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Retaining original MGB Speedo and Tach

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Q-Ship MGB Silver Member Robert Wilson
NELSON, BC, Canada   CAN
1973 Norton Commando
1977 MG MGB "The Money Sink"
May have been covered before, but....

I wanted to retain the original look to my dash, and after some internet sleuthing, found a device that takes the VSS signal from the GM T-5 gearbox and uses that to vary the RPM of the box' internal electric motor to drive a short speedo cable. It is the "Speedbox", offered by the Speedhut gauges people in Utah. Although their website says the cable connection is only for American cars, they advised me that any speedometer shop could make an adapter and their warranty would still be valid. But guess what? The supplied short cable from their box threaded smoothly on to the cable input on my 1977 MGB's Smiths unit and spinning the inner drive cable by hand causes the speedometer to function OK. The Speedbox also uses a GPS antenna as backup so you have suspenders and a belt for car speed determination. My car is in the garage with some other projects to do before Spring so haven't tried it on the road yet, or calibrated it.

Tachometer - I bought a Dakota Digital SGI-8E tach adapter from Summit Racing. It's not much bigger than a matchbox. This rig can be programmed to take any ignition signal from 1 to 16 cylinders and convert it to any output signal between 1 and 16. So it should be able to translate the tach signal from the 3.4V6 coil pack and drive the original 4-cyl tach.

Photo shows the Speedbox and cable connected to my B's speedometer.

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DSC01218.JPG

BMC Avatar
BMC Gold Member Brian Mc Cullough
Minneapolis, Minnesota, USA   USA
Nice. I don't know if I am continuing rumors or if there is truth to this but supposedly, Speedbox is manufactured by Classic Innovations:
https://www.classicautoinnovations.com/product-page/classic-speed-early-adopter-unit
We will be using a couple of these on varied projects currently in the shop.

The tach drive- please let us know if it's smooth. Every one of these I've tried has failed and the tachometer is anything but smooth or correct. It may be the tachs are all worn out electrically, or the units are not giving the signal required. Either way, I think it's best to have the tachometer rebuilt with new internals, otherwise it's quite opposite of the KISS principle as too many things have an opportunity to fail.

-BMC.


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ValveCoverGasket Avatar
Portland, OR, USA   USA
thats a pretty slick speedo setup - for the tach it does seem like you could have it rebuilt and skip the intermediate box.



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Q-Ship MGB Silver Member Robert Wilson
NELSON, BC, Canada   CAN
1973 Norton Commando
1977 MG MGB "The Money Sink"
Hello, Brian: none of the components look the same as the Classic Automotive Innovations item as seen on their site, but I asked the people I dealt with at Speedhut. They replied that their Speedbox is manufactured in their own facility and has nothing to do with Classic.

Once I have it and the tach adapter tested and in use, I'll report to this forum.

Attached is a photo of the tach adapter. It's actually more like the size of a deck of cards. At $80 I figured it was a better plan than sending my (low miles/hours) OE tach away to have the internals modified. Figured that option would be way more expensive and if there are future problems with it - you're hooped. Pretty sure I have a spare tach somewhere in my parts stash, so....



Edited 1 time(s). Last edit at 2019-02-05 03:01 PM by Q-Ship MGB.

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Ray Bee Avatar
Ray Bee Ray B
Cobourg, ON, Canada   CAN
Rob
I have used that same tack adapt from Digital Dakota for the past 3 years on my 3.4l v6 and it works great. Just connect the white wire from your 3.4l ICM to the tach adapt input, attach the remaining wires , program the tach adapt and it should work. I just bought another one from Summit for my next v6 project.
Ray

Q-Ship MGB Silver Member Robert Wilson
NELSON, BC, Canada   CAN
1973 Norton Commando
1977 MG MGB "The Money Sink"
Thanks, Ray - great to know. Can you recall the No. of cylinders you programmed for input to the adapter from the ICU? I was thinking 6, but as there are just 3 coils and the wasted spark system.....?

