John Bartholomew wrote:
>
> I have just taken my 74B out on it's first test drive since rebuilding the
> engine and tranny. I am puzzled now, why my speedo reads low. Assuming the
> tach reads accurately, in O/D top gear at 3K I have an indicated road speed
> of 50MPH, not a tad over 60MPH as I had expected.
> I do not recall any problem with the speedo before the rebuild, but then I
> have only driven this car a total of about 2 miles, ever.
> It is possible I missed the fact that the indicated speed was off when I
> drove it, as it was just around a residential block to check that the O/D
> and tranny worked OK. The O/D did not engage on my test drive so I checked
> out the electrical side and all was in order, so the assumption was that the
> mechanical side had the problem. This car has sat for 16 years under cover
> but is in great shape otherwise.
> My fix for the O/D was to swap it with a rebuilt unit from a 79. Both units
> were identical from the exterior, however, now I am thinking that the drive
> ratio to the speedo pinion must be different. Could this be so? Are there
> any people out there with the necessary knowledge to comment. I would
> appreciate all offers of help with suggestions. Mr Twist are you listening?
> ----------------------------------------------------------------------
> E-mail jdb70@juts.ccc.amdahl.com John Bartholomew Amdahl San Jose CA.
> 408-746-6361 07:00-16:00 PST. ** USUAL DISCAILMERS APPLY **
> 1969 MGBGT;1974 MGB;1976 MGB-RESTORED;1979 MGB;1972 MGB daily driver.
> ----------------------------------------------------------------------
As the saying goes, been there, done that.
You have stumbled across a popular topic of conversation on this list.
As I prepare to do a tranny swap, I can offer you a quick rundown.
Two types of transmissions were fitted to the B. The first, a 3-synchro
type, was fitted through early 67, and it's O.D (D-type) is unique to
this transmission. Starting in 67, cars fitted with an overdrive used
an LH type. For cars from 67-76 a different speedometer was used for
overdrive and non-overdrive cars. Later cars used a single speedo for
both O.D. and non-O.D. The early LH type O.D.'s can be identified by a
black label on the solenoid cover, while the later types have a blue
label.
To my knowledge, the proper speedo drive gear and pinion for the early
LH cars is no longer available, unless you can find used. Cost was
quite high when they were available. Besides this, pulling the engine
and tranny to tear down the O.D. to replace the drive gear probably
isn't too appealing to you. The proper speedo for the tranny from a 79
B won't fit your dash.
Based on all of this, I would recommend having your speedo
re-calibrated. There is a firm that does this in Minnesota (by mail
order), that is listed on the Monster List. If you are in a major
metropolitian area, there is probably someone who will do this locally.
Cost should be aroound $100.
Of course the option is to live with the faulty readings.
Best Regards,
Chris Delling
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