Re: [Classic Mustang] Re: 65 mustang speed issue...

Wow Flick, that's a brilliant piece of sleuthing.  And these days, with the age of these cars (and their mufflers), its probably appropriate to think about some kind of blockage like this.

I was going for the Occam's Razor approach myself.  Perhaps a tweak of the idle adjustment screw on the carburetor might raise the curb idle RPM back to 750 or so, as a low idle would cause it to stall in drive or reverse, but not neutral or park.   (This alone doesn't address the overheating problem.)

In any case, I couldn't agree with you more... don't throw parts at it; certainly not a $2K transmission without having a professional diagnosis first.  A Shop manual is a must - no doubt about it.  Buy it; read it; absorb it; ; live it.  But of one's own skill level must also be sufficient for the task.  Perhaps finding a reputable general purpose mechanic might be a good step in the right direction too?

A slipped timing chain will cause the engine to run over temp - and I mean WAY over temp.  (DAMHIKT!) If it slipped forward, it would be backfiring so much you couldn't drive it.  (No report of that, either.)  If it slipped the other way, mechanical timing would be so retarded that I don't think anyone could prevent it from boiling over with simple radiator modification(s).

However, poor initial distributor timing and/or maladjusted points would also cause the car to overheat  and not run particularly well at cruising RPM.  We've gotten so used to electronic ignition systems (after market or otherwise) that we loose the bubble on the basics - like dwell setting.

So maybe a tweak of the carburetor idle setting and an electrical tune-up?   AND a shop manual? :-o)

-Michael

Flick01@Aol.Com wrote:

Ok..... just a shot in the dark but this will cost nothing to diagnose. At first, when you said the car wouldn't go over 65 I was thinking something like a slipped timing chain. I've seen 289s and 302s run 2 teeth off in the retarded position and though they'll run as slow as mud, they'll run. But then I got to thinking about the heat issue and the fact it stalls when in gear but runs in neutral, coupled with what sounds like a possible vacuum/modulator problem. So here's a suggestion. Get a vacuum gauge and a repair manual (it's been so long I don't remember what to tell you what to look for but a shop manual will, someone on here will, maybe even find it online) and check for a clogged exhaust system. There is a way to check it with a vacuum gauge I just don't remember the specifics off the top of my head. An internally collapsed muffler, at least from what I have seen in the past, can give all the symptoms you describe. Too much heat at the rear of the engine but the front radiator is normal, erratic shifting because the vacuum is restricted, and stalling in drive because the back pressure is building up to the point where it just won't run with any kind of a load on it, these are all classic signs of a clogged exhaust. I haven't come across a clogged exhaust since the late 1970s when I saw a station wagon trying to go up a hill, it wouldn't go past 25 mph and sounded like a 747 trying to take off against a headwind. Take a lesson from "the voice of experience." Diagnose the problem before you replace parts. Nothing would make you throw up your hands in disgust more than replacing the tranny and still having the same problem, especially if it could be diagnosed for free with a vacuum gauge.


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