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TH400 to a ?

Started by Larry Reeves, June 23, 2007, 03:16:54 AM

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Larry Reeves

I am losing the second TH400 in my 1981 Fleetwood commercial chassis. Is there another bolt-in transmission that will reliably stand up to 7000 lbs? Are there any issues with putting in an overdrive trans? Is there an overdrive trans with the BOP bolt pattern?

The Tassie Devil(le)

G'day Larry,

The TH400 is about the toughest Passenger Car transmission around, but if you are having trouble with it failing, maybe you need to get it rebuilt with extra Heavy Duty parts.

Maybe you could find an Allison Auto Transmission that has the Chevrolet Bellhousing Patern, and use a BOP conversion adaptor?

But, as far as an Overdrive Unit, I would be suggesting you contact Gear Vendors and see if the Hone Overdrive Unit will stand the strain.   That unit will replace the rear extension housing of your TH400, but they aren't cheap.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

TJ Hopland

I agree with Bruce, the 400 was the strongest one they made. The only od trans they made that is a direct bolt up was the 200R4 which was not known to be strong.  I guess now days they can be built fairly strong but it gets expensive.  400's were the 3 speed HD truck transmissions till the allisons came out.  Light trucks got the 700's which were never made in anything other than a chev bell pattern.  If you keep burning up 400's I would look for a differnt builder or brand of parts.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

35-709

"If you keep burning up 400's I would look for a differnt builder or brand of parts."

I think that is the key here.  TH 400's are usually as bullet proof as they come!
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

Doug Houston

I've had, and still have a THM 400 in a '70 DeVille convertible. I did send it to Hydra-Matic, and they toughened up the shifts so  that when it shifts, by Neddie Dingo, you KNOW it. What the job amounted to was to put a shift kit into it. The transmissions that Cadillac, Buick and Oldsmobile ordered were set up for soft shifts. They didn't want to jar the frail old ladies, I guess. the guys at Hydra-Matic were livid about that, because when a transmission shifts, IT SHOULD SHIFT.  There are 6 ball checks that are in the valve body that cause the clutches to close slowly, and give slippery shifts. If you remove those ball checks, the thing shifts like it means it, and the way it was designed. The other thing thay did was to put in a regulator valve spring, as used in Corvette, to increase the mainline pressure in the transmission.  There is a guy in the SE Miochigan area who worked at H-M in the engineering garage, and he did the work on my transmissions. He once did work on transmissions at home, but doesn't any more. He set many of them up for racing, so as already said abnove, you're not going to find a tougher transmission anywhere.

One of my cronies, and a sometime visitor here, had a Pontiac Grand Am, with a 455 engine, and a THM 400 transmission. He had this guy rebuild it, though it was working OK, and again, make it shift like it should. Bob had to make a tight entry into a highway, so he kicked it in the pants. It broke traction on each shift. The thing was sort of scary. I once driove it. It was not a light car, in any sense of the word.

Talking with a friend in Houston (who also posts here occasionally), told me just what is needed to install a THM 400 on a '56 engine. I'm toying with that idea. You just can't beat the thing. .  Understand, I don't like messing with original configurations, but the THM 400 and the '56 Jetaway are on the opposite ends of the reliability scale. I dislike having cars towed home.

Larry Reeves

I've got a Jet-away Hydromatic 4spd in my 61 hearse, and I am always amazed that it doesn't explode... I have had it rebuilt 2 times in 6 years, and about a year ago it was stuck in 2nd for a month... Then one day it just...fixed itself. No trouble shifting since then, but I am just waiting...

Toystoretom

When you rebuild or replace a tranny you must flush the radiator. Skipping this step dooms your rebuild.