TH350 rebuild tech
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The ideal situation is a shift that gets progressively harder with greater throttle openings. I recommend drilling the 2nd feed to 0.125" and the 3rd feed from 0.125"-0.140" | The ideal situation is a shift that gets progressively harder with greater throttle openings. I recommend drilling the 2nd feed to 0.125" and the 3rd feed from 0.125"-0.140" | ||
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Also note the 2-3 accumulator hole marked in the upper portion. This hole can be blocked but it is easier to block the passage in the VB or the 2-3 accumulator piston as previously mentioned. | Also note the 2-3 accumulator hole marked in the upper portion. This hole can be blocked but it is easier to block the passage in the VB or the 2-3 accumulator piston as previously mentioned. | ||
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=Valve body= | =Valve body= | ||
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[[file:TH350reverseVB.jpg]] | [[file:TH350reverseVB.jpg]] | ||
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| + | ==Valve body modifications== | ||
| + | Removing check balls and opening up orifices in the separator plate is a common modification to firm up shifts. Just remember the one check ball that needs to stay is the one just below the modulator. | ||
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| + | ===Shift kits=== | ||
| + | Often shift improver kits are installed at the time of the tranny rebuild. Various manufacturers make shift improver kits, Trans Go has a good reputation. | ||
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| + | ==Governor== | ||
| + | Image below of an OEM T-350 governor and cover. | ||
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| + | [[file:T-350_governor.jpg|thumb|left|300px|Note the direction of the plastic drive gear teeth. If the plastic gear breaks or wears out, there will be no upshifts since the governor is not rotating.]] | ||
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| + | [[File:B&M Governor recalibration kit.jpg|thumb|300px|left|B&M Governor recalibration kit.]] <br style="clear:both"/> | ||
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| + | ==Shift point changes== | ||
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| + | ===Modulator adjustment=== | ||
| + | The following is from Dean Mason of TransLab Engineering: | ||
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| + | <Blockquote> Modulator adjustment is not about setting the shift timing where you want it, especially at max throttle. Modulator is for LINE PRESSURE BOOST, and here's how it works:</Blockquote> | ||
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| + | <Blockquote> The modulator is a spring loaded vacuum canister. At high vacuum, the force of vacuum opposes/cancels out the spring force. As vacuum drops, the spring exerts an increasingly greater force against the modulator valve, until at near zero vacuum maximum line pressure boost is achieved.</Blockquote> | ||
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| + | <Blockquote> Now, line pressure boost is needed when torque is increased, so that clutches and bands won't slip. But we don't need boost sitting in park or neutral idling in the parking lot. This just causes premature pump gear and sealing ring wear. Therefore, line pressure should not be boosted at idle. If you use your car as a daily driver, the best setting is that which provides maximum boost during acceleration without unnecessarily high line pressure when it is not needed. That is, NO BOOST AT IDLE, BUT AS SOON AS YOU BEGIN TO ACCELERATE (that is, you drop 1" of vacuum off idle) you want RAPID/RESPONSIVE BOOST.</Blockquote> | ||
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| + | <Blockquote> Here's what you need to know: | ||
| + | WHAT IS THE VACUUM READING AT IDLE IN DRIVE? | ||
| + | The following work is most easily done on a lift with all 4 wheels off the ground and the emergency brake firmly locked!</Blockquote> | ||
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| + | <Blockquote> We want the engine fully warmed up for this test, and take the reading at the ''tranny'' end of the vacuum line. Unplug the modulator hose from the vacuum modulator assembly. Attach a vacuum gauge to the hose. Start the engine, turn on the air conditioner, put the shifter in DRIVE, and write down the vacuum reading on the gauge.</Blockquote> | ||
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| + | <Blockquote> Next, get yourself a pocket screwdriver and a new modulator "elbow" (keep the elbow in your pocket). INSTALL PRESSURE GAUGE ON MAIN LINE PORT. Plug the engine side of the vacuum line (so you won't have a vacuum leak). Get a hand operated vacuum pump and attach it to the modulator. Get your little screwdriver and punch it thru the rubber hose (yes that's right!) about 1/2" behind the modulator stem. This way you can adjust your modulator inside the hose with it attached and the engine running!</Blockquote> | ||
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| + | <Blockquote> Now, what was the vacuum reading you wrote down? Let’s say your engine pulls 16 in/Hg in D, HOT, with AC on. We want to drop ONE in/Hg of vacuum, then start to increase line pressure. So, start the engine (neutral is OK for this part), raise idle to 800-1000 rpm, and pump up 15" on your vacuum pump (you may need someone to help maintain a steady 15" on the pump with the screwdriver punched thru the hose due to very minor leakage). </Blockquote> | ||
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| + | <Blockquote> Typically a SBC 350 will run about 60-65 psi at idle, but there are variations in PR springs. If it is much higher, back the modulator adjustment out until there is no more "drop" on the gauge. Now, start to screw IN on the modulator adjuster until you see the pressure gauge start to lift and STOP right there. To check this, pump up 20", watch gauge and start to bleed vacuum off very slowly and the gauge should start to increase exactly at 15".</Blockquote> | ||
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| + | <Blockquote> If you took your initial readings correctly, you now have a perfectly adjusted modulator. For a slightly steeper boost rate with higher max line pressure, use a 2" modulator instead of the 1 9/16" can size and adjust it exactly as described here. Once you have set it this way you are finished with the adjustment procedure.</Blockquote> | ||
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| + | ===Detent cable adjustment=== | ||
| + | <Blockquote> Unclip the cable locking mechanism and then press the accelerator pedal to the floor. Be sure there's nothing under the pedal and the linkage is allowing full throttle at the carb. Floorboard the gas pedal and the detent cable should just pull tight as the throttle reaches wide open. THAT'S IT! If it doesn't pull tight, readjust, bend bracket, or whatever is necessary to achieve this. If it doesn't pull tight you will not have full detent at wide open throttle. If it pulls tight BEFORE full throttle, you'll break the cable end.</Blockquote> | ||
| + | {| | ||
| + | |[[File:Kickdown1.jpg|thumb|180px|center|Unlock detent clip by prying up on it.]] | ||
| + | |[[File:Kickdown2.jpg|thumb|180px|center|Clip in unlocked position.]] | ||
| + | |[[File:Kickdown3.jpg|thumb|180px|center|Open throttle (should be done from inside the car to assure proper travel).]] | ||
| + | |[[File:Kickdown4.jpg|thumb|180px|center|Push clip down to lock.]] | ||
| + | |} | ||
| + | <Blockquote> Now that the detent and modulator are set correctly, we are ready to think about shift scheduling. Road test the car. You will need to know minimum and maximum throttle shift speeds for the 1-2 and 2-3 shifts, the RPM for the max throttle shifts, and the highest speed you can get a 3-1 and a 3-2 kick down. Also, what is the [http://www.crankshaftcoalition.com/wiki/Gear_ratio_check axle ratio].</Blockquote> | ||
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| + | <Blockquote> From this point we work with governor weights, springs, and shift valve springs.</Blockquote> | ||
==Fastener size and torque values== | ==Fastener size and torque values== | ||
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| − | + | ==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"/> | ||
| − | + | '''NOTE:''' The Sessions and ATSG manuals are the preferred texts. | |
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==Resources== | ==Resources== | ||
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