MG Sports Cars

I have two questions.

(1) In Volume VIII, 1 Jan 2000 Kurt Schley wrote an article “Converting the MGB Tachometer to V-8 Calibration,” where he said “the 1972 RVI 1439/00 Tachometer already has a built-in pot that can adjust the rpm range quite a bit. It is possible that there is enough adjustment in the pot that it can he calibrated for V-8 use without modifications. I [he] did not have access to a '72 car to attempt the adjustment, so any readers who have a '72 MGB give it a try.” I have a 72 with this tach and hope this might work. Has anyone tried this yet? As I have nothing to lose I was planning to try it and assume the pot adjustment is the small white screw in the hole. Does anybody have any info or advice? Also the other gauges don’t have the spade connectors marked; does it matter which blade is the 12 volt power and which goes to the sending unit?

(2) I also plan to use the speedometer and need info on a cable and drive gear that will work between it and a Ford T5 5speed.


Any assistance would be greatly appreciated.



Edited 2 time(s). Last edit at 08/26/2010 06:35PM by pspeaks.

Paul,
D&D has the correct speedo cable to mate a Ford T5 to a stock MGB speedo...cost is $65. Depending on your tire size and RA ratio the driven gear might have to change (but that is 10 second job).

From D&D's website:

$65.00 616327-F Speedometer Cable – To connect B/W T-5 Ford transmission to M.G. speedometer, includes speedo gear. Must specify year of vehicle.

EDIT: You need to determine which drive gear (6-black,7-yellow or 8-green teeth) you have in the xsmn and based on tire size and RA ratio, you can specify which driven gear you need when ordering from D&D.

Joel Voelkers has this nifty calculator for determining the driven gear tooth count.
[www.roverv8.com]



Edited 2 time(s). Last edit at 08/26/2010 10:50PM by ex-tyke.

Thanks Graham, I really didn't want to use aftermarket gauges because I like the look of Smiths and I already have a full set. I have an electronic set in my roadster, changed the speedometer twice and still can't get it to work. Thanks so much for the info, "P"

Paul, I'm not sure about adjusting that resistor, seems I tried that and I think it does not have enough adjustment, but let us know if you get it to work. I use an add-on board in mine that replaces the stock drivers for the movement, and that is adjustable for a wider range. So there are several options on the tach.

JB

Thanks Jim, when it comes to electronic work I'm an idiot but I'm gonna try like I knew what I was doing and if it doesn't work I'll blame it on my son if he isn't home at the time. Do you have to make the add-on board or can you buy it and if you have to make it, is it diffacult? I also have a 1971 tach that I can use for a training aid before messing with my good one.

"P"

It's a ready made board sold by Theo Smit, a Tiger owner but I think the board has gotten rather pricey. I'd try the add on resistor first.

JB

Thanks Jim, as an airplane guy I think I'll ask one of our electronic techs to do it for me. I also have no clue which connection is which on the tach, therefor, where the associated wires go. I assume (A) on the attached picture is a case ground but I don't know about (B), (C), and (D).

It has a 302 in it so the origional wiring diagram isn't helping me. I know one goes to the coil and one goes to the ignition but I don't know which is witch or if the blade is used at all (instrument power, again I asume).

PS Update: Well, I guess my little tach adventure has come to an end. I finally got the nerve to open the 72’ tack I thought was good and found the white wire that loops through the coil to be fried to a crisp. I also opened the 71’ tach and found one of the tiny red wires from the coil broken at the board. Does anybody sell a V8 Smiths tach or can these be repaired? Frankly I’m a little disgusted with the whole thing and though I’d rather not, I’m about to go with an electronic Shark set. Wouldn't look as good, but would be much easier and less costly.

Don't guess it matters which wire goes where now, does it!





Edited 4 time(s). Last edit at 08/29/2010 04:49PM by pspeaks.

Hello Paul, Found this old post about MG tach. I'm a Sunbeam owner and trying to help a fellow Sunbeamer by fixing his tach which uses the identical circuit found in this MG tach. Do you still have this tach? Did you fix it, get it fixed? I'm an electronic engineer and could probably fix the tach I'm working on but I need to know more about the main device inside it - the transistor or Unijunctiion or whatever is that MT59/A . Once I figure out the internal circuit I could probably be a resource for MG owners on these.

Tom Hayden
Lakewood, OH

Hi Tom,

Another new source of help and info would be great. I'll be struggling with the exact problem in a year or so. Any new info would be greatly appreciated.

NCtim

Hi Tim,

If your tach looks like this one on the rear, with the two "bullet" connectors then you willl be struggling along with me. This is from a 69-72 or so MG. But if yours is a 64-69 or so, and has a metal U-clip on the rear that the white wire loops though, then I have those nailed down and know them well.

See this article I wrote for our Sunbeam group:

[www.sunbeamalpine.org]

Tom

You can buy the tach at several sources including
[www.nisonger.com]
www.holden.co.uk

Paul, I modified the tach in my 73 Midget to work with my V6 using Kurts directions but a diffrerent value pot. Worked fine and is pretty accurate compared with a modern electronic tach I used to calibrate with.
As for the speedometer, I used a MG cable and a modified MGB angle drive to make the connection, but it hasn't been very reliable, mostly because of the bends in the cable itsefl with cause early breakage. The angle drive has held up pretty well through all this though. Just filed the stock cable spur that goes into the speedo gear to fit the T5 gear and used the T5 threaded ring on the angle drive. I had to use the angle drive because of clearance problems with the tunnel on my car, but if you have room for just a cable then I'd think most any competent speedometer shop could make up a cable to fit both ends, Just take them the T5 fitting and a Smiths speedometer and the length you need and they should be able to do the rest.

I finally gave up and went with a set of aftermarket mechanical gauges. Not much in the interior is original MG anyway, including the fiberglass dash which for the most part looks like a MG dash but you guys would notice the difference; I don’t guess it hurt the appearance all that much. I decided to go with a mechanical speedometer because of all the problems we had with the electronics on T-Buckets. At present I’m modifying the forward console so I can use a modern square shaped satellite radio with Bluetooth phone. Pictures as soon as I get it presentable.

Paul, If you still have the old tach would you be willing to send it to me so I could disect it and maybe use the knowledge (and parts?) gained to help others?

Tom

Another approach to keeping stock gauges is to use the guts of a modern tach inside the original case. I really wanted to keep all the original gauges in my Healey, but it came with a mechanical tach that I couldn't hook up to my SBF. I ended up using a Stewart-Warner tach inside the old gauge. You can see how i did it on my Projects page: [forum.britishv8.org]

Rick

Tom, I think I still have some guages here, may take me a couple of days but PM me a mailing address and I'll round up what I have. I can't sware to there quality or if they're complete internaly, but hope they help.

Thats a great idea Rick, I didn't think of that but probably wouldn't have had the skill to do it anyway.

Paul