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. | |
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| − | + | *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 It has good pictures, a lot of good info, but has some outdated info.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. | |
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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. | |
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| − | == | + | ==Variations of the T-350 family== |
| − | There was also a T- | + | |
| + | 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. | ||
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. | 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. | ||
| − | Only the larger | + | Only the larger Transmission / Converter companies build high stall torque converters for the T-350C because of the low demand for them. |
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| + | The T-250C has a band adjuster stud and locknut on the passenger side of the case near the cooler lines. It looks much like a T350 other than the adjuster (same physical size, same pan shape). | ||
=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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===Case prep=== | ===Case prep=== | ||
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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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*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|frame|none| | + | |
| + | [[file:T-350_acumilator02.jpg|frame|none|pressure ports circled.]] | ||
=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). | ||
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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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| − | + | To prevent excessive end play, a pump thrust washer can be installed on top of the input planet, then the regular thrust washer. Then install the small outside snap ring to hold it all in place. | |
Check the output shaft for proper rotation, there will be some drag, especially in one direction. | Check the output shaft for proper rotation, there will be some drag, especially in one direction. | ||
Check for excessive output end play. If end play is excessive, it can be tightened up by dis-assembling and shimming up the output ring gear bearing from the case. | Check for excessive output end play. If end play is excessive, it can be tightened up by dis-assembling and shimming up the output ring gear bearing from the case. | ||
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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 0.835", | + | Stock measurement is 0.835", machine the piston 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, no 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. |
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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| − | + | It is recommended to always use a new intermediate roller clutch for HD builds. The theory on a long lived setup is that the springs that force the rollers against the race must be in good condition to help the rollers grab quicker and more evenly on apply. | |
The parts go on the direct drum. | The parts go on the direct drum. | ||
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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. | ||
| − | + | Internally dual feeding is preferred because it leaves out the additional gasket and eliminates that one extra possibility for a pressure loss resulting in burnt 3rd gear clutches. | |
All transbrakes will require dual feed of the direct clutch, as well as many manual valve bodies. | All transbrakes will require dual feed of the direct clutch, as well as many manual valve bodies. | ||
| − | Shown below is the passage that must be blocked. | + | Shown below is the passage that must be blocked. One method is to tap this hole with a 3/8" tap, and cut off the end of a 3/8" bolt. I then slot the head of the bolt so I can use a flat-tip screwdriver. |
| − | + | Don't thread the passage completely to bottom. It's best to have the "plug" to seat on the unthreaded portion. | |
This passage may also be plugged by using a roller from a direct drum or sprag to drive into the passage, but this will be a more or less permanent modification due to the difficulty in removing the roller. | This passage may also be plugged by using a roller from a direct drum or sprag to drive into the passage, but this will be a more or less permanent modification due to the difficulty in removing the roller. | ||
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You can omit the center seal, plug this passage, enlarge the 2nd and 3rd feed holes in the stock separator plate and you will have greatly increased the torque capacity of a stock TH350 as well as gained a firmer shift. | You can omit the center seal, plug this passage, enlarge the 2nd and 3rd feed holes in the stock separator plate and you will have greatly increased the torque capacity of a stock TH350 as well as gained a firmer shift. | ||
| − | Even firmer shifts can be accomplished with check ball removal and modifications to the accumulators. | + | Even firmer shifts can be accomplished with check ball removal and modifications to the accumulators. It is recommend to NOT modify the 1-2 accumulator. Retain the cushion spring and do not block the circuit. The 2-3 accumulator can be blocked by several methods. |
