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MG MGB Technical - 71 B Overdrive Questions

Apologies in advance for the request for quick responses to the following questions. I am away from my copy of Original MGB and need answers before I pick up a Black Label overdrive gearbox this evening.

Here are my questions:

Is the speedo the same for the non-overdrive
and Overdrive equipped cars? will my existing speedo work - since the overdrive is a black label and would have been the type used for a 3/71 production car?


Should I ask for the speedo cable from the donor car if the cable is there?


Thanks in advance. I am picking up the unit this evening and just wanted to check on these last minute rhoughts/questions.

Jeff
Jeff Delk

Jeff. Get the speedometer. There was a slight difference between the ratios of the OD and non-OD speedos. Yes, the overdrive speedometer cable is longer than the non-overdrive cable and should be taken from the donor car.

Les
Les Bengtson

The TPMs were the same for OD and non-OD from the Mk2 in 1967 onwards. It was 1280tpm until rubber bumpers, then 1000tpm after that. Where OD was fitted the LH-type on chrome bumpers was black label, on rubber bumpers blue label.

Also get/keep the right-angle drive at the gearbox end if there is one. It makes for a more direct routing and a slightly shorter cable, although many cars now don't have them and just use a slightly longer cable.
PaulH Solihull

Paul/Les- Any chance I can swap the drives from a blue label to the black label I now have in the 79 car? Or better to go to the speedo guy after and just recalibrate the 79 speedo shortly about to be spun by a black label OD. That is if I can adapt the LH motor mount bracket of the replacement engine ( GB-1965) to the single stud oval mount. Les tells me I can take about 3/8 " off the outside gallery "bump" to approximate the clearance of the 18V's..........
otherwise a BFH? VEM
vem myers

Vem, you would need to pull the rear flange off the OD unit just to get to the speedometer drive gear. I think getting the speedometer recalibrated is the simpler way to go, especially considering that it is 33 years old. RAY
rjm RAY

This thread was discussed between 29/05/2012 and 04/06/2012

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