I have read that with the replacement of the overdrive relay in 86 4+3 the shift will smooth out. My questions is which relay is it? Is it the one on the firewall or is it the one on a bracket, both are located near the brake booster, or is it neither and I should be looking elsewhere? If it is the one by the brake booster, what does it's sister do. I noticed they have the same part number? Thanks in advance.

Bob

 

The front one The rear one is fuel pump relay

 

A service manual will tell you that info. It will also tell you that is probably not the problem. It will tell you the problem is more likely something is sticking in the overdrive internal valves.
Throw money at a book instead of at indiscriminate parts.

 

I have never seen a service manual that dictates a solution to every problem that could be present or not. As an Engineer I can tell you that when a relay closes it can "oscillate" and not make a good contact thus producing a sinusodial wave of voltage that could affect the solenoid in the transmission. It makes sense from an electrical view point to change the relay before pulling the overdrive. The relay is the original relay in the car and at a cost of $9 from the factory it is a far cry at the cost of a service manual that may or may not help, nor will I spend the time to open the relay up and use crocus cloth to clean the contacts. In fact I was going to replace bith relays for kicks since I was already in the area. I have read to many posts from 4+3 owners that a replaced relay makes a huge difference whether it's true or not I will know by weeks end.
Bob

 

If you mind was made up, why did you ask?

RACE ON!!!

 

If your mind was made up, why did you ask?

RACE ON!!!

 

He didn't. He asked which relay he needed to replace, not whether he should.

While you're at it, check the wires where they go into the relay harness. As they age, the insulator tends to shrink and expose the wires. I've been left stuck when the fuel-pump relay wires shorted together and kept the pump from pressuring the system on startup.

[RICHR]

 

I orginally did not plan on replacing both relay's until I called to find what the cost was it was then at that time I decided to replace both.

Thanks Rich for the suggestion I will definately look at the wires more closely to check for problems. I just do not think the General used high quality wiring in these cars at the time of production. Seems the insualtion gets hard and cracks, even when not exposed to heat and harsh environments.

Bob

 

On your 86 the two relays should be the fuel pressure relay and the OD relay. According to the GM Parts & Illustration Guide the OD relay should be to the left of the fuel pressure relay when looking at them from the front of the car. While I don't support throwing parts at a problem, I do agree with you on this issue, at $9 each it is a wise choice to replace them if you suspect that they are originals.

While replacing the relay may solve the OD shifting issue, it might also be due to old or insufficient ATF n the OD. Even if you just had the OD serviced, it could be that the OD wasn't filled to the correct fluid level.

There is no sensor or warning (other than non-operation prior to failure) if the OD fluid level is too low. You might want to double check that you have NO leaks from the OD pan. Even a small leak means a lot to the small capacity 4+3 OD.

In Richard Newton's book "101 Projects for Your Corvette 1984-1996" he mentions in project 24 that the 2nd gear switch tends to go bad over time and leads to intermittant or inoperative OD shifting. By rewiring the switch to itself (taking it out of the system) he disabled the automatic OD action by the ECM, but retained the ability to still actuate the OD manually via the console or shifter button. You check the 2nd gear switch for its condition and/or try replacing the switch.

 

Thank you very much for the information, I will definetly look into the 2nd gear switch as to I like to have control over the OD as opposed to the computer. I just recently changed the fluid and it as the top of the fill hole when the car is level, so this relay may or may not fix the problem, if it is not raining when I get home I will put both in tonight and check it out. Thanks Mike for the book I will look into getting a copy. I usually depress the clutch when engaging in/out of OD but ometimes the computer takes over and I get the heavy shift. Thanks a bunch.

Bob

 

Last time this came up, someone mentioned that GM was trying a new type of wiring in the C4 and as an experiment it failed... it was supposed to be MORE heat-tolerant and was for a while but apparently it aged badly...

Keep us posted on whether replacing the relay does fix the hard shift. I'm using the clutch right now whenever I can (esp. downshifts out of OD) because the whole car shakes.
[RICHR]

 

rrubel I need your help, when I pulled both relays out I was 'shocked' to see that the insulation on the wires on the OD relay had pulled back/shrunk about 1/2" what did you do your fuel pump relay wires? I could cut them and install heat shrink, solder them back, and then shrink the tubing. It looks to be a tedious job, you do not happen to know if the General sells the replacement plug for the relay? Also just wnated to let you know that I was supposed to get two relays in today but I just got one so I installed the new one on the fuel pump (furthest back and slightly harder so I chose that one first)and just for kicks I took the fuel pump relay and installed it on the OD and took it for a spin and what a differnce it made, not perfect though but downshifts are smoother and upshifts are better also. I am keeping my finger crossed on the new relay. I will keep you posted.
Bob