TH350 rebuild tech
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==Overview== | ==Overview== | ||
| − | The GM Turbo Hydra-Matic 350 transmission (aka " | + | The GM Turbo Hydra-Matic 350 transmission (aka "T-350", "Turbo 350", THM350, 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. |
==Basic rebuild information== | ==Basic rebuild information== | ||
{{Note1}} | {{Note1}} | ||
*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 It has good pictures, a lot of good info, but has some outdated info.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 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 It has good pictures, a lot of good info, but has some outdated info.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 | + | *This is not a step-by step tutorial. That said, the following should help give a better understanding of the T-350 and possibly help when a question arises. |
*The following page was inspired by an original Hotrodders forum thread by jakeshoe, titled [http://www.hotrodders.com/forum/th350-rebuild-tech-145361.html ''TH350 Rebuild Tech'']. | *The following page was inspired by 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 T-350 family== |
| − | There is also a | + | There is also a T-350C and T-250C 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, similar in appearance to the 200C/2004R and 700R4/pre-LSx 4L60E. 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. Same also holds true with the oil pump - "C" is cast into the pump cover and pump half. |
| − | Don't confuse the | + | Don't confuse the T-350C with a T-350 '''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. |
Hughes, TCI and Boss Hog make TH350C torque converters. | Hughes, TCI and Boss Hog make TH350C torque converters. | ||
| − | ==Rebuilding the | + | ==Rebuilding the T-350== |
===Bushings and thrust washers=== | ===Bushings and thrust washers=== | ||
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*Front port (blue) is third gear pressure | *Front port (blue) is third gear pressure | ||
| − | [[File:T-350_acumilator02.jpg|thumb|300px|left| | + | [[File:T-350_acumilator02.jpg|thumb|300px|left|T-350 pressure ports circled]] <br style="clear:both"/> |
=Transmission reassembly= | =Transmission reassembly= | ||
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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. | ||
| − | [[File:T-350_low_piston.jpg|thumb|300px|left| | + | [[File:T-350_low_piston.jpg|thumb|300px|left|T-350 low-reverse piston has three seals on it, creating two separate sections]] <br style="clear:both"/> |
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| − | This gasket on a | + | This gasket on a T-350 sits against the valve body. Notice the open line in the gasket that will parallel the support plate that bolts on at front of the valve body. |
[[file:T-350_v-body_gasket02.jpg|frame|none|Notice the open line in the gasket, this gasket installs against valve body, not the case]] | [[file:T-350_v-body_gasket02.jpg|frame|none|Notice the open line in the gasket, this gasket installs against valve body, not the case]] | ||
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Below is a picture of the feed holes. These regulate the amount of fluid, or how fast it can apply the clutches. Drilling them bigger allows a faster apply. However, bigger is not always better. | Below is a picture of the feed holes. These regulate the amount of fluid, or how fast it can apply the clutches. Drilling them bigger allows a faster apply. However, bigger is not always better. | ||
| − | [[file: | + | [[file:T-350feedholes.jpg]] |
Remember that as the load increases on the trans, so does the pressure. The increase in pressure will cause the fluid to move faster and shifts to be firmer. If you drill the holes ''too'' big the shifts become too harsh at light throttle openings. This causes undue wear on the internal transmission parts, rear differential and axles, drive line and u-joints. | Remember that as the load increases on the trans, so does the pressure. The increase in pressure will cause the fluid to move faster and shifts to be firmer. If you drill the holes ''too'' big the shifts become too harsh at light throttle openings. This causes undue wear on the internal transmission parts, rear differential and axles, drive line and u-joints. | ||
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Coan reverse manual valve body. Notice the machining of passages. Please note the DIY cannot just mill the valve body as valves have also been changed in the valve body. | Coan reverse manual valve body. Notice the machining of passages. Please note the DIY cannot just mill the valve body as valves have also been changed in the valve body. | ||
| − | [[file: | + | [[file:T-350reverseVB.jpg]] |
=Governor= | =Governor= | ||
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Brass screened filter allows for more flow. Avoid the cloth looking material filters for the TH350 | Brass screened filter allows for more flow. Avoid the cloth looking material filters for the TH350 | ||
| − | [[file: | + | [[file:T-350HPfilter.jpg]] |
=Vacuum modulator= | =Vacuum modulator= | ||
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*Intermediate Band Adjust Nut- 15 ft/lb | *Intermediate Band Adjust Nut- 15 ft/lb | ||
| − | = | + | =T-350 dimensions and tailshaft housing (or ''extension'' housing) lengths= |
[[File:TH350 dimensions.jpg|thumb|left|400px|]]<br style="clear:both"/> | [[File:TH350 dimensions.jpg|thumb|left|400px|]]<br style="clear:both"/> | ||
| − | You will find the | + | You will find the T-350 with 6", 9" and 12" tail housings. |
There is also two 4WD output shaft lengths, the shortest and more common is seen below. A longer 4x4 output shaft was used for around 1.5 years. It is a 2WD shaft of 6 inch length that is cut off about 1.250 inches. Used on 208 transfer case with adapter. | There is also two 4WD output shaft lengths, the shortest and more common is seen below. A longer 4x4 output shaft was used for around 1.5 years. It is a 2WD shaft of 6 inch length that is cut off about 1.250 inches. Used on 208 transfer case with adapter. | ||
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