MaroonMonsterLS1

Built 2 trans in the last year and both have had the same issue. An issue that is new to me as a builder. I do some more budget minded stock rebuilds for guys that want them and when doing these, I reuse the solenoids. Specifically the shift solenoids. I always ohm test them to ensure they are in spec per the atsg, and will do a bench test to ensure they engage, then will test them with a scanner once installed and they perform fine. The screens were always cleaned and recleaned and inspected for blockages

Except for these 2 trans that I spent more time than I care to admit. The trucks would both start in 2nd. Regardless if I was in OD, D, or 1st on the column. Or even if I commanded 1st with the scanner, it would start in 2nd.

After chasing the problem to no avail, I rebuilt 1 trans completely again, including the valve body and retested all electronics to be within spec. Same problem. I finally did what I SHOULD'VE DONE from the get go and just replaced the damn solenoids. Once I did, the trans worked flawlessly.
This same thing happened for both.

Now time for my actual question (if you've made it this far). What could cause this behavior in a solenoid that ohm's fine, "clicks" appropriately, and even seems to seal fine internally when light air pressure is applied on the bench. Is there an internal seal that leaks, is there instances where the magnet in the solenoid isn't strong enough to fight the fluid pressure, etc?

I'm just curious what the root cause for this undetectable failure is.

Ps, new solenoids will be a definite part of EVERY build from here on out.

henery97

Just because it ohm tests ok doesn't mean some of the windings aren't shorted together. This would weaken the solenoids magnetic field and not allow it to do what it needs to do. A better test would be an impedance test, but you would need a rather expensive meter to do the test. Cheaper to just replace them.