Mini motor home gearing

[wizard07]

Bought a 1979 Datsun Mini motorhome and made a flat bed from it. Gearing is godawful low. Bought a 4.375 pumkin to change out the one in it now but it has the same gear ratio (4.375). I was told that this is the lowest ratio they made for 74 thru 79 trucks. It has a 4 speed manual trans. Are not all 4th gears 1.00 ratio. I can not find any info on these mini motorhome units.Did they do some oddball gearing in these trucks? All I know is Im going 65 on the freeway and it sounds like Im reving 10 grand. Any help would be great . Thanks

[datzenmike]

The lowest gear ratio (highest numerically) in the 620 truck is the '72-'74 automatic at 4.625.(1)

 

The camper or cab chassis option only available in '79 came with a 4.375 ratio differential and only with a 4 speed. All other '79 (4 or 5 speeds) came with a 4.11 ratio diff. All other previous trucks 4, 5 speed or automatic were 4.375 with the exception of (1) above.

 

Yes forth gear (even on a 5 speed) is 1:1 or straight through. You have confirmed that you have a 4.375 ratio so you know that you are not at 10,000 RPMs. I don't know the camper tire size but stock 620s come with 6:00 X 14" which are, I believe the same as 175 75R 14 and 24" tall. This works out to 3980RPMs at 65MPH

 

All I can say is everyone complains that it sounds like it's revving much higher than it actually is. If it's any consolation you won't hurt an L motor.

 

If you want a lower diff ratio the 4.11 is in the 4 or 5 spd '79 truck only. Alternatively try the 720 trucks. The 4.11and 3.889 were used in several 2wd models.

 

Check your clutch fan water pump. The blades should turn by hand but feel firm. The clutch fan is designed to limit fan speed to 2,100 when cold and about 1,600 when warmed up but they have been known to seize internally and turn at full engine speed. They roar like an F-18 taking off. Even a perfectly working one tends to have a distinctive whine.

 

Whining sounds can come from the transmission too. If you have never changed the oil do so with 2 pint og GL-4 90 W gear oil. If you have check the oil level. Low oil can cause bearings to whine.

[wayno]

I have a 1971 datsun flatbed with 437 gearing and I just drive the shit out of it. Do you have the 1 ton dually axle? Pictures do help a lot, we like pictures.:lol: If you have the 1 ton axle the only choice you have is to order 411 ring and pinion gears from nissan, I talked about it with them at the dealership, and that was the best hiway gearing they had for the axle, but there are guys out there that really know there shit, and one of them might know how to do what you want with parts made by nissan, but nissan never put it together that way, they never had an application for that gearing in there opinion. Nissan never put together a truck shortshaft 5 speed that would bolt to a L block, but they made all the parts to make one, I put one together. wayno

[nismo dr]

I can't see the pics :hmm:

[wayno]

I can't see the pics :hmm:

 

 

:lol:Your stick people are awesome.:lol:

[wizard07]

Datsenmike and Wayno

Thank you for the info. I think most of what we are hearing is the tire noise as they have an adgrisive tread and there is nothing under the flat bed to keep the noise out like a wheelwell. I like the idea of taller gears like the 4.11 and will look aroud for a set. It does not have a 1 ton rearend but came with the after market duelwheel adapters but I am only running a single on the rear. Again THANK YOU for the help.

[wayno]

Datsenmike and Wayno

Thank you for the info. I think most of what we are hearing is the tire noise as they have an adgrisive tread and there is nothing under the flat bed to keep the noise out like a wheelwell. I like the idea of taller gears like the 4.11 and will look aroud for a set. It does not have a 1 ton rearend but came with the after market duelwheel adapters but I am only running a single on the rear. Again THANK YOU for the help.

 

If that is true and you have a normal rearend with a single tire then you can put any number of gear ratios in it, I heard that the rearends that were used with the dually adapters had better bearings in them, but that is what I heard. A normal 1979 datsun rearend is capable of running 488, 460 something, 437, 411, 388, and 370 gears, I even seen a 330 something once, some of these ratios have differant spider gears in them, but they can be changed out for the ones needed. It all comes back to if you are going to use it like a car or a truck, treat it like a car with no hauling or towing and you can probably get away with 388s, if you use it like a truck, leave the 437s in it. wayno