TH400 3 Spd Auto - She is dead - Pontiac GTO Forum
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post #1 of 12 (permalink) Old 08-05-2016, 07:50 PM Thread Starter
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TH400 3 Spd Auto - She is dead

Hey everyone,

So, just two days ago my 69 GTO was running great. Parked it to run inside to pick up my daughter from daycare, came out and gave her hell and the engine revved but no power to the wheels. Ugh oh! Yeah, took it in today and the transmission is completely shot. They don't even recommend rebuilding it, they're recommending remilling it. This will end up costing me about $2800 for everything out the door.

I don't need to stick to stock! I don't care if I keep this original transmission since the engine isn't stock nor paint color. The one I have is only a 3 speed and honestly, I'd love a 4th gear for highway driving. Do you guys have any recommendations? Should I stick with my 3 spd or buy brand new/rebuilt? I really wish I could do a manual but I know there is alot of work there and it would basically double my cost, which I don't want to do so I think I am going to stick with an auto. Any help would be appreciated!
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post #2 of 12 (permalink) Old 08-05-2016, 09:06 PM
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Took it in where?
If this is AAMCO telling you this go somewhere else.
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post #3 of 12 (permalink) Old 08-05-2016, 09:57 PM Thread Starter
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It wasn't. It is a local, reputable shop.

J&M Transmission in Sioux Falls, SD
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post #4 of 12 (permalink) Old 08-06-2016, 08:13 AM
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$2800 is very STEEP price for rebuilding a T400 with quality parts and R & R. Have had at least a dozen T400's bench built from $200-850. Higher priced ones included more hard parts than a quality stock rebuild. I'd never give up an early T400, ESP one original to a '67-71 GTO. original cores out HO or RamAir cars are very desirable. the standard performance BOPC '72-79 T400's need upgrades.

Wanting to go overdrive, a well built 200R4, converter can be done for 2K. Proper TV cable adjustment at the carburetor is critical. a performance built 200R4 is a better fit for the torque band of Pontiac V8 over a 700R4.

Last edited by Pinion head; 08-06-2016 at 08:27 AM.
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post #5 of 12 (permalink) Old 08-06-2016, 08:47 AM
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Jegs sells a ready-to-go TH400 for $900. JEGS Performance Products 60315 | Buy JEGS Performance Transmissions at JEGS A basic rebuild kit goes for about $70 and a good Hi-Perf rebuild kit is around $230. TH400 Alto Red Eagle Deluxe Chevy Performance Transmission Rebuild Kit Level 2 | eBay

For a rebuilt/remanufactured upgrade/conversion to a 4-speed automatic with OD, torque converter, and all the required modifications to make it work, ie a complete turn key out-the-door package without any other BS excuses or add-ons, then $2800 sounds reasonable. You will have better gear ratios in the trans (better performance) and the OD for cruising.

BUT, if you wanted to do a manual (rebuilt Muncie 4-speed) conversion, it would seem the consensus on the forums is about $3000 and that will probably go up. The 5-speed goes much more and you have to modify/cut your trans tunnel UNLESS you go with the new Richmond 5-speed which I recall will fit without tunnel mods. However, expensive Richmond Gear 7020526B | Buy Richmond Super Street 5-Speed Transmissions with Overdrive at JEGS So this gives you a comparative cost.

So, MY OPINION. If you have the funds and there is no rush to get it done (whatever time frame they quoted you), then I would go with the upgrade to a modern 4-sp auto w/OD to take advantage of the benefits they offer.

For ease of installation, I'd have the TH400 rebuilt/new converter (a nice "tight" 2500 RPM stall) as it will be an easy in & out with no snags and you are driving it again. If you choose to go another route, do your research, get honest pricing for parts & labor, and save towards it and do it at a later time. I don't think the TH400/converter should be more than $800 - $1,000 with good quality parts.
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post #6 of 12 (permalink) Old 08-06-2016, 02:43 PM
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I agree. $2800 is an astronomical price for a TH400 rebuild. You should be able to buy 3 complete new transmissions for that price, and then some.

