[TN68GTO]

So working on my engine and getting ready to put the finishing touches on it, I have a few questions about the vacuum. On the distributor there is a vacuum advance/retard. I assume this was standard on all cars in 68?

Does the carb use the hollow stud on the passenger rear of the carb to attatch it to the manifold?

[dataway]

The Advance/Retard was a 68 only thing, and I think only used with auto-trans, the manual had some additional vacuum hardware on it. The retard port, the one pointing inward toward the distributor shaft usually doesn't work on original units, and in late 68 there was a service bulletin where they by passed it by looping a vacuum hose on two ports of the five port Thermo Vacuum Switch at the front of the intake manifold.

The retard port had a hose that led to the TVS, from the TVS a hose went to a port on the rear passenger side of the carb. The service bulletin said to remove these two hoses and loop them at the TVS. If you plan on using the retard function, first make sure it works (the retard diaphragm in the advance unit), second be aware that the Service Bulletin disabled it for a reason.

The TVS was also supplied with vacuum from other sources too. The retard function used it's own two ports on the TVS that are isolated from the others internally.

If your retard diaphragm doesn't work, then it will probably have a vacuum leak, which means you don't want to hook it up. If you decide not to use the retard function ... DO NOT cap the fitting on the retard unit, as that will prevent the advance diaphragm from working.

I think the standard procedure these days for an absolutely correct early 68 model is to run the lines as if they are working, but plug them in some hidden fashion so they don't, keeping in mind not to plug the retard fitting.

There is a long thread on this subject somewhere in this section. I think it has photos of the Service Bulletin.

Service Bulletins and other info can be found in this thread http://forums.maxperformanceinc.com/...74#post5385274

[TN68GTO]

Thanks for the info. Did you ever get ahold of those TSB's? That stuff is pretty interesting. None of that stuff is in the restoration guide.

[dataway]

Yep, I downloaded them from the thread I linked to in my post.

Wish I had the whole book of them, I'm sure they solve a lot of problems that we come across working on these cars.

[TN68GTO]

Yes, I bet that book is worth some $$. I downloaded them also and filed them away.