TH 250 C trans

Roy Ale

Member
Oct 20, 2020
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Victoria BC
My 82 Delta 88 has a 307 engine with a TH 250C trans with Lock up , the 250 also has the adjustable band screw on the outside of trans . No issues so far with the 250 , but from what i read on line if someday have issues do not put any more money into it . The TH250C could be replaced with a TH350 with no lock up . I am not sure the 250 would do another long steep hill climb road trip , so thinking about changing it out . What do i need to know for a swap ?
 

Olds 307 and 403

Well-known member
Oct 4, 2018
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Melville, Saskatchewan
Just the matching converter if it is a non lock up trans, they won't swap between lock up and non lock up. Just remove power to the lock up circuit, otherwise a direct swap. Honestly, I got 450,000 km out of one behind an Olds 307. First gear didn't last the first day behind a 403.
 

Roy Ale

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Thread starter
Oct 20, 2020
62
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Victoria BC
So you got 450 , 000 km out of the TH250C trans behind a 307 . Where i live in all directions there is a steep hill climb. And a long steep hill climb over the Coquihalla Highway 5 , Hope to Kamloops. I am told this route is faster but an automatic transmission killer . Not sure if a 250 is up for that ? Or maybe all the 250 needs to make that climb is a separate trans cooler. The lines now go into the rad .

So if i do make a change the 350 is a direct swap , bolt pattern lines up to a 307 , no issues . But will need a none lock up converter . I see there is a trans tail shaft length option . What 350 trans tail piece will i need ? Drive shaft, use the same drive shaft ? What about kick down cable ? use the same cable ?
 
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Olds 307 and 403

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Oct 4, 2018
990
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Melville, Saskatchewan
Sorry you need a BOP case with the short tail shaft. The Chevy case has a peak in the top of the bell housing, the BOP a valley. If there is an electrical connector on the drivers side, it is a lock up. The lock up lowers highway rpm by 200 to 300 rpm. I would start with a trans cooler.
 

Roy Ale

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Thread starter
Oct 20, 2020
62
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Victoria BC
OK thanks , i looked up BOP Buick Olds Pontiac . Also says bolt pattern is different than Chev . Do all BOP TH 350 s have the lock up ?
 

Olds 307 and 403

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Oct 4, 2018
990
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Melville, Saskatchewan
No lock up before 1981 on all TH250/350.
 

Olds 307 and 403

Well-known member
Oct 4, 2018
990
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Melville, Saskatchewan
Yes, done it with a 4L60E on an Olds 350. There are plenty of BOP 350 trans available buy outright or get rebuilt.
 

Roy Ale

Member
Thread starter
Oct 20, 2020
62
13
8
Victoria BC
This is a picture of the top of the 250 trans . Can see the dip / valley on the top . I had the distributor out when this picture was taken .
 

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Olds 307 and 403

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Oct 4, 2018
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Melville, Saskatchewan
Yes, valley BOP, peak chebby.
 

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