Removing the 2-3 accumulator spring and using a spacer (nut, washers, cut down section of tubing) between the piston and the E-clip is the "shade tree' method. You can also block the feed in the valve body to the 2-3 accumulator. | Removing the 2-3 accumulator spring and using a spacer (nut, washers, cut down section of tubing) between the piston and the E-clip is the "shade tree' method. You can also block the feed in the valve body to the 2-3 accumulator. | ||
| − | Installing the direct piston will require some patience, a lip seal installed or 0.010" feeler gauge, and a trick | + | Installing the direct piston will require some patience, a lip seal installed or 0.010" feeler gauge, and a trick to use is a section of plastic cut from a 3 liter soda bottle to use as an outside installer tool. Set it in the drum, and it will force the lip seal into the drum without using a tool around the entire circumference. You may however need to work the exposed part of the seal into the drum with the feeler gauge or seal tool. |
| − | Use care using the lip seal tool, | + | Use care using the lip seal tool, use a push-in technique more than a work-around-the-drum technique. If you slide around the drum, and it catches the seal it will cut it and then you must get a new lip seal and start again. Good lighting, patience, and technique are key here, and a good air check. |
| − | Once you have the piston seated in the drum you can install the return springs and retainer. You can buy or make a tool similar to the one pictured below, or use 2 or 3, 5" or larger C-clamps | + | Once you have the piston seated in the drum you can install the return springs and retainer. You can buy or make a tool similar to the one pictured below, or use 2 or 3, 5" or larger C-clamps . |
[[file:TH350directspringtool.jpg]] | [[file:TH350directspringtool.jpg]] | ||
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===Forward drum inspection=== | ===Forward drum inspection=== | ||
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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 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". | ||
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| − | This is an example of | + | This is an example of to air check the forward and direct drum. After everything is assembled, I place the drums on the pump (above a hole in the bench) with all sealing rings in place, thrust washers or bearings. |
Use a rubber tipped air nozzle to apply air to the passages around the pump circumference. As you apply air to the correct passages, you will see and hear the drums apply the clutches. Be sure there are no leaks from the lip seals. There will usually be some minor leakage at the sealing rings. Iron rings air check better than teflon on the bench. | Use a rubber tipped air nozzle to apply air to the passages around the pump circumference. As you apply air to the correct passages, you will see and hear the drums apply the clutches. Be sure there are no leaks from the lip seals. There will usually be some minor leakage at the sealing rings. Iron rings air check better than teflon on the bench. | ||
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==Shift point changes== | ==Shift point changes== | ||
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| − | + | ===Governor adjustment=== | |
| − | + | 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. | |
| − | + | The springs have a greater affect on shift points at light throttle. After about 5/8 throttle the weights have more affect on shift points. Gear ratio and tire size will also play apart of the shift points and changes made. | |
| − | + | [[File:B&M Governor recalibration kit.jpg|thumb|300px|left|B&M governor recalibration kit.]] <br style="clear:both"/> | |
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==Filter== | ==Filter== | ||
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==Fastener size and torque values== | ==Fastener size and torque values== | ||
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*Pump Cover to Pump Body- (5/16-18) 15 ft/lb | *Pump Cover to Pump Body- (5/16-18) 15 ft/lb | ||
| − | *Pump assembly to case- (5/16-18) | + | *Pump assembly to case- (5/16-18) 15 ft/lb |
| − | *Valve body and support plate- (5/16-18) | + | *Valve body and support plate- (5/16-18) 10 ft/lb |
| − | *Oil channel support plate to case- (5/16-18) | + | *Oil channel support plate to case- (5/16-18) 10 ft/lb |
| − | *Parking lock bracket- (5/16-18) | + | *Parking lock bracket- (5/16-18) 20 ft/lb |
*Oil suction screen- 40 in/lb | *Oil suction screen- 40 in/lb | ||
| − | *Oil pan to case- (5/16-18) | + | *Oil pan to case- (5/16-18) 10-12 ft/lb |
*Extension housing to case- (3/8-16) 35 ft/lb | *Extension housing to case- (3/8-16) 35 ft/lb | ||
*Modulator retainer to case- (5/16-18) 12 ft/lb | *Modulator retainer to case- (5/16-18) 12 ft/lb | ||
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====Oil cooler line connectors to transmission case==== | ====Oil cooler line connectors to transmission case==== | ||
| − | *Straight Pipe Fitting- | + | |
| + | *Straight Pipe Fitting-20 ft/lb | ||
*Tapered Pipe Fitting- 15 ft/lb | *Tapered Pipe Fitting- 15 ft/lb | ||
*Oil Cooler Pipe to Connectors- 10 ft/lb | *Oil Cooler Pipe to Connectors- 10 ft/lb | ||
====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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*Detent Cable to Transmission- 75 in/lb | *Detent Cable to Transmission- 75 in/lb | ||
*Intermediate Band Adjust Nut- 15 ft/lb | *Intermediate Band Adjust Nut- 15 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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==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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[[Category:Transmission]] | [[Category:Transmission]] | ||
[[Category:Good articles]] | [[Category:Good articles]] | ||
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