Which is better? TH400 or a C6

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Re: Which is better? TH400 or a C6

Post by nickpohlaandp » Sun Sep 24, 2017 1:04 pm

Coloradoracer wrote:TH400 all the way. Here's why: A basically stock 400, properly assembled, will easily hold that amount of hp and will do it for a very long time. TH400's are very stout transmissions and require few mods until the hp gets over about 1000. They are also readily available, have a wealth of parts availability, and can be found pretty much anywhere. They are also very easy to work on, even for someone with little experience. For the cost of a decent rebuild kit, some attention to detail, and a couple of easily done and pretty much free mods, you'll have a trans that will last a long time....
That's good to know. I was curious about what the stock internals would handle. I know they're a stout trans, but just how stout, I don't know.

So are you saying with a good rebuild kit, clutches, etc, I could throw on a manual valve body and let it ride and not have to worry about breaking input/output shafts, drum, etc?
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Re: Which is better? TH400 or a C6

Post by Coloradoracer » Sun Sep 24, 2017 1:11 pm

Add in the dual feed mod to the direct clutch and restrict the pump feed. Keep line pressure about 200-225 psi and make sure clearances are correct. It will live a long time.
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Re: Which is better? TH400 or a C6

Post by nickpohlaandp » Sun Sep 24, 2017 2:09 pm

Coloradoracer wrote:Add in the dual feed mod to the direct clutch and restrict the pump feed. Keep line pressure about 200-225 psi and make sure clearances are correct. It will live a long time.
Guess I'm gonna need to get a book on the TH400 to better familiarize myself.
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Re: Which is better? TH400 or a C6

Post by Coloradoracer » Sun Sep 24, 2017 4:02 pm

That's a good investment
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Re: Which is better? TH400 or a C6

Post by kirkwoodken » Mon Nov 06, 2017 5:43 pm

I can't recall the exact number, but the TH400 was factory rated at over 700 Ft. Lbs. torque in stock condition. (740, I think.) Also, a steel girdle used to be made for the C6! Never saw one of those for a TH400. TBOMK, the modified C4 is superior to the C6. The TH400 is a stout piece, but it needs the clutch drums replaced if you make a lot of power. My 400 TB has all stock insides and so far has held up fine behind my SBC 406 and Turbo Action trans brake. The 406 makes no where near 700 Ft Lbs.

DON'T get a Chevy case from 1969 TH400. They switched case alloy that year to something weaker, so I've read. The TH350 is a more efficient design but will have to be built up to equal the strength of the stock 400.
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Re: Which is better? TH400 or a C6

Post by nickpohlaandp » Mon Nov 06, 2017 6:01 pm

kirkwoodken wrote:
Mon Nov 06, 2017 5:43 pm
I can't recall the exact number, but the TH400 was factory rated at over 700 Ft. Lbs. torque in stock condition. (740, I think.) Also, a steel girdle used to be made for the C6! Never saw one of those for a TH400. TBOMK, the modified C4 is superior to the C6. The TH400 is a stout piece, but it needs the clutch drums replaced if you make a lot of power. My 400 TB has all stock insides and so far has held up fine behind my SBC 406 and Turbo Action trans brake. The 406 makes no where near 700 Ft Lbs.

DON'T get a Chevy case from 1969 TH400. They switched case alloy that year to something weaker, so I've read. The TH350 is a more efficient design but will have to be built up to equal the strength of the stock 400.
All good info, thank you! I’ve got my TH400, it’s from a GTO, and not a ‘69, so that’s good. A friend of mine has a Chevy TH400 freshly rebuilt that he’d like to trade for my Pontiac TH400. I don’t care either way because I’m cutting the bellhousing off to install my JW bellhousing.

Two questions. Was the weaker alloy in 69 ONLY for 1969? Second, and I know I could probably google and find out but I’m here so I’ll ask, is there an easy way to determine the year of the case casting?

