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Author Topic: HT754CRD Lockup override question -- SOLVED  (Read 9978 times)
Don Fairchild
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« Reply #15 on: June 14, 2006, 04:41:33 PM »

brian;

Now what you need to do is along with the valve you have, install a versa valve or simler valve. You will plum from the electric valve to the versa valve in, from the out to the lockup port from the ex port back to the trans pan. If you don't the lock up clutch wont release. Use #6 hose as #4 wont flow enought oil in either driction. You can also hook your electrial up to your jake brakes so lockup will stay ingaged intill  your jakes turn off.

Hope this helps

Don
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Brian Diehl
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« Reply #16 on: June 14, 2006, 06:19:42 PM »

Hi Don,
I'm a little confused by your post.  Right now I don't know if I'm even on the lockup port for the output from the "main" port.  Do you think the port I'm connected to is right?  If I am on the right port, any ideas on why I'm not getting lockup?

Next, what is a "versa valve"?  Next, what/where is the "ex port"? 

I'm using the 1/4" copper pipe on the current install.  How does that compare to #6 (or #4)?

Do you have some sort of diagram that would help me visualize the installation you are suggesting?
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Don Fairchild
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« Reply #17 on: June 15, 2006, 08:25:45 AM »

Brian;

The versa valve is a shuttle valve that will move one way or the other depending on if you want pressure or to exhaust the pressure.

I was looking for my diagram but could not find it. Several moves and I still have some things in storage, things do get lost over the years. I will try to find some part numbers and a diagram for you. Might take me a few day's to come up with it though.

Not shure on how to draw a picture on the computer and I don't have a scanner. I'll come up with something for you.

Don
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Brian Diehl
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« Reply #18 on: June 15, 2006, 07:25:23 PM »

---- SOLVED ----
I am VERY happy to report that I've got the torque converter lockup override WORKING!!!!!  Yes, I am very excited about it.  The funny thing is the lockup port I found by trial and error is not listed in any of the manual pages I have.

The lockup override works very nicely.  As soon as I'm moving fast enough to be solidy in 1st gear I can turn on the override and the lockup happens immediately in 1st.  Then the normal shift to 2nd happens without me having to disengage the lockup.  The shift from 2nd to 3rd, 3rd to 4th, and 4th to 5th happen normally as well.  Of course, lockup happens regularly at the end of 2nd gear so the shifts in 3rd and 4th are no different.  I will probably use this override even when I'm not in the mountains as it makes the acceleration through 2nd gear much quicker and I'm sure more energy efficient.  However, there is a very large RPM spread between 1st and 2nd so I probably won't use lockup override regularly in 1st during normal driving.  The lockup does work at all speeds so of course I have to disengage the override before coming to a stop so I don't kill the engine.

The lockup port ended up being the port right next to the "main" output.  This is the port immediately next to the raised (lower physically) section containing the main pressure port in the center of the trannsmission.

Thank you everyone for your help and ideas on this problem.  I am just pleased as all get out that it now works exactly as it was described to work!
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TomC
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« Reply #19 on: June 15, 2006, 09:01:14 PM »

Brian- as you discovered, the ratio gap between 1st and 2nd is very large.  Allison geared it this way with the slip of the torque converter in mind.  I would highly recommend that you NOT use the manual lockup all the time, rather only when you are in that gear and especially not from 1st to 2nd locked up.  Remember that the lockup clutch on the torque converter is just a single plate dry clutch that is holding together all of the torque the engine is passing through.  Just my recommendation, you'll do it your way (and hoping nothing will happen).  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
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« Reply #20 on: June 15, 2006, 09:44:46 PM »

So.... Can I do this on my 643 ?
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1962 Crown
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« Reply #21 on: June 15, 2006, 10:38:47 PM »

Should since the MT643 is just a smaller version of the HT740.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
JackConrad
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« Reply #22 on: June 16, 2006, 04:12:43 AM »

Brian,
   CONGRATS!!  Glad to see you got it working.  So how did you firgure out which port was the lock-up port?  Jack
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« Reply #23 on: June 16, 2006, 05:51:52 AM »

Tom, Thanks for the advice on the internals of the lockup.  I'll definintely not use the lockup as part of the 1st to 2nd shift unless absolutely necessary given the information you've given me.  Very valuable advise for sure!

Jack, I found the port by simple trial and error.  On the non-retarder based HT740 and HT750 series transmissions there are only 4 ports on the bottom of the tranny up by the torque converter.  The pictures I had from Detriot Diesel showed some models using the outermost port for torque converter lockup and when compared to my tranny it was the most closely identical to my tranny that I picked.   However, the outermost port was not the lockup.  I then saw some models had the lockup port next to the outermost port.  I decided I had nothing to lose to try that port.  It didn't work either.  I was about to tear everything off of the tranny when I decided I had nothing left to do but test the 3rd and final port.  I decided to try and was immediately glad I did.  In the end I think I have a slightly different tranny configuration than was has been published in the standard Allison manuals.  I don't know why, just given what I've experienece with DD on the phone and such I've got a "wierd" tranny to deal with.

Of course the good news is I got it to do what I really wanted it to.
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Dallas
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« Reply #24 on: June 16, 2006, 07:30:29 AM »

Tom, Thanks for the advice on the internals of the lockup.  I'll definintely not use the lockup as part of the 1st to 2nd shift unless absolutely necessary given the information you've given me.  Very valuable advise for sure!

Jack, I found the port by simple trial and error.  On the non-retarder based HT740 and HT750 series transmissions there are only 4 ports on the bottom of the tranny up by the torque converter.  The pictures I had from Detriot Diesel showed some models using the outermost port for torque converter lockup and when compared to my tranny it was the most closely identical to my tranny that I picked.   However, the outermost port was not the lockup.  I then saw some models had the lockup port next to the outermost port.  I decided I had nothing to lose to try that port.  It didn't work either.  I was about to tear everything off of the tranny when I decided I had nothing left to do but test the 3rd and final port.  I decided to try and was immediately glad I did.  In the end I think I have a slightly different tranny configuration than was has been published in the standard Allison manuals.  I don't know why, just given what I've experienece with DD on the phone and such I've got a "wierd" tranny to deal with.

Of course the good news is I got it to do what I really wanted it to.

Brian,

Is there a chance you could take pictures of what you've done and maybe write it up in a text form so that we could put it in the archives and the help section?

Thanks,
Dallas
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Don Fairchild
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« Reply #25 on: June 16, 2006, 04:57:58 PM »

Brian;

Glad you found the port you needed. Nice pic's. 1/4" and #6 are the same size.

Don
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JackConrad
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« Reply #26 on: June 16, 2006, 05:12:53 PM »

Brian,
   I would like to see a photo of the area where the ports are.  I am planning to put a pressure switch in the lock-up port on our 740 that will shut off my Jake (not installed yet) when the torque converter comes out of lock-up mode.  Thanks, Jack
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Brian Diehl
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« Reply #27 on: June 16, 2006, 07:56:35 PM »

Hey guys,
Sure, I can write something up.  I'll take a few pictures of the final install and put something together.  How should I post it for all to see?

BTW, I'll be out much of the weekend, so I don't think I'll get to this until next week.

-Brian
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gumpy
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« Reply #28 on: June 17, 2006, 06:11:00 AM »

Put it on  your website and post the link. Then you won't lose it when something happens to board.
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Craig Shepard
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Brian Diehl
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« Reply #29 on: June 19, 2006, 08:44:10 AM »

Good Idea Craig.  I'll take that approach!
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