74 Mercruiser Shift Problem

[akeemo]

Hi All

Symptom -- dies only when shifting back to neutral from either forward or reverse. We just had everything off and resealed everything at the end of last boating season. No rust or signs off water contamination what so ever. And just for good measure, the boat is in the water, no issue on land with muffs.

I have read about the interupter switch system and understand how it works.. BTW excellent article!(Actually printed it and added to my documentation binder... thanks) My setup is a bit unique. I have narrowed this issue down to two possibilities.

1. lower shift cable which i havent tested yet. To test it -- I was going to mark the neutral position of the roller and the switchs blade with a sharpie and shift to WOT forward or reverse and then back to neutral to see if the cable returns the roller back to the original position. -- is this a reliable test of the lower shift cable?

2. (This is more interesting) I have converted the ignition system from points ignition to HEI (insert manly grunt here ) However my theory is that the momentary cutout in ignition is enough to "snuff out" the workings of the solid state workings of the distributor. -- Is this a possibility? If so, what do the newer style mercruiser setups have that my vintage 70's setup doesnt to support the HEI?

Thanks so much for any help!!!!

Best regads and safe boating!!!

Noel

 

[jtmarten]

Re: 74 Mercruiser Shift Problem

I'm assuming your symptom is engine faltering/dying when shifting, especially in reverse? You didn't clearly explain the issue.

The issue with lower cable failure isn't whether it'll return to original position or not. The old style upper shift shaft bushing seal is probably shot, allowing water to enter the shift slider/cable cavity. Once water starts getting into the lower shift cable, the core begins to corrode and gets a little stiff, or sticky. If it sticks, it'll allow too much interupter time and the engine falters or dies. Both of my lower cables had water contamination, and a slight bit of rust on the core. Had her out today for the first time since replacing both; no more sputtering and dying going into reverse.
You'll need to replace the shift shaft bushings with the new style upper or the new lower cable will fail quickly. Since you likely have the original style lower cable, you'll have to slightly modify the bellhousing to use the new style lower shift cable.

 

[akeemo]

Re: 74 Mercruiser Shift Problem

heheh,,, your right didnt explain the symptom...

dies only when shifting back to neutral from either forward or reverse. We just had everything off and resealed everything at the end of last boating season. No rust or signs off water contamination what so ever.

thanks for your replies.

Noel

 

[Bt Doctur]

Re: 74 Mercruiser Shift Problem

A binding lower shift cable. Exactly what type of HEI is this?

 

[akeemo]

Re: 74 Mercruiser Shift Problem

thanks for your replies,

Yes ever ything is pointing this way. I worked the cable by hand when we had it apart but i dont have enough experience to tell the difference between a brand new cable and an older bound cable. Its looking like im going to pull the boat out and replace it anyway, just to eliminate doubt. The HEI unit is a ford aftermaket unit (GM Style).

Regards,

Noel

 

[swihartart]

Re: 74 Mercruiser Shift Problem

Yes...lower shift cable... same problem you have and LSC fixed it.
You'll need to tap out your bell housing for the newer style cable (can't buy old style) cause it installs from the aft side. You will also need to get a 9/16" deep socket with the hex head on back so you can turn with wrench or slide second socket over it. The manual goes over the procedure pretty well.