TH475 vs TH400

[magnethead]

So if I undertsand my research, the TH475 is a TH400 with straight cut gears, a 6 bolt convertor, and a fixed yoke? I'm starting to think my truck has a 475 based on the convertor and yoke.

[MylilBowTie]

If you can get the info off the id tag, I'll see what it brings up.

[liljon285]

never heard of that.

[Ivan D.]

And it was supposedly used in heavy vehicles like motorhomes and such... yer truck is freakin huge, it just don't get bigger than that, so it might actually be a TH475.

[magnethead]

Sorry haven't checked back...I'll look for an ID tag, but i don't remember seeing one when we dropped it. The bellhousing wasn't marked like the 375's were, so i'll go back and look for an ID tag, if it's still there.

[magnethead]

hard to see it with the trans in the truck..via flashlight and knowing how to operate the advanced function of the camera, i got it though. It's a 1600x1200 pixel file..shouldn't be too hard to read the numbers.

http://img.photobucket.com/albums/v2...6-05-07004.jpg

[magnethead]

here's one for you- if you look closely (thank goodness for hi-res photography), there's some green and orange text painted on the tag that's been worn off over the 30 years this thing's been around. Anybody know what it might say?

FYI the VIN say's it's a 77, the motor date is Jan 14th 1977, and the trans code is 77. Who wants to bet that this thing is numbers matching, after pulling trailers ever since it was brand new, and with close to 150,000+ towing miles on it?

[MylilBowTie]

It shows up as a 454 v8 Series 30. For 77 truck series the th475 where CS -454 v8 Super Goose, CL - Mobile home chassis, GT - GMC school bus

But it does have the hd torque convertor with 6 lugs vs regular 3 lugs.

[magnethead]

so it's a 400 with the allison TC and fixed yoke but helical gears?

[MylilBowTie]

77 is for the year and the letters are the designation for the type.

Bolt on yoke is pretty common for th400s in a long bed truck. Being a 1ton crew cab I would be really surprised if wasn't a bolt on yoke. You do have a deep transmission pan for better cooling and extra fluid capacity. The 475's have a lower gear ratio for 1st - 2nd and heavier duty internals. Its the heaviest duty automatic that could be gotten I believe. I'm not sure about the newer Allison automatic line.

[magnethead]

well neiter of those three are what it says, so what is it? It's code CC, it's got a 6 bolt allison convertor and a fixed yoke. It's never been dug into so nobody knows what the gear type is.

I know the 77 is the year and 4645 is the serial number, but what does CC come up as far as either 475 or 400, and what does 547 mean? If it's may 4th, would that be logical if the engine was jan 14th for it to be a numbers matching unit?

[MylilBowTie]

It came up as a th400. The serial number should be part of the vin number and when it was built. To get a th475 it has to be pretty heavy duty to need one. Not saying your truck isnt heavy duty. The only th475's that I see are heavy motor home chassis, school buses, and the super goose I would assume would be for a fithwheel type 1ton.

I dont have anything for decoding the date codes and things like that. Its mainly just the year, vehical type, and transmission type.

[magnethead]

so they made 400's with the allison's and bolt on yokes? ok. This topic should make for a good research page for google.

[magnethead]

I just thought of something...I wonder when the transmission shift kit was put in, perhaps the previous owner maybe had 475 internals put in it...because from what i understand, 400's just didn't simply come with an allison convertor and bolt on yoke?

[MylilBowTie]

I seen plenty of th400 with bolt on yokes in 3/4 ton and 1 ton trucks. I've also seen them in vans. Both trucks and vans had two piece driveshafts. As for the "allison type" torque convertor. I believe it is a normal hd torque convertor with 6 mounting lugs vs the non hd 3 lugs. One thing that may be possible is that it could be a diesel convertor instead of a gas. But I would assume that would be a remote possibility.

Th475 parts can be put in th400 to make them th475. I used to know the specifics of what was different but cant think of all of them. I know the sprags are different, carrier, few other things. One of the part has to have another part so they will work together and doesn't work with the stock one.

[60-66 Nut]

I think the "supergoose" may refer to a type of gooseneck beverage trailer that we used back in the late seventies - early eighties. It was called the Swan SuperGoose, made in Powhattan, Virginia. They were designed to be pulled by 1 ton pickups, and I think they had the trucks built to their specs, since the truck and trailer were sold together as a rig. All of the trucks we had were 76-79 Chevy Dullys, and they all had the 454 engine, 4.56 gears and the TH400(or 475, whatever it was called) except for some of the 79's which had the SM465 4 speed.

I can't remember if they were called 475's or not, but I do know they were different from a regular 400. For one thing they had no park gear, because they claimed the park gear may have not been able to hold the weight of the trailer. They also had different drums, sprags, clutches and other parts that had to be ordered anytime we had one of them worked on. They did have the 6 bolt convertor and bolt on yoke, but I believe those are both very common to truck 400's. Most all of the truck 400's I've seen had the bolt on yoke, and we had some 78' model 3/4 tons with the 6 bolt convertor.

I do know that if we stuck a regular 400 in their place, they wouldn't live long. The trailers were very heavy when fully loaded, around 32,000 lbs.

60-66 Nut

[magnethead]

oh ok, thanks for clarifying. My dad just hadn't ever seen a bolt on yoke or a 6 lug convertor before.