R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Engine, Transmission and related drivetrain.
shaddai
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R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by shaddai » 10 Jan 2021 15:20

On the first of the year I finally got the dime up on the highway... so far it's just been an in town car. It did fine for the most part... just the revs were really high (no tach yet... I have a SpeedHut one on order finally) and it vibrated quite a bit. The gearbox also makes some noise, and I just checked it's still full of gear oil.

BUT... something didn't seem right... driving in town I can put it in fourth gear around 30 MPH and it's fine. Fifth is not far away from fourth (280zx wide ratio box). Finally, this weekend, my son does some google fu and we notice that perhaps this is an R180 diff, not a R160. Obviously... we need to take the thing apart(ish?) and find what the ratio is, but this could explain why the gearing seems so off.

Pics for reference... I still have little knowledge of datsuns or mechanical work in general (I'm new to wrenching).

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And pic of the highway drive destination for giggles

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datzenmike
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by datzenmike » 10 Jan 2021 15:56

Most likely your imagination without a tach. I don't mean that in a bad way. You said you just got it on the road and it does have a 3.592 first gear now rather than the 3.382 of the 510 4 speed. 30 mph isn't that low on such a light 2,300 pound car even with an L16. Assuming you have a near stock tire diameter of 22.75"...

a 3.70 diff will rev 1,650 in 4th .
a 3.889 is 1,725
a 4.11 IS 1,825

Having changed the transmission did you also check and change the speedometer gear to the same number of teeth as what was in the original 4 speed? Usually this is a black 17 tooth. Depending on the Z that it came out of and the optional rims and tires it could be as high as a 19 tooth or reading about 4 MPH lower speed so when reading 30 you are closer to 34 MPH.

Re-computing for actual speed of 34 MPH a 3.70 differential will rev 1,860. Just saying there may be an answer to this.

Do you feel like the speedometer is out 4 MPH? Can you run it through one of those school zone radars?
Last edited by datzenmike on 10 Jan 2021 16:05, edited 1 time in total.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

shaddai
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by shaddai » 10 Jan 2021 15:59

I changed the 17 tooth to a 22 tooth and it's spot on. GPS, those school radar zones, etc all line up now. It was insanely high before (like 25% high).

datzenmike
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by datzenmike » 10 Jan 2021 16:19

17 vs. 22 is 29.5%!!! which is around 9 MPH at 30. I got mine down to below 4 MPH with a 20 tooth. Then acquired a 22 tooth and bingo!

I have a 710 with the same transmission but 4.11 differential. I too put a 22 tooth in and now within 1% at 30 so that's 0.3MPH at 100.

I have 195/60 14 tires which would be 23.25" diameter
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

shaddai
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by shaddai » 10 Jan 2021 16:41

So obviously I need to figure out what the diff ratio is... but is this an r180? What's my best upgrade path? LSD?

datzenmike
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by datzenmike » 10 Jan 2021 17:20

Need RPM and speed and then the differential ratio can be worked out.


I can't find any R-180 which came with an LSD option

The 280z, 280zx and 910 Maxima had terrible 3.545 and 3.364 ratios R-180

The 810 had 3.70 R-180

The S12 CA20 has a 4.11 R-180

4wd truck front R-180s came with 3.889, 4.11, 4.375 and 4.625 No LSDs.


That said, LSDs are over rated unless you're able to spin the tires through 3rd. A car is more recoverable in snow, mud, or wet with an open differential.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

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James
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by James » 10 Jan 2021 17:51

Couldn't one jack the car and count driveshaft revolutions and compare with tire rotations to determine the gear ratio of the diff?

I do agree with Mike though - if you haven't driven a datsun (or other old car) the highway revs are a totally different animal than newer cars which keep everything at 2k or under. Figure out what you have first. The higher gear (numerically) will make the car much more responsive and typically fun to drive around town. With the overdrive you can compensate for that a bit. Curious to see what you come up with.
Finished is better than perfect......

datzenmike
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by datzenmike » 10 Jan 2021 18:29

On an open differential while in neutral, raise one wheel and turn it twice around counting the drive shaft turns. I doubt you will be able to tell the difference between 3.7 and 3.9 turns. Just over 4 would obviously be 4.11

Four wheel turns would be 7.4 for a 3.70 and 7.8 for a 3.90... that you could probably distinguish.

