Best Years for a turbo 400

[650Rider]

Ok all you tranny guys, I am wondering what is the best year and vehicle to find a good base to build a t400, if there is such a thing or will any case do and just build any old t400.

[JEFFRPM]

1970-1979 class A motorhome or 2 ton truck/van chassis, have fun they are getting scarce due to all of the scrapping in the last 8 years.

[philofab]

1970-1979 class A motorhome or 2 ton truck/van chassis, have fun they are getting scarce due to all of the scrapping in the last 8 years.

I have one from a 73, fixed yoke. No one seems to want it.

[scottm]

The 4x4 truck models have a stronger case that uses a stout cast alum converter cover, and can be built with a normal tailshaft and output yoke. The rv model they are talking about is called a turbo 475 I think. Many if not all have a huge drum parking brake on the output shaft. The main internal difference is the gears are straight cut rather than helical, so they make less end thrust, and should last longer. But a good offroad tranny guy (Alger, A&S Trans in Phx) told me he doesn't see a difference in life with the straight gears. All are pretty good, but avoid ones from the 1960's. You can't go too far wrong with a 2wd model from an 80's 1 ton pickup with a fixed output yoke. I see them on craigslist all the time. I have three and havent paid more than $100 yet.

[FABRICATOR]

Ditto on the above. The 60's will work too, BUT, some 1965-1967 had the switch pitch converter so you would need to find another pump. Some had no provision for a mechanical speedometer drive. And some were set up for a one-of-a-kind filter assembly. Most of the wierdness and upgrading ended prior to 69, so from there forward you can't go too wrong if the case is in good condition.

Many of the car 400's had the long tailshaft and housing, but these can be changed over to short. And of course you will want the right bell housing bolt pattern for you engine.

[JEFFRPM]

The 4x4 truck models have a stronger case that uses a stout cast alum converter cover, and can be built with a normal tailshaft and output yoke. The rv model they are talking about is called a turbo 475 I think. Many if not all have a huge drum parking brake on the output shaft. The main internal difference is the gears are straight cut rather than helical, so they make less end thrust, and should last longer. But a good offroad tranny guy (Alger, A&S Trans in Phx) told me he doesn't see a difference in life with the straight gears. All are pretty good, but avoid ones from the 1960's. You can't go too far wrong with a 2wd model from an 80's 1 ton pickup with a fixed output yoke. I see them on craigslist all the time. I have three and havent paid more than $100 yet.

This is true but the straight cut gears make ALOT less heat and they dont load the thrust bearings at all.

[motorhead]

This is true but the straight cut gears make ALOT less heat and they dont load the thrust bearings at all.

Why are most diff gears helical if staight cut gears last longer, make less heat and don't pull on the pinion bearing?

[JEFFRPM]

Noise, A straight cut gear in the rear end would make your ears bleed

[philofab]

Why are most diff gears helical if staight cut gears last longer, make less heat and don't pull on the pinion bearing?

Differentials use the gears in a different way than a transmission.

The main reason is noise. Straight cut gears make lots of noise.

[philofab]

Noise, A straight cut gear in the rear end would make your ears bleed

It also would not allow hypoid offset and create a weaker rear end.

[motorhead]

Noise, A straight cut gear in the rear end would make your ears bleed

I have Motive helical gears in my 9" diff with .007" clearance and it whines obnoxiously loud when at crusing speed on the highway, but very minimal noise when I'm decelerating with my foot off the gas or accelerting at any rate. Is my backlash set improperly or is the noise level normal under the stated conditions? Didn't mean to change the thread subject but figured it was better than starting a new thread for a simple question :o.

philofab - What is hypoid offset? Hypoid gear oil is the only thing that comes to mind and was under the impression it reduces froathing of the oil.

[JEFFRPM]

Check your gear pattern sounds to me like the pinion is not "IN" far enough or the pinion bearings don't have the proper preload at any rate the gears are all ready toast.

[scottm]

Jeffrpm, I agree straight gears should be better, but the tranny guy says they still go bad.

Hypoid is the design of the gearset, and comes from the tooth form being a hyperboloid. It allows the pinion to be below center on the ring, plus has more tooth contact for strength. The teeth slide across each otheras they turn, so they require a special 'hypoid' gear lube.

[philofab]

philofab - What is hypoid offset? Hypoid gear oil is the only thing that comes to mind and was under the impression it reduces froathing of the oil.

Scottm beat me to it. FYI, the lower a pinion from center line of the diff the stronger a rear end can be, the closer to center line the more efficient it is. This is one of the reasons a 9" is so strong and inefficient, the pinion is very low. The distance from center line is known as "hypoid offset".

[motorhead]

Check your gear pattern sounds to me like the pinion is not "IN" far enough or the pinion bearings don't have the proper preload at any rate the gears are all ready toast.


I willl find out if they are toast when I swap the spool out for a locker in a few weeks. I haven't driven the truck very much so the gears might not be toast just worn a little uneven. I can hope right:D.

Scottm and philofab - Thanks for the explanation, I've noticed different offsets but never gave it any thought. Any numbers regarding efficiency loss vs. teeth strength? I now might have another reason other than weight to run a Toyota 8" in my next project since I only plan to have 200 hp.

[philofab]

I willl find out if they are toast when I swap the spool out for a locker in a few weeks. I haven't driven the truck very much so the gears might not be toast just worn a little uneven. I can hope right:D.

Scottm and philofab - Thanks for the explanation, I've noticed different offsets but never gave it any thought. Any numbers regarding efficiency loss vs. teeth strength? I now might have another reason other than weight to run a Toyota 8" in my next project since I only plan to have 200 hp.

Here is a link to a car craft article comparing 12 bolt GM, 9" ford, and Dana 60. Lots of good info that can be applied to our sport.

http://www.carcraft.com/techarticles/ccrp_0806_chevy_chevelle_rear_axle_swap/index.html