The Stovebolt Site Forums The Shop Area Engine Shop Vacuum Advance Doesn't Advance

I recently had my distributor out to replace the vacuum advance on my '54. When I put it back together and started the engine, it didn't appear to be advancing. I grabbed the distributor to see if it would move and it would not rotate. Everything appears to be in place and the center indicator mark on the advance base is lined up with the mark on the block.

The new advance looked a bit different than the old one, but like many other things on this truck, I figured that the PO had just used the wrong part. The base plate on the old one had an angle to it, while the new one appeared straight (the vacuum diaphragm is parallel to the center indicator mark on the base). Looking in the catalogs, there only appears to be one style of vacuum advance from 47-59.

Any ideas what is going on here?

Thanks for any advice.

When you apply vacuum to the line will the digapram collapse and move the linkage? When you remove the distributor cap and grab the rotor then twist, will the rotor move about 3/16 to 1/4 inch. (mecanical advance) then spring back when released?

You should be able to turn the distrubutor counter-clockwise, against the vacuum advance spring, with the engine stopped. The vacuum advance should have ported vacuum to it; if you connected it to manifold vacuum, you will get full advance as soon as the engine starts and the distributor will not move further by hand. Watch the movement while some starts the engine- if the distributor moves immediately, you have manifold connected to the advance chamber, otherwise, it sounds like something is binding the mechanism.

Harvester

The distributor will not rotate in either direction by forcing it by hand. Also, I tried to move the vacuum advance actuator by hand; it was stuck too.

The engine definitely sounds like it is not advancing as it should when you try to accelerate. It hesitates, surges, and sometimes backfires. It idles nicely though.

It may be that the distributor is stuck in the block. Disconnect everything and squirt penetrating oil around the base, let is soak for a while, then see if you can move the distributor. You might have to keep up the penetrating oil routine for a while. Also, try moving the distributor when the engine is hot, if you haven't already tried that. If nothing else works, you might have success using a slide hammer with a yoke to fit around the distributor bowl and pulling it with the slide hammer. There are devices made for that, but they are not especially common. If you use a slide hammer, be careful not to break off the grease fitting on the side of distributor. Alternately, a strap wrench, along with penetrating oil, might give you enough leverage to turn the distributor and loosen it in the bore.

You likely have something else going on with the surging and hesitation, but you need to get the distributor situation resolved, too.

Harvester

Thanks for the tips Harvester. I shouldn't have any trouble getting the distributor out as I just had it out. It sounds like I may have made the mistake of thoroughly cleaning the distributor an putting it back in dry. Should I lube the shaft with grease before replacing it? Would lithium grease be acceptable to use?

When I replaced the distributor, I gave the grease cup a bit of a turn, but maybe this wasn't enough to make up for a totally dry shaft.

Is this a new or rebuilt distributor? Or did you take the shaft out of the housing? It doesn't really matter, but the shaft should be lubricated. Chassis grease was the standard for filling the grease cup, but if the cup is fairly empty, you might have to fill it and turn in a couple of turns to force the grease into the bushings, etc. It sounds like there is something amiss with the assembly. Did you remove the vacuum control from the housing? If so, you may have installed the control in the wrong place and it is binding against the housing when you tighten the retaining bolt- the octane selector bolt. Remove the octane selector bolt and see if the distributor turns freely- it should. Also, loosen the large fillister-head screw behind the distributor that clamps the vacuum control to the housing. That should let the distributor turn freely in the engine.

If the distributor turns freely in the engine when you have all the hardware loose, let the distributor rest in the oil pump (it has engaged the oil pump, hasn't it?), then snug the octane selector bolt at its zero point, then tighten the fillister-head screw on the vacuum control clamp. There should be a space between the top of that clamp and the top of the machined surface that goes into the engine. I don't remember a specific distance for that space, but something around 1/4" or 3/8", I think is typical. Maybe someone else has a distributor to look at and can give a good measurement.

Harvester

throw a piece of hose on it then suck on the hose to see how freely it moves, might have bad diaphram.

It is just the old distibutor that was in it when I aquired the truck. I don't think that I removed the shaft from the housing. I removed the whole assembly in order to replace the vacuum advance. The old one was full of oil on the carburetor side when I removed it. I will remove the assembly again and check the items you mentioned. I will also do a vacuum check on the advance unit and report back.

Okay, this thread has been dead for a while but I am back working on this again. As I mentioned previously, I had replaced the vacuum advance, but the new one looks different from the old one. Stupid me, I threw away the old one assuming that the previous owner had used the wrong one. I have some pictures at the link below showing the two different vacuum advance units.

Vacuum Advance Pictures

The one label VC 435 resembles the original that I removed and stupidly threw away. The VC 310 is similar to the one that I used as a replacement. The VC 310 type is what is commonly available from the usual suspects. You will note that these two have very different specifications.

Could it be that the Hydramatic version used a different vacuum advance? There are other things like this about the truck such as the automatic choke that was unique to the Hydramatic. Another question is if the VC 435 style advance unit is the correct one, would any unit that looks like this work?

