Custom 320 gauges; new gear ratio questions

[ol' 320]

Hello:

I am relatively new to Ratsun. Greetings from Visalia, CA This is my first new topic post.

 

I found my 320 online and bought it from a fellow Ratsun member: "Stoffregen Motorsports" who lives up in the Gold Country area in northern California. Anyway, I will start a proper build thread soon, but I wanted to share one project that was part of the purchase agreement: installing all new gauges and calibrating them accurately.

 

When the previous owner bought this truck, the gauge panel had already been bastardized by someone who installed a piece of plastic junk with old gauges that bounced around like a drunken sailor waving at a hottie. Not good.

 

Matt, the seller, is a superb fabricator. This is the guy rich dudes take their 4WDs to in order to refit them with working, high-end suspension that will survive the Rubicon Trail. Not the type of jacked up suspension all the Valley folks around here drive on their dairies ... suspension that work, don't bind and don't break, or throw you upside down and leave you crushed to death because they require an orchard ladder to get into the cab and centers of gravity up in the nosebleed area..

 

I went to Matt's place to check out his old Datsun 320, and ended up spending more time looking at his 1957 Landrover equipped with all Toyota EFi running gear and custom transfer cases and suspension, his 1937 GMC truck project, and his brace of old military Jeeps - including one that seems destined to become a rockcrawler sleeper powered by a Lexus V8, or some such thing.

 

Very cool guy. And who doesn't love a talented dude with a shop bigger than most people's homes and a great four post lift?

 

I found out about Matt while checking out some fabrication threads on the Pirate 4x4 forum, and decided it was worth it to drive 4.5 hours to go look at his customized 320 to see what it was really like.

 

Long story short, we made a deal, with Matt agreeing to install a 720 frame clip (see the "320 balljoint" thread Matt started), with rebuilt front suspension, upgraded front brakes and improved steering, and to fabricate a new instrument panel to fit all new gauges and some other custom details.

 

I knew I would have silly money in a retro-modded 320, but I'd eventually have something unique with style, that is vastly more fun to drive than a stock 45-year old import, and (hopefully) for less than the price of a late model import truck.

 

I drive a lot in remote places in my rural county, and I've owned too many old cars with bouncing speedos, dead or malfunctioning fuel gauges, and temp gauges that are as predictable as the stock market.

 

Matt started by making a new metal gauge panel insert that mimics the dash styling of the glovebox and has blind studs on the back for mounting. I like classic Smiths gauges, the kind that any fan of British sports cars such as the big Healeys, Sunbeams, MGBs had. I also like the gauges Smiths made for Cobras and the GT40s. But I also wanted modern movements so these retro gauges would be as trouble-free and accurate as possible.

 

Custom gauges mean custom wiring, senders, and speedo sensors and/or speedo cables. I wanted calibrated speed readings, even though this is just a 320, not a high speed sports car.

 

Complicating things, Matt had installed a dogleg five speed, so I had to figure out how to adapt a Japanese mechanical speedo drive to a programmable electronic speedo. Here's how we solved this puzzle:

 

Custom Smiths gauges? Call Chuck. Chuck is the dude who answers the phone at ( www.gaugeguys.com ) Gauge Guys. Chuck has 40 years experience selling, rebuilding and retrofitting gauges. I called him to buy an electronic programmable speedo with old 60s styling and chrome bezel, a GT40 8,000 rpm tach which Chuck customized with a chrome bezel that matched the speedo(Matt used to build engines at Rebello Racing, and installed s blueprinted, hooped up A12 in this 320, so I wanted something that registered the higher RPM this engine can hit), and I ordered a Cobra replica Smiths fuel gauge with modern Aircore movement, also with a chrome bezel. I wanted the old style Cobra face, without the modern little fuel pump icon, The Air core movement is particularly nice, because old style fuel gauges tend to read accurately at some point in their range, usually in the empty zone, but stay at full too long and drop quickly when the tank is less than half full. Their accuracy is not linear, but Aircore technology ten to be closer to dead on all the way through the arc of motion. So when an aircore gauge says you are low on gas, you really are;)

 

Anyway, the electronic speedo needs no voltage regulator. The tach looks like a mechanical gauge but is electronic. The Cobra fuel gauge requires a tricky ohm range five bolt sender that cannot be easily puzzled out online. Just call Chuck;)

Oh, Matt appreciates modern technology, but prefers an old school mechanical temp gauge. He also loves old British sports cars, and had installed a Smiths "dual" gauge in the dash years ago when he bought this 320. This gauge has a mechanical temp gauge that is very accurate, as long as you don't destroy the capillary tube installing it. It also has a nice 80 pound oil pressure gauge, but after 40-plus years the dual gauge face was pretty patina'd.... So I bought another one.

 

If you have a calculator and know anything about Smiths gauges prices, you now know I have exceeded the budget for most people's engine overhaul budget just buying gauges. And we don't have the new retro-look old school-looking chrome over brass bezel indicator lights with modern LED innards yet.

 

With Matt's metal skills, the gauge panel now looks awesome, but what about that speedo drive? Since this truck project is sort of like that old Johnny Cash song, "one piece at a time" and incorporates an assortment of parts from different eras and vehicles, the speedo drive calibration was an interesting challenge.

