Auto to manual swap, regarding differential

[411tony]

Newbe here. I have a 67 RL411. The guy I bought it from swappped the BW auto transmission for a 4 speed trans from a roadster. It feels very low geared. I recently acquired a 5 speed tranny I plan to swap.

 

Question: Is the gearing in the differential specific for the automatic? I have a donor car with a manual transmission. Would I benefit by swapping the differentials?

 

 

My thinking is that not only would the 5 speed be benificial, but swapping the differential would make a difference.

 

So, back to my question: (if you don't mind), is the differential for the automatic different from the manual?

 

Thanks.

[datzenmike]

Usually, Nissan runs a lower (higher number) rear end in an automatic vs. the same car with a standard. For example a 3.889 automatic vs. a 3.70 for a standard. Usually.

 

Regardless, if it feels low then an over drive transmission will reduce highway RPMs and should improve economy. You get to keep the low speed acceleration and gain highway fuel mileage.

[411tony]

Usually, Nissan runs a lower (higher number) rear end in an automatic vs. the same car with a standard. For example a 3.889 automatic vs. a 3.70 for a standard. Usually.

 

Regardless, if it feels low then an over drive transmission will reduce highway RPMs and should improve economy. You get to keep the low speed acceleration and gain highway fuel mileage.

 

 

 

Thanks K R.

 

I understand now that there is a difference. I can't wrap my noodle around what the numbers mean exaxtly.

 

Here is my experience. In first, I've gone about 30 feet and the need to shift seems premature compaired to must cars I've driven especially my 2000. My tranny isn't turning the spedo cable but top speed feels around 60-65 mph.

 

Does it make sense that if I use the differencial from the manual car, I will have an improved top speed, or the opposite? Thanks.

[411tony]

Well.......

 

For the record, it makes no difference. I switched the diffs and there was no difference. I hope this might help someone else someday.

[Charlie69]

Usually, Nissan runs a lower (higher number) rear end in an automatic vs. the same car with a standard. For example a 3.889 automatic vs. a 3.70 for a standard. Usually.

 

Regardless, if it feels low then an over drive transmission will reduce highway RPMs and should improve economy. You get to keep the low speed acceleration and gain highway fuel mileage.

 

My 1980 720 FSM lists 3.889 for L20B auto & standard trans. I have physically comfirmed this by checking the build plates on the vehicles both run a 3.889 rear gear ratio. This is why I chose to use the 1980 720 gears in my 66 520 L20B automatic.

[Datsun fan]

What RPM you get when driving 60 MPH ?

What size of wheel/tire ?

Does the problem get worse when uphill/downhill ?

Have a load on that thing you drive, 400 KG or so then drive it on a level road without inclines, Is the difference

in power BIG ?

[datzenmike]

My 1980 720 FSM lists 3.889 for L20B auto & standard trans. I have physically comfirmed this by checking the build plates on the vehicles both run a 3.889 rear gear ratio. This is why I chose to use the 1980 720 gears in my 66 520 L20B automatic.

 

The 520 is also lighter than the 720... good move.

[411tony]

What RPM you get when driving 60 MPH ?

What size of wheel/tire ?

Does the problem get worse when uphill/downhill ?

Have a load on that thing you drive, 400 KG or so then drive it on a level road without inclines, Is the difference

in power BIG ?

[411tony]

I'm not sure about the rpm. I don't have a tac. I estimate that it's around 3500 at 65 mph. I'm sure I'm off a little but that should represent some perspective.

 

I'm running 14" wheels instead of the 13" stock. That should actually help.

 

Going up or down hill doesn't really play into it really. It's not underpowered, it just seems low geared. It has plenty of power I have the 1600 instead of the 1300.

 

I'll give an update after I slap that 5 speed in.

 

Thanks Datsun Fan.