72 LS5 advance solenoid?

[Ken C.]

a few questions, I have a 72 BB, auto.
Car has complete smog system. After a points, condenser change i started to adjust the timing, I adjusted the initial fine and started mapping out the distributor advance. I was under the impression that the advance solenoid that goes to the dist. advance solenoid would have vac. in rev. or high gear. I had a friend get in and put in reverse and noticed no vac. stayed the same as in park/neutral. the connections to it have a blue and tan wire. is theyre any diff in which way this connnection goes on? blue up, tan down. or tan up, blue down? Am i missing something here
Also for the numbers experts. Having no luck at GM getting parts or numbers for the distributor stop bushing and retaining clip? Again distibutor is correct for car.
thanks in advance

[Terry M.]

Re: 72 LS5 advance solenoid?

There is no electrical difference in how the connector mounts to the solenoid. The solenoid should work fine with the connector in either orientation.

I take it you have no vacuum at the distributor actuator. Was that test at idle or at some RPM? Engine cold or warm? When we test the system at meets the engine is generally cold or just started and reverse should show a noticeable increase in rpm -- the rear of the car wants to rise up against the brakes.

Do you have vacuum at the hose going into the solenoid (from the carburetor)?

Could be bad vacuum actuator, solenoid, or sensor at the transmission, or low transmission line pressure (low fluid), or even bad wiring -- perhaps a poor connection? Lots of possibilities and a little troubleshooting is in order before you start throwing parts at it, especially expensive and hard to find parts.

[Paul O.]

Re: 72 LS5 advance solenoid?

If I remember correctly it takes 30-45 sec's in high gear before you would get power to the solenoid there is a built in time delay. Paul

[Bill C.]

Re: 72 LS5 advance solenoid?

One other note ...

The vacuum line to the TCS selonoid comes from a ported vacuum source on the carb.
It will not begin to pull any vacuum until the RPMs are around 1000 or so.


To test the TCS selonoid:

Warm the car to operating temperature.
With the engine off, put the tranny in D or R, you should here a click sound comming from the TCS selonoid. The 30 second delay was only a feature on SB cars, all BB cars have no delay (jumper in harness replaced the relay).

There is a fuse in the panel just for TCS, it powers the electrical source to the TCS selonoid.


Hope this helps some ..

[Paul O.]

Re: 72 LS5 advance solenoid?

Missed the part about Big Block. Paul

[Terry M.]

Re: 72 LS5 advance solenoid?

And I completely forgot about the time delay -- even though it doesn't apply in this case. Good catch on the electrical source Bill -- I missed that one too.

[Jack H.]

Re: 72 LS5 advance solenoid?

If I remember the circuit properly, there should be NO change in RPM observed doing the test as Terry outlined (fire up a cold engine and shift into reverse)...

I remember the circuit logic to be:

(1) 30-45 seconds after intitial start (hot or cold engine), the distributor IS given vac advance to increase RPM and speed the warm-up process.

(2) After the 30-45 second interval, the distributor CONTINUES to receive vac advance until the engine has reached 'normal' operating temperature as observed by the temp switch in the RH cylinder head.

(3) When the engine has run long enough to have warmed up, THEN vac advance to the distributor IS controlled by transmission gear selection and ONLY automatic transmission equiped cars provide distributor vac advance in reverse gear...

So, what I'm saying is you won't see an idle RPM change based on tranny shift lever position UNTIL the engine has been started and reached its fully warmed up operating profile. But, if I don't remember the circuit specifics correctly, you'll find a handy dandy theory of operation thumbnail in your copy of the Chassis Service Manual under the emission control section.

[Ken C.]

Re: 72 LS5 advance solenoid?

thanks guys,
bill, will check out system as u suggested when i get home. I'm trying to remember how hoses are hooked up to carb. Looking from front of carb I think the ported, no vac at idle, at base of carb (towards drivers side) is hooked up to pvc. And the hose from diverter valve is going to the carb at the top front of carb. on passenger side. giving full time vac. I bought car from owners that had it since 75. This is the first time i've really looked at tcs. since i put points, etc. in. Will check and see if i get clicks tonight when i get back. Thanks all
another question? I've searched the archives. The vac can in car is a 436 20, should it be a 436-16 or what could i replace it with with todays numbers.

[Bill C.]

Re: 72 LS5 advance solenoid?

99% sure 436-20