TH350 rebuild tech
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| − | That said I hope this helps some understand the | + | That said I hope this helps some understand the T-350 or maybe it'll help when you're elbow deep and have a question. |
| − | + | A T-350 is known to be rough on bushings. | |
| − | A | + | |
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. | ||
| − | Be prepared to replace almost ALL the bushings in a | + | 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. |
Once the case has been cleaned, all threads checked and or repaired, and the rear case bushing installed you can start assembly. | 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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For racing and heavy towing use, you will want to machine the direct clutch piston down approximately .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. I try to keep a few machined on hand, and machine several at a time when I do so. If you need one email me and if you can supply a core, I MAY be able to sell you a piston. | For racing and heavy towing use, you will want to machine the direct clutch piston down approximately .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. I try to keep a few machined on hand, and machine several at a time when I do so. If you need one email me and if you can supply a core, I MAY be able to sell you a piston. | ||
| − | Stock measurement is | + | |
| + | Stock measurement is .835, I cut them to .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 ~.010" clearance per friction. So a 5 friction direct setup would work great with .050" clearance. It will work with less, I wouldn't go less than .040", and will work with quite a bit more, but excessive clearance can result in delayed engagement, busted lip seals, and unsatisfactory shift quality. | ||
Stock 4 piston direct piston vs. machined for 5. Check the thickness of the piston, it should be NO less than .700 thick at the widest point. If the piston is too low, the bottom flat steel plate can drop below the grooves in the drum and bind up the piston. May leave out center cushion seal if dual feed is used. Set maximum clearance at 0.050. | Stock 4 piston direct piston vs. machined for 5. Check the thickness of the piston, it should be NO less than .700 thick at the widest point. If the piston is too low, the bottom flat steel plate can drop below the grooves in the drum and bind up the piston. May leave out center cushion seal if dual feed is used. Set maximum clearance at 0.050. | ||
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| − | The HD applications should also get a | + | 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 weakest single part of a | + | 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 weakest single part of a T-350. |
| − | This is not to say a | + | This is not to say a T-350 is not tough, they are under-rated and can reliably handle in the 600HP or lb/ft range based on my experience. |
[[file:TH350intspragraces.jpg]] | [[file:TH350intspragraces.jpg]] | ||
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| − | The direct drum should use a wider bushing even on stock rebuilds. Stock is | + | The direct drum should use a wider bushing even on stock rebuilds. Stock is .500 a wider .750 is available in some bushing kits. Most bushing kits include the wide one. |
There is a lot of load on this bushing, and it should ALWAYS be replaced on overhaul. | There is a lot of load on this bushing, and it should ALWAYS be replaced on overhaul. | ||
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Take note of the orientation of the seals, the lip will face towards the "oil" side of the piston, not the clutch side. | Take note of the orientation of the seals, the lip will face towards the "oil" side of the piston, not the clutch side. | ||
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| − | + | This is a hi-performance T-350 and I did NOT install a lip seal in the drum that would separate the two halves of the direct piston. | |
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. | ||
You can do this on any rebuild but you must also block a passage in the case near the pump to prevent loss of pressure to the reverse circuit. | You can do this on any rebuild but you must also block a passage in the case near the pump to prevent loss of pressure to the reverse circuit. | ||
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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 | + | Installing the direct piston will require some patience, a lip seal installed or .010" feeler gauge, and a trick I 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, I 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, oh, and a good air check | Use care using the lip seal tool, I 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, oh, and a good air check | ||
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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 | + | 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 .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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