Can anyone provide information on the optic-sensor distributor used on the 94 and early 95 corvettes? I have been told that these units were sealed and were prone to premature failure due to moisture condensation. Later units, and those that replaced these failed units, used engine vacuum as a vent to remove moisture. Does anyone have additional information or more details on this issue? Thanks.
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Re: 94 optic-sensor distributor
Art-----
The opti-spark distributor was used on Corvettes with LT-1 engines from 1992 through 1996. It was also used on Camaros and Impala/Caprice models with Gen II small block engines over the 1993-1998 period. There were 3 different opti-spark "iterations":
1) early 1992 (to about s/n 8000). GM #10470956. These units were non-vacuum ventilated and had NO vent holes drilled on the bottom of the aluminum casting. Cars with these units installed were recalled and the distributors replaced with the unit described below. Some of these cars had the distributors fail before they were brought in for replacement. In fact, I have one of those cars and experienced the problem "first hand" at 3000 miles. This distributor is a
pin drive" unit;
2) 1992 after about s/n 8000 and retro-fit via recall to the first 8000 cars and through the 1994 model year. GM #10457158. This distributor has 3 small vent holes drilled in the bottom of the aluminum housing, but is otherwise identical to the above-referenced distributor. They have proven quite reliable in service, and I have confirmed that fact with several municipal fleet operators of cars with this engine (93-94 police cars);
3) 1995-96. GM #1104032. This distributor uses a positive ventillation system which operates from engine vacuum. Also, it is a "paddle drive" type unit. Municipal fleet operators report that the failure rate of these distributors is about the same as the above-referenced GM #10457158 unit (95-98 police cars).
The mid-1992 through 1994 distributor can be modified to utilize positive (vacuum) ventillation, but it is quite an involved process and several exsting parts have to be modified and others added. Some of the parts are parts from the 95-96 system (e.g. 2 vacuum harnesses and vacuum fittings)and some are fabricated (e.g. distributor vacuum ports). The distributor must be removed from the car for this modification process.
The 95-96 distributor can be retrofitted to 92-94 applications but many parts have to be changed/added/modified. Included in these are the distributor, engine front cover, and distributor drive. Vacuum harnesses and vaccum fittings have to be added. Intake manifold has to be modified to add vacuum fitting. Camshaft has to be changed or modified to be compatible with "paddle drive" distributor.In Appreciation of John Hinckley -
Re: 94 optic-sensor distributor
Thanks Joe, this is just the information I was looking for. It appears I can use GM #10457158 and be confident it will be reliable.Comment
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Re: 94 optic-sensor distributor
Art,
The biggest threat to the opti-spark is that it is right below the water pump. When (not if) the water pump eventually leaks, it runs onto the opti-spark and the moisture destroys it. I had a '94 Camaro Z-28 that this happened to at about 65K miles. If you are in any doubt, change the water pump at the same time.
LarryComment
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Re: 94 optic-sensor distributor
Art-----
The 92-94 Opti-Spark distributor is now known as GM #10457702. It GM lists for $652.46, less through Delco and competitive GM dealers.In Appreciation of John HinckleyComment
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Re: 94 optic-sensor distributor
Joe, thanks for the part number change. Larry, thanks for the advice on the water pump. It doesn't appear to have been leaking but I think you're right in that I sure don't want to have to do this again later when the pump goes out.Comment
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94 optic-sensor distributor mod
You can add a plastic tube to the drain hole (RTV it in the hole) before you put the new water pump in. I think about eight inches of tube will get the outlet beyond the distributor. Some folks tap the hole for 1/4-28 threads and put in a grease fitting that has had the ball check valve drilled out, then add a plastic tube to the grease fitting. That allows for the use of a larger internal diameter tube.TerryComment
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Re: 94 optic-sensor distributor mod
Thanks Terry, I'll probably try one of these to avoid having to do this again in the near future.Comment
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