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MECHANICALS With a 30 year-old automobile, there will always be discussion here - maintenance, modifications and mechanicals.

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Old 6th March 2019, 11:07 AM
sean sherry sean sherry is offline
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Smile Late uo shifts

And again I say, that no Automatic Transmission will work properly unless the Engine is in Tune. Just sorted another one for a friend by checking the Vacuum at the Inlet Manifold. Reading 14 , advance the Timing to max at idle 19 , retard 2 inches to 17 . Problem solved. But now the Engines Pings.... what petrol are you using... 92 with a compression Ratio of 8.5. You get what you pay for. Did he listen.. I don't know and i don't care.. his problem.
What was the Car ? It does not matter, as to whether it was a Cable or Vacuum Modulator controlled Transmission, a retarded spark or a bad Engine equals a confused Transmission. Late sloppy Shifts. Shifts soften my virtue of the Governor Valve reducing the Line Pressure as Road Speed increases. Shift quality is best at early Shift speeds before the Governor Valve gets to rule the Roost !
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Old 7th March 2019, 01:19 PM
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c107 c107 is offline
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Default Re: Late uo shifts

Quote:
Originally Posted by sean sherry View Post
And again I say, that no Automatic Transmission will work properly unless the Engine is in Tune. Just sorted another one for a friend by checking the Vacuum at the Inlet Manifold. Reading 14 , advance the Timing to max at idle 19 , retard 2 inches to 17 . Problem solved. But now the Engines Pings.... what petrol are you using... 92 with a compression Ratio of 8.5. You get what you pay for. Did he listen.. I don't know and i don't care.. his problem.
What was the Car ? It does not matter, as to whether it was a Cable or Vacuum Modulator controlled Transmission, a retarded spark or a bad Engine equals a confused Transmission. Late sloppy Shifts. Shifts soften my virtue of the Governor Valve reducing the Line Pressure as Road Speed increases. Shift quality is best at early Shift speeds before the Governor Valve gets to rule the Roost !
Sean when you check vacuum at idle, do you first disconnect vac advance/retard like you would with a timing light, or do you leave it connected up?

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Old 7th March 2019, 03:56 PM
sean sherry sean sherry is offline
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Talking Re: Late uo shifts

Probably better to disconnect the Vacuum advance line as some Cars draw the vacuum from the Carburrater which can trigger some advance if the butterfly is not sealing it off 100%. The Vacuum advance device is purely an economy aid. The mechanical is the Power adjustment device.
The Vacuum advance mostly comes into Play at cruise speeds when vacuum is high. This middle range is set to run with a weaker mixture as the Engine does not need a lot of fuel when the Car has a lot of kinetic energy built up. A weak mixture needs more time to burn , so the spark is set to come in earlier, via the vacuum advance device..
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Old 7th March 2019, 05:48 PM
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Default Re: Late uo shifts

Sean, that is the depth of knowledge that comes from vast experience.
And it makes me think that restricting the vacuum advance on my 6.3 will help with the slight pinging I've battled for so long.
The ping is generally experienced under load at 2/3 to 3/4 throttle after coasting for a bit.
Am I on the right track?
It's a 6.3, economy is sorta moot.
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Old 7th March 2019, 07:38 PM
sean sherry sean sherry is offline
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Talking Re: Late uo shifts

Under load the vacuum disappears .... The timing is solely controlled by the Distributor Mechanical springs. I would check the timing with a Strobe light. Generally at around 2200 Revs the advance should be in the 20% range.
With ageing Cars the distributor Springs lose their tension and allow the timing to advance to quickly. A new set of springs would be my starting point. In the Days of yore we had a Bench Strobe- a -scope to run up the distributors and check the advance curve through the Range.
Of course there also could be too much Carbon in the Heads. An effective cleaning method is to spray water down the inlet at a very fast idle. You have nothing to lose..I would also do the vacuum gauge Timing method as per my last Post. A vacuum reading gives a good indication of the Engine condition. There is a site on the Net that explains what all the various gauge reading are telling you.
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