Technical Is this a GV unit

Seen this online and wanted your experienced eyes on this. Says it's out of a rv what do you think. And if it is what marking should I look for

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Looks like a turbo 400 with drum parking brakec not a GV unit.

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Oh, thank you. And that makes sense too. Got me worked up for nothing lol. Thanks

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BIG truck or motorhome trans, with a parking brake attached, alaq the old MOPAR transmissions. That trans most likely has the thicker case and straight cut gears, making them stronger. Racers like them for just that reason; some of those do not have the parking brake attached however. Those are the ones really sought after. I am Butch/56sedandelivery.

 

Are those the gears that are louder I've heard of?

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Besides the stronger gears and case, are their any disadvantages running these gears? Will I be able to swap it in a bop case

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If anyone can answer me this question I would appreciate it to. When asking around what year th400 to choose from I was told to pick a 70-73 th400 from a big buick because they have a more responsive valve body due to the larger diameter of the valve. I have a chance at a 68 from a firebird. Is the 68 inferior to the older th400? Where is the weakness, can it be fixed?

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Those do have "louder" gears because they're straight cut. The cases used to have HD (heavy duty) cast on them to ID them. Never heard of a "larger valve in the valve body". The earlier TH400's did have a better/stronger roller clutch drum that usually gets backdated to when building a stronger TH400. The trans with the attached parking brake may have a different output shaft also; I don't know that for sure. You can't use that extension housing at all. I had an old dual range Hydramatic (Hydro) long ago that had a parking brake attached; I got that trans for parts. I would stay away from the trans you've posted here about; find one that's meant for a p***enger car to start with. Even some/most of the trucks TH400, that don't even have an attached parking brake, use a bolt on yoke that requires a special slip yoke in order to use in a p***enger car (3/4 ton and up GM trucks used a 2 piece driveshaft that used an integrated slip yoke in the front shaft). Basically, make your life simple; don't start with something that you have to work around. Don't order a TH400 from JEGS either; see the thread about that here on the HAMB; trans arrived all busted up.
I am Butch/56sedandelivery.

 

If you're hoping to stumble upon a GV, this is what one looks like behind a TH400.

 

This is where I read the info Butch, I didint know either.


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How loud is loud guys? Will it cloud the sound of a strong engine with good pipes.

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All right thanks Bud. I remember that saving that photo.

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watch Two Lane Blacktop, listen for the rock crusher transmission...that's the type of sound. But the gears in an automatic only turn in 1st and 2nd, not in 3rd, so you wouldn't hear it most of the time.

 

Butch thanks for the info on p***enger cars vs truck slip yokes. Appreciate that

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If you want to have even more fun with TH400 slip yokes, look into the small one they used on the early Buick th400s, and the even smaller one they used on the TH375 in wagons in the early 70s.

 

I'll do that, good info to have.

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Cool I'm off work and going to watch it.

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The roller cluch was the other part I was told about just like Butch said above. Thanks but I still don't understand because in the post above it says " The earlier TH400's did have a better/stronger roller clutch drum that usually gets backdated to when building a stronger TH400."

So does earlier mean before 1970?
And the backdated statement? Does that mean they get tossed during a rebuild?

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That means they go to the stronger 34 element sprag, but that gets expensive because you have to go to the early style direct drum.

 

Unless the trans you have is junk inside you would probably be better off having someone bench it and have it fresh than trying to swap guts from one to the other by the time you bought that trans, bought the gasket/seal kit and swapped parts or paid someone to swap parts. You should be able to use your tailshaft and extension housing unless the tailshaft doesn't jive with the internals of the mh trans.

 

Thanks guys.

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Wish I has found one of those when we were building the bus. The parking brake would have been easier.
The cure for loud gears is louder exhaust.

 

or enjoy the sound!

 

I've had RV T400's and I never noticed excessive noise from the planets.
I think the output shaft is the same as the std. shortie. It just has the hole tapped like a Corvette.

 

So only drag racers like these gears huh. I wonder what other advantages they have and when or is your able to feel them driveability wise.

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Trucks and drag race cars need strong transmissions.

 

I'm a try to get the guts for a steal. Let's see how it goes

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Is a parking brake on the trans stronger or weaker than on the axle due to the rear gear ratio?

 

I didn't see any mention of this, but if you're looking for a GV unit, get one specifically for your ******, otherwise you have to source the adapter and coupler. Big $$ through GV.

 

Theoretically, the trans mounted brake should provide more braking due to the multiplication thru the ring and pinion. In reality, I'd call them one of the most dangerous pieces of **** ever installed on a large number of vehicles.

The primary application has always been on medium duty trucks like F600 Fords and C60 Chevys with hydraulic brakes. A F600 will have either 15x5 or 15x6 rear brakes, and equivalent size Chevys will have brakes the same size. The trans mounted parking brake is about the size of a p***enger car drum brake.

So, you're using one drum, 10-12 inch diameter and a couple inches wide, to act as a parking brake on an axle that uses 2 drums half again as large in diameter and 2 to 3 times as wide for normal braking. If you ***ume the same friction levels for both parking and service brakes, the axle ratio would have to be in the range of 6:1 to 10:1 to provide the same resisting torque with the trans mounted brake as you'd have by energizing the service brakes for parking. Most medium duty gas engine trucks for highway use have rear axle ratios in the 4.3:1 to 5.3:1 range, which leaves them short of the necessary multiplication for effective parking brake action.

Then you add the fact that, in the real world, most of the trans mounted brakes end up oil soaked in a relatively short time, and you have a parking brake that will barely hold on flat ground and won't do much of anything on any sort of grade. As a general rule, anyone who works with or around trucks with trans mounted parking brakes soon learns to never trust them. They put it in low gear and chock the wheels for parking.

By comparison, the same truck with air brakes will have spring actuated parking brakes operated by a spring chamber piggybacked onto the service brake chamber. The spring brake will apply a force equivalent to about 50psi of air pressure. These parking brakes work so well that you're guaranteed to wring the driveshaft out before you'll overcome the braking force.

The only logical reason for trans mounted parking brakes is that they're cheap as compared to a system that actuates the service brakes in a manner similar to that used on cars and light trucks with drum rear brakes.