Aaron,

VC 310 is the geometry/angle of the bracket-angle for the units on the two 1954 235 Hydra-Matic engines that I have 9and on my other 54 trucks). This same unit was used on all 6-cylinder engines from 39-51 and on all 1952 through 1955-1st series trucks.

The angle of the other unit is, I think, more like the angle used on automobiles 235s from 52 and upwards (and maybe on 55 and later trucks?).

Part # 2.140 this is the vacuum control unit, not the bracket.

Those images are very interesting - I never knew that there were different specs on the vacuum control units. Does the catalog where you found the images indicate car or truck engines?

Here are photos of the two different style units. All my 54 truck units are like the unit on the right.

Yes, I'd like to know what catalog you used for those units also?

DG

Tim and Danny,

I'm not sure what catalog those images came from, but I found them in these Ebay posts.
VC 435 on Ebay
VC 310 on Ebay

I also found some others that resemble the VC 435, with various claims as to the model and years that they would apply to.
1116076
1918889 V539
59-62 car and truck?
E1169 V541
076 for 53-54 Vette?

It's enough to make your head spin. I am starting to have some doubts about the identification of this engine. I took a quick look at the block numbers this morning and came up with:

Stamped by distributor: F630B
Cast above starter: CON8 F258

I'm less certain of the second number above as it was hard to read. I will try to get a better read of it tonight. I'm having trouble matching up these numbers with the references available here and from other online sources. At any rate, I'm fairly certain that it was made on June 30th at the Flint factory sometime about or prior to 1960 (since the month in the stamped code does not have the leading zero). I am also suspecting that it was orignally mated with a Powerglide and not a Hydramatic due to the "B" at the end of the number stamped by the distributor.

Any thoughts?

1958 car with a Powerglide transmission?

Stamped by distributor: F630B
F = Flint, MI
6 = June
30 = 30th
B = for use in a Powerglide car (having hydraulic lifters)

Cast (date) above starter: CON8 F258
F = June
25 = 25th
8 = 1958

In what year truck will you be installing this engine? Use the truck vacuum advance unit for that year. Or, use at least the mounting bracket used for that year truck - the angle of the bracket may be dependent on the location of the front motor mount. A truck with a front motor mount would use the straight bracket vacuum advance, as on VC310; and, the angled bracket (as on VC435) would be used if your truck has side-mount front motor mounts?

The two different types of vacuum advance control parts (group 2.410 in Tim's catalog link) are shown in the Chevs of the 40s catalog. I believe that it is also required to use the matching clamp/arm (group no. 2.414) for the controller. There was thread last summer concerning a similar problem. If the arm/clamp screw is backed off does the distributor rotate?

Hoyt

Tim,

Thanks for the info on the numbers. You are obviously more skilled than me at interpreting these.

This is the engine that my 54 Hydramatic-equipped 3100 came with.

Wouldn't the configuration of the distributor and vacuum advance be completely determined by the engine itself and not be affected by the vehicle in which it is installed?

The distributor will rotate if the clamp is loosened, but when the clamp is tightened, the distributor will not move.

If the engine really is a a "car" engine, then it would seem that I need the car (angled) bracket. It's starting to look like I have a car engine with a truck vacuum advance paired with a car clamp.

This maybe a really poor answer to your delima. My vacuum advance did not work because it had a busted diaphram. I replaced it and the diaphram worked but I only got a small travel. Problem was I had tightened the clamp bolt on the shaft too much...loosened, works fine...good luck with yours

A minor update, the engine block casting number is more like:

CON 3 F258

I also grabbed the casting number off the cylinder head if that helps. It is:

B52 848 850 (the last 3 numbers appear below the first 6)

Well I just ordered the vc310 that was in Rightys post, will let you know how it turns out. It is going in a 54 with the original 235 and hydramatic. One of the part #'s they list with it is in my parts book for 1938-46 gmc trucks(canadian printing) #1909343 and says it is for all 46's except 97 series which seems to have a 248.5 cu. in. engine. Murray

Murray,

If you have the original engine, it would seem you could expect the normally specified part to work. Out of curiosity, what does the bracket look like on your existing vac advance? I presume it is the 'straight' one like the VC 310.

I will try to have a look at it this weekend and see about a pic.

I have had the same issue you are having. I bought a vacuum advance a few years ago from Oreilly Auto parts for a 1955 Chevy first series truck. When I put it on, it mounted differently than the original, and it resulted in a bind that would not allow the distributor to rotate. My advice is get on that is designed for the year of your engine. Also, there is a small L shaped tab that protrudes up through the area of the vacuum advance called the "octane selector"/timing advance marks. That little tab prevents the distributor from rotating to far. If that little tab is bent over to much, it will cause severe binding and no distributor rotation at all.

Righty The bracket is the same as the new one in tims post (tclederman), but the control unit looks like the old one beside it. The #'s on my old one are 043 on the bracket and 774 on the flat bar that moves in and out of the control.

OK Righty I got the vc310 in the mail to-day and here is my first attempt at putting on a photo link.It shows the old and the new (or at least unused) vacc. advance. They both have 774 on the flat arm and delco remy usa stamped on. I would appreciate if someone would just post if the photo link to flickr works Thanks Murray www.flickr.com/photos/46gmc/5471991173/

picture link works fine.
How about the advance?

regards,
Leon