The type 4 (412) transmission is actually the same gearbox as the type 3. It is a 003 automatic.
That being said, there are a few differences. I can't remember off teh top of my head if there was a final drive ratio difference on teh 412 but I beleive there was not. Either way, teh difference in final driveratios that wer available bwteen ttype 3 and 4 were slight and still better than one from a bus by a long shot.
You should ...just for driving sake....go ahead and do the adjustment of the pressure modulator valve. Look in the Bentley brown type 3 book for the how to. It should be done for age alone and also because you are going toa lighter vehicle. There may be some vacuum and load differences.
Also..since you have the tranny out....always eplace the seal between teh final drive and the auto section and the 0-rings...or you may be sorry. These are good for 7 years or 70k miles only.
Check the CV flange diameter as compared to the type 3. You may need to swap the inner CV's from the 412.
The transmission suspension for automatics is critical. Bear in mind that the way these are designed is that the transmissions total weight is really suspended from the cross member above where the tranny mates to the engine. The rear hanger bar is simply a bumper to arrest mostion and so is the tail end bushing.
In the haynes manual I think there is a small blurb that tells how much the rear hanger bar to engine bushings are to be compressed....when the bar is properly adjusted. It may be in the automatic section of the late bus for haynes.
So the sequence is to load in the tranny and engine, suspended on teh center hanger, install and adjust tension on the rear engine hanger bar...then adjust tail cone bushing so it has no load on it anywhere.
Don't forget to bring along the relays etc that may exist in the 412 for electric deceleration valve (if it has it). Ray
do you know if the wiring harness is the same, i'm thinking of the multi plug(white thing all the wires go into) for the ECU ?
i found something on the net saying there was a speed or gear (?) output to the brain of the T4.
but from what i can gather it's the same but i want to confirm it
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T3 had a 3.67 final drive while the T4 had a 3.73 for the fasty and a 3.91 for the SB.
my Q here are whats best 3.67 or 3.91 and is it notisable ?
There's no center hanger on a Type III.
D-Jet harnesses are subtly different nearly every year within the same model, I wouldn't expect to be able to use a `70 III harness on a `73 III let alone a `73 IV. If it's all you've got it can probably be made to work, but I think it'd be a better plan to use the one that goes with the engine.
The 3.67 trans might give you a hair better fuel economy, the 3.91 really isn't needed in the lighter vehicle...but it's not a huge difference (~6½%) so I'd probably go with whichever one I had the most faith in. I think the 412 unit has one more clutch for 1st.
Type IV CV joints are thicker and won't fit all the way onto Type III axle splines, so you'll need to use the Type III final drive flanges.
You can tell its been a while since I have driven a type 3. I had forgotten that there was no center hanger bar.
It must be the extra weight of the type 4 engine. Its something to think about. I have seen the warnings and have seen firsthand the longterm wear it does to the long shaft inside the auto boxes....when you run without (or in my case with bad bushings) the center hanger. All the cars with type 4's and autos have a center hanger if I am not mistaken.
Now..whether its just preventing "bouncing" of the engine on the end of the tranny or if it must have no load what-soever...I do not know for sure. you might ask around to see what luck others have had without the center bar with an automatic AND a type 4 engine.
The very late...like August of 71 on type 3 D-jet harness was virtually identical to that of the D-jet 412. It made no difference wether it ran a 4 pin or 5 pin throttle valve switch. As long as it had the late diaphram type MPS...its will f it. Ray
Marc wrote:There's no center hanger on a Type III.
more correctly there is no hanger on pre 68 Type III's. All IRS equiped Type III's had a hanger bar, as the rear tranny/engine support is somewhat lacking on the IRS subframe.
That can make sense. As far as I know, because of the design and the end to end pump drive shaft system in the automatic gearbox...it must be supported at the bell housing end to limit flexing of the case.
Do you know if the pre-68 had an option of having an automatic? If it did not....then there is your reason the early ones had no hanger bar.
With the automatic on the 412...it was not an issue of whether the rear hanger bar can handle the weight of engine and tranny...thats no problem.
It was the issue that the gerabox should not be suspended in this manner (tail cone on one end and engine weight on bell housing face)...because it caused case flexing. Since the type 4 auto IS the type 3 auto....eiether they found that the issue was true in either vehicle or was just due to the heavier type 4 engine. Ray
Let's not get confused here......there is no CENTER hanger bar over the transaxle in a type-3 like there is in a type 4.......but both vehicles used a REAR hanger bar at the rear of the engine.
The interesting thing with the type 3 is that the tranny is essentially mounted solid then between the mount on the grearbox tail and the engine with its rear hanger bar.
It must be a difference somewhere because factory literature is explicit on the issues in the type 4 with suspending at the ends compared to the center....and I have seen firsthand the damage not doing it correctly causes on the type 4.
Must be either engine length and leverage exrted or the weight. Ray
- hope you guys can help 