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Re: Which is better? TH400 or a C6

Post by kirkwoodken » Mon Nov 06, 2017 10:41 pm

Yes, just 1 year for weak housings. If you are cutting the front off, can't you use a BOP? Don't they just bolt to the pump bolts? I've never used one, but you can find BOP's for scrap prices,where as Chevy housings are higher dollar. If you don't have a TH400 yoke, look for one still sticking out of a transmission in a junk yard. Otherwise you may have sticker shock.

Just reread your post. DON'T cut the front off a Chevy TH400. Sell the Chevy and cut the front off a BOP. Just makes better sense to me. If you know someone with a large lathe, you can mount the case between centers or hold the front by the pump extension; cut the big front bell off with a band saw or saber saw, and use the lathe to turn the case even to the front pump surface. Just give it some thought. It will work. DON"T run it without a blanket!!! If the transmission blows and a piece comes through the floor, you can get an unexpected hot oil treatment. Not good.

Dating stuff:
http://chevellestuff.net/qd/th400.htm
Last edited by kirkwoodken on Mon Nov 06, 2017 11:07 pm, edited 1 time in total.
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Re: Which is better? TH400 or a C6

Post by nickpohlaandp » Mon Nov 06, 2017 11:02 pm

kirkwoodken wrote:
Mon Nov 06, 2017 10:41 pm
Yes, just 1 year for weak housings. If you are cutting the front off, can't you use a BOP? Don't they just bolt to the pump bolts? I've never used one, but you can find BOP's for scrap prices,where as Chevy housings are higher dollar. If you don't have a TH400 yoke, look for one still sticking out of a transmission in a junk yard. Otherwise you may have sticker shock.

Just reread your post. DON'T cut the front off a Chevy TH400. Sell the Chevy and cut the front off a BOP. Just makes better sense to me. If you know someone with a large lathe, you can mount the case between centers or hold the front by the pump extension; cut the big front bell off with a band saw or saber saw, and use the lathe to turn the case even to the front pump surface. Just give it some thought. It will work. DON"T run it without a blanket!!! If the transmission blows and a piece comes through the floor, you can get an unexpected hot oil treatment. Not good.
BOP?
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Re: Which is better? TH400 or a C6

Post by kirkwoodken » Mon Nov 06, 2017 11:09 pm

Buick, Olds, Pontiac = BOP bell housing style.

Dating= http://chevellestuff.net/qd/th400.htm
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Re: Which is better? TH400 or a C6

Post by nickpohlaandp » Tue Nov 07, 2017 8:50 am

kirkwoodken wrote:
Mon Nov 06, 2017 10:41 pm
DON'T cut the front off a Chevy TH400. Sell the Chevy and cut the front off a BOP.
Why would you say to NOT cut the bell housing off a Chevy TH400? Seems to me there's probably more of them... maybe I'm wrong.

The one I have is a Pontiac TH400, and my buddy has a Chevy TH400 freshly rebuilt. He needs a Pontiac trans though to go behind a Pontiac 400 cid he has. He wanted to trade and I was fine with that because as far as I'm concerned I don't care about he factory bell housing. I've got a JW bell housing adapter.
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Re: Which is better? TH400 or a C6

Post by kirkwoodken » Tue Nov 07, 2017 1:01 pm

My point is: A Chevy core has value. Last time I bought BOP cores (Complete Transmissions) for parts they cost $18.00, which was scrap price. Chevy empty cases at that time were going for $100.00-$175.00 in my area, if you could find one. Repeat: That Chevy bell housing has value.
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Re: Which is better? TH400 or a C6

Post by nickpohlaandp » Tue Nov 07, 2017 1:23 pm

kirkwoodken wrote:
Tue Nov 07, 2017 1:01 pm
My point is: A Chevy core has value. Last time I bought BOP cores (Complete Transmissions) for parts they cost $18.00, which was scrap price. Chevy empty cases at that time were going for $100.00-$175.00 in my area, if you could find one. Repeat: That Chevy bell housing has value.
I see your point as far as value. I think in this particular case though it probably doesn't matter. His TH400 is from a 1971 Corvette (I went over and looked at the data tag during my lunch break) and the bellhousing has been cracked and welded. I would imagine that it would have to be a non-damaged/repaired bellhousing in order for the case to be worth anything, correct me if I'm wrong.

