Speedo replacement tips?

[Gundy]

The wife's B has a non-working trip odometer however the speedo works.
I sourced a nice used speedo from Merry ole England.
Any tips on the install? I haven't crawled under the dash as yet but it looks like a bear to get up in there.
Please tell me this can be changed without removing the dash.
(crosses fingers and toes)
Any tips appreciated. It's a 1971 MGB.

 

[bob67bgt]

You will probably have cuts on your hands when you get done. You can access the lower thumb screw then you can turn the speedo to get to the upper one. Then pull the unit out enough to remove the dash light and cable. Install in reverse order. It can be a butt of a job. Bob

 

[Gundy]

Thanks Bob! Heck my old hands look like they have been chewed by a puppy already from a header install on a FJ60. A few more
won't be noticed.
It's good to know others have managed the feat without dash removal.
I always laugh and say a little blood sacrifice insures a job well done.

 

[MGZT260]

To be kosher and correct with authorities you should have odometers of old as installed and new compared by any reputable car dealer and get a certified (might cost you a little, might not) mileage not original statement. Even though your B may no longer be subject to such rules it would be a nice gesture for the next owner.

 

[DrEntropy]

Hire a dexterous 10-year-old. :wink:

It is a beast of a job but not too bad. Just remember to disconnect the battery FIRST. Some funny things can happen under there when you start stickin' yer mits into th' harness for access to the fasteners.

 

[NC Mike]

I sourced a nice used speedo from Merry ole England.
Any tips on the install?

Gundy,

Assuming that you're talking about a Smiths speedo, THE MOST IMPORTANT thing to look at is the fine print at the bottom of the speedo face.

There is a three or four digit number, (on my 74 parts car and 74.5 rubber bumper GT, it's on the bottom right, near the 120 mph mark - 1000 on one, 1280 on the other).

That number represents turns per mile. Translating into english, that is the number of speedometer cable turns required to advance your odometer one mile, and also represents the turns per minute of the cable while traveling 60 miles per hour.

I learned this the hard way when I replaced the broken-faced original in my 74.5 GT (manufactured in Nov '74) with the unit from the 74 GT parts car manufactured in Feb '74. The original was 1000, the replacement 1280.

Math being what it is, the 1280 was looking for 1280 rpm, or 1.28 times more than my 74.5 was providing. SO, when I sped up to provide sufficient turns for the 1280 model to indicate 55 mph (and lead me to believe I was traveling 55) I was actually traveling about 70mph. Needless to say, it was an error that the local constabulary was more than willing to bring to my attention.


Here's a link to a very useful chart -

https://www.mgb-stuff.org.uk/speedo2.htm

and a link to a great speedo repair guide -

https://home.comcast.net/~rhodes/speedo.pdf

As for removing the dash - having replaced my speedo twice now, the only thing I've had to move out of the way is the trip odometer reset cable. Taking that out of the mounting lug first gives just enough room to squirrel your hand deep enough to reach the thumb screws/nuts on the back of the speedo. Turning the screws/nuts can prove to be another story.

As mentioned in an earlier response, disconnecting power is a good idea, not only for preventing an electrical short if the wrong item becomes dislodged, but also to prevent the courtesy light from draining the battery while you try to free your hand from behind the dash .

Have fun!

 

[tony barnhill]

A hint: remove the driver seat & possibly the steering wheel so you can lay down on your back comfortably while you work.

 

[Gundy]

To be kosher and correct with authorities you should have odometers of old as installed and new compared by any reputable car dealer and get a certified (might cost you a little, might not) mileage not original statement. Even though your B may no longer be subject to such rules it would be a nice gesture for the next owner.

I have no idea what the mileage on the B. The current speedo reads 18000...I know that can't be right. It was replaced during the rebuild a few years ago.
The "new" one reads 36000 or so. I doubt that is close either.
I'd just state it is over 100K and let it go at that if I ever sell it.
That's what we put on the DMV form for our transaction.

 

[Gundy]

Hire a dexterous 10-year-old. :wink:

It is a beast of a job but not too bad. Just remember to disconnect the battery FIRST. Some funny things can happen under there when you start stickin' yer mits into th' harness for access to the fasteners.

Good tip Doc! Thanks.

 

[Gundy]

I sourced a nice used speedo from Merry ole England.
Any tips on the install?

Gundy,

Assuming that you're talking about a Smiths speedo, THE MOST IMPORTANT thing to look at is the fine print at the bottom of the speedo face.

There is a three or four digit number, (on my 74 parts car and 74.5 rubber bumper GT, it's on the bottom right, near the 120 mph mark - 1000 on one, 1280 on the other).

That number represents turns per mile. Translating into english, that is the number of speedometer cable turns required to advance your odometer one mile, and also represents the turns per minute of the cable while traveling 60 miles per hour.

