design is very durable, you will find professional builders have their own preference. | ||
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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. | ||
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[[File:T-350_acumilator01.jpg|thumb|300px|left|T-350 Accumulator cover, spring and piston with sealing rings.]] <br style="clear:both"/> | [[File:T-350_acumilator01.jpg|thumb|300px|left|T-350 Accumulator cover, spring and piston with sealing rings.]] <br style="clear:both"/> | ||
| − | Right side of | + | Right side of TH350 case. Pressure ports are circled. |
*Rear port (yellow) is main line pressure. You will see pressure here in all gears for most valve body configurations. Some race-only valve bodies may not have pressure at this port or the others. | *Rear port (yellow) is main line pressure. You will see pressure here in all gears for most valve body configurations. Some race-only valve bodies may not have pressure at this port or the others. | ||
*Middle port (red) is 2nd gear pressure. | *Middle port (red) is 2nd gear pressure. | ||
*Front port (blue) is third gear pressure. | *Front port (blue) is third gear pressure. | ||
| − | + | [[File:T-350_acumilator02.jpg|thumb|300px|left|TH350 Pressure ports circled.]] <br style="clear:both"/> | |
| − | [[File:T-350_acumilator02.jpg|thumb|300px|left| | + | |
=Transmission reassembly= | =Transmission reassembly= | ||
==Low-reverse piston install== | ==Low-reverse piston install== | ||
| − | + | 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. | |
| − | 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. | + | |
In the rare application that does not need reverse or low gear engine braking the low piston and low clutches can be deleted, and the feed holes in the case blocked. | In the rare application that does not need reverse or low gear engine braking the low piston and low clutches can be deleted, and the feed holes in the case blocked. | ||
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Install new seals on the low piston, these are square cut seals, not lip seals. | Install new seals on the low piston, these are square cut seals, not lip seals. | ||
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[[File:T-350_low_piston.jpg|thumb|300px|left|T-350 Low-reverse piston has 3 seals on it. That creates 2 separate sections.]] <br style="clear:both"/> | [[File:T-350_low_piston.jpg|thumb|300px|left|T-350 Low-reverse piston has 3 seals on it. That creates 2 separate sections.]] <br style="clear:both"/> | ||
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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:T-350caselowpiston.jpg|thumb|300px|left|T-350 Low-reverse piston installed into case.]] <br style="clear:both"/> | [[File:T-350caselowpiston.jpg|thumb|300px|left|T-350 Low-reverse piston installed into case.]] <br style="clear:both"/> | ||
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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:T-350_low_pist_springtool.jpg|thumb|300px|left|Tool used to compress the springs & retainer to install the retaining snap ring.]] <br style="clear:both"/> | [[File:T-350_low_pist_springtool.jpg|thumb|300px|left|Tool used to compress the springs & retainer to install the retaining snap ring.]] <br style="clear:both"/> | ||
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