C3 Distributor noise

[John H.]

Re: C3 Distributor noise

The noise is gone but after I took it out for a short road test, I now notice the Tach is not smooth anymore, it bounces very rapidly when it sets at a certain RPM. (looks like it has the shakes) I did buzz it up to 4500rpm when shifting. Do you believe I damaged the cross gear?

I can't win for losing.

Andrew P

Pull the distributor and remove the cross gear to inspect the teeth on the gear and the mainshaft; if they look like the photo below, both are history and must be replaced.

[Duke W.]

Re: C3 Distributor noise

I don't know the specs for the "437" VAC, but they should be in your CSM.

You can go to napaonline.com and cross reference 1116437 and put in the vehicle data to see what they show as the OE replacement. Then check for consistentcy.

My recommendation is that you convert to full time vacuum advance (including bypassing TCS, if installed), then use the VAC I recommend for base engines converted from ported to full time advance.

I posted this information a zillion times.

One of the several benefits of converting to full time vacuum advance is 5-10 percent better fuel economy in around town driving, so the 10-20 bucks you spend for a new VAC, vacuum tubing, and tee to patch into a full time vacuum source will pay for itself in a few hundred miles.

Duke

[Joe L.]

Re: C3 Distributor noise

Great suggestions!!

I did check earlier to make sure the breaker plate was moving smoothly and it looked ok. The VAC is original to the car, even has a grease marking on it. Where could I get a replacement VAC? (# on can 437)

The noise is gone but after I took it out for a short road test, I now notice the Tach is not smooth anymore, it bounces very rapidly when it sets at a certain RPM. (looks like it has the shakes) I did buzz it up to 4500rpm when shifting. Do you believe I damaged the cross gear?

I can't win for losing.

Andrew P

Andrew----

The specs on the GM #1973437 vacuum control are:

inches of vacuum to start plunger= 7-9

maximum crankshaft degrees= 16@ 14-16" Hg

A replacement is available under NAPA/Echlin #VC-1802, GM #19138052, Delco #D1308A, or Standard Motor Products #VC-171. All will be stamped B22.

[Andrew P.]

Re: C3 Distributor noise

Thanks guys for all the info!!!!!

John I will pull the distributor tomorrow and check the cross gear, thanks for the pic. How would I know if there is any damage to the cable?

Duke thanks for the suggestion on the full time vac advance.

Joe thanks for the part numbers and VAC info.


Thanks,
Andrew P
48361

[Jack H.]

Re: C3 Distributor noise

The original '437 distributor vac advance is pretty hard to find as a correct factory original NOS part... It's advance profile was tailored to the Combined Emission Control (CEC) system that made its debut in 1971.

Your noise might also result from the tach cable. The end of the inner drive cable that inserts into the distributor drive is square in shape. If the cable hasn't been lubricated periodically OR if it was removed and re-connected to the distributor without the cable being TIGHTLY torqued down, you can suffer tach drive cable damage.

One form is the square drive end of the cable (at the distributor) 'jumps' out of the distributor's drive resulting in a clicking noise AND the square end becomes 'rounded' off. A careful visual inspection will confirm/deny.

The other form of damage is the inner cable actually breaks inside the cable's sheath resulting in a different 'grinding' noise . Both forms of tach cable damage result in erratic operation of the tach's pointer needle. To confirm/deny the second form of damage, you have to remove the inner cable from the sheath and see what condition it's in.

But, if this IS your problem (damaged tach cable), it's generally a cheap/fast fix! You simply remove the inner cable, measure it, and buy a speedo/tach cable repair kit from your local autoparts store (by specific length) and replace the damaged inner drive cable...

[Duke W.]

Re: C3 Distributor noise

The specs Joe gave for the 437 are the same as the "B22" replacement, and this is the one I recommend for all base engines with manual transmissions, including those converted from ported to full time vacuum advance.

For base engines with auto trans I recommend the "B20" which provides full advance at 12" since auto trans idling in Drive don't pull as much vacuum as a manual trans idling in neutral.

The point is that idle vacuum should keep the VAC "locked" at full advance with at least 2" Hg. margin.

Duke

[Andrew P.]

Re: C3 Distributor noise

Hey Jack,

Thanks for the info!!!

The noise was definitely coming from the the VAC. After applying vacuum with the pump the noise has not come back. I was planning on rebuilding the distributor this winter anyways.

Now I have the tach problem as well. The inner tach cable at the dist end does not look rounded. I also put the inner cable at the dist end in a drill and the tach worked perfectly, so I'm assuming its the cross gear in the distributor.

If I did want to replace the inner cable are there any tricks in replacing it?

Thanks,
Andrew P
48361

[Jack H.]

Re: C3 Distributor noise

It's a pretty simple job to rebuild a speedo/tach cable, but a few points of proceedure are in order...

Disconnect the tach cable from the tach and from the distributor. Remove the existing inner cable from the drive end (distributor).

Consider 'flushing' the outer sheath to remove encrusted, dried, lubricant using a can of brake cleaner being careful to capture the cleaner as it exits the cable sheath (brake cleaner will dissolve paint!). Allow the sheath to THOROUGHLY air dry after flushing it!

Now, cut and assemble the replacement inner drive cable to size using your original as a template for length. Lubricate the replacement inner cable (your choice of lubricating agents--different folks have different opinions on what's best) and re-insert it into the original sheath.

Connect the drive end first (cable to distributor) to keep the inner cable from 'walking' inside the sheath. Connect the driven end last (cable to tach). You're done!

[Bjorn N.]

[Terry M.]

Re: C3 Distributor noise

When the driven gear is damaged the main shaft almost always is also damaged. It is not a good idea to replace either the gear or the main shaft without replacing the other unit. Also check both the endplay of the main shaft and the endplay of the driven gear. For those with distributors without the button the driven gear contacts, consider installing it. Make the endplay of the main shaft .005 or so, and lube the gearbox well.

[Bjorn N.]