I learned this the hard way when I replaced the broken-faced original in my 74.5 GT (manufactured in Nov '74) with the unit from the 74 GT parts car manufactured in Feb '74. The original was 1000, the replacement 1280.

Math being what it is, the 1280 was looking for 1280 rpm, or 1.28 times more than my 74.5 was providing. SO, when I sped up to provide sufficient turns for the 1280 model to indicate 55 mph (and lead me to believe I was traveling 55) I was actually traveling about 70mph. Needless to say, it was an error that the local constabulary was more than willing to bring to my attention.


Here's a link to a very useful chart -

https://www.mgb-stuff.org.uk/speedo2.htm

and a link to a great speedo repair guide -

https://home.comcast.net/~rhodes/speedo.pdf

As for removing the dash - having replaced my speedo twice now, the only thing I've had to move out of the way is the trip odometer reset cable. Taking that out of the mounting lug first gives just enough room to squirrel your hand deep enough to reach the thumb screws/nuts on the back of the speedo. Turning the screws/nuts can prove to be another story.

As mentioned in an earlier response, disconnecting power is a good idea, not only for preventing an electrical short if the wrong item becomes dislodged, but also to prevent the courtesy light from draining the battery while you try to free your hand from behind the dash .

Have fun!

Good to know. I just assumed...dangerous...that a 71 speedo
would be correct since it's a 71 B. What was I thinking?
I'll check those numbers this evening.
Thanks!

 

[Gundy]

A hint: remove the driver seat & possibly the steering wheel so you can lay down on your back comfortably while you work.

Gotcha Pal! It's tight quarters for sure. I did see that me fingers appear skinny enough to reach up in there but ..man,
they touched a LOT of stuff in route to the speedo.

We're going on a LBC over nighter with the FBCC this weekend so
this task is going to have to wait till we return. Long trip
means MGB....we're too old to take the BE on such a trip.

 

[Gundy]

Well, it's better to be lucky as they say. Both are 1280s. Whew. Looking at them the thought has occurred to me that
maybe all I'll need to do is attach the trip odometer cable thingie from the "new" one to the "old" one in the dash.
Worth a shot anyway.

 

[Gundy]

Well....aren't I a dummy? The previous owner said the trip odometer didn't work after the "new" one was installed.
As stated earlier I bought one with the odometer reset thing on it.
Yesterday I crawled under the dash to begin the removal of the existing speedo. Whaaaaa...There plain as day was the trip odo reset thing. I tried it and DANG....it works perfectly fine.
I don't get it. The little old man I bought the B from even kept note pads he custom cut in the ashtray so he could keep track of mileage since the fuel gauge was inaccurate.
BTW...gauge works now too once it went low and I topped the tank off and took some spirited drives.
He also told me the nice CD player/radio never worked. I found
the speaker wires had been pinched apart and after I fished the wires out of the door and re-attached them the stereo works great.
Brakes lights didn't work. It had been an on going problem he sought to get fixed several times.(receipts to prove it too)
Found a loose connection at the fuse block. They work fine now.
It would cut off coming to a stop. Didn't like to sustain an idle. Well....a few spirited runs an ...shazaam... idle went
WAY up. I lower it idle speed and now it purrs at idle and no more cutoffs coming to a stop.
Bless his heart. I guess he NEVER put his foot in it and was
also at the mercy of some shady shops.
He kept all the receipts and some were quite shocking.
I guess these old LBCs just need a bit of a mechanic for an owner and need to be DRIVEN like a sport's car.


Anyway...anybody in need of a nice MGB speedo?

 

[MGZT260]

Requirement #1 for caring for an older British car is an extra storage shelf or two for parts you buy in anticipation of changing out and then, as you did, coming to the realization that a little reassembly goes a long way.

 

[vping]

Requirement #1 for caring for an older British car is an <span style="font-weight: bold">extra storage shelf or two</span> for parts you buy in anticipation of changing out and then, as you did, coming to the realization that a little reassembly goes a long way.

What am I doing wrong. It turned into a garage or two of spare parts. These suckers multily like rabbits!!

 

[DrEntropy]

I'd post a photo of one long wall of my garage but for th' embarrassment of condition...

 

[tony barnhill]

You guys don't want to see my buildings full of spare parts!

 

[Gundy]

I'm slowly acquiring a pile-o-parts for our LBCs.
Let's see....spare B speedo, Mk1 front fine spline
wire hubs, 3.7 Mk1 diff, shorty tonneau, early model tach,
course thread front wire hubs with rotors and parking brake handle. Pretty short list. I can see it growing as time and
projects advance.
Now Land Cruiser parts....don't get me started.