hows it going. havent torn down anything yet but curious if there is a speedo conversion kit out there, or do i need to send out my tail housing? Im running a ford 9 inch with a 3.50 gear. will the t56 ratio be ok with that set up as far as 1st and 6th being too short. as far as electrical, is the pigtail for the brake switch the same for the auto? same with reverse lights? also any little tricks or tips would be much appreciated. esp with the misc stuff, bolts, plugs. i have a 87 iroc with a built L31 and long tubes. coming out is built 700r4 with tci flywheel 2100 stall converter, b&m shifter and b&m external cooler with braided lines and earls fittings with maybe 8000 miles will now be for sale


thanks for any help

 

https://www.thirdgen.org/forums/tran...ap-thread.html

Feel free to ask specific questions, but that is going to answer a lot of them.

 

3.50 isn't really enough gear.

I have the weenie stock gear in my car (3.73); 1st is too high, and 6th is still almost useless. I wish I had ALOT more gear.

I know of no cable speedo gear conversion that's currently available, except possibly the one that's basically a little motor that spins a programmable # of ° for each pulse it receives from a VSS. Sorry, can't recall the brand or anything. Not sure that's even still available. It was $$$$$ in any case.

 

Yippeee!!

I put my cattle prod to the correct brain cell:

It's the Abbott Cable-X. You can probably still get it.

 

Dakota digital also sells an electronic to cable conversion box, price is ridiculous at 300 USD though.

 

I have a 3.45 in my car with the .5 6th and it's great. I can put it in 6th at about 40-45 around town.

Not really, it is a very involved product. I think it is appropriately priced.

 

I have 3.27 in my car now and moving to 3.50 ford this winter. I wanted to bring the RPM up 250 or so. You should be fine.

 

https://www.speedhut.com/ecommerce/p...peed-Converter similar to the dakota digital, I've never used either so I can't really comment to the quality.

The price comes into play on the quality of the driver motor, it must spin hours on end, somewhat quietly, without over heating or dragging etc.

I've also thought you could probably make a drive gear that slips on to the spline of the driveshaft, then use a secondary gear to get the right ratio and drive the speed-o cable off this vs a full retro fit.

I've seen a few tail house mod companies and t56 aftermarket tail housings that have the mechanical option added but I don't know enough to recommend one.

Your other (and probably cheaper) option is to get a later model cluster with a electronic speedometer.

 

I forgot about that option. I had someone mod my LS T56 tail housing to also have a mechanical drive. I never wound u using it though, and I probably never will now. Would consider trading and some cash for an unmodded one

 

Jags That Run used to do that mod. They discontinued it about 10 - 15 yrs ago.

A guy that used to post on here as Alloy used to do it. Haven't seen him around here for many moons now. I have one of his: a bit crude in a way, but quite accurate and works perfectly.

Don't know of anybody else that does it, although that is NOT the same as saying "there's nobody else that does".

Problem (well, … it's not really a "problem", … it's more of, ... an "opportunity for a solution") is, the existing VSS port in the ext hsg is directly in line with the mainshaft, which is fine for a VSS; but a gear drive needs to be offset from that. By approximately the radius of the drive gear on the mainshaft, plus the radius of the driven gear attached to the cable. Works out to moving the hole in the ext hsg by around 1½". Don't know the exact # but it's in that neighborhood. Then, the problem with that is, it puts the new hole location in a place in the casting that is ABSOLUTELY NOT prepared as the site of a hole AT ALL WHATSOEVER. Which is probably why any attempt to fake a hole in at that spot, is bound to be a bit … crude … no matter what. Nonetheless, Alloy's work is leak-free and allows the cable setup to function correctly.

He used to charge just about $300 if memory serves, acoupla decades ago. JTR was about the same IIRC. Can't say the $$$$ exactly because I got mine used, from somebody that for some reason needed a stock ext hsg to replace his modded one; I did an even trade with him for it. So I never had to come off the hip in person. I suspect that it really can't be done for much less, and that both were a pretty friendly price and not making much money off of it. One look at what has to be done and you'll see why I say that.

