TH350 rebuild tech
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==Overview== | ==Overview== | ||
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The GM Turbo Hydra-Matic 350 transmission (aka "T350", THM350 "TH350", "T-350", "Turbo 350", etc.) was used between 1968-'86 in RWD and 4WD GM vehicles in the USA. The T-350 was still produced many years beyond 1986 for 'export sales' only. 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 "T350", THM350 "TH350", "T-350", "Turbo 350", etc.) was used between 1968-'86 in RWD and 4WD GM vehicles in the USA. The T-350 was still produced many years beyond 1986 for 'export sales' only. It is a relatively rugged, compact transmission that lends itself to a wide variety of applications and modifications. | ||
==Basic rebuild information== | ==Basic rebuild information== | ||
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'''NOTE:''' | '''NOTE:''' | ||
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*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. | *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. | ||
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*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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==Variations of the T-350 family== | ==Variations of the T-350 family== | ||
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| − | + | There was also a T-350C & 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. 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. | |
| − | Only the larger | + | Don't confuse the TH350C 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. |
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| + | Only the larger Transmission / Converter companies build high stall torque converters for the T-350C because of the low demand for them. | ||
=Rebuilding the T-350= | =Rebuilding the T-350= | ||
===Bushings and thrust washers=== | ===Bushings and thrust washers=== | ||
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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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===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| | + | [[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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==Output shaft install== | ==Output shaft install== | ||
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Next you install the output shaft. | Next you install the output shaft. | ||
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==Rear planetary unit install== | ==Rear planetary unit install== | ||
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Next goes in the output planetary to output ring gear bearing or thrust washer (depending on year). | Next goes in the output planetary to output ring gear bearing or thrust washer (depending on year). | ||
Then the planetary unit. Replace the bushing in this planet. | Then the planetary unit. Replace the bushing in this planet. | ||
| − | [[file: | + | [[file:T-350planet.jpg]] |
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. | ||
| − | [[file: | + | [[file:T-350lowclutchesinstalled.jpg]] |
'''Note here:''' | '''Note here:''' | ||
If you have a light duty core with low count low pack, unless it is a transbrake application or will be manually shifted into low for engine braking often, fewer clutches is OK. In some cases where you are after every last bit of ET, using fewer clutches can cause less frictional loss in 2nd and high gear. "Turbulator" steel plates from a 4L60E will also help and are a direct drop-in. | If you have a light duty core with low count low pack, unless it is a transbrake application or will be manually shifted into low for engine braking often, fewer clutches is OK. In some cases where you are after every last bit of ET, using fewer clutches can cause less frictional loss in 2nd and high gear. "Turbulator" steel plates from a 4L60E will also help and are a direct drop-in. | ||
| − | I am using Alto red frictions in this unit, however a stock tan clutch ( | + | I am using Alto red frictions in this unit, however a stock tan clutch ( like Borg Warner brand) is more than adequate for even very high HP cars. A Hi-Energy Borg from a 4L60E is also a good choice. |
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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 drive shell and front planetary unit== | ==Install drive shell and front planetary unit== | ||
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Drop the sun shell/gear in, spinning in the output carrier until it falls in place. | Drop the sun shell/gear in, spinning in the output carrier until it falls in place. | ||
[[file:TH350inputplanetthrust.jpg|frame|none|This shows drive shell installed with planet and thrust washer in place.]] | [[file:TH350inputplanetthrust.jpg|frame|none|This shows drive shell installed with planet and thrust washer in place.]] | ||
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| − | The HD applications should also get a heat treated intermediate sprag race. It is darker colored than a stock piece. The intermediate sprag race and intermediate sprag (actually 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 T-350. This is not to say a T-350 is not tough; they are under-rated and can reliably handle in the 600 HP or lb/ft range based on experience. | + | The HD applications should also get a heat treated intermediate sprag race. It is darker colored than a stock piece. The intermediate sprag race and intermediate sprag (actually 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 T-350. This is not to say a T-350 is not tough; they are under-rated and can reliably handle in the 600 HP or lb/ft range based on my experience. |
