Classic Delco distributors are among the most rugged domestic distributors ever done. We’re rebuilding a cast-iron tach-drive distributor from a small-block Chevy. However, this tutorial applies to virtually any classic small- or big-block Chevy distributor out there because they all employ the same basic architecture as the more bread and butter Delco sparkers out there. This heavyweight distributor was used in a broad spectrum of small- and big-block high-performance Chevy V-8s from the 1960s through 1973 when HEI electronic ignition arrived and replaced point-triggered ignition in the Corvette.
Because the Delco tach-drive distributor is hardy by design, rebuilding and returning it to service is easy, especially when you consider how easy it is to ditch those classic ignition points and opt for the PerTronix Ignitor III retrofit. It is simple to do the PerTronix upgrade with the distributor installed in the engine or you can pull the distributor and freshen it up on your workbench.
PerTronix offers three levels of Ignitor upgrades for your Corvette’s tach-drive distributor. There’s the original classic black Ignitor module. The Ignitor II in red has many of the same great features that the original Ignitor has plus smarter technology. The Ignitor II senses the coil’s current saturation level and uses a powerful microcontroller to adjust dwell. Variable dwell helps to maintain peak coil energy. The Ignitor III is the most advanced Ignitor system to date with all of the great features of the Ignitor and Ignitor II along with an adjustable, built-in rev limiter. The rev-limiter keeps you out of trouble.
When you complement the Ignitor system with a Flame-Thrower ignition coil, cap and plug wires you get an unbeatable ignition system that offers you the same fierce reliability of GM’s HEI ignition without the hassle of a swap. You can install the Ignitor family of ignition retrofits in the car and be back on the road in an hour.
All vintage Delco distributors have a means to identification. This comes in handy when you’re shopping for a replacement for your restoration. Expect to see a model number and date code. From 1955-’56 Delco used a tag riveted to the distributor housing. From 1957-’74 Delco went to an aluminum strip or band that wrapped around the distributor neck. Dual-point distributors continued to have the Delco-Remy tag.
After 1974, Delco distributors had the model and date stamped into the housing. Date codes were an alphanumeric code looking something like 8B23; which meant 1968, February, 23rd day. Delco distributors were also color-coded for easy identification at the factory and quick installation in the engine. Assembly workers wouldn’t have to read numbers. Instead, they would observe the color and install it into the corresponding engine without confusion.
1. The cast-iron Delco tach-drive distributor was employed on Corvette small- and big-block V-8s from 1962-’74. It is easily the most rugged OEM distributor ever made for an American automobile. We’re going to take this proven dynamo and retrofit it with the PerTronix Ignitor III, which has precision spark-timing features and an adjustable, built-in rev limiter. Corvette America had all the replacement parts we thought weren’t even available, including the shaft, bushings, advance kit, shims, tach drive and cable.
2. There really is a difference in distributor caps. PerTronix distributor caps have brass terminals for better conductivity. Distributor caps with aluminum terminals have a cost advantage over brass. Your choice depends on your budget and how you drive your Corvette. It is virtually impossible to tell the difference between the two once you’re behind the wheel.
3. Before disassembly, get acquainted with your Delco’s important reference marks. The advance head (shown) and the distributor drive gear at the other end must be in proper alignment. This square hole (arrow) is one of the rotor’s reference marks (the opposite hole on top is round to ensure you don’t install the rotor backwards). The square hole must be aligned with a dimple on the distributor gear at the other end of the shaft.
4. This particular distributor drive gear doesn’t have the reference dimple just mentioned. When the gear doesn’t have a reference dimple, use the tension pin for reference and how it relates to the square hole at the top.
5. With the distributor drive gear and tach drive removed, the shaft slides out.
6. Stubborn distributor shafts can get help from penetrating lube and working the shaft back and forth until the carbon deposits loosen up and free the shaft.
7. These are the mechanical advance flyweights, which swing outward via centrifugal force against spring pressure as rpms increase. As these flyweights swing out with engine speed they advance the cam, thereby advancing spark. The vacuum advance does its work at low rpm coming off idle. This gives you grunt at low rpm. As engine speed increases, the vacuum advance loses manifold vacuum, seguing to the mechanical advance going to total advance at 3,000-plus rpm. The total advance should never be more than 36-38 degrees BTDC.
