zerngl

I am getting my 72 vette ready for sale and replaced the HEI ignition and MDS box and VDO tach with the stock equipment. I ordered one of those 90 degree offset tach cable adapters because the mechanical tach cable binds so badly on the back of the distributor. Sure enough, last night the cable snapped. Now I have to order the cable and adapter. What a cheesy design. What kind of an engineer would design a mechanical tach drive that comes straight out of the back of the distributor and binds on the fire wall. The Corvette may be a beautiful car, but the engineers were definately more interested in appearance than solid mechanical design. Just look at the bumper brackets!

wcsinx

Well that one was fixed later at least. How about the placement of the power steering cap? Or the fact that you have to disassemble half the car to get the brake booster out. or or or :lol:

ram82fire

It is just 30 plus year old technology ,,,,,,,,,, ya better get used to it when you work on these cars ,,,,,,,,,,,,,,

gman

sray454

ALL early vette distrubutors were installed in the "CORVETTE" position, not in the service manual position. They were done this way on the line and by all experience mechanics of the day. You can not follow the service manual for distributor placement. Basically, the "covette" position is 2 teeth offset clockwise. This will have your vacumn advance pointing almost striaght at your right fender - AND ALLOWS FOR YOUR TACH CABLE TO HAVE A STRAIGHT SHOT to the distributor. NO Bends needed.




[Modified by sray454, 11:24 AM 4/6/2004]

lars

zern -
For this reason, GM issued a Service Bulletin that rotated the distributor to straighten the cable out. You need to use the Service Bulletin orientation for your distributor. This will give you long cable life without the use of the 90-degree adapter. I can send you the distributor installation article I have that shows this, but here is the excerpt from my instructions on how to do this:

"Due to the relationship between the distributor tach drive cable and the firewall on the C3 Corvette (1968 – 1974), GM issued a Service Bulletin allowing an alternate distributor installed orientation in order to straighten out the tach drive cable and to promote longer cable life.

The distributor orientation shown in the above photos installs the distributor so that the vacuum advance control unit pokes out in front of the distributor shielding. In order to straighten out the cable and still retain the shielding, GM allowed the distributor housing to be rotated clockwise 90 degrees. This rotation pokes the vacuum advance out from behind the shielding, pointing it towards the rear flange of the passenger-side valve cover. This orientation straightens out the tach drive cable. When doing this, the spark plug wires were all shifted 2 towers counter-clockwise in the cap, so that the plug wires retained their same relative positions to the engine/vehicle (#1 wire was placed in the previous #7 cap location, thus retaining the #1 wire as the forward, passenger-side plug wire).

It is recommended that C3 distributor installations be done according to the Service Bulletin Alternate Orientation in order to increase cable life and to simplify cable & distributor installation."

LemansBlue68

The motor doesn't care what the orientation the distributor body is in as long as the wires are in the correct firing order and the tower on the cap that is connected to #1 cylinder is in the correct orientation with the rotor. In other words, you could install the distributor body in 8 different positions and as long as the relationship I mentioned with #1 cylinder and the firing order is maintained it will work correctly. As Lars mentioned, you might as well choose the position that puts the least strain on the tach cable (which is straight).

A more troublesome aspect of the Delco tach drive distributor design, in my opinion, is the lack of good lubrication to the upper bushing and the cross gears which often fail as a result. I'm hoping my needle bearing equipped cross gear addresses this problem. There's a small lubrication well in the upper part of the distributor for this, but who's going to routinely check to make sure it's not going dry? The service manual says this is intended to last the life of the distibutor (yeah right, if you expect a distributor life of only 20K miles).

R 73 454

I think the brainiac should have his photo displayed in the men's room at the Corvette Museum. Along with the fan shroud genius. :U

jdunne

Just wait till the moment arrives when you want to undo the cable outer from the back of the tacho and realize that not even a triple jointed monkey with a 2" wide arm can reach it without taking out the seat,dropping the steering column and removing the dash,you have no idea of the joy involved in removing and replacing the dash while trying to stop all the little bulbs falling out...john :eek:

KenSny

C'mon guys.

1. You are dealing with 30+ year old tech that is squeezed into a VERY small dash and engine bay. Look at the room in an early '70s engine bay....

2. GM NEVER intended, or wanted, these cars to still be on the road after 30 years. They wanted them all in junk yards. How will they ever keep selling cars if the old cars last forever and never need maintenance.

3. As for the dash - have you ever priced getting a new digitial cluster "fixed" when a light is out? Just call your local GM dealer and ask for the labor charge on a new Corvette then thinking it will be so much cheaper try calling about one of the new Trucks, Vans or SUVs......

Aflac

Make it a 3some of stupidity... Add the guy that decided using engine vacuum to raise the headlights instead of electric motors!!!! :mad

DJ Dep

I would think that the parts you replaced would have been PREFERRED to the factory junk you are trying to hook back up. Especially if a guy knows his stuff about early Vettes and the accuracy of mechanical tachs. I'd just hand him the box with the original crap and tell him "go at it if you want to replace it".

Dep