A/T not shifting into 4th gear

Snomad74 · Post by **Snomad74** » Wed Mar 29, 2017 9:12 pm

I'm sorry for the redundancy on this topic, but I have not received a response from others that have posted about this issue and could really use some feedback. I have a 1990 L300 Star Wagon with 4sp A/T that hasn't been shifting into 4th gear ever since I drove it down to Lake Tahoe, CA after buying it in Vancouver on Feb 22. It drove flawlessly straight through on that trip, ~1500 km, then developed the issue immediately after. It does shift into 4th after about 30-60 minutes of driving, but it seems to be taking progressively longer. I was going to start by having the A/T fluid and filter changed, but other forums have suggested the coolant temp sensor, OD sensor, and solenoid. I'd be grateful for feedback from anyone who has solved a similar issue. Thanks.

ynwa · Post by **ynwa** » Thu Mar 30, 2017 8:50 am

Hey, my l300 had this issue, well it never had a 4th gear after I acquired it. The fix was the overdrive solenoid. Try to find a wrecker as they don't fail that often. Installed the used one and instantly had 4th. Hope that helps! The test was to run power to the unit and drive. If still no shift, that's the issue. (wisdom regurgitated from GrowerBearNZ) :)

Here's a link to it's location. Call these guys for a used one: http://www.ccautos.ca/.
http://pajero.myfreeforum.org/Overdrive ... ut123.html

Post by **Growlerbearnz** » Thu Mar 30, 2017 3:26 pm

Here's the actual thread with fresh, unregurgitated wisdom: http://www.delica.ca/forum/viewtopic.ph ... 1&p=132334

Interesting that it eventually selects OD- it may be that the solenoid is gummed up inside, and only works when it's warm enough to melt the goo.

These transmissions are ridiculously primitive. No sensors or ECU at all, the only electronics are the OD solenoid, switch box on the side which controls the dashboard lights, and AT Overheat warning switch.

The "temp sensor" that stops OD/4th being selected when the transmission is cold is just a calibrated port in the transmission- if fluid viscosity is too high (like when it's cold), it can't make enough pressure to activate OD. I've recently switched to lower-viscosity Dexron 6, and it'll select OD anytime.

Is your current fluid clear and red or is it sludgy and black? If it's dark, definitely change your fluid. Consider a transmission flush too.

Snomad74 · Post by **Snomad74** » Thu Apr 06, 2017 4:50 pm

Much thanks to both ynwa and Growlerbearnz. You're feedback on this issue is very helpful and appreciated. I actually still haven't had a chance to really get it figured out since I've been traveling for work a lot lately and I haven't been able to find any mechanics really willing to work on it in the Lake Tahoe, Reno, Carson City area. Also, I will have to order parts from BC prior to taking it to a shop. So I'm trying to troubleshoot the problem as much as possible, so I get the right part(s) and be specific about what I have (probably) a transmission shop do.

From both of your descriptions of the problem, I think it really could be the "temp sensor" stopping the OD from being selected. Hoping that before having to do ahead and replace the solenoid. Maybe the tranny fluid and filter change with Dextron 6 is the fix? However, the fluid is clean and red. Is is possible for old fluid to not have been completely flushed during a recent, supposed change by Mardy (Amazing Auto)?

Cheers.

Post by **Growlerbearnz** » Fri Apr 07, 2017 3:15 pm

If the fluid is clean and red, it's likely fine and I'd look elsewhere for the fault. Transmission fluid has to be pretty gross before it starts causing shifting problems. My recent switch to Dexron 6 was because I had the transmission upgraded and that's what the workshop specified. I don't know if DX6 is suitable for a stock transmission (but it's supposed to be backward-compatible).

I'd start with the solenoid, but do a little diagnostic work before buying a new one: listen for the old one clicking, check there's power at the solenoid when OD is switched on.

Snomad74 · Post by **Snomad74** » Fri Apr 07, 2017 4:25 pm

Thanks again on the suggestions for troubleshooting the issue and saving me the time and cost of changing the transmission fluid for no reason...although I was kind of hoping that would be the easy fix. I will definitely start by checking the OD solenoid. Is it any indication that it's functioning properly if the OD button works to drop me into 3rd when I'm in 4th gear? I tested this numerous times on a long drive last week and it worked every time.

Post by **Growlerbearnz** » Fri Apr 07, 2017 5:41 pm

Welll... if it works fine when it's warm then I guess the wiring must be ok.

Given that the fluid looks clean, If it were my van I'd replace the OD solenoid first, and then (if that didn't resolve the problem- eek!) have the transmission thoroughly flushed.

I hate giving advice when I'm not familiar with the fault, but usually when there are OD selection problems on these transmissions it's the solenoid.