• Hey Guest!
    British Car Forum has been supporting enthusiasts for over 25 years by providing a great place to share our love for British cars. You can support our efforts by upgrading your membership for less than the dues of most car clubs. There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Upgraded members don't see this banner, nor will you see the Google ads that appear on the site.)
Tips
Tips

TR4/4A Overdrive fade when engine is running warm

Share this page

T

Tony P

Member
Offline
I was on a run over the weekend of Oct 19th. It was a rather long run of about 210 miles, the first half up hill, and the second half downhill in the Sierras east of Sacramento to Lake Tahoe.
I did use the overdrive whenever possible both uphill and downhill. On the last 20 miles my overdrive started shifting in and out while cruising about 60mph on the freeway. Engine was running about 180 to 190 degrees.
The next day I checked the OD to see if the solenoid would click on and it did. So it has to be in the trans.
Any ideas?
 
Is it fading, or actually shifting in and out? I had the shifting in and out problem, it turned out to be an intermittently faulty switch on my steering column. It would randomly shift out, and then back into OD.... R and R'd switch, and problem went away. I thought it was the solenoid at first, and then low fluid. Neither were the case... At least for me.
 
I wouldn't assume it is inside the OD. All sorts of electrical problems can cause similar symptoms, and may only show up when hot or at freeway speeds. I've got an isolator switch that was temperamental for awhile, before failing entirely (fortunately it's the one for 2nd gear, so not too critical). And before that, the ground connection to the solenoid (on a J-type which has a separate ground wire) was just a tiny bit loose when pushed fully home on the tab, causing similar problems. I got lucky on that one, and happened to notice that there was some play in it.

So double or triple check that you have no electrical issues first (they're a lot easier to solve than pulling the gearbox). One approach is to semi-permanently connect a 12v lamp directly to the solenoid, and route the wires out where you can see them while driving. If the light blinks when the OD cuts out, you know it is an electrical issue.

Did it "kick" when going back into OD? That would be another clue that the problem is electrical, the kick means there was plenty of pressure in the accumulator. If the pressure was gone (due to low oil or whatever) then it will kind of ooze back into OD as the pressure builds up enough to move the clutches.
 
A worn o/d with low oil pressure will drop out when oil gets warm. If the electrials all check out, then change oil and go a little thicker.

Marv
 
I have yet to check the oil level. That is on my list to do once my neglected chores are done. Yes the OD did ooze in and out as I drove. I noticed the RPMs go up and the engine speed drop as it went out. And then it did ooze back in and RPMs went down and speed went up.
I am sure the engine and the trans were running hot after a long run. And you know, the installation of a service light for the OD is a good idea, I tend to forget to switch it off after getting off the freeway and then I am shifting with the OD on and it lugs the engine.
 
Back
Top