TH350 rebuild tech

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(Add torque values, images, ID info.)
(Format, add images; add text, spelling; small clean up.)
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*This is not a step-by step pictorial, don't assume it is shown where every part goes, there will be some thrust washers not illustrated that were installed and not taken an individual picture to show it because of bandwidth considerations.
 
*This is not a step-by step pictorial, don't assume it is shown where every part goes, there will be some thrust washers not illustrated that were installed and not taken an individual picture to show it because of bandwidth considerations.
  
That said the following should help some to better understand the T-350 and possibly help when a question arises.
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That said, the following should help give a better understanding of the T-350 and possibly help when a question arises.
  
 
==Transmission ID==
 
==Transmission ID==
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|[[File:TH350 ID governor cover.jpg|frame|left|ID stamped into governor cover.]]
 
|[[File:TH350 ID governor cover.jpg|frame|left|ID stamped into governor cover.]]
 
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There was also a TH350'''C''' version that has a lockup torque converter (TCC). 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. Not to be confused with an electrical connector on the passenger side.
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There was also a TH350'''C''' version that has a lockup torque converter (TCC). 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. Not to be confused 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. There have been reports of some TH350 trannys having a temp sender in this area as well.
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There aren't a lot of places making high stall torque converters for the TH350C. Torque converter makers for the “C”: Pats, TCI, and Keisler are three.
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The TH250 has a band adjuster stud and locknut on the passenger side of the case near the cooler lines.
  
 
==Bushings==
 
==Bushings==
A T-350 is known to be rough on bushings.
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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.
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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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.
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{|
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|[[File:TCI pn 313700 TH350 bushing kit.jpg|thumb|300px|left|TCI p/n 313700 TH350 bushings.]]
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|[[File:TCI pn 313600 thrust washers.jpg|thumb|300px|left|TCI p/n 313600 thrust washer kit.]]
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|}
  
Once the case has been cleaned, all threads checked and/or repaired, and the rear case bushing installed you can start assembly.
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==Rebuild kits==
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[[File:Hughes Performance transmission rebuild kit pn HP3288.jpg|thumb|300px|left|Hughes Performance transmission rebuild kit p/n HP3288.]] <br style="clear:both"/>
  
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==Fluid level==
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If the dipstick is missing or not correct, the fluid level should be from even with the pan to ¼” above the pan when the fluid is hot.
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==Tailshaft (extension housing) lengths==
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You will find the TH350 with 6-, 9- and 12-in. tail housings. Overall lengths are 27-11/16”,  30-11/16”,  and 33-27/32”, respectively.
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==Gear ratios==
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Ratios on the TH350 are consistent throughout its production:
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First gear, 2.52:1; second gear, 1.52:1; third gear, 1.00:1; reverse, 1.93:1.
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An aftermarket low-gear planetary can be purchased that will bump first gear up to an optional 2.75:1, if a taller first gear is desired.
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==What vehicles came with the TH350?==
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TH350 was used in some Y- and F-body cars in 1968, then across the board in 1969 to 1980. Then from 1981-’86 the TH350C was used
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*1969-'84 Buick, Chevrolet, Olds and Pontiac full-size cars
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*1969-'81 Buick, Chevrolet, Olds and Pontiac A-body, G-body and F-body cars
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*1973-'79 Buick, Chevrolet Olds and Pontiac X-body cars
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*1969-'78 Riviera
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*1975-'82 Corvette
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*1975-'80 Buick, Chevrolet, Olds and Pontiac H-body cars (Vega, Monza, Skyhawk, etc.)
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*1981-'82 Cadillac Fleetwood and Deville (uni-bell and TH350C versions)
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*1973-'85 Chevy and GMC 2- and 4WD pickups, Blazers, G-10, G-20 Vans and Suburbans
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===Valve body modifications===
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====Shift kits====
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==Shift point changes==
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===Modulator adjustment===
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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:
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WHAT IS THE VACUUM READING AT IDLE IN DRIVE?
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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===
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<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>
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<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>
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==Governor modifications==
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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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=Transmission reassembly=
 
==Case prep==
 
==Case prep==
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Once the case has been cleaned, all threads checked and/or repaired, and the rear case bushing installed you can start assembly.
  