The box that Aviator posted is in the same $$$$ neighborhood as the one I did, or the Dakota Digital. I'm thinking... it takes about that much to put together what it takes to accomplish that functionality. I don't care whose name is on the outside, it just kinda IS what it IS.

You will HATE HATE HATE HATE HATE HATE 3.50 gears with that T-56, if it has the 2.65 (or so) 1st and .5 6th. It's just absolutely in no way enough gear. Put 4.11s in it at the bare minimum before it's too late and you already have it in the car and you discover what a mismatch it is and it's harder to fix and you have to do extra work to undo how you shot yourself in your shorts to show yourself what a good idea it was to discharge a pistol out of your front pants pocket aimed down and toward the center. I've been dealing with people who have close-ratio stick-shift transmissions like that since the early 70s, and it's been the same since then... Chevelle SS396s, Torino GTs, YOU NAME IT, that came with 3.73s from the factory, it was NOT enough gear. You're not gonna rewrite the laws of physics, trust me. (yes I am a physicist and mathematician) You'll still burn up your clutch at stop lights and find 6th to be useless below 80 mph or so. Some things NEVER change.

 

I am curious if those "HEADS UP DISPLAYS" the units that project your dash on the windshield would work for the speedo. They have G.P.S. that tells you everything; Does anyone have experience with this? cause I would like to know how fast im going. Unit plugs into OBDII port

 

Probably wonderful.

These cars don't have OBD2 though. So, not applicable.

 

Old thread. Just to add for future reference.

All this info is for a 1991, 305TPI, LB9, MT, 3.42 rear gear, 730 ECM (SD system)

I have a Ford 9" with a Motive 3.89. T56 is an aftermarket (#1386-000-011) made back than to fit OEM bellhousing and shifter location. It's basically a T56 with a T5 tail housing and bellhousing adapter plate. So all I had to do was use the same OEM VSS but change the 19 teeth driven gear for a 21 teeth. Knowing what I know now, all I'd had to do was modify the tune (VSS - Pulse/Min (0x15)) with no need for modified driven gear. Speedometer on 91s are electronically controlled by ECM.

Here's a pretty good estimate of your MPH vs RPM with this simple calculator:

MPH = Tire Radius/168 * RPM/Rear Gear Ratio/Transmission Ratio

RPM = 168*Rear Gear Ratio*Transmission Ratio * MPH/Tire Radius

Example:
Tire Radius = Tire Diameter/2 = 25.7/2 = 12.85 (that would be for a standard 245 50ZR16)
RPM = 5500
Rear Gear Ratio = 3.89
Transmission Ratio = 2.95
MPH = 12.85/168*5500/3.89/2.95 = 36.7mph

Here's a chart of mine at 5500 rpm (you can plug any shift point you want)
1st (2.95) = 36.7
2nd (1.94) = 55.7
3rd (1.34) = 80.7
4th (1.00) = 108.2
5th (0.80) = 147.5
6th (0.62) = 190.2 (i doubt I can reach that without killing myself lol!!!)

So let's assume I cruise on the highway, with my set-up, at 65mph, my engine RPM is 2050 rpm. This estimate is pretty close to what I observe all the time. Now If I switch to a 4.10 gear, that would increase my RPM to 2160, still tolerable.

Let's assume your T56 has a 0.50 ratio on the 6th gear with a 3.50 gear and OEM tire size. You would be at 1487 rpm!!!! With a 0.62 ratio, that gives you 1844 rpm.

Now while we're at it. The drive shaft RPM is calculated as follow:

Drive Shaft RPM = ((MPH/60*63360) / (Tire Radius*3.14159))*Rear Gear Ratio

So at 160MPH, with my set-up, Drive Shaft RPM = ((160/60*63360) / (25.7*3.14159))*3.89 = 8140 RPM
With a 4.10 gear, I get 8579 RPM
That's a good estimate to compare to your drive shaft critical speed and also if high speed balancing is used.

Hope this helps

Cheers