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MG MGA - *%$#ˆ*y Richfield

Thinking I was on the last job to getting my car back on the road after last summer's mishap, I finally got back under the car to fit the replacement bits for the right angle adapter for the T9 box speedo drive. The Speedograph Richfield unit failed within a few hundred metres of the first run with the new engine in the autumn.

It took weeks of pestering to get a replacement part, which I finally installed tonight. Only to find that the speedo STILL didn't work. Having spend almost an hour under the car to get the thing on, and not relishing the thought of the same to get it back out, I cut a square hole in the tunnel to get access (took only five minutes with the drill and the air saw, most of which was waiting for the compressor to build pressure from few months of being empty.

On removing the right angle adapter, I found that the input shaft has also failed in exactly the same manner as the output shaft. See photo - the flex shaft in the gear has sheared from its gear.

Now I have to go through the pain of getting a new part in time for the MOT that is due in ten days time. I can't get a pass without a functioning and accurate speedo (tested with a radar during the test, which also includes a hill start to check the clutch...)

Has anyone else had similar issues with these adapters, or have I just been unlucky. I can strongly recommend that if you do have one fail, check BOTH ends before picking up the phone


dominic clancy

FWIW. I had installed a new speedometer cable during restoration only to have the new cable shear similar to yours. Replaced it and same thing happened again. Much to my surprise the speedometer was bound up tighter than a drum causing the cable to shear. Didn't know that could happen. Had the speedometer rebuilt (MOMA) and everything is fine. Maybe its your speedometer. Good luck.
Lmazoway

I used to have the same trouble with tach drives on my big truck. It was invariably an instrument problem that caused the failure. I could replace the drive a couple of times before the clock would seize solid, but it never lasted long. Any tightness in the cable as installed will do the same. One common thing is that the drive or cable end is too long and bottoms when the cable is installed. Right angle drives frequently came with a required copper washer that prevented this. Measure carefully!!

That little stub is made by squashing a piece of cable to suit at any speedo shop, or you can make a solid piece out of square stock. Some drives leave the stub loose to float in there, while others have it staked in place, fix to suit. The bitchy part is getting the busted cable stub out. I recommend aluminum or brass, because if it is too strong it will break the gears next time; better that the stub act as a shear link. I replaced about 10 of the damn things (near to a million miles) with broken gears, and really wished mine had had the stub. Mine had a slotted gear shaft sleeve that was hardened steel and broke like glass. Finally figured out that if the drive broke you replaced the tach for $50 instead of another drive in a month or three for $100 (1980s prices), and any time you heard the slightest noise or needle anomalies you pulled the cable and lubed everything.

FRM
FR Millmore

Tested the speedo with another cable - it's absolutely fine
dominic clancy

Bummer. Well that rules that out. Perhaps next time hook up at the transmission end and don't hook up the cable to the back of speedometer. Go for a test drive and watch the cable spin. Maybe your speedometer occasionally (intermittent) ) binds causing the problem.
just a thought.
Lmazoway

Dominic,

I got mine from Speedy Sables in the foreign country of Wales. Might be worth a shot as an alternative supplier to Speedograph?

Good luck,

Grant :-)
G Hudson

Dominic.

Probably a silly question, but I assume you are using the correct right angle drive which takes the original MGA cable and not the one that has a Ford cable output drive, requiring a cable with the Ford squared-off end at the drive end and an MGA squared-off end at the instrument. This type of cable has to be used if you are not using the right angle drive.

With that cable, the inner cable did not match the outer (too small a diameter - recently been sorted I believe), causing it to 'wind up', giving erratic speedo readings. Mine eventually broke like yours.

My break resulted in an engine and gearbox removal. The replacement cable gave no reading on the dial. I thought the plastic speedo drive shaft in the gearbox had sheared. It was a gearbox out job to replace that drive. On inspection it was ok. Turned out that I was not locating the cable fully into the drive shaft!

Re the MOT. Perhaps you could tape your sat nav to the instrument panel to give you a correct KPH for the test?!!!

Steve
Steve Gyles

Well credit to Richfield, they are sending a whole new unit and have asked that I return the old one for inspection.

I have tested each section of the system in sequence: Turning the rear wheels moves the output on the gearbox with no eccentricity or strange effects.

The cable spins freely, and when attached to the speedo the needle flicks with a twist of the cable. Mounting the output ferrule of the Richfield box to the cable at the gearbox end , and then using the gearwheel to spin the cable also shows that everything is moving completely freely and without any restriction.

The right angle Richfield box however is not as smooth as I would expect it to be. As everything else moves completely freely it can only be this.

I now have to fabricate a sheet to cover the large hole in the gearbox tunnel.
dominic clancy

You could always use a bicycle speedometer/computer.

There is at least one midget with type-9 having one fitted.
Dave O'Neill 2

Trouble is, a bad reduction drive might shear the input, but it would not shear the output - that must be the cable or instrument. It is certainly possible that the initial event damaged the drive, or the drive has a problem of its own, but the drive cannot have been the cause of the first failure. I've heard of speedos with problems related to the odometer gearing, which might be intermittent, most aggravating! If the speedo works now but there is such an intermittent problem, it will sooner or later break the drive again as well as the speedo/odo workings, so it might be a good idea to dismantle the speedo before that happens. I've seen a fairly good writeup on this but I don't remember where,
Found it: http://home.comcast.net/~rhodes/speedo.pdf

FRM
FR Millmore

Trouble is if I dismantle the speedo I lose the calibration, and won't pass the MOT either...

I'm fairly certain that the reduction drive is at fault as every other component was used in the old standard setup and was absolutely fine, and all is spinning freely and goes together easily as well.

dominic clancy

Here's the hole I cut in the tunnel to get at it easily, will make a removable plate to cover it all up


dominic clancy

Wow! That's a hole and a half Dominic. Bit late now, but I got by with about half that. I was able to remove and replace the right angle drive within the tunnel. I just needed the cut out to tilt the item into place. I glued sponge on the inside of the cover to cushion and help hold the drive in place.

Steve
Steve Gyles

Steve: The thinking was "if you are going to make an access hole, then it should be big enough to get both hands in without scraping the skin". There was also a dose of utter frustration in play.

The replacement angle drive arrived today, went straight in without any fuss (much easier through the hole) and worked immediately. Had to try two speedos to find one where the speed is more or less correctly registered (can't figure out why my MGB-diff one is right, but standard one is over-reading by about 20%, must have got the figures mixed up somewhere). The individual pieces spin freely by hand, but the extra resistance when coupled together is quite amazing. I tried with three cables, one in the car, two on the floor without any curves, and always had the same results, so I'm certain that all is as it should be.

I have made a nice plate up to cover the hole, cut to follow the gasket around the cross member and secured with about 16 short self-tapping screws. All looks very nice from underneath, on top covered by the carpet.

Now I just have to fix the squirty thing for the wipers, clean up underneath with the pressure washer, and it's ready for the safety test at the beginning of May.

dominic clancy

This thread was discussed between 12/04/2011 and 19/04/2011

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