 
===1-2 accumulator===
 
===1-2 accumulator===
 
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|Accumulator cover, spring and piston with sealing rings]]
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[[file:T-350_acumilator01.jpg|frame|none|Accumulator cover, spring and piston with sealing rings.]]
  
  
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I also like to always use a NEW intermediate roller clutch for HD builds. My theory on a long lived setup is that the springs that force the rollers against the race must be in good condition to helps the rollers grab quicker and more evenly on apply.
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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.
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[[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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I also like to always use a NEW intermediate roller clutch for HD builds. My 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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Also of note, if you are using almost any aftermarket kit, these kits use a feed plate between the support plate in front of the valve body and the separator plate. This feed plate dual feeds the directs and plugging this hole is unnecessary. Also most manual valve bodies, trans-brakes, etc will have you omit the direct drum center seal and the sealing ring on the stator but plugging of this hole is also unnecessary due to the design of the separator plate.
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Also of note, if you are using almost any aftermarket kit, these kits use a feed plate between the support plate in front of the valve body and the separator plate. This feed plate dual feeds the directs and plugging this hole is unnecessary. Also most manual valve bodies, trans-brakes, etc. will have you omit the direct drum center seal and the sealing ring on the stator but plugging of this hole is also unnecessary due to the design of the separator plate.
  
 
Don't assume you need to plug this hole. Only plug this hole if you plan on building a unit yourself.
 
Don't assume you need to plug this hole. Only plug this hole if you plan on building a unit yourself.
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===Forward drum inspection===
 
===Forward drum inspection===
Pay attention to this polished stub of the input shaft, it goes into the bushing that is in the end of the out put 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.
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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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Here's a pic 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.
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Here's a pic 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:TH350feedholes.jpg]]
 
[[file:TH350feedholes.jpg]]
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*Extension housing to case- (3/8-16) 35 ft/lbs
 
*Extension housing to case- (3/8-16) 35 ft/lbs
 
*Modulator retainer to case- (5/16-18) 12 ft/lbs
 
*Modulator retainer to case- (5/16-18) 12 ft/lbs
*Inner Selector Lever to Shaft- (M10-1.5) 27 N.M. (20 ft/lbs)
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*Inner Selector Lever to Shaft- (M10-1.5) 27 Nm (20 ft/lbs)
 
*External test plugs to case- (1/8-27) 8 ft/lb
 
*External test plugs to case- (1/8-27) 8 ft/lb
*Transmission mount to transmission (M10-1.5) 48 N.M (35 ft/lb)
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*Transmission mount to transmission (M10-1.5) 48 Nm (35 ft/lb)
*Speedo sleeve retainer on extension housing- (M6.3-1.0) 17 N.M (150 in/lb)  
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*Speedo sleeve retainer on extension housing- (M6.3-1.0) 17 Nm (150 in/lb)  
*Detent cable to case- (M6.3-1.0) 8.5 N.M. (75 in/lb)
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*Detent cable to case- (M6.3-1.0) 8.5 Nm (75 in/lb)
*Nut on outer end of shift selector shaft- (M10-1.5) 27 N.M (20 ft/lb)
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*Nut on outer end of shift selector shaft- (M10-1.5) 27 Nm (20 ft/lb)
 
*Converter to Flexplate Bolts- 35 ft/lbs
 
*Converter to Flexplate Bolts- 35 ft/lbs
 
*Torque converter dust cover pan to transmission case- 110 in/lbs
 
*Torque converter dust cover pan to transmission case- 110 in/lbs

Revision as of 23:44, 19 March 2012

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