Trevor Boicey had this to say:
>Max Heim wrote:
>> Wow, that makes it sound complicated. I put a late OD in my 66 B and all
>> I did was run two wires -- one from the fuse box to the dash switch, and
>> from there to the lockout switch (on the tranny), and one from the other
>> side of the lockout switch to the OD solenoid. I frankly had no idea
>> there was a relay...
>
> The later cars use smaller solenoids that don't need
>relays. The thought was though that the older style solenoids
>pulled too much current to run without a relay.
>
Well, I have a late solenoid OD (77, I think), so that explains it. I
guess I looked at the wiring diagram for the late model when I hooked it
up, which makes sense, but explains why I didn't know about the relay.
> It's not a safety issue though, so if it works, it works. What
>you might find though is too much voltage drop through the thin
>wire and switch contacts to engage the solenoid. Evidently, this
>isn't happening. ;>
>
Not with mine (see above), but this is potentially an issue for the
original questioner...
>> and a vacuum switch involved. I am not quite sure why
>> there is an issue with the OD engaging with the throttle closed (which it
>> seems to be the purpose of the vacuum switch to prevent).
>
> I think it's more the opposite, to stop the OD from
>disengaging when the throttle is closed.
Oh, right, that makes more sense. As someone noted, Bentley's is less
than clear on this point.
>
> As you probably found out, this can be kind of violent. I
>have overdrive in my 75 Midget, and I don't use it in third
>gear mostly for this reason. It's smooth to engage, but
>if the revs are anything less than 3000rpm the disengaging
>gives the car a good "snap" and sometimes makes a tire
>squeal. (no problem in fourth though)
>
Actually, I have never really noticed this effect. Probably because the
very late OD I have doesn't function in 3rd, only 4th. This is probably
another reason why they felt they could dispense with the vacuum switch,
now that I think of it...
> The above happens a bit actually, let's say you
>go first, second, third, then overdrive third and
>coast along. Then you coast into a stop light or
>something, and flip out overdrive when revs are
>low and foot off. Squawk!
>
> With the vacuum switch, the car won't actually
>come out of overdrive in these situations. It'll
>only allow you to downshift when you are on the
>throttle, like going from OD 4 to just plain 4 to
>pass somebody on the highway.
>
A few people have posted comments about their cars not wanting to come
out of OD, or having a slight delay. Maybe this is what they were
experiencing. Interesting.
> I don't think it's essentual though, it was dropped
>of course...
>
Ah, but with the early OD, used in 3rd, it may very well be something to
think about.
>--
>Trevor Boicey, P. Eng.
>Ottawa, Canada, tboicey@brit.ca
>ICQ #17432933 http://www.brit.ca/~tboicey/
>"No offense..." is usually followed by great offence.
>
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the red one with the silver bootlid.
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