The Stovebolt Site Forums The Shop Area The HiPo Shop TH400 or sm420

I am running 70 Buick 455 engine in my panel.
I would like to keep the SM420 in my truck if I can. Its a floor shift and my truck is being built to go off road as needed or for fun.
I have a BOP th400 , but its hurting and needs rebuild.
My SM420 is in great shape. The 10.75" clutch is good too.
Might upgrade it though.
I am running a divorced NP205. I want to mount it in carrier bearing location. This will give me equal length drive shafts.
If I use the th400 , due to its length my short shaft will be real short. might only be enough room for yokes.
My SM420 can be mounted in its stock position and short shaft reused (if it can handle it?).
I would still have to have my crank modded for the 455 to be used in manual operation but it is what it is.
I think my diffs are 3.08's . I cant remember at the moment but I remember them being in that range...
I am working on a deal with a friend for manual BOP bell and fork. Thinking about hydraulic mod added also. But Ill get to that.
please chime in with your opinions, experiences etc ?

Go with the sm420, a lot of the 4X4 rock boys use them, they can take a lot.

Root is correct. The Jeep rock crawlers use the SM420, especially for the low first gear. There is a company called Novak that supports the SM420 for the purpose of that crowd. They sell all the parts you would need if you can't find them through the normal Chevy truck channels.
Kent

Seems to me Buick V8s were sold to RangeRover/LandRover. Perhaps a bellhousing from Range/LandRover could also be used.

3.08 gears are not desireable in a wheeler, however they should work fairly well with a sm 4.20 with the 7.05:1 first gear. If I were building it, I would look into using an NV4500 5 speed, and lower gears. How low the gears are depends more on Tire size.

28 inch tires 3.73 gears
31 inch tires 4.11 gears
35 inch tires 4.56 gears

Thanks guys.
As far as gearing is concerned , I think the 3.08 will be fine for my application. I have yet to confirm the gears though.
This truck will see highway , and will see trails/mud. More road than trails though. I figured when I combine the 1st gear of theSM420 with the low of the np205 , I should get plenty low enough.
Maybe with a tall tire and those 3.08's I will see a good RPM drop at speed in high gear.
My mind is made , I will be definitely using SM420. I will keep looking for bell.
side note : I have been knocking around the idea of a 4200 gm straight 6 also. Not sure about sm420 compatibility there. 4l60e is not my favorite transmission. There are a lot of these motors available around here.
The big block buick is cool , but not very practical this day and age.

Found a BOP 4 speed bell and extra parts on CL not far. Im going to see him tonight.

BOP Bell fit really well so far.

I have an idea for reusing the repo master I bought for the original brakes. I am using the power brakes from the 87 donor truck. Pedal off the dash/firewall.
What if I connect the rod end to the 49 clutch pedal linkage instead of the old brake? Then connect a slave to the clutch with mounts/linkage off the bell some how?

Linkages , column position, motor position , pedal position

I have to get the fully dressed motor here to really check things over.
I might be able to get away with just mounting my spare heads to the mock up block.

@NV4500 comment... manual trans compare pic looks like same bolt pattern as sm420, but spline and shaft are way smaller.

Details on parts in case someone needs the info...
11" gm coarse spline clutch and flywheel. Flywheel needs to be balance matched to flexplate if 455 is not originally a 4 speed set up.
Also check to make sure there is a provision on the crank for pilot bushing. The pilot bushing is standard buick/olds 4 speed part. The ID is the same as original 49 pilot bushing but is not the same OD. Always check bushing for clearance. Most people have had problems with rollers , so I recommend staying away from these types.
Standard gm 11" pressure plate . Throw-out bearing is also a stock gm part.

Ended up using stock 1949 throw out bearing. Here is my transmision pics for the day. The original fork probably could have been used but it had no clip and I have the brand new B.O.P. fork w clips . My new fork would have to be drilled out for the linkage but I think it will work out nice. I can retain original clutch linkage. I might switch to hydraulic master some how still.
These parts are also used for Saginaw backed 455.

Bigbadswingdaddy....
I looked into Nv4500 some more. It apears to come in both coarse and fine spline. The coarse spline seems to be compatible with my setup. I might upgrade someday. I will have to keep my eyes open.
At that point I would probably find a donor truck and take the 6.0l or whatever is in the truck with it.
There was one here local that has been sitting a long time. I have talked to the guy on many occasions , he never wants to sell when I have the money. To bad its got the same matching leather bucket seats I have in my truck . 6.0l and 5 speed. Last talk I had was actually with his new wife/gf and she says he is fixing it. August supposedly he is sending it to a shop. Sept I will try again.

The NV4500 has a different bellhousing interface than an sm420. I use a 94-97 dodge version when I do the conversion because the dodge version has a pilot shaft that is 1 inch longer. The early dodge 2wd versions have a mechanical gear on the tailshaft of the transmission that drives a pulse generator. this could be easily swapped out to a speedo pinion for a mechanical speedometer. On a 4wd, the speedo pinion is on the transfer case, so that last fact is not so important. I then use an adapter plate from Advance adapter to go between the transmission and the bellhousing. I got the heavy duty dodge diesel version with the 10 spline 1.25 inch pilot shaft. I ordered a new 10 spline 1 1/8 pilot and a new bearing retainer which I spun down on a lathe to match the diameter of the chevy bearing retainer. Long story short... I use the stock clutch disc, pressure plate and throwout bearing for my truck. I have to use or make a custom pilot bushing because the tip of the transmission is bigger than a typical chevy transmission.

The NV4500 is longer than the sm420, and the shifter is about 5 inches further back.

I was over at Advanced looking around. No adapter to B.O.P. They got a BOP to sm420/465. They got an adapter for nv3500/4500 for just about everything.
I thought I read the bells were part of the tranny on some of the nv4500's . Do you know if there is one that has a removable bell? then I could just swap bells and get matching 10 spline etc. What size clutch does it usually come with? I am running an 11".

While I am here I am kinda stuck at mounting my tranny.
The sm420 used to mount using the bell. My bell is aluminum and does not feel right sitting in between 2 massive pieces of iron.
I would like to support the tranny. I am thinking about a mount that comes from the stock mount and goes back a lil to mount to the rear of the mounting holes to the bell on the tranny. The 2 lower holes with the nice flat tabs on them. I am using a divorced transfer case so I cant use the adapter mount. Is there another mounting option I do not know of? Should i make a new post about this problem?

It will take a little precision machining to locate the center hole accurately, but it's possible to sandwich a piece of 1/4" steel plate between the SM 420 and the bellhousing that can be mated to a square tubing crossmember bolted to the frame rails. You might need to fabricate a longer than normal pilot bushing to accommodate the rearward movement of the transmission.
Jerry

NV3500 is integral bellhousing. NV4500 would mount to a bellhousing similar to your BOP housing. The BOP has the standard Muncie GM pattern. The center hole is 4.686 inches. The sm465 has the same bolt pattern, but the center hole is 5.125 inches. AA has an adapter plate for the bellhousings that fit the sm465 to the NV4500. There is a raised lip that is indexed for the 5.125 inch center hole. With a large lathe, it is possible to turn that indexing lip down to 4.683 on the AA plate to mount a NV4500 to your BOP bellhousing. It may also be possible to mount your bellhousing to a mill and open up the center hole to 5.125 inches.

It can all be done, just takes some creativity.

X2 on the 1/4 inch plate between transmission and bellhousing for a mount.