MGB: Speedometer is too slow, what about mileage?

This spring I had what I believe to be a late model OD transmission installed in my early CB '74. When I'm cruising the interstate and keeping up with everyone I know that I'm going way faster than the 50 mph my speedometer tells me I'm traveling. I've got a 1280 speedometer and know I need to switch to a 1000 tpm speedometer. Can I make the assumption that if the speed is off that the mileage will also be wrong?

Additionally where is the black/blue label on the transmission that everyone keeps talking about so I can make sure I know which transmission I really have.

Finally (and I'll post this in the trader section too, does anyone have a 1000 tpm speedo for sale?

Thanks.

That would be the case.
The label is back and under, but if you have a top fill o/d in a 74, you should be good with a 1280 tpm. What size tires are you running?

Yes, your mileage will be off. Maybe get a couple of FRS radios and get someone to follow you.
Don't know about the label.
Might be better to get your speedo recalibrated. I think Nisongers can do that.
Good luck.

chris Wrote:

I thought that if you had a late transmission in an earlier care (Like a 73-74), it need a 1000 speedo or the 1280 speedo would read too fast...

You will read low (and the odometer will be low as well). Your speedometer expects 1280 turns per minute at 60 MPH and you are only seeing 1000, so your speed (and odometer reading) are about 78% of true.

Instead of getting a new speedo, why not send your speedo to Nisonger for conversion? They can easily change the gearing and hairspring to be correct for your 1000 TPM transmission.

There are a couple of clues about whether you have 1000 or 1280 TPM transmissions (other than labels). The hole in the bell housing where the clutch lever passes through is a different shape (squarish?) than the 1280 TPM transmissions. The speedo gear is larger than the earlier units.

Early (1280tpm) O/D 'box.

The black or blue label is facing straight down....you can probably slip a mirror under the car with some light and see what color it is without having to jack it up, etc. The label is to the rear of the transmission about 9" in front of where the driveshaft attaches. Black label=1280 tpm, Blue label=1000 tpm.

Late (1000tpm) O/D 'box. (Top)

The Blue Label faces the ground. The Black Label is on the right side.

There seems to be a lot of confusion about what takes what. But I can tell you this much..... I have a '75 with a 4-speed gearbox and it definitely needs the 1000 speedo (unless by some miracle I actually have an OD gearbox and have never noticed!). I found this out when I inadvertently replaced the 5320/13 1000 with a 5230/06S 1280. Symptoms are the same......reads 40mph'ish when everyone around me seems to be doing 65-70mph.

They come up on eBay with some regularity. Some of the professional vendors want big money, like $75 and up (and people even pay that!). But some from individuals can be had reasonably, if you don't get into a bidding war.

I just missed out on one @ $29, but ended up with a full set of gauges for $36 shortly thereafter. I'm thinking I can perhaps unload the un-needed gauges for pretty close to what I paid - last tach I bought by itself was close to $60 and I've seen oil gauges go in the mid-$30 range before.

I generally have been searching eBay as follows (with search title and description checked). But there is only one on there as of today:

SN:5230/13
SN5230/13
5230/13

(I think the 5230/13 is the only 1000 speedo applicable to the MGB )

Edit: Did find one on eBay UK - http://cgi.ebay.co.uk/MG-SMITHS-SPEEDO-SN-5230-13-1000_W0QQitemZ220270195465QQcmdZViewItem?hash=item220270195465&_trkparms=72%3A1121%7C39%3A1%7C66%3A4%7C65%3A12%7C240%3A1318&_trksid=p3286.c0.m14

Assuming this new speedo I've got coming turns out to be OK.....I was toying with the idea of marrying the broken 1000 speedo I have (trip and odo don't work) with the needed parts from the 1280 to make a good 1000 speedo.....I'd be happy to pass along the 1000 to you at nominal cost so you could try the same? Basically you'd take the speedo drive mechanism from the 1000 and the trip and odo dials from the 1280. Should be as easy as removing the needle and face, and then undoing the screws holding the two halves of the speedo together. Reassembly would be the reverse of removal, naturally.

Thanks for all of the information everyone ... I crawled under the car (I only weigh 140) and found a blue label. Then about 30 minutes later I found someone close by with a 1000 tpm; I picked it up this afternoon and already have it installed. That's the good news .... The bad news is that I also this afternoon found out that the guy that "completely" rebuilt the front end of the car didn't replace the front springs .... GRRRRRRRR .... I now have a new project ...

So Steve, is it reading correctly now...??

gsj28 Wrote:

Well that's just nuts! I looked on a chart that showed a 73 should have the 1280 tpm so didn't bother changing it out and I read just fine with the top fill 4-synchro o/d. And wheels from Hap! :)

You know how I was saying earlier "unless by some miracle I actually have an OD gearbox and have never noticed......". DUDE! I TOTALLY HAVE A FRICKEN' OVERDRIVE!!!!!

Congratulations, but you'd better wait until after you do a good cleanup. That might just be an O/D shaped lump of oil and dirt.

realmwalsh Wrote:

I guess I've never really seen a "blue label" unit before you posted that picture Derek, so I guess I was expecting the profile and orientation associated with the "black label" type. Not to mention, as you noticed, it's dirty as crap (what blue label?). Plus there's nothing in the car - no OD gearknob.

Gotta see the PO at work today and find out if she or her hubby removed the OD gearknob out and why.

See if the wiper switch shifts forward causing the o/d to engage. Congrats on your fortune!

Poop, my bonus OD doesn't work. I did find the OD switch on the wiper stalk. Got up to freeway speed in fourth and flicked it forward. Nothing happened.

I'll check electrical first. By coincidence the reverse lamps don't work either, so I think all is not well in that section of the loom.

There's no reason a "Blue Label" OD wouldn't work off the column mounted switch, assuming it was all hooked up and otherwise working? I mean I don't need to find a shifter mounted switch simply because my OD is a "Blue Label" version?

No need. A switch is a switch. You could even twist 2 pieces of wire together. Not recommended while driving.