If the wheel won't turn you may have an LSD so only raise the other wheel. Only one turn of the wheel is needed to get the ratio.

I totally am in love with the 4.11 in my 710 goon. Really wakes it up.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

shaddai
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by shaddai » 10 Jan 2021 20:06

I'll try the "jack the car up and count turns" method soon. I'd love to get it to be geared better on the highway - one day I'd love to take this on a trip of sorts... but it seems unthinkably buzzy and high revved at the moment.

shaddai
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by shaddai » 10 Jan 2021 20:13

Also... unrelated... but here's the camshaft. It's on the 2 position (engine is not at TDC, for the record). From reading the manuals and various references online, it seems like it's in a good spot, although I probably need to either replace the chain or adjust the guide(s).

Image

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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by datzenmike » 10 Jan 2021 20:53

I don't see why. Can't tell it' s on the number 2 hole until you do set TDC and then check.

To check that the cam is properly set for timing with or without chain wear do the following...

Set accurately to TDC on the #1 cylinder compression stroke using the ignition timing pointer and the 0 (zero) mark on the crank pulley. It's important that you turn the engine clockwise up to, and stop on the mark. This may take many tries as it easily overshoots. If you, (when you) overshoot, back the pulley up at least 1/4 turn and try again. This will keep the tension side tight and the reading most accurate.

Once accurately set, look down through the hole on the cam sprocket (a flash light is handy for this) and you will see a Vee or U shaped notch on it's back side and tight above it on the cam retainer is a small horizontal etch mark.

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(you can just make out the etch mark directly below the top bolt. It's quite small)

As shown the notch must be below or just slightly to the right of the etched mark. If the notch is over to the left of the mark the sprocket should be removed* and advance to the next number. This one as shown is on the #1 hole. Moving it one hole to number 2 will retard the cam about 4 degrees or roughly the width of the etch mark. This is perfectly timed and is an L16 or L18 which came from the factory on the #1 hole. The L20B was sent out on the #2 hole.

All that matters is the relation of the notch being to the right of the etch mark, or just below it. Doesn't matter what hole you end up on. Everything else is secondary. This is why setting the TDC accurately is so important.

There are three holes intended for making the cam timing adjustment. Never ever seen the #3 used. The sprockets and chains might wear but they don't stretch. People change them when they replace the guides so they never get to wear out.


* For pity's sake do NOT loosen or attempt to remove the cam sprocket without learning how to block the timing chain tensioner from falling out!!! Don't be that guy.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

shaddai
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by shaddai » 10 Jan 2021 21:57

Sorry that's a horrid pic of mine. I aligned the crank pulley to zero and the notch was perfectly to the right at the crankshaft. I made a wooden block to secure the chain but didn't end up using it.

demo243
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by demo243 » 11 Jan 2021 11:51

I skimmed through quick, so didnt see if it was confirmed that you have an r180 or not... Judging by the distance between the fill plug and the bolt to the right of it, along with the half shafts I think you might have a r180 from a z. Those halfshafts are different then all the spare 510 ones I have.

Get your tach installed and report back - Its OK to rev the L engines! I ran mine with a 4.44 rear end on the highway. Yea the revs were higher - 3500-4000 at 75 if I remember right, but its no problem. Still got decent milage for a hopped up L with dual sidedrafts. Its more fun when the car is up in the power band anyway!

Assuming this is a Z car r180 the quickest ratio it could be would be a 3.9 which is the same as stock 510 (I believe). Anything else would actually drop the revs and cause the car to feel sluggish. http://www.zhome.com/ZCMnL/tech/GearRatios.html

Just get some ear plugs and REV it! hahaha
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iceman510
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by iceman510 » 11 Jan 2021 13:40

demo243 wrote:
11 Jan 2021 11:51
Those halfshafts are different then all the spare 510 ones I have.
I agree those halfshafts appear to be the Z versions that had the stub shaft as one with the inner U joint coupling.

Were those ever used with R160 diffs? I vaguely remember seeing some from a 610 before.

shaddai
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Re: R180 diff? Something seemed off and the car's geared really short... best avenue to fix?

Post by shaddai » 11 Jan 2021 13:55

Previous owner was an... interesting... fellow. He fetched quite a few parts from other junkyard datsuns... L18 (from a truck?), 280zx five speed, and now the rear diff... so bizarre. This car has been fun to work on (for many reasons!). Who knows what else I haven't found yet that's different.

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