Edit: The data tag looks like this:

.......................442
71-CK................6067

From what I could gather this means the trans was built on March 19, 1971, serial number 6067, and it was for a Corvette (CK)
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Re: Which is better? TH400 or a C6

Post by SupStk » Wed Nov 29, 2017 4:58 pm

Clear back in the 60s Ford used C-6s in the first flipup bodied funny cars. The engines of the time were 1500-1800 hp. Supposedly the C-6s were production pieces. Anyway I wouldn't consider 'em weak sisters.
Working in tranny shops earlier in my career seen my share of burned up C-6s. Most could be contributed to Fords mickey mouse valve body. They used an aluminum valve body, a screen and about 30 valves to do what GM did with 8. If building a C-6 for racing the VB will be replaced so a moot point.
The neat thing about a 400 is there is a constant flow of power as units are added during the upshifts. None of the band releasing, clutch applying monkey motion many other trannys incorporate. The cost of that for racing is the use of high element sprags instead of roller clutches. GM makes the pieces needed but the good stuff is in like TH475 motorhome transmissions. Of coarse you could always buy everything needed aftermarket.
Just one point on the JW bell. I dont like the idea of 6) 5/16 bolts keeping the pieces together and handling all the torque.
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Re: Which is better? TH400 or a C6

Post by Coloradoracer » Wed Nov 29, 2017 5:29 pm

Pump bolts handle the load just fine with the Ultra bell...never seen one fail regardless of hp input...

One thing to mention on the Chevy vs. BOP case issue. What some don't know is that there is a difference in the two cases besides the bell housing. There are fewer pump bolts in the BOP cases than the Chevy cases. The bolt bosses are there, just not used. I think they dropped two of the bolts if memory serves me correctly. It's not a big issue, as you can use an old pump for a guide and drill them to tap, just something to be aware of. As to the th475, believe it or not, the gear sets in those are typically weaker than the passenger car/pickup versions. On the strength of the drum issue, the direct drum is the problem. It has to go from reverse to stopped on the 1-2 shift, then accelerate instantly to driveshaft rpm on the 2-3 shift. This is what eats all the hp. If the rpm are low and gradual increase, the hp loss is not much. If it's very sudden and high rpm such as in a racing application, it eats a ton. Best mod here is an aluminum direct drum with steel inserts. This keeps the drum from wearing out prematurely but still offers the safety and benefit of the lighter part. Less mass to accelerate.

One last thing, NEVER NEUTRAL A TH400 OR KILL YOUR ENGINE AFTER THE STRIPE! Keep it in gear until you pull to a stop. If you have a clean neutral valve body, you can shift to the neutral position after high gear, but MUST keep the engine running. The problem is that if you shut off the engine or neutral the trans, the direct drum will INSTANTLY go from drive shaft rpm to 2 1/2 times driveshaft rpm IN REVERSE! This will cause the drum to explode, and even a good shield will likely not contain it....
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Re: Which is better? TH400 or a C6

Post by pdq67 » Thu Nov 30, 2017 4:54 am

I read somewhere years ago that the TH400 was good for like 800T(?) and 500,000(?) miles, but after GM's, "Bean-Counters", got done with it, it dropped some T and was good for like 200,000(?) miles!

I think it was after they started using plastic parts in it, but don't know for sure?? I bet an older tranny rebuilder guy could tell you for sure about this....

And I will say that MOPAR's 727 auto trans is a good one! Sucker shift's like, "the kick of a shotgun"!

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