Re: 1953 Delco Vacuum Advance
Posted by DavidPackard On 2023/8/31 19:00:47
My ’54 copy of “Motor’s Auto Repair Manual” establishes that for the Delco 1110841 distributor the chamber plunger should begin to move at 5-7 inHg, and achieve maximum stroke of 4-6 degrees (distributor) at 11 inHg. I think we can read into this information that the design intent is to have full vacuum advance at cruise power . . . now, what hardware feature establishes the maximum stop?
As I understand that system the spring material & geometry (wire diameter, OD of coil, number of active coils), coupled with the chamber area, establishes the amount of vacuum pressure that is required to stroke from ‘begin to move’ to the maximum stop. The free length of the spring and the shimming establishes the vacuum required to begin the stroke motion. Ross is correct (we would expect nothing less), if only the diaphragm is changed, and you started with all of the correct ‘hard-parts’ then you will likely have a working unit for your car.
Now for some intrigue:
A few years ago I ran into another detail concerning vacuum chambers for Delco distributors, that is, what feature establishes the ‘high-stop’ limiting the travel of the chamber. The ‘Motor’s’ manual establishes so many inch of mercury to achieve the maximum stop, but otherwise is silent on what feature represents the maximum stop. There are two possibilities, the first case is coil binding in the compression spring, while the second case is a hardware feature that inhibits further diaphragm motion.
See attached file for details of what I believe controls the maximum stop. When I mention ‘failed unit’ in the presentation that would be the chamber that was installed in my ’54 Cavalier when I purchased the car, and the ‘replacement unit’ refers to a replacement I bought from one of our trusted suppliers.
If I have interpreted the situation correctly the geometry of the opening in the actuation arm controls both the minimum and maximum stop. The maximum stop is therefore not likely achieved by coil binding. I believe Delco would tailor a chamber to the customer’s needs by matching arms and springs, while most of the remaining parts were unchanged, which results in many vacuum chamber part numbers that would physically fit the distributor body, but perhaps have completely different performance characteristics. I believe each arm geometry is identified by a unique number, and there are many arms that will physically fit in a distributor intended for a Packard distributor. The minimum stop arm geometry is likely identical among many Delco units because that is a detail required to specify the free length of the compression spring. My sample size is far too small to draw conclusions, but my concern is there are vacuum chambers with actuation arms that were not intended for Packard applications, or the Packard application has been misidentified. At this point it is speculation whether a rebuilder installed an inappropriate arm (the arm would be re-riveted to a new diaphragm during the rebuilding process), or our supply pipe-line has been contaminated with chambers intended for different automobiles.
The search for the patent documents continues. Those document are likely to justify the means to achieve the maximum stop as a ‘unique feature’.
I guess what I’m trying to say is “just because the chamber fits the distributor there is no guarantee that the calibration is correct” . . . but if you look at the air gap between the ‘tang’ and the opening in the arm you can estimated the total stroke (some arithmetic required).
dp
Attach file:
VacuumChamber002 [Compatibility Mode].pdf Size: 536.10 KB; Hits: 41
As I understand that system the spring material & geometry (wire diameter, OD of coil, number of active coils), coupled with the chamber area, establishes the amount of vacuum pressure that is required to stroke from ‘begin to move’ to the maximum stop. The free length of the spring and the shimming establishes the vacuum required to begin the stroke motion. Ross is correct (we would expect nothing less), if only the diaphragm is changed, and you started with all of the correct ‘hard-parts’ then you will likely have a working unit for your car.
Now for some intrigue:
A few years ago I ran into another detail concerning vacuum chambers for Delco distributors, that is, what feature establishes the ‘high-stop’ limiting the travel of the chamber. The ‘Motor’s’ manual establishes so many inch of mercury to achieve the maximum stop, but otherwise is silent on what feature represents the maximum stop. There are two possibilities, the first case is coil binding in the compression spring, while the second case is a hardware feature that inhibits further diaphragm motion.
See attached file for details of what I believe controls the maximum stop. When I mention ‘failed unit’ in the presentation that would be the chamber that was installed in my ’54 Cavalier when I purchased the car, and the ‘replacement unit’ refers to a replacement I bought from one of our trusted suppliers.
If I have interpreted the situation correctly the geometry of the opening in the actuation arm controls both the minimum and maximum stop. The maximum stop is therefore not likely achieved by coil binding. I believe Delco would tailor a chamber to the customer’s needs by matching arms and springs, while most of the remaining parts were unchanged, which results in many vacuum chamber part numbers that would physically fit the distributor body, but perhaps have completely different performance characteristics. I believe each arm geometry is identified by a unique number, and there are many arms that will physically fit in a distributor intended for a Packard distributor. The minimum stop arm geometry is likely identical among many Delco units because that is a detail required to specify the free length of the compression spring. My sample size is far too small to draw conclusions, but my concern is there are vacuum chambers with actuation arms that were not intended for Packard applications, or the Packard application has been misidentified. At this point it is speculation whether a rebuilder installed an inappropriate arm (the arm would be re-riveted to a new diaphragm during the rebuilding process), or our supply pipe-line has been contaminated with chambers intended for different automobiles.
The search for the patent documents continues. Those document are likely to justify the means to achieve the maximum stop as a ‘unique feature’.
I guess what I’m trying to say is “just because the chamber fits the distributor there is no guarantee that the calibration is correct” . . . but if you look at the air gap between the ‘tang’ and the opening in the arm you can estimated the total stroke (some arithmetic required).
dp
Attach file:
VacuumChamber002 [Compatibility Mode].pdf Size: 536.10 KB; Hits: 41This Post was from: https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=261004