Shutter speed inconsistent on Graflex RB Super D

[Sam_PNW]

I have a 4x5 RB Super D (serial #474432) that I've been cleaning up, and the shutter speeds are inconsistent from the top to bottom of the focal plane by approximately 1/3 of a stop. I've read that it is is typical for this style of shutter to have a somewhat variable speed, but I'm wondering if there's any adjustment that can be made? I've shot some film through it already and looking at the negatives I'm not sure that I can even notice 1/3 of a stop difference across the frame.

Here is the raw data, with the difference between the bottom and top of the shutter as well as the difference from the average measurement to the expected shutter speed.

I measured using Shutter Speed phone app + photodiode, which is perhaps not the most accurate method, but the numbers are consistent across multiple firings. And I've tested other cameras / lenses with this setup and the numbers are very very close compared to the results from a professional test.
I did not measure D-L (800) or D-H (1000) as the app doesn't work very well much above 1/500.

 

[shutterfinger]

474432 is near the end of an order listed on 4/1/1952 with the next order for Super D's in 1956.
It is normal for the shutter to pick up speed as it travels across the film plane. When I test I use two photo diodes, one at the top right and the other at the bottom left with both about 5/8 from the edge of the image frame side, top, and bottom.
Go back and test with the sensor about center of the image frame and go by that speed. The top of the image frame on the camera is image bottom which is normally darker than image top which may be sky or white ceiling so the darker image bottom will benefit from the extra 1/3 stop and the top will not be adversely affected by 1/3 stop less exposure. 1/3 stop exposure is just detectable in wet printing.

When I test I look for consistency across the speed range of tensions and apertures not the table speeds.

This Focal Plane Servicing Guide/Instructions https://drive.google.com/file/d/0B1sPJkp-MdghRkRId1EwT0dpNkk/view?usp=sharing will apply to your camera.
Clean and lube the bushings and roller shaft ends and the wind gear train to gain a slight improvement in operation.