dist vacuum retard test

334charlie

334charlie

Member
how do you test and adjust the vaccum retard break on old ford dist 2 or 3 bolt i tried to apply 20 " vacuum to both dist and neither would hold the pressure and would not move the piston. how should this work and how do you adjust them .these dist are in nice shape pistons are not stuck.
 
If the pistons are free in the distributor bore and have a light film of grease on the skirt they should move up with 20" of vacuum applied. This, of course, will require that the spring pressure adjustment is backed off sufficient to allow movement. In use, there must be a good leather cap on the piston. There must also be a rubber seal in the rear face to mate with the vacuum hole on the 2 bolt front cover. Begin tuning with the spring pressure rather light. Drive the vehicle through all the normal ranges of operation and at each occasion where excessive "pinging" is noticed tighten the spring adjustment a turn or two depending on severity. Keep at it until the MINIMUM spring pressure , which allows happy motoring, is found.
 
Our 46 pings slightly on long uphill climbs at 45 to 50 mph. My hearing is not too good so I can't hear it but the wife can. I thought a little ping on those conditions was O K. Am I right or should I try "tweaking" it a bit? Thanks
John
 
The 46-48 repair manual says: "Back off the adjustment on the vacuum brake until the engine pings on a road test under load. Then turn the adjusting screw in just enough to remove the ping. Tighten the adjusting screw lock nut."

The ideal is to have NO ping, but just barely.
 
A big problem with these distributors is: The vacuum brake piston hangs up. Of the last few crab distributors I've worked on these were stuck. Polish up the piston and put a little Vaseline n it.
 
If they are stuck on a distributor you are taking apart, you can get a grip to remove them by taking off the adjuster and running a tap into the hollow piston. Memory leaky, but I think I used a 1/4" pipe tap last time...
When you back off the adjustment, do it slowly by hand because it is easy to pop the spring seat off of the adjusting bolt if turning with a wrench at end of travel.
 
You guys are way more experienced than I am, but the few distributors I've taken apart seem to have a loose piston from wear. I've used some vasolene on the piston to see if it would help seal it in the chamber. There is no way of telling if it actually moves under load is there? My 221cu flathead never pings - even with the screw the whole way out. Seems to have plenty of power but gas mileage is abt. 12mpg around town and 14-15mpg on the highway.
 
Yea Macs has them but the spring is n/g diam too big for some pistons with a smaller diam. hole.Spring has to be a loose fit in the piston to work right. ken ct.I also dont care for the rounded nose on the leather.It will quickly wear down. Mine are flat across.I have new pistons with flat leather installed.$12plus shipping.with spring.
 
59AB, 265 c.i., 3/4 cam, usual 4 degree idle advance, advance works (checked with timing light) regular gas... I left the piston out, no vac hook up, and there is no pinging under load or otherwise... Karl
 
The last one I worked on didnt have a piston in it at all! It worked way better after Larry Murch went thru it and tuned it on his Sun machine. Thank goodness for old tools and good friends!
 
On the piston removal...someone, I believe Ron himself, reported that having the brake totally out results in a bit of timing drift as engine runs. This makes sense, as the brake disc would be free to drift within the range of the slots when pins aren't at the end of travel held tight by advance. I think you want the piston in there at near minimum adjustment for most uses...real drag is generally not necessary with modern gas.
 
I have also read that, but whenever I have tested one on my Sun machine, I do not notice this problem with a good distributor. Besides under most normal (high vacuum) driving conditions, the piston should be pulled away from the disc.
 
Is there any kind of gasket between the distributor and the cap that holds the spring adjuster? I have a ton of old distributors here and none have a gasket or seal of any kind. I find it hard to believe that there isn't a vacuum leak from that cap.
 
Dave D said:
Is there any kind of gasket between the distributor and the cap that holds the spring adjuster?
Click to expand...

Neither of these diagrams of the distributors show any gasket for the cap. Must be tight enough without it.

44534125.jpg
 
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