How strong are 620 4 speeds?

[smokehouse_83]

Decided to turn my 620 into a 4wd/rock crawler and instead of aftermarket gears for the tcase I have decided to do dual transmissions since the input and outputs are the same I can use a cut down slip yoke to connect them. My question is how strong are these suckers? Is the second tranny gonna be able the handle the torque from the L28? Yep I put a L28 in the 620 and no don't try it unless you are building a off road rig where it don't matter. Front trans is a 280z unit and the rear trans is from the 79 KC. Also do later hardbody and frontier tranny's have the same spline and diameter input shafts by chance?

[Lockleaf]

Seems easier to use a d21 4x4 transmission with an L series bell housing on it. Then put a 720 T100 divorced Tcase behind that. Way less effort than trying to cut down a bell housing and mount a giant transmission under the middle of the truck.

[datsunaholic]

The 280Z and 620 transmissions are the same 71B  gearbox.  Well, unless the 280Z one is a 5-speed, than THAT is the weaker one, only due to the overdrive being more torque sensitive. 

[smokehouse_83]

They are both 4 speeds. I thought about using a d21 trans and tcase but the header is gonna be in the way for the drivers drop tcase. Sooo it's either dual tranny's and a 720 tcase(cheap) or a Samuai tcase with 5 or 6:1 gear set(expensive). I am just worried the trans might not be up to the task. I could use a 2wd d21 trans and the 720 tcase I guess if I run into durability issues, heard those are tough. But are the inputs the same as the 280/620 tranny's?

[Lockleaf]

Yes inputs match. L series is L series regardless of how many cylinders

[datzenmike]

Don't know why a 280z engine when there are better 4 cylinder options. People only use a six cylinder because they just happen to have an old Zcar laying around and it's free. Plus two transmissions and a slip yoke? That's 5 + feet feet right there, plus a T-100? Another 15+ inches. How will this articulate with a 6" driveshaft?????

[Lockleaf]

Honestly though, I'm not sure how twin trannies is easier than modified/custom exhaust.

 

The amplified torque being applied to the second transmission will be tremendous. It's entirely possible that without a full perimeter bracket built in to the middle of the second trans, you will begin tearing that aluminum case apart very quickly.

 

Talk to Matt, screen name Stoffregen Motorsports, on here. He builds extremely hardcore 4x4 vehicles for a living and could better inform you about the likely problems you will have to overcome.

[datzenmike]

The H-190 is good for about 300 ft lbs torque.

 

L20B is good for about 90 ft lbs

 

First gear is 3.592 on the '79 so 310-ish? multiplication of torque. Second transmission, say mid ratio with a  3.321 fiirst and we're over 900 ft lbs. A T-100 is just a c hair over 2 to one so 1800 ft lbs. Naturally the tires are going to slip and relieve the stress just like a fuse. But 48" swampers or w/e rock crawler tires are today are going to really load that differential up

[smokehouse_83]

Gonna extend the wheelbase a few inches but still gonna be a short rear shaft. No different from jeep guys, they do all the time. Also yes I have a rebuilt L28 and 4speed out of a Z. Kinda a throw together cheap build here guys. Planning on using a 33 spline pathfinder/xterra rear and would love to build a h233 front with super duty knuckles for the front, but probably end up with a toy 8" front. I plan on keeping it low on 37's or maybe 40's if I can get the 9" front built. The dual tranny's give me a lot of gearing options that's why I like the idea, I was planning on using some plate steel and making a cradle that goes from trans mount to trans mount and attaches to the second tranny at the lower bolts of the front bearing support since the bell housing is gone.

[DanielC]

My gut feeling is that the second Datsun transmission will not be able to handle the torque of the L-28 multiplied by the first transmission.  If using a second transmission, find a transmission that was intended to be on the back of a V-8, preferably a big block V-8.

Tall tires put a lot of torque back into the drive train.   I imagine the shock loads from rock crawling might not help either with transmission long liveability.

[wayno]

He is talking about a rock crawler here, no transmission was made for this kind of abuse, the whole drive train isn't made for that kind of abuse.

