Boxer Speedo failure

Hi the speedo on my 365bb has stopped working. The speedo head has been checked and is ok. The sender unit has been replaced and still no joy. Any thoughts?

Hi Greg,

Welcome to Ferrari-Talk!

The speedometer on your BB is electical and mechanical, in nature. If your confident that both the speedo head and impuse transmitter are working correctly...there are few addition items worth taking a look at.

-Verify that you have voltage at the speedo head
-Verify the continuity (in the wires) from the impuse transmitter to the 6/8 prong plug begind the dash board.
-Carefully inpect the 6/8 prong plug to insure that the wires haven't backed out of the male/female parts of the connector.

-If all checks out electically, remove the impulse transmitter from the transaxle...but leave it connected to the vehicle wiring harness, once removed. With a helper in the car...and the key on, manually drive the impuse transmitter with a drill and a piece of shaped heavy gauge wire, hence simulating the vehicle moving. There is a remote possiblity that the gear set, off the mainshaft of the transmission is damaged, or has come free...which would result in the impulse transmitter not receiving it's mechanical input.

-If you have a Parts Manual, you can see how these two gears drive the implse transmitter.

-You'll need a WSM to verify wire colors at the back of the speedo head.

...Do any of the functions on the speedo head work? Lights, odometer, etc?

Regards,
David

Thanks David

I had the speedo head serviced at an instruments specialist who assured me it was ok. The lights work but the odometer doesn't. When I had an almost flat battery once, the needle would flicker upon turning the key to the starter positio(?why). When I have a free weekend I'll have a go having a look at it as you suggest. I kinda have a feeling that the gear set off the transmission may be damaged(sounds expensive and complicated to fix!!!) I'll let you know how I go. Thanks very much for replying to my post

Cheers

Greg

Hi Greg,

The speedo could go full scale, flicker and act eratically under a low battery condition. This is quite normal...

If the problem turns out to be the gear set which drives the impulse transmitter, the repairs can be done with the gearbox still in the car. There are two gears...One which actually drives the impulse transmitter. This can easily be removed for inspection by simply removing the pinch bolt on the impulse transmitter tubular housing. It is a single 8mm bolt. Simply remove the bolt...and twist the entire housing whilst pulling downward.

On the other hand, the gear on the transmission is a bit tougher to get to...Likely, you'll have to remove the alternator (oh, what joy!)...and then remove the entire speedo drive housing. Once the housing is off, you'll see a helically-cut gear on the end of the transmission shaft. The gear is held on with a snap-ring. The gear will slide off, with little force required. There's a small woodruff key that prevents this gear from free-wheeling on the shaft. No further disassembly is required...

As Ferrari used this geardrive set-up on most of the BB cars...I'd bet that Ferrari-UK has these parts.

Regards,
David

Greg - Do I understand correctly that the speed indicator works but the odometer does not?

This is a common failure mode. I have experienced the same. My odometer is intermittent, and I continue to search for the culprit. I suspect it is an electronic issue within the speedometer head itself.

Jim S.

David

Thanks again for taking the time to answer my query. I'll let you know how I get on

Jim
neither the speed indicator or odometer work

Greg

Well, before I started stripping the gear set, I thought I'd get the speedo head checked out again by someone else and surprise, surprise, they found a problem with it (IC needed replacing) Now it works just fineMoral of the story is don't be afraid to get a second opinion!!

Well it lasted for 18km, then died again. Must be shorting out something in the speedo head. Out it comes again

Greg,

Sorry to hear you're still having problems with the BB. If you get in a bind for parts, I have the electronic guts for the 365 speedo head...as well as a known good, used impulse transmitter.

BTW, be sure to check the 6/8 pin connector for the speedo...as those wire spades can fatigue, and back out of the plastic connectors .

Regards,
David

(Message edited by fastradio2 on June 26, 2004)

Thanks David

I'll let you know how I go

Greg