[[file:TH350intspragraces.jpg]] | [[file:TH350intspragraces.jpg]] | ||
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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. | ||
| − | [[File:ATI direct drum and sprag.jpg|thumb|300px|left|ATI | + | [[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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==Dual feeding== | ==Dual feeding== | ||
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This is part of the process of "dual-feeding" the direct clutches. On a stock rebuild you would normally install this lip seal. | This is part of the process of "dual-feeding" the direct clutches. On a stock rebuild you would normally install this lip seal. | ||
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===Dual Feed direct drum=== | ===Dual Feed direct drum=== | ||
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Dual feeding doubles the area of the piston that has pressurized fluid on it in 3rd gear, more than doubling the capacity of the clutch. It is accomplished by most valve body kits without doing so internally but requires a "transfer" plate and gasket to be added under the support plate in front of the valve body. | Dual feeding doubles the area of the piston that has pressurized fluid on it in 3rd gear, more than doubling the capacity of the clutch. It is accomplished by most valve body kits without doing so internally but requires a "transfer" plate and gasket to be added under the support plate in front of the valve body. | ||
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===Forward drum inspection=== | ===Forward drum inspection=== | ||
| − | Forward drum procedures are almost identical. No center seal to worry about on a | + | |
| + | Forward drum procedures are almost identical. No center seal to worry about on a TH350, it typically already has a 5 clutch pack, except light duty applications. Same 0.700" thickness piston for 5 frictions and steels. Removing the wave plate will cause harsh forward engagement. Reduce clearance of the stack to 0.040". | ||
Forward clutch pack clearances can be tighter than usual; however it must have some clearance. If too tight it can creep in neutral. | Forward clutch pack clearances can be tighter than usual; however it must have some clearance. If too tight it can creep in neutral. | ||
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===Governor adjustment=== | ===Governor adjustment=== | ||
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Shift point changes made via the governor weights and springs. Stronger springs and heavier weights will bring earlier shift points. Lighter springs and weights have the opposite affect. | Shift point changes made via the governor weights and springs. Stronger springs and heavier weights will bring earlier shift points. Lighter springs and weights have the opposite affect. | ||
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[[file:TH350HPfilter.jpg]] | [[file:TH350HPfilter.jpg]] | ||
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| + | ==Vacuum modulator== | ||
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| + | The vacuum modulator senses vacuum in the intake manifold as an indicator of engine load. As the throttle is opened, vacuum decreases. The modulator on the transmission will raise the main line pressure in the transmission | ||
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| + | [[file:T-350_modulators.jpg|frame|none|Two types of modulators shown. Low vacuum design on left, ID by the black and red strips. It is larger diameter too]] | ||
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====Oil cooler line connectors to transmission case==== | ====Oil cooler line connectors to transmission case==== | ||
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*Straight Pipe Fitting-20 ft/lb | *Straight Pipe Fitting-20 ft/lb | ||
*Tapered Pipe Fitting- 15 ft/lb | *Tapered Pipe Fitting- 15 ft/lb | ||
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====Other torque values==== | ====Other torque values==== | ||
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*Gearshift bracket to frame- 15 ft/lb | *Gearshift bracket to frame- 15 ft/lb | ||
*Gearshift Shaft to Swivel- 20 ft/lb | *Gearshift Shaft to Swivel- 20 ft/lb | ||
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==T-350 dimensions and tailshaft (extension housing) lengths== | ==T-350 dimensions and tailshaft (extension housing) lengths== | ||
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[[File:TH350 dimensions.jpg|thumb|left|400px|]]<br style="clear:both"/> | [[File:TH350 dimensions.jpg|thumb|left|400px|]]<br style="clear:both"/> | ||
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==Gear ratios== | ==Gear ratios== | ||
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Ratios of the T-350 were consistent throughout its production: | Ratios of the T-350 were consistent throughout its production: | ||
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==Aftermarket parts== | ==Aftermarket parts== | ||
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*An aftermarket low-gear planetary is available that will lower the first gear ratio to 2.75:1. | *An aftermarket low-gear planetary is available that will lower the first gear ratio to 2.75:1. | ||
==Reference material== | ==Reference material== | ||
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[[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"/> | [[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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