The problem you're likely to run into with an OD replacement is fitment - most I'm aware of require at least some modification to the transmission tunnel in the car floor to get clearance. It's likely also to need either a new custom drive shaft or modification to the one you have. Next to that, if you've got a healthy engine, is torque handling capacity. Make sure you read the fine print there and get one that's strong enough to handle what your engine makes. None of the commonly used overdrive transmissions are going to be up to the task in pure stock form.


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post #7 of 12 (permalink) Old 08-07-2016, 08:28 AM Thread Starter
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Guys, I appreciate all of the information you have provided!

Although a 4 speed OD is enticing, I think I am going to stick to the TH400. Ideally, I would love to keep the original TH400, but I am not going to spend $2800 to do so when I can buy one in the $900-1400 range new. One thing to keep in mind is that this isn't a rebuilt he quoted me, it was for a complete remill. This is how bad the tranny was he said, he could rebuild it but he doesn't trust the other components within the tranny. With that said I still agree $2800 is ridiculously high.

So, I think I am going to go the route of getting a new TH400 that has some upgrades done to it to help with performance. If any of you have links to Summit/Jegs/etc for higher quality TH400s then please share. I don't have all of the information on the history of my engine in terms of HP/torque, but I believe it is slightly above stock as I think there is a mild cam in it. I just took off the aftermarket headers and installed the oversize 2.5" stock exhaust manifolds for the 455. I am guessing I am in the 350-400hp range. I would like a tranny that is equipped to handle up to 500ish HP just in case I decide to amp it up in the future.

Thanks again for all of the suggestions guys!
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post #8 of 12 (permalink) Old 08-07-2016, 10:18 AM
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Mt brother and his BowTie buddies have used Hughes transmissions when local shops failed them. Hughes allegedly has a good rep and a quality product. Their TH400 for our cars is 34-1B. A good Hughes convertor is GM20-400bp or GM25-400bp

Street and Strip - Hughes Performance

Heavy Duty / Street & Strip - Hughes Performance

Summit has these available: and

This should give you some ideas. Ideally I would mate the Hughes TH400 with a Continental Convertor as they have great stall speeds yet drive like a stock convertor.
Torque Converters , Continental Torque Converters

Best of luck with your difficulties!
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post #9 of 12 (permalink) Old 08-07-2016, 11:37 AM
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Hd th400

Having raced several, and broken a couple, I feel that I can share a little info about the TH400.

The TH400 is very easy to build for high performance or race use. Just a GOOD rebuild, along with a 34 element sprag & firmer shift upgrade, will provide a trans that will easily hold up to low 12 sec drag strip duties, for sure--and probably a lot quicker.

BUT, without the 34 or 36 element sprag, 500ft lbs of torque will break the stock int sprag or roller clutch(if you get traction). The earlier TH400, up thru about '70, had a 16 element sprag. A 34 element is a direct replacement for this sprag.

BUT, the later model TH400's had a weak roller clutch. For these models, the entire drum/sprag/race unit must be replaced with one from either an early TH400, or a later 4L80E. Ebay usually has several of these used units for a reasonable price.

34 element th400 sprag in eBay Motors | eBay

If you have an active drag strip, in your area, you can probably ask some of the racers and find out the name of one or more good tranny guys, who can build a good TH400, for a reasonable price.

But, if not, there are lots of places to buy, on the internet.


TSI TH 400 Turbo 400 Bop Street Strip Buick Olds Pontiac | eBay


TH400 Transmission

TH-400 Chevy Street & Strip w/4" Tail HSG & Slip Yoke B.O.P.

Last edited by bigD; 08-07-2016 at 11:56 AM.
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post #10 of 12 (permalink) Old 08-07-2016, 06:34 PM Thread Starter
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Awesome, thanks guys!

I do have a guy in town that can build me a TH400 with whatever I want. I will use your guys' information and bring it to him. Big thanks!
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