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A type overdrive not working

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Plumcrazy Avatar
Plumcrazy Craig Bentley
Perkasie, PA, USA   USA
Greetings,
As the subject line states, my overdrive doesn't work.
A little background. It was somewhat recently rebuilt by Wishbone Classics. It operated flawlessly for maybe 1000 miles then it started acting funny. It would not engage until the transmission warmed up. Maybe 5 miles or so. Then it stopped working al together.
What I have checked so far:
Gear oil level, it's perfect. I'm running AC Delco synthetic transmission oil 75w-90 GL4 as per the recommendation of the rebuilder.
The solenoid, it's clicking loudly, pulls less than 1 amp when engaged.
Operating valve adjustment. 3/16" drill bit fits into hole in case without any resistance.
I've played around with adjustment a little bit just to see if it would make any difference, no luck
Overdrive pressure. It's high, like close to 600 psi at higher RPM's. It takes a second or two for the pressure to build once the main shaft starts turning. It will hold just under 300 psi when I shut the engine off. It eventually bleeds off but it's there for at least 5 minutes. When I shut the engine off and operate the overdrive switch the pressure does not change. This is what I'm thinking is the clue that something hydraulic is fouled. I had the operating valve, ball and spring out when I hooked up the pressure gauge. I was hoping to find a bit of debris or something in there but it's clean. The valve, ball and spring are currently reinstalled.
I'm probably going to drain the unit and check my filter next but have been hesitant to do so thus far because for once in my life I actually have a Triumph transmission that doesn't leak!
Any other ideas?
Regards



Craig Bentley
1971 TR 6
CC 65025 L
Damson / Black



Edited 1 time(s). Last edit at 2018-02-13 06:30 PM by Plumcrazy.

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TR3driver Randall Y
Confusion, Los Angeles, USA   USA
Remove the plug, spring and plunger and check that the ball actually moves. It's common for the linkage from the solenoid to wear until the ball doesn't get lifted against full pressure. The Buckeye articles show how to do it with a dial indicator, but you should be able to see the ball move just by lifting the solenoid plunger by hand. (Don't energize the solenoid with that plug out, or it will launch the ball into low earth orbit.) Here's a link to the Buckeye article http://www.buckeyetriumphs.org/technical/AOD/AOD4/AOD4.htm

600 psi is worrisome too; it's not supposed to go that high. I'm guessing that your rebuilder made the same mistake I did, and shimmed the main accumulator spring up (a common fix for low pressure) just a little bit too much. The spring doesn't reach coil bind at lower rpm; but at higher rpm it does, and the piston can't move far enough to fully uncover the relief ports. It works when testing at relatively low rpm, but the pressure goes way high at redline (especially with cold oil). If that's the case, it's quite possible you have the same result I got : the force literally drove the clutch plate out of the carrier bearing.

Sorry, I was too disgusted to take pictures, but I've still got the ruined plate in the junk bin somewhere.

One more thought : make sure the OD is really not engaged, as opposed to staying engaged all the time. At 60 mph in 4th gear, you should be seeing close to 3000 rpm. If it's down around 2500, your OD is engaged. Sometimes it's hard to tell.



Randall
56 TR3 TS13571L daily driver
71 Stag LE1473L awaiting engine rebuild
7? Stag awaiting gearbox rebuild



Edited 1 time(s). Last edit at 2018-02-13 06:53 PM by TR3driver.

rjc157 Avatar
rjc157 ralph c
pearl river, NY, USA   USA
When you say somewhat rebuilt I wouldn't start messing around with it their way to complicated for a diyer call them up if they gave you a guarantee for their work let them fix it taking a tranny out is no small job if you start messing around with it you going to f--k it up

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rjc157 Avatar
rjc157 ralph c
pearl river, NY, USA   USA
I would give John at Quantum Mechanics in Conn he's very nice look him up he might be able to guide you better

AllanJ71MGB Avatar
AllanJ71MGB Allan Johnson
Princeton, NJ, USA   USA
1971 MG MGB "Batmobile"
1971 Triumph TR6
Agreed on John. Taking my OD up to him to look at next weekend.

