H42 4-Speed or SM420

[bdiemer]

Ok, it finally happened, I kept saying I wasn't going to change my stock 3-speed transmission to the 4-speed that came with my 72 FJ40 until it died. It appears that a little bird has crawled up in the clutch or the throwout bearing is chirping and on its last leg. The H42 came with drive shafts, linkage, shifter and adapter gear. PO said it would be turnkey. Question is: At this point do I want to do a SM420 for a granny first gear? What is the 1st gear ratio difference between using a 420/stock 72' 3-speed transfer case combo and a H42 4-speed/stock 72' 3-speed transfer? It appears that it is a no brainer because I've got all the parts to do do the H42 and just need a clutch and pressure plate. I run 33" tires with Aussies front and rear with an F-motor, 4" spring under. Problem is that the rocks keep getting bigger here in Arizona

 

[Markh]

Well here are the numbers for the H42 and Sm420:

H42 1st gear 3.55:1
SM420 1st gear 7.05:1

Mated with a 3 spd transfer case:

H42 3.55x2.313=8.2:1
SM420 7.05x2.313=16.3:1

If you have stock 4.11 gears:

H42 3.55x2.313x4.11=33.75:1 over all 1st gear ratio
SM420 7.05x2.313x4.11=67.02:1 over all 1st gear ratio

If you bought an Orion transfer case and used the H42 it would be:

H42 3.55x4.0x4.11=58:1

Cheers

 

[dmaddox]

SM420 will be like driving a grain truck from the 50's. Ive used both the SM420 and SM465. At least with the 465, it's a bit more driveable. I say stick with Toyota, espeically with only 33's. I ran an SM465 with 37's and it was "ok", but not awesome. If you have the 3sp "low" in the t-case, go with the Toyota. It will drive much better than an old clunky 420.

My .02

 

[bdiemer]

Thanks Markh! As a matter of fact I WAS driving old grain trucks on our farm in TEXAS back in the early 80's when I was like 11 or 12. The H42 appears to make more sense for what kind of wheelin I do. So its off to the parts washer to see what I've got. Anybody order a 4-speed clutch recently?

 

[Cruiserdrew]

For offroading, the SM420 is hard to beat and you have all the components to make it work. You have the correct bellhousing, the correct transfer etc. No doubt it shifts like a truck transmission, but based on the size of the counter and main shaft, it is much, much stronger than an H42. That low first gear is also the mach daddy for going slow on the cheap.

If it is only going to see mild offroading, than stick with the H42.

 

[bdiemer]

Cruiserdrew, since your in Sac, we have a house in Truckee, it is foreseeable to grab the trailer and drag the 40 up to the Rubicon in the future for an organized event. Do you think the H42/72'-3 speed transfer/33's/aussies/8274/longs would work well?

 

[Cruiserdrew]

Cruiserdrew, since your in Sac, we have a house in Truckee, it is foreseeable to grab the trailer and drag the 40 up to the Rubicon in the future for an organized event. Do you think the H42/72'-3 speed transfer/33's/aussies/8274/longs would work well?

Anything can work. That's about how I went through the first time 9 years ago. You would find it much easier with the SM420. I ran through more than a dozen times with a 4 inch lift and 35s with the Sm420. It worked great.

The H42 is a nice shifting tranny, but unfortunately, it's first gear is too high. Remember the SM420 will be moving at half the speed relative to the H42 on a given obstacle.

There is no substitute for being able to go slowly.

I have an SM420 now and am strongly considering an Orion. Then I can go stupid slow.

 

[Pin_Head]

The sm420 (and sm465) is like driving your old 3 speed on the road, except that first gear (second on the 420) will now be synchronized. You only use the low first gear of the 420 off road or when you are hauling a load of grain.

 

[calico kid]

Have you thought about the h41? I have one in my pig and I like it.

 

[Josie'sLandCruiser]

Hi All:

For all-around, general purpose use the H42 would be nicer than the SM420 or the old J30.

For off-road use the SM420 is the definite choice, for its deep first gear ratio. Like "Pinhead" mentioned, on the street the SM420 will be like the J30.

Just so you know, the "F" engine bellhousing will not work with a H42 (but will with a SM420.) The H41/42 four-speeds require use of a 2F bellhousing.

Good luck!

Alan

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Ok, it finally happened, I kept saying I wasn't going to change my stock 3-speed transmission to the 4-speed that came with my 72 FJ40 until it died. It appears that a little bird has crawled up in the clutch or the throwout bearing is chirping and on its last leg. The H42 came with drive shafts, linkage, shifter and adapter gear. PO said it would be turnkey. Question is: At this point do I want to do a SM420 for a granny first gear? What is the 1st gear ratio difference between using a 420/stock 72' 3-speed transfer case combo and a H42 4-speed/stock 72' 3-speed transfer? It appears that it is a no brainer because I've got all the parts to do do the H42 and just need a clutch and pressure plate. I run 33" tires with Aussies front and rear with an F-motor, 4" spring under. Problem is that the rocks keep getting bigger here in Arizona

 

[bdiemer]

PO had planned on this swap, so I have the 2f bell housing. It looks like I am only missing the tcase to tranny gasket. I'll talk to Kurt at Cruiseroutfitters.com on Monday.

 

[CruisinGA]

Like everyone has said here, it all depends on the use.

SM420- cheap, simple gearing at the expense of on road driveability. Also getting harder to find conversion pieces and parts due to age.

I love my Sm420, but I would also love another 40 with an H42 and 33's.

 

[cruiser_guy]

Remember, putting a 3 speed transfer on a 4 speed tranny also requires the output gear and transfer shifters from a 4 speed transfer.

I'm also for considering the H41. 4.9:1 first gear and it shifts like an H42 not a grain truck.

 

[pbgbottle]

i love driving our grain truck 454 bigblock sm420 drives great . as for driving grain trucks at 12 years of age my daughters been driving tractors since she's been 3 . she is just backing the tractor up to the bailer in this pic.

all joking aside . i agree depending on desired use . the h41 is great and shifts nice but if ya hit the trails quite often you will love the 420 i switched to a 465 behind a v8 and i love the gearing ,on road and offroad. if running a v8 i would probably go 420 using the F i would choose the H41. unless you do alot of wheeling and are gonna need the lower gear.

 

[marks69cruiser]

I have a rebuilt sm420, from transmission exchange company out of Portland. I'm very impressed with the way it shifts. I drive it as a three speed, only using granny low for offroad. With my 4:10 gears, gm 350, and 35" mtr's on or offroad it works well. Hope that helps. Mark