RPM at highway speeds in 4th gear?

[Zs-ondabrain]

I must have a 3:70 in the early 72' cause I'm right there with ZForce. (about 4000 at 80 mph) and maybe 3200?? at 60 ish

[Zs-ondabrain]

^ thanks! On the same note, is filling the diff as simple as pulling the upper plug and using a manual pump to fill it until the fluid starts to dribble out the hole like with most Japanese gearboxes?

Yes, it's that simple

[Arne]

^ thanks! On the same note, is filling the diff as simple as pulling the upper plug and using a manual pump to fill it until the fluid starts to dribble out the hole like with most Japanese gearboxes?

Yes, it's that simple

Well, yes and no. Pumping it in is that simple. But nowhere in the Nissan manuals does it state that you pump it in until it starts to dribble out. The factory always states that "the proper (measured) amount of lube should be added".

It has been my experience with the early-style (Type A) transmission in the '70-71 240Z that if you fill until it dribbles out, you will have overfilled it by 1/4 to 1/2 quart or liter. If you do this, you risk having the excess leak past the front input seal. I wonder if this might be true for the differential as well. I would strongly recommend not overfilling it, but to pump in the specified amount only.

Edited June 1, 2010 by Arne

[beandip]

I had a R-200 with 3.90s and in forth I was tacking 3K+ on the Freeway. The car performed super with all kinds of low end. I changed back to 3.54s and now the gearing is right on . At least for me. I am right at 2100 at indicated 60 mph. I now dropped in a 5 speed and it is even much better. Driveabilithy is much better and I am getting 30 MPG to boot. And this is with a moderate cam and a 280 engine .

[Bonzi Lon]

^ thanks! On the same note, is filling the diff as simple as pulling the upper plug and using a manual pump to fill it until the fluid starts to dribble out the hole like with most Japanese gearboxes?

A little cleaner method of putting oil in: Remove spare tire well plug above diff, snake a 2 ft section of garden hose through the hole and down into the diff fill hole. Proper amount can be put in without any drips on the floor. This method can be used on the tranny also but the shift boot must be removed.

Bonzi Lon

[sblake01]

With regards to Andy's original question, this transmission calculator might be of some help:

http://webspace.webring.com/people/cz/z_design_studio/

[Gary in NJ]

205/60R14, probably an inch or two shorter than stock tires.

The stock tire (175/78-14) has an overall height of 24.75", or 6.48 ft/rev, or 815 rev/mile. Your tires have an overall height of 23.69", or 6.20 ft/rev, or 852 rev/mile. So your speedometer will indicate a higher speed by 4.5% (i.e 62.7mph indicated will be 60 mph).

I seem to think that my '71 showed 3100 rpm @ 60mph. My '72 shows 2600 rpm @ 60.

[BTF/PTM]

I love this idea. The center console is out of my car anyway, so getting to the transmission plug won't be difficult.

A little cleaner method of putting oil in: Remove spare tire well plug above diff, snake a 2 ft section of garden hose through the hole and down into the diff fill hole. Proper amount can be put in without any drips on the floor. This method can be used on the tranny also but the shift boot must be removed.

Bonzi Lon

[Gary in NJ]

I checked my speed-o last night. At 60 mph (indicated) I'm showing 2740 rpm. That tells me I have a 3.36 gear ratio in my differential (which makes sense because that's what came on the '72's). I'm not running an OEM tire size. So here's how I calculate actual rpm at 60 mph:

oem - 175/78-14: 815 rev/mile (5280/(24.75 x 3.14/12)) x 3.36 = 2740 rpm

now - 225/50-15: 846 rev/mile (5280/(23.86 x 3.14/12)) x 3.36 = 2840 rpm

[deadflo]

I have a 3.90 rear end, running 215-60-14's.

Still have the original A type four speed.

I run just under 4000 RPM at 70 MPH.

[sawdust2005]

My Speedo is off by about 12%. To keep tabs on how fast I'm going I just use my GPS.

[Gary in NJ]

I have a 3.90 rear end, running 215-60-14's.

Still have the original A type four speed.

I run just under 4000 RPM at 70 MPH.

Does 3757 sound about right?