8. This is the advance head located at the top of the distributor shaft. The advance limiter pin (arrow) limits how much advance occurs via the mechanical advance. A plastic bushing wrapped around the limiter pin further limits total advance. It also acts as a shock absorber for the advance head. If this bushing is missing you will get way more spark advance than you want. Corvette America has provided us with a complete mechanical advance kit for our tach drive distributor, including this bushing.
9. Replacement mechanical advance weights are not created equal. Some aftermarket advance flyweights are made of a soft steel and they wear badly (bottom arrow). Original GM advance weights and those from Corvette America are made of a super-hard tempered steel alloy. Check your flyweights for wear. The holes should be perfectly round (top arrow).
10. Vacuum is applied to the vacuum advance can to check its function and also clear one of the two vacuum advance screws located near the advance diaphragm for removal.
11. When vacuum is applied to the vacuum advance, the breaker plate moves just enough to expose this screw, which secures the vacuum advance. You can also use a screwdriver to move the breaker plate to access this screw.
12. The vacuum advance can is removed and discarded. Corvette America has provided us with a new one.
13. The breaker points and plate are removed next. Remove the breaker pointer from the plate.
14. The worn distributor bushings are driven out with a 1/4-inch drive extension or a long drift.
15. New bushings from Corvette America yield precision quality, especially when mated to a new shaft. We opted for a new shaft and bushings for a perfect fit. The longer bushing has a cutout in order to clear the tach drive.
16. Corvette America provided us with this cool bushing driver for ease of installation. It keeps us from damaging the bushings.
17. This is the tach-drive port where the drive gear and support are inserted. Some of these have a thrust button made of either nylon or brass. This particular distributor, which has never been apart, didn’t have a thrust button. Note the Delco-Remy identification tag.
18. The bottom bushing has been driven into the case flush as shown. These are extremely rugged bushings designed to last the life of an engine when properly lubed going in.
19. This lubrication pocket in the top of the distributor housing is packed with wheel bearing grease, which provides bushing lubrication.
20. First a nylon washer and then a felt washer are installed on top of the grease, then lubricated with penetrating oil to provide a continuous flow of lube to the bushings. This felt washer should be lubed any time you change spark plugs or service the distributor.
21. The breaker plate and vacuum advance can have been installed. The breaker plate is retained with a small C-clip, which Corvette America has provided. Don’t forget to reinstall the black ground wire shown here. Without a ground wire, you will not get a spark. Literally every part to this distributor is available from Corvette America.
22. The PerTronix Ignitor III is the latest evolution of the very successful line of retrofit electronic ignition systems from PerTronix. The Ignitor III employs all of the great features of the original Ignitor and Ignitor II, plus an adjustable rev-limiter.
23. Corvette America provided us with a new mechanical advance limiter bushing, which must be replaced during any distributor rebuild. This bushing limits advance travel and absorbs shock with changes in rpm.
24. The distributor shaft and advance head are installed at this time. Make sure you have lubed the shaft and bushings thoroughly.
25. New flyweights and springs are installed next. Corvette America has a variety of advance springs available depending upon what you want the engine to do. Because we’re building a stock 1968 Corvette with a small-block, stock replacement springs are fine.
26. Before you are two tach drives. On the left is the new one from Corvette America with the thrust button. On the right is the original tach drive. Our tach-drive distributor wasn’t equipped with a thrust button or the hole necessary to accommodate the button.
27. The tach drive is lubed up and readied for installation. This new tach drive from Corvette America is also fitted with a thrust washer for proper endplay.
28. When you install the tach drive, slowly turn the drive clockwise in small increments and observe the rotation as you turn the distributor shaft. Keep turning the tach drive until it seats. If there is any binding or the fitment is poor stop and check for problems. Add or subtract thrust washers and observe the fitment and freedom of movement.
29. Ted Granger of Ted’s Carburetor in Lancaster, California, puts our tach drive on a good old-fashioned Sun distributor tester for tuning. He finds the tach drive in perfect tune for a 1968 327 small-block. Once this distributor is installed, Hot Rods by Dean will need to do some on-engine tuning, including the adjustable rev-limiter.
30. The tach-drive distributor rebuild is complete and ready for shipment to Hot Rods by Dean for installation. Corvette America set us up with everything we needed to make this rebuild and tune a great success, including the tach-drive cable.
Photography by Jim Smart