Ray Bee Avatar
Ray Bee Ray B
Cobourg, ON, Canada   CAN
Hi Rob
It's been while but I am pretty sure that I selected 6 cyl in and 4 cyl out. For the speedo I purchased a VSS adapter (model 4pac) from "Jags That Run". It fits inline with the speedo cable. I converted my T5 speedo output to a mechanical type (bullet style). Been working for 3 years now and no problem.
cheers
Ray

Woodysrods Avatar
Woodysrods Silver Member Brian Woods
Westbank B.C., Canada   CAN
This is very interesting topic for me, as I would love to use the stock gauges with my 3400 SFI V6
conversion in my MGA.
Brian



1954 MGTF 1800
1962 MGA MKII

1744 Avatar
1744 Gold Member Bill Guzman
CA, USA   USA
1973 MG MGB GT "Renegade I GT"
1974 MG MGB "Renegade"
Yes they do work great. The tachometer unit works well just pay attention to the instructions.
The speedometer all of them work great.

Have a 66 GT and planning on having the gauges rebuild tach and speedo. and use both units. It may cost more money but it will look original.


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RJBrown Avatar
RJBrown Randy Brown
Queen Creek, AZ, USA   USA
In reply to # 3887005 by Woodysrods This is very interesting topic for me, as I would love to use the stock gauges with my 3400 SFI V6
conversion in my MGA.
Brian

The stock MGB tach referenced here is electrical and fits a smaller dash hole than a MGA.
The stock MGA tach is mechanical. I have a 65-67 MGB tach in my 57 MGA.
It had an engine without tach drive when I bought it and now has a RX7 engine in it. The early (Smiths) MGB electric tach 65-67 is the same size and looks like the (Jaeger) MGA tach. The 65-67 tach uses an inductive loop in the coil feed wire. The smaller unit used in later MGBs is the one discussed here.
http://mgaguru.com/mgtech/electric/et202c.htm See here for a discussion of using a MGB tach in a MGA.
The solution discussed above in this thread would allow you to keep the MGA speedometer but does not reference a solution for your tachometer.

BMC Avatar
BMC Gold Member Brian Mc Cullough
Minneapolis, Minnesota, USA   USA
Great to know some have had success with the tach drivers. My experiences with those have always been poor, but a different brand/type I should say.

One issue that many overlook is TIME. I take a much greater consideration of how old something is than how low of miles it has on it. If there are still good tachometers out there, then the use of these devices is good And cheap. If all else fails, I suppose a person could sell it off as a down payment to having the tachometer repaired later. It's probably worth taking a chance if the tachometer is a known good unit.

I'm also glad to hear that the speed hut unit is different for the speedometer. I have several cars we are ordering for so I might just order at least one of each and then make up my mind which we prefer in the future.

-BMC.


Member Services:
Minnesota's only Fully Dedicated British Classic only shop providing Professional Restoration & Services & Specialty Products including- proper L.E.D. tail lights, Wiring looms and Engine and five speed Conversion Kits
Paul755 Paul H
Fairfax, VA, USA   USA
1974 MG MGB MkIII
1979 MG MGB MkIV "Nemesis"
I have rebuilt a couple of tachs using the Spiyda programmable board. It can be calibrated for 4 or 6 cylinders and with the additional signal conditioner it works fine with a V6 conversion using the DIS tach signal on keeping the existing tach. Most of the 30 year old tachs need the capacitors replacing anyway and the IC used is not available any more.

https://www.spiyda.com/tachometer-electronics.html

V8MGBV8 Avatar
V8MGBV8 Carl Floyd
Kingsport, TN, USA   USA
In reply to # 3887299 by RJBrown
In reply to # 3887005 by Woodysrods This is very interesting topic for me, as I would love to use the stock gauges with my 3400 SFI V6
conversion in my MGA.
Brian

The stock MGB tach referenced here is electrical and fits a smaller dash hole than a MGA.
The stock MGA tach is mechanical. I have a 65-67 MGB tach in my 57 MGA.
It had an engine without tach drive when I bought it and now has a RX7 engine in it. The early (Smiths) MGB electric tach 65-67 is the same size and looks like the (Jaeger) MGA tach. The 65-67 tach uses an inductive loop in the coil feed wire. The smaller unit used in later MGBs is the one discussed here.

Not if I understand what you are trying to convey. The OP has a '77 B. The '68-'76 B uses the smaller speedo & tach. The '63-67 AND '77-'80 both use the larger size.

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