mystery TCS problem

[Pat M.]

Hi everyone. I have a strange TCS problem with my 1970 350/300, and I've found no help in the tons of archive posts on this subject.

In short, I'm getting continuous vacuum advance no matter what gear I'm in. The strange part is everthing seems to be working fine - I clearly hear the solenoid click only in third and fourth gear, just like it should. The fact that it does this would seem to eliminate any trouble with the trans switch and relay.

I thought sure it was the solenoid itself, but I tried not one, but two, brand new solenoids - no change. Then I thought it must be the temp override switch, but I disconnected it, like the shop manual suggests, and - you guessed it - no change.

What gives? I would really appreciate any advice. Thanks, Patrick Moresi #45881

[Harmon C.]

Re: mystery TCS problem

Patrick
You have tested the system and have done a good job could you have a hose with an extra tee or some of the hoses hooked to the wrong place? Dr. Rebuild has good pictures of the hoses and routing in his catalog.
Lyle

[Jack H.]

Things to check...

(1) Is the distributor vac advance working properly (might be sticking)? When you disconnect and plug hose connected to the vac advance, does timing retard as it should?

(2) Do you have the 'plumbing' right on the vac hoses? The TCS solenoid has three nipples on it. One is vac input (from manifold), the second is vac output (to the distributor) and the third is a vent to allow the distributor's vac advance collapse when the solenoid fires.

I've seen guys think for some reason that all three nipples had to be connected (big cockpit problem!) which resulted in the distributor seeing full time vac regardless of the TCS solenoid's switching state!

[john daly]

Re: Things to check...

A "benefit" to this problem is that the car probably runs better with full time vacuum advance in all gears....it did for me.

john

[Pat M.]

Re: Things to check...

Thanks guys. Jack - yes, when I disconnect the vacuum hose leading to the advance, it does idle down about 300 rpms - just like it should. So the advance is not sticking.

As to plumbing, based on other pictures/diagrams I've seen, I believe it's correct. I have the main vacuum source coming in to the front of the solenoid from the top/front of the carb. At the back of the solenoid, there's a little "T" connection,with one nipple going straight back, which I have routed back to the carb for fresh air. There's another nipple at a 90 degree angle pointing to the passenger side, which I have connected to the advance. This is how the 1970 shop manual shows it should be connected.

Since you suggested it, I just looked and it does appear that Dr. Rebuild's diagram shows the rear hosing reversed. I will try that to see if it works. If it doesn't ...

And yes, the car runs great getting advance all the time. But, as you all know, I'm gonna need this stupid system to work for PV.

Patrick Moresi #45881

[Duke W.]

Re: Things to check...

I don't have the PV procedure for your year, but I don't think it includes a TCS functional check, so if the judge hears the solenoid click at the right time during driving, that's all that's necessary.

I could be that some clever person figured out how to "bypass" the TCS without altering visual appearance or apparent function.

Duke

[Patrick H.]

Re: Things to check...

Patrick,

Take a look at this picture. Your 70 should be set up in a similar manner. The "one port" is the one that needs a foam filter and is open to the air. The "two port" shaped like a T or L is the one you need to use for the distributor vacuum.

Patrick

[Pat M.]

TCS problem solved?

Duke - On page 13 of the First Edition PV manual I have for 1970 it says there is a check - with the engine in third and fourth gear, there should be a 300-700 rmp increase.

I may have found the problem(s). The main problem was my fresh-air vent hose was attached to a passenger side carb nipple that had vacuum. I believe this had the effect of sending vacuum to the advance hose through the rear "T" valve even when there shouldn't have been vacuum. When I disconnected the vent hose, it worked perfectly ... for a moment. Then I heard the solenoid click by itself. So I disconnected the temp override switch and it worked perfectly the entire time.

So apparently the vent tube should not have vacuum, and my temp switch must fail intermittently.

But this brings a new question: where should my vent hose connect to? There doesn't seem to be another free nipple. I've seen pictures on base engines where this hose connects to a nipple on the rear of the carb, but mine has no nipple there. Instead, it has a square hole with what looks like two screw holes on the top and bottom. Should something with a nipple be screwed on there? If not, where should the fresh air vent connect to?

Thanks so much for the previous responses, and any further help you can give me. Patrick Moresi, #45881

[Pat M.]

Re: Things to check...

Patrick - this setup sure seems to make more sense than the other way around, but every diagram/picture I've seen (Dr. Rebuild, 70 service manual, article in the restorer) shows the T or L pointing towards the rear. Are you sure is should be configured this way? Thanks, Patrick Moresi #45881

[Duke W.]

Re: TCS problem solved?

Thanks for pointing that out.

Duke

[Patrick H.]

Re: Things to check...

Patrick,

Mine is a 72, and I can guarantee you that it functions well in this configuration. If possible, I'd like to see a picture of your 1970 solenoid (although I believe I have a couple of them). I note that in the DR catalog, yours and mine do differ. The pictures in Dobbins' book of a 1970 also match the DR catalog.

To further diagnose yours, you need to know 1) is vacuum being provided to the solenoid from the Front or the Rear of the carb, and 2) when the solenoid is on (or off - either answer will help) which two ports of the valve are "open." This can be discerned by just blowing into one of them with a hose. If air goes through the solenoid, which two ports is it travelling through.

Once you confirm the above by testing it yourself, then we can see what's really happening.

Patrick

[Roberto L.]

Re: Things to check...

In 70, electric connector points forward, thats the difference

All my best, Roberto NCRS #30019, RMC

[Jack H.]

Roberto's correct...

The TCS solenoid is essentially the same for '70 and '72 but there's a PN change and the orientation of the valve with respect to the integral mounting bracket flips between the two...

[Dennis D.]

Re: Roberto's correct...

As someone once told me,(Jack), the vent is provided as a sort of vac break to keep the distributor vac from locking up. Vents to the rear upper nipple of the carb

[Patrick H.]

Re: Roberto's correct...

Hmmm.

The 70 appears to work the opposite of a 72.

On mine, when the solenoid is energized it pulls away from the L (or T) shaped fitting, and allows vacuum to "pass" thereby enacting the vacuum advance on the distributor in 4th gear (or when overheating). See my picture above for clarification of direction, if needed. Apparently a 70 must default towards the L-shaped end when in gears 1 through 3, and move towards the L-shaped end when in 4th.

Does anyone happen to know if the solenoid is actually turned ON or OFF in 4th gear (i.e. energized or not)? If it is energized in 4th gear, and that causes the plunger to move toward the L, then it has the opposite winding and/or magnetic property from all the ones I've otherwise tested. I suspect that in real life 4th gear DE-energizes the solenoid but I'd be very interested to know for sure.

Patrick