 

I needed to figure out what thread the speedo drive off the old dogleg was, the circumference of the tires, the rearend gearing, and so on. I also need to convert the mechanical drive speedo arrangement off the trans to an electronic pulse that the modern programmable speedo could read. If anyone wants to know the hard way to do this, but to have a speedo reading accurate to two feet within a measured mile, PM me. If found a guy who retired from the NSA to go into the Pro rally racing equipment business. He hooked me up with a way to use technology that the Subaru WRX dudes use for driving their mega-$$$ rally computers off the Subaru mechanical speedo drive.

 

SInce I could already finance the Greek government for a year with what I've invested in this gauge project, I passed on that option. Although the Terra rally computers are really, REALLY trick.

 

The retired spymaster's geek squad leader was amused and took pity on my wanting an accurate speedo in a "primitive 320" (I sent him a picture of the truck after my first conversation, but then he emailed me back pics of MY TRUCK that they somehow sourced without my having given them my name, just using my ISP address). He researched the tread size of the old dogleg Datsun trans, cross-referenced it to the known Subaru drive solution, and then recalculated how the pulse speed sensing arrangement differed on the high-tech Terra computer adapters and the Smiths programmable speedo. Short story, he told me two ways to do this speedo conversion- all without seeing the vehicles or gauges in question and despite any published factory listings for the specifications for pulse sending/reading.

 

I took what the NSA guy's geek said and communicated this to old school Chuck, who built me a solution and promised "if what you're telling me is correct, this will work!"

 

Solution = Datsun Dogleg speedo drive > Custom 18 inch long speedo cable, with Chuck's "Japanese" speedo fitting on one end (good for Datsun or Toyota) and a 5/8 (US standard) speedo fitting on the other>Dakota Digital Speed pulse generator>then wire the electronic leads from pulse generator to Smiths speedo.

Note: Most Smiths speedos are calibrated for 1,000 revolutions per mile. You can use a tire calculator to figure out your particular setup's RPM.

Then, with the trans to speedo connection made, there are two ways to calibrate:

 

1) If you have the older "dipswitch" programmable speedo, take your tire rpm and look up the Smiths instrument conversion dipswitch code on the web. Flip switches on back of speedo accordingly, and you are done! Change rearend gearing or tire size, well, do a recalculation of how many rpms per ile your new setup is, get new dipswitch code and set and forget.

 

2) There is another option. Some of the newer programmable speedos such as Classic Instruments use a "push button, drive a measured mile and release button" calibration approach.

 

Now, some of you Ratsuners may be semi-Luddites like me and need this kind of step by step guide. I had to make several calls and do a bunch of research to get a known solution for converting the dogleg Datsun to a Smiths electronic gauge, from my living room 4.5 hours away from the 320 and the actual gauge. But I have no doubt that this problem would not intimidate the pioneers on here who regularly throw caution to the wind and adapt modern discs to old spindles and retrofit custom ITB-injected computer controlled engines to old primitive analog Datsuns using half-assed tools only McGuyver would approve of.

 

 

I'm going to try to post pics of the gauge panel and speedo sensor. If I can't master this I'll send them to Wayno and beg for his help. IF you check out Matt's "320 balljoint" thread you'll see some pics there as well.

 

--------------

New rear gear questions:

 

I have PM'd several Ratsuners asking for advice on regearing the 320. I'm not a mechanic, so I ask a lot of questions. I found Mike Klotz's pictorial on how to adapt 3:89 gears to a 320 truck rear, and found that very helpful. But for a guy who knows how to change plugs and who's most ambitious project was once changing heads on a 40hp VW, this is still sort of like showing a moron a set of jet airplane blueprints and saying "Good luck with that..."

 

I'd like to get as much advice as possible, then I'll find a smarter friend to install the new gears for me and supply the beer and do what I'm told:)

 

I'm really interested in finding a set of 4:11 gears in a pumpkin that will fit right into the 320 rearend. If I could buy another rearend already fitted with higher gears, new gaskets and bearings as needed, that would be ideal.

Remember, I don't really know what i'm doing. I've never done a brake job.

 

First choice: 4:11 gearset, ready to install in a pumpkin that will fit into a 320 rearend. IF someone has one, with an extra set of 320 side gears, cool!

Second choice: 4:37s, also in a pumpkin ready to go into the 320.

 

I think I would like the economy of the 3:89s, but the 4:11s would likely really make a difference when balancing acceleration with economy. I want to be able to drive this 320 across country to see family, possibly haul home sone antiques, but in reality I'm never going to beat it to death.

 

I appreciate any comments, suggestions from other folks who have actually driven similar trucks with 3:89, 4:11, or 4:37 gearsets and can compare these sets to trucks they have driven with 4;88s

 

I doubt I will ever go much over 80 mph, and will mostly use this truck as a cruiser. It would be nice to be able to cruise at 70 mph and not feel like I'm driving a mechanical buzz bomb. But I still want to be able to rev it up and scoot off the line.

 

Sorry about the length of this post. However, if you too want to spend silly money putting Smiths gauges into your old Datsun, you may need this info. And if you have a really nice 4:11 gearset you would sell, shoot me a PM!

 

Thanks.

[datzenmike]

All I can add is the H-190 4.11s are found in:

 

All 4 or 5 speed '79 620s, not the automatic.

'80 2wd. Cab Chassis option

'80 2wd long bed 5 speeds.

'81-'82 all 2wd automatics

[wayno]

Here you are.

 

 

 

I do not know why they are such small photos, but I am unable to make them bigger. wayno