carpecursusII Drew H
Oklahoma City, OK, USA   USA
The 600 PSI indicates coil bind. The 3/16 drill bit method almost never works, you need to put the car up on jacks and just actuate the lever with your hand, if the unit actually engages then you can follow the process for setting up the solenoid. If you cannot get the unit to engage by operating the lever by hand then you have a bigger problem. Even with the engine off if you have more than about 150 PSI stored in the spring you should be able to actuate the lever and hear the clutch move. As Randall said, its very worth while to make sure your not stuck in OD, given the high pressure I would venture to guess your actually stuck in OD. Either way, at 600 PSI i think you need to take off the side cover and check out the shim situation under the spring and bring that down to about 450-470. I would also make a note about the oil, you need an oil that does not have detergent in it, redline MT-90 or oriely auto ND40 is a very good option, for a box that may leak or if you just need oil to test it go pick up the oriely stuff.

Plumcrazy Avatar
Plumcrazy Craig Bentley
Perkasie, PA, USA   USA
Thanks for the replies.
Yes 600 PSI is too high. I don't know positively if my overdrive is engaged full time. I am pretty confident that it is not. I know the last time I put it in reverse nothing abnormal happened, I.e. the car went backwards. The transmission doesn't make abnormal sounds and shifts rather nicely. I am aware that serious internal damage can occur if the overdrive doesn't disengage and the car is reversed. My understanding is that the one way clutch fails. Does this also mean that you would lose forward drive?
I called the rebuilder today and big surprise, went into voicemail. I'm going to drain it and remove the filter and just have a look see if something obvious is apparent.
I don't understand why I don't see a pressure drop when I manually operate the lever. I did check, my valve is moving. I didn't measure it with a dial indicator yet but it is certainly moving.
Regards



Craig Bentley
1971 TR 6
CC 65025 L
Damson / Black

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exhibit399 Avatar
exhibit399 Ben J
Macedon, NY, USA   USA
X2 what Andrew said about the oil. Electrically you sound OK. Hydraulically you're way over at 600 psi obviously. If you can test it on jacks and check the pressure when you engage the solenoid that'd tell if you really have a hydraulic issue. PSI should drop momentarily, then build back up pretty quick. I suspect it's mechanical. You've been running double the psi needed to engage overdrive and with oil that I wouldn't recommend, ask John at Quantum @ synthetics in Overdrives. Could very well be the outer clutch is compromised or the sliding member isn't sliding any more. You might find the clues you're looking for in just the filter, might need to get the side cover off as well. Either way, I'd prepare for bad news.
To answer your question, if the one-way clutch goes you won't lose any gears or reverse, just overdrive. So that could be it as well, though not as likely unless you went in reverse while stuck in OD. Good luck

johnstydo Avatar
johnstydo John Styduhar
Hermitage, PA, USA   USA
Your first mistake was letting Wishbone Classics work on your part. And don't waste your time on warranty return with them because you may never get it back.

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Plumcrazy Avatar
Plumcrazy Craig Bentley
Perkasie, PA, USA   USA
Greetings,
I thought I'd give this thread an update.
My overdrive is up and functioning again. The outward symptom of a bigger issue was that the operating lever slipped on the operating shaft. It slipped on the shaft I believe because of extreme oil pressure. During one of my tests I really put my thumb pressure on the adjusting lever and it moved some more.
KERBANG!!! In went the overdrive. Scared the living daylights out of me.
My 600PSI gauge was totally maxed out. That gauge is now broken. I bought a new 1000psi gauge. My overdrive was putting out around 850 PSI at higher mainshaft speeds! I pulled the accumulator cover and springs and what do I find? 5 washers stacked between the piston and the spring! .340" total.
I pulled the piston and filter. I found some metal and the back side of the accumulator cover got beaten up by the spring. I'm hoping that's the only source of metal. The piston, rings and bore looked pretty good.
I flushed the transmission twice with 30w ND motor oil and have refilled it with Redline MT90. I put three washers back in. My oil pressure after a good run remains steady at 380psi. The overdrive shifts in and out quickly and consistently. It's not leaking..........yet so I think I'm going to put the tunnel back on and start driving.

A big shout out to PhilsTR6 for his time and expertise. Several phone consultations and some parts assistance were EXTREMLY helpful to me Thanks Phil!

Regards



Craig Bentley
1971 TR 6
CC 65025 L
Damson / Black

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