Th350 vs Thm250c, whats the difference?

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ck1984

Apprentice
Sep 19, 2021
52
24
8
I have an 84 cutlass supreme brougham. I already swapped in a 5.3L truck LS thinking i had a Th350 like typical specs showed, but i guess having a canadian sold or built model i seem to have the weaker (M31) TRANSMISSION,AUTOMATIC 3-SPEED(THM250C)
Not sure if i just got lucky but it bolted right up and has been driving flawlessly for 2 months now.
Anyways i cant really find online if theres any difference between the 3 forward gear ratios or are they exactly the same?
whats all different ? someone mentioned 1 less clutch disk and band?.....

if i blow this transmission and want overdrive is it better to go with a 4L80 even though i would have to re-add the wiring?
or will a 2004R also bolt up to a 2002 5.3 L Ls?
is the 2004R same length as th350 and save me a new driveshaft by chance?
 
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Oct 14, 2008
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Melville,Saskatchewan
The 2004R is dual pattern. It is not strong in stock form. Over 400 ft/lbs, a $400 US billet forward drum is needed. The 4L80E needs a controller of some type, wiring and the drive shaft to be cut. A good used 2wd 4L80E go for at $500 in Saskatchewan from what I have seen. They handle 600 ft/lbs with a line pressure mod.
 
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g0thiac

G-Body Guru
Sep 6, 2020
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29EA0D9F-1B9F-47FC-972D-29A84A668491.jpeg
I have an 84 cutlass supreme brougham. I already swapped in a 5.3L truck LS thinking i had a Th350 like typical specs showed, but i guess having a canadian sold or built model i seem to have the weaker (M31) TRANSMISSION,AUTOMATIC 3-SPEED(THM250C)
Not sure if i just got lucky but it bolted right up and has been driving flawlessly for 2 months now.
Anyways i cant really find online if theres any difference between the 3 forward gear ratios or are they exactly the same?
whats all different ? someone mentioned 1 less clutch disk and band?.....

if i blow this transmission and want overdrive is it better to go with a 4L80 even though i would have to re-add the wiring?
or will a 2004R also bolt up to a 2002 5.3 L Ls?
is the 2004R same length as th350 and save me a new driveshaft by chance?
I had no idea the bellhousing for the 250C could fit LS engines like that.

But the TH350 I think came in different lengths so idk.
 
Oct 14, 2008
8,806
7,746
113
Melville,Saskatchewan
I assume the sbc and LS have the same bell housing pattern? Our cars came with the short 6" extension. The major difference between a TH250 and a TH350 is the TH250 uses a band to apply 2nd gear. The TH350 uses a sprag and a clutch. It also has a band but it is for manual downshifts. I actually fried first. I didn't realize it was missing till ran the 1/8 mile. Talk about slow times but I didn't cook the second gear band, launching with slicks.
 

ck1984

Apprentice
Sep 19, 2021
52
24
8
I had no idea the bellhousing for the 250C could fit LS engines like that.

But the TH350 I think came in different lengths so idk.
HAHA, i had no idea there was such a thing as THM250c let alone fit my LS engine.
i think the LS has 5 or 6 boltholes and only 4or 5 lined up but thats supposed to be perfectly ok.
 
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ck1984

Apprentice
Sep 19, 2021
52
24
8
The 2004R is dual pattern. It is not strong in stock form. Over 400 ft/lbs, a $400 US billet forward drum is needed. The 4L80E needs a controller of some type, wiring and the drive shaft to be cut. A good used 2wd 4L80E go for at $500 in Saskatchewan from what I have seen. They handle 600 ft/lbs with a line pressure mod.
So whats the 1st to second gear spread like on a 2004R? What should a used one be worth in saskatcheewan? and a rebuilt one would be how much more?
Yes ive seen several used 4L80s under $500 in saskabush.
you still have the RIP 88 cutlass?
 
Oct 14, 2008
8,806
7,746
113
Melville,Saskatchewan
No, I let the 88 go, crushed. It was getting rough and no Classic license being a 88 and there never will be. Both cars were getting neglected, the 70 is worth more and costs me $140 a year to license. I buy a 87 442, which I almost did, it will cost the same. I will pick up a H/O or 442 eventually. The gear spread and ratios are the best of any 4 spd OD. The D9 which any non performance core seems have flash stalls around 1900 rpm, 300 more than your TH250C will. Be aware, some including the last one I bought shift 3000 rpm at full throttle. The small weight needs shaved to raise the shift points. I paid $400 for a 73 Olds 350 and a good 2004R. I see them for $150 to $200 on Kijji.
 

doood

Amateur Mechanic
Sep 24, 2020
549
753
93
I had the THM250C in my 84 v6 Monte, and I gave it away with 21000 miles on it. Tried to offload it at the transmission shop, and they said they couldn't use it. If it had been a 2004R, I'd have bolted it up to the 5.3L, but with only 3 speed and nearly certain destruction behind the V8 I didn't bother. The only thing I could have used it in would have been a cheap flip down the road.
 
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64nailhead

Goat Herder
Dec 1, 2014
5,659
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Upstate NY
250C is not worth the time to hook it up to an LS or anything else. It's not worth the the effort. They suck balls.

A 200-4R needs a couple of upgrades to be reliable, just the same as TH350. Decide if you want a 3 or 4 speed. Bulletproof is a TH400 (3 speed) or 4L80E (4 speed).

I understand budgets and being cheap, but a 250C is not worth the time to bolt it back in.
 
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Ribbedroof

Comic Book Super Hero
Supporting Member
Jan 4, 2009
4,861
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Wellston, OK
Despite the heavy performance bias on this board, i have found the TH250C to be a capable trans behind a stock 305 as a daily driver-type trans.

Would I use one in any kind of performance application? Nope, but for that person that just needs a working trans, they're "OK". Still better than the TH200/C
 
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