What is Holding This Speedometer Gear Housing in??

[rivdat620]

OK gentlemen, just put a 791/2 720 5 speed in my 74 620. Everything is perfect except for the speedometer doesn't work! Let me tell you this is the first time I have driven my truck with a 5 speed and it is awesome. So started checking out the speedometer housing and found it looked really weird in fact it doesn't even have the Key holding the assembly in. Please look at the pics and give me your opinion on how the hell it is held in and what is missing. Once I get some feed back I will try and yank it out? It is a junk yard tranny so I am worried it is JB welded in or something. This is how it was in the 720 with a cable hooked up!

 

 

 

 

[AZ_L320]

I found its easiest to leave the cable hooked up and just remove the 10mm bolt that holds the little clamp on. Then just pull on the cable and the whole thing comes out. Once its out, unscrew the cable housing.

 

Its just the large o ring holding it in.

 

[wayno]

See the threaded hole, that has a 10mm bolt with a keeper that holds the speedo drive assembly in.

here is the drive with the parts that hold it in.

[rivdat620]

Thanks for the responses and pics that helps me get an idea of what is in there but if you look at the pictures I posted the whole assemble is in there pretty deep and it doesnt have the 10mm bolt or locking key but it doesnt appear to be falling out. Almost as though it is just being used as a plug! Just trying to figure out whats in there before I go to yanking! If depth is regulated by the assembly then why is this one so deep?

[darrel]

As stated earlier, screw the cable back on, then use a couple of screw drivers or pry bars on the edges of the assembly and lever the housing out. Clean up threads if they get buggered up before putting it back in.

 

As far as the depth it is now, I can't tell why it is that deep. When you get it out you might be able to tell then.

[datzenmike]

It's a pre '80s transmission for sure but 720s were all '80 model year and I've never heard of a 79 1/2 720. Did a wrecking yard tell you this?

 

This is what the lock down bolt should look like.

 

 

Yours looks like it has been machined down, but too far.

 

 

Have to ask.... are there threads in that small hole for the bolt????

 

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[littlejason]

rust?

[datzenmike]

Well if not threaded there is a reason for that but I'm going to wait and see.

 

The plastic cog on the end of the pinion can go in any distance (within reason) because it rides on a worm gear on the output shaft. It does however need the key to hold it at that 12 o'clock position so it does not rotate. Because the cog is on an eccentric, turning it will change the gear lash and could grind the teeth away.

[ggzilla]

The 720 Pickup was manufactured starting in 1979, but was sold as a 1980 model. So some people called the early ones "1979 1/2" but they were not called that by Datsun.

 

A car "model year" in USA starts as soon as Jan 2 of the previous year. See http://en.wikipedia.org/wiki/Model_year#USA

[rivdat620]

It is a model year 1980 but the truck production date was July 79 so it still had the L series and 5 speed that bolted right into my 74. The small hole is threaded. Everything looks normal on the outside except the depth of the assembly and the lack of anything holding it in. It is just interesting that someone obviously modified it and maybe it is just the oring holding it in. Wish I would have noticed before installing the tranny but now I have to risk yanking on it and opening up someones previous can of worms. Were some of the speedo assemblies on different 5 speeds shorter or were they all the same length?

[datzenmike]

The 720 Pickup was manufactured starting in 1979, but was sold as a 1980 model. So some people called the early ones "1979 1/2" but they were not called that by Datsun.

 

A car "model year" in USA starts as soon as Jan 2 of the previous year. See http://en.wikipedia..../Model_year#USA

 

The HL 510 is that way. Some call them '78s but I can't find one. They're just early '79s.

 

 

rivdat620: Drain the tranny first or you'll be taking a bath. Avoid twisting the pinion, lightly 'wiggle' it and pull straight out. You could stop once the key way is exposed and slip a new key and bolt in to secure it.

 

Did you raise one tire off the ground and turn the motor over in gear and see if the pinion end turns?

[rivdat620]

Yup I had it on jack stands and wheels turning no go! Well I guess pulling it out is the next step! It's like a box of chocolates.

[datzenmike]

I aaaaaate suuuum.

 

 

Remember it has to be installed with the slot for the key up. Maybe it was turned when installed (yeah, what are the chances, right?) and the teeth not engaged. Yeah pull it out and see if the cog is ruined. Take a look inside with a flashlight and tell me what you see.

[ggzilla]

The interior drive gear is metal, so not likely to be damaged. You will probably find that the plastic driven gear is trashed. Pull it out and you will see. No big deal.

[datzenmike]

The majority are metal like this on from my '79 zx 5 speed.

 

 

... but I swapped a 720 diesel tail on and just to be safe I kept the ...

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[rivdat620]

Thank you all for the feedback! I will post pics when I get the nerve to yank it out!