Speedometer Cable Routing

The speedometer on my '62 AH 3000 Mk II BT7 tri carb has never worked properly. The needle simply waved over the likely possible speed. I suspected the cable so ordered a replacement and at the same time had the speedometer cleaned and calibrated. The angle drive was missing the recommended brass washer so I replaced that unit as well. Interestingly, the old cable was 4 ft long where the Moss replacement for my car's serial number is 4 ft 8 in long; the cause of the waving needle likely solved. I found the old cable exiting the transmission tunnel to the instrument panel from under the upper lip of the Extension Panel, Moss part 807-115, item number 16, page 138. Since this route prevents the Extension Panel from fitting tightly against the bulk head, I am wondering if this route was chosen only because of the shortness of the old cable. I don't, however, see any unused holes or plugs where the cable might exit but maybe I missed it. Could it be looping up and coming in through the bulkhead behind the instrument panel? Can anyone help me with this?

Doug Cavill
Gabriola Island, BC

This may or may not be appropriate as a solution. It worked for me:

My car, having been converted from a non-overdrive car back in the day, happens to have a home-made extension panel. The routing at the time put an awkward bend in the cable.

With the extension and tunnel removed, I routed the cable from the angle drive up to the speedo. The cable housing rests against the heater plenum below the left side of the heater box. I positioned the extension panel over the cable, marked it and cut a slot in the panel flange to allow the cable to pass through the extension in its "natural" position.

I have a Toyota gear box, so my '60 BN7 is a bit different. Early on I decided to replace the defective speedo cable, purchased one that was a bit long, and found that the existing cable was "trapped" behind the extension panel you describe. As I soon had reason to take the transmission cover out of the car, I chose to drill a hole through the transmission tunnel just behind the extension panel you describe. Looking from the driver's seat at the circular top portion of the transmission cover, I made my hole at about 11 a.m. This was large enough to pass the cable through beneath the carpet and then up to the instrument. I padded the hole a bit, of course, and now can simply pull the cable in and out without removing either the tranny cover or the extension panel. There is often the question of the Toyota right angle drive that directs the cable forward from where it plugs into the transmission. Since those drives are expensive and reportedly trouble prone, I chose to buy a longer cable that enabled me to use a very gentle curve on the cable (and housing) as it went up and over the transmission and out through the hole I described earlier. The challenge I had was fitting the cable end bit that inserts into the transmission, basically the drive tab. I had to do it twice because I failed to first connect the instrument end of the cable to determine the final length of the internal drive cable. I made it too long, and thus I could not tighten down the cable housing and one end or the others. So I did it twice, getting it correct on the second try.
So, how did that work? No problem whatsoever for several years until recently. I am saying the speedo ran smoothly with no bounce. However, after I disassembled my speedo in an effort to improve its function, upon reassembly I found the magnetic piece that drives the bit that transmits the cable rotation to the instrument's needle was no longer turning that vital part. No explanation for why that happened. I then replaced original the magnetic bit from an old speedo, and then found my speedo worked but had the bounce familiar to those who experience cable problems. I have no idea why or if changing the magnetic piece prompted the speedo needle to start bobbing when the car was driven at a consistent pace. I did try adding lubricant to the cable and attempted to reposition the cable in the hope that it would remove the bounce. No success. I also tried another method suggested by a veteran Healey owner, backing off the threaded coupling at the speedo a half turn or so. Didn't work. You must be a masochist to work on these cars. I'm considering buying another long cable

Looking at my firewall from the engine side, there are two holes to the right of the fuse holder. My speedometer cable lies on the transmission and passes under the extension panel (part #16), between the rubber heat shield and bell housing. It comes up the engine side of the firewall and passes through the lower of the two holes to the right of the fuse holder and straight into the speedometer.

John Turney said:

Looking at my firewall from the engine side, there are two holes to the right of the fuse holder. My speedometer cable lies on the transmission and passes under the extension panel (part #16), between the rubber heat shield and bell housing. It comes up the engine side of the firewall and passes through the lower of the two holes to the right of the fuse holder and straight into the speedometer.

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John - after perusing Anderson Moment and Clausager, I believe the pictures show on most cars the choke cable goes through the upper grommet. Nothing shows a cable going through the lower grommet.

Anderson Moment, p.105 has a picture of the heater which shows what looks like the speedo cable slanting up from behind the carpet, just below the heater. Regarding the grommets to the right of the fuse holder, engine compartment pix (p.76) seem to show the upper one to be for choke cable; lower one for wires. P.146, BJ7 has the upper one blanked. This is in line with the choke being moved to the center dash. P.147 shows a choke cable coming out of the upper one.

Moss catalog, "Miscellaneous Trim Fittngs" section, item 33, "Grommet, speedometer cable" - is shown on the front flange of the centershift tunnel. This would likely be appropriate for Doug's car. Maybe there's already a hole there. No such grommets are shown for the earlier tunnels.

Thank you everyone for your input. My BT7 was manufactured in July 1961 so still has the side shift gearbox. The centre shift gearbox configuration in later '62 BT7s got rid of the extension assembly and as Steve noted the tunnel has a grommet assigned to the speedometer cable. I suspect I will go with Steve's slightly modified extension panel to get a good seal between the tunnel and bulkhead. I am looking forward to finally seeing how fast I have been driving around our island.

Doug Cavill
Gabriola Island, BC

steveg said:

John - after perusing Anderson Moment and Clausager, I believe the pictures show on most cars the choke cable goes through the upper grommet. Nothing shows a cable going through the lower grommet.

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Oh, you want a concours answer! Looking through Anderson, Moment and Clausager, I think you are correct that the speedometer cable is routed as it was Doug's car originally.

My choke cables are like those on a BJ8, coming from a bracket in the center.

BT7Doug said:

Thank you everyone for your input. My BT7 was manufactured in July 1961 so still has the side shift gearbox. The centre shift gearbox configuration in later '62 BT7s got rid of the extension assembly and as Steve noted the tunnel has a grommet assigned to the speedometer cable. I suspect I will go with Steve's slightly modified extension panel to get a good seal between the tunnel and bulkhead. I am looking forward to finally seeing how fast I have been driving around our island.

Doug Cavill
Gabriola Island, BC

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Doug - you won't have to modify the extension panel.

A friend and I were at Russ Thompson's shop this morning for firing up his rebuilt engine. Russ knew about the centershift grommet and said the earlier models squish the cable between the firewall and top flange of the extension panel. He puts a layer of foam tape on the firewall and another on the extension panel flange and the cable is clamped in between.

The picture in Steve's post is exactly how I did mine (also an early BT7). It seems to work fine.
Keith

A soft squish with some seal tape, too easy. Thanks again everyone for taking the time to reply,

Doug