I would have used two 720 4wd short shaft transmissions though, it would make the whole setup 10 inches shorter, unless the 620 4 speed is an early short shaft 4 speed, then it would be 5 inches shorter with the second short shaft, still 5/10 inches is a lot in these types of situations.

[scooter]

Find an adapter or make one to bolt a toyota tranny on it, then use the marlin crawler double t case setup.

[datzenmike]

If running an L28, two transmissions and a transfer case all stuffed into a 620 I doubt this will be an expensive build.

[smokehouse_83]

I did some measuring and the rear shaft would be 10 or 12 inches long which is doable and with a 720 tcase and low cog truck I could use a normal u joint shaft. A H233 Frontier/Xterra/Pathfinder rear is around 300 bucks shipped, I will weld the spider gears on it and they come with stock 33 spline shafts=never break it with 37's. I imagine I can find a 720 tcase for a few hundred. A fj80 front axle is 400-800 will use a stock elocker and long field shafts=never break it with 37's. A toy truck steering pump and IFS steering box will be a few hundred. I have the engine, tranny's, link material, heim joints, ect. Most expensive part of the build will be rims and tires. So yes it will be a extremely cheap build. Guessing less them 4 or 5k. I will buy a few spare tranny's, 4 speeds are a dime a dozen and extra 720 teases. Dudes are doing double tranny's with Toy W56 tranny's which I would guess are on par with these datsun units.

[datzenmike]

The H-233 comes with LSD 4.375 and 4.625 4 pinion diffs. No welding.

 

What about your 5 speed and two T-100s laying on their sides joined input to output. That's about 3.592 X 2 X 2 multiplication or just under 66.5 times with a 4.625 ratio diff. At a 700 RPM idle it takes almost 5.7 seconds to turn the rear wheels.once. Too fast? 

[wayno]

I think 2 Transfer cases is a better idea than two transmissions which would be a bitch to drive anywhere, or would the second transmission be left in fourth gear to drive normally?

[Lockleaf]

H233 is even clutch limited slip. You can repack the diff with extra plates and make it as stiff a breakaway as you want.

[smokehouse_83]

Two offset output tcase's would be kinda funky. Rough stuff makes a nice housing for the H233 diff and with Dana 50 knuckles and 35 spline inner blanks cut down to 33 spline would make a sweet front axle. Probably still be around 3k to build though.

[datzenmike]

The H-233 comes with LSD 4.375 and 4.625 4 pinion diffs. No welding.

 

What about your 5 speed and two T-100s laying on their sides joined input to output. That's about 3.592 X 2 X 2 multiplication or just under 66.5 times with a 4.625 ratio diff. At a 700 RPM idle it takes almost 5.7 seconds to turn the rear wheels.once. Too fast? 

 

If someone finds fault with my math or thinking please feel free to disagree. Rather have it right.

[smokehouse_83]

Well I did alittle more research and found that Nissan's 33 spline is the same diameter as Toyota's 30 spline and there are really no options for cromo axles.  Also looking around for Toyota steer axles and people want stupid money for them and they still need aftermarket birfs.  I can get a Dana 60/14 bolt out of a Chebby for cheaper then a set of Toy axles, but then the week link is def gonna move up to the tcase and tranny's.  Really thinkin about pullin the L28 out and stickin the Vh45 and auto tranny I have here  and going for the 500 dollar adapter and an Atlas tcase.  Gonna have to chop the frame and firewall and pull the brake master out and do a custom firewall for the fugger though.  But then I know it will be build right and have plenty of power.

[scooter]

Well I did alittle more research and found that Nissan's 33 spline is the same diameter as Toyota's 30 spline and there are really no options for cromo axles.  Also looking around for Toyota steer axles and people want stupid money for them and they still need aftermarket birfs.  I can get a Dana 60/14 bolt out of a Chebby for cheaper then a set of Toy axles, but then the week link is def gonna move up to the tcase and tranny's.  Really thinkin about pullin the L28 out and stickin the Vh45 and auto tranny I have here  and going for the 500 dollar adapter and an Atlas tcase.  Gonna have to chop the frame and firewall and pull the brake master out and do a custom firewall for the fugger though.  But then I know it will be build right and have plenty of power.

This, but not a vh45. Unless you allready have one.