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Speedometer 5 speed tranny swap


620owner

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I pulled the output gears tranny gears on both boxes. My original 4 - speed has a Red 20 tooth and the 5- speed has the blue 18 tooth.

I believe Mike you say to just cut a slot opposite (180) and use the original 4-speed Red tooth.

When I look at them this would put the gear offset to the other side, does this than make up for the difference in gear size and allow the output gear mesh with the worm gear OK ?

 

Others say due to the difference in gear sizes to replace the whole unit. 

 

One other question, I thought all 620 trucks came with 4.375 rear ends. The Red gear would indicate that my 620 has a 4.11 rear end or it would have ben a purple gear … right ?

 

Now the pictures of my output gears. (Had to heat the tranny cases a little to pop them out)

 

Lhpx41j.jpg

 

 

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The 71B 4 speed was used from '74 through '79

The 71B 5 speed was used from '77 through '79. Earlier 620s used a different transmission so I'll leave them out of the discussion. Also automatics as the gears do not fit the standards.

 

In these years the 4.375 differential was used except '79 when it was a special 'Camper' option and a 4.11 was used.

 

4.375 uses a 20 tooth Red plastic gear 

4.11 uses a 19 tooth White plastic tooth gear. The White may be slightly tinted but it's really white.

 

These are the only two gears used on the 620. Blue is 18 tooth and probably the 5 speed is from a car with a lower differential ratio or larger diameter tire or both OR from an '80 720 which used them with 3.889 differentials..

 

You don't say what the 5 speed is out of or what year it is. The bolt that holds the sleeve into the transmission.... is it at the top like the 4 speed or down below at 6 o'clock????

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Mike I came across a 1980 720 king cab L20B automatic that had the 411 gears and the red gear.

 

Could the trans with the red gear from the OP actually be a 1980 720 4 speed with a 411 gear ratio?

 

Just the other day I came across a 1985 720 Z24 5 speed regular cab short bed that according to the tag on the passenger fender has a 370 in it I am going back on Sunday to pull the speedo pinon to see what color the gear is.

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I'm dealing with this too right now so hopefully I can join this discussion....

 

I came across this info which says the red is for 4.11, not 4.37 gears.....

 

Screenshot_20180518-065851.png

 

So what is true?

 

I pulled 3 Speedo gear assemblies out and they were all the same.... I have a 521 and 620 4spd... 63 series 26 1/2 long...

One had a 16 other 17....

 

And my 71b 5spd, 80 720. 26 1/2 long Also had the same black 17 tooth....

 

All 3 look like this...

 

20180518_215223.jpg

Other 2 have black gears....

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I pulled the output gears tranny gears on both boxes. My original 4 - speed has a Red 20 tooth and the 5- speed has the blue 18 tooth.

I believe Mike you say to just cut a slot opposite (180) and use the original 4-speed Red tooth.

When I look at them this would put the gear offset to the other side, does this than make up for the difference in gear size and allow the output gear mesh with the worm gear OK ?

 

Others say due to the difference in gear sizes to replace the whole unit.

 

One other question, I thought all 620 trucks came with 4.375 rear ends. The Red gear would indicate that my 620 has a 4.11 rear end or it would have ben a purple gear … right ?

 

Now the pictures of my output gears. (Had to heat the tranny cases a little to pop them out)

 

Lhpx41j.jpg

So what are the 2 transmissions?

Those 2 assemblies look to be the same length?

How long are those Speedo assemblies?

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Well the more I look up the more confused I get....

 

This here!!!

 

 

It's very confusing. That list may be for a specific vehicle like a Z car. Optional aluminum mags and tire diameter also affects the speedometer so what works on a truck with 3.889 may not be just right for a car with 3.889. RED is definitely for the 620 with 4.375 differential.

 

 

I tried to use an automatic pinion assy. once with the correct color gear and it wouldn't fit at all. Part numbers were very different also.

 

In '80 the mounting bolt that secures the sleeve moved from top to bottom or under the sleeve. In some cases you can cut a new key way to flip the sleeve to match. My current '79 zx 5 speed has this but with a (now) 4.11 it really needs an Orange 22 tooth from a JDM Cedric to slow it down. I have a 20 tooth. 21 is purple. I tried making a 22 tooth from two cut up gears and some JB weld. I got it close but it was a tight fit and the speedometer worked for two car lengths and the gear was crushed.

 

1nuRNNU.jpg

 

The thing is, the gear increases in diameter with added teeth so it's impossible for a 21 to fit where an 16 was although it may fit where a 20 was. The gear teeth are deep enough that you may be able to use one size larger or smaller without crushing the gear. The sleeves offset the spindle with the gear on it so that the plastic teeth are not crushed against the worm gear on the transmission main shaft. The gear may even be too far from the worm gear and not be turned at all.  

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Mike,

The original 4 speed tranny is out of my 1977 620 (Has the RED gear) - Original tranny 39,000 miles on it. (Bolt hole at 12 o'clock) F4W71B

 

The 5 speed unknown doner. I checked the gearing it's:

1st -  3.062

2nd - 1.858

3rd -  1.308

4th -  1.000

5th -  0.745

Single ear, bolt hole at 6 o'clock

I believe it's an FS5W71B (Non-Turbo z) 1981-83  ?? (BLUE gear)

 

They both measure 3 1/16 inches long.

The blue gear is 5/8 diameter.

The red gear 1 inch diameter.

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Hope I can just do the notch and 180 swap...

Just found one listed. (Crazy Price)

 

HSsgCnS.jpg

 

They also listed these:

 

Applicable models: Datsun 240z, 260z, 280z, 280zx (1970-1983). Also, Datsun 510 (1968-1973). Datsun 200SX (from 07/81-07/83)

Gear Ratios
16 Teeth Gear: 3.36 Ratio
17 Teeth Gear: 3.54 Ratio
18 Teeth Gear: 3.70 Ratio
19 Teeth Gear: 3.90 Ratio

20 Teeth Gear: 4:11 Ratio

Datsun Models & Corresponding Diff Ratios (from factory)

240Z 70-73 MT (3.36) (R180)
240Z 70-73 MT 5spd. (3.90) (R180) - non US
240Z 71-73 Auto (3.54) (R180)

260Z 74 MT (3.36) (R180)
260Z 74 Auto (3.54) (R180)

280Z 75-76 (3.54) (R200)
280Z 77-78 MT (3.54) (R200)
280Z 77-78 Auto (3.54) (R180)

280ZX 79 MT,4 Spd,2 Seater (3.36) (R180)
280ZX 79 MT,5 Spd,2 Seater (3.36) (R180)
280ZX 79 All With Automatic(3.54) (R180)
280ZX 79 MT,4 Spd,4 Seater (3.36) (R200)
280ZX 79 MT,5 Spd,4 Seater (3.70) (R200)
280ZX-GL 79 (3.70) (R200)
280ZX 80 MT,2 Seater (3.54) (R180)
280ZX 80 Automatic 2/4Seat (3.54) (R180)
280ZX 80 MT,4 Seater (3.90) (R200)
280ZX-GL 80 (3.90) (R200)
280ZX 81-83 Automatic all (3.54) (R180)
280ZX 81-83 Turbo - all (3.54) (R200)
280ZX 81-83 MT (3.90) (R200)

Datsun 510: 1968 (3.70) (R160)
Datsun 510: 1969-1973 (3.90) (R160)

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Six o'clock is an '80 or newer transmission so '80-'83  zx or '80 810 and '81-'84 Maxima IF it only has the switch for the reverse lights. If there are top gear or neutral switches then from a 720 truck.

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