TH350 rebuild tech
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==Variations of the T-350 family== | ==Variations of the T-350 family== | ||
| − | There was also a T-350C | + | 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. |
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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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=Rebuilding the T-350= | =Rebuilding the T-350= | ||
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Be prepared to replace almost ALL the bushings in a T-350. Might as well order a bushing kit, as well as a thrust washer kit. I would recommend you get at least 2 additional sun gear bushings individually also. | Be prepared to replace almost ALL the bushings in a T-350. Might as well order a bushing kit, as well as a thrust washer kit. I would recommend you get at least 2 additional sun gear bushings individually also. | ||
| − | In the photo is shown the 2 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. | + | In the photo is shown the 2 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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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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*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= | ||
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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. | ||
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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 install the return spring and retainer using the tool pictured. | Then install the return spring and retainer using the tool pictured. | ||
| − | [[file:TH350lowspringtool.jpg|frame|none|Tool used to compress the springs | + | [[file:TH350lowspringtool.jpg|frame|none| Tool used to compress the springs & retainer to install the retaining snap ring.]] |
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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. | 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 | + | 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. |
Now you drop the input ring gear on, spinning into place. | Now you drop the input ring gear on, spinning into place. | ||
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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", machine the piston to 0.700". Ideally you would | + | 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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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. | 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. | ||
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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. | ||
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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. | 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 | + | 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 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. | 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. | ||
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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. | ||
| − | Pay attention to this polished stub of the input shaft, it goes into the bushing that is in the end of the output shaft. It is a high wear area. Be sure it is smooth. Minor scoring can be smoothed down. May consider use of teflon bushing, only a lubrication passage, no pressure, no lateral loading. | + | Pay attention to this polished stub of the input shaft, it goes into the bushing that is in the end of the output shaft. It is a high wear area. Be sure it is smooth. Minor scoring can be smoothed down. May consider use of teflon bushing, only a lubrication passage, no pressure, no lateral loading. |
[[file:TH350forwardwear.jpg]] | [[file:TH350forwardwear.jpg]] | ||
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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]] | ||
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