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· Master Story Teller & Fabricator
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Discussion Starter · #21 ·
I'm no expert

I'm certainly no expert and I'm just going by what I've read in the Service Manual and what tranny shops have told me about TH180 trannies. The Opel Service Manual clearly states that nothing should be pulling on the cable until full throttle is achieved. If the cable isn't being pulled at all under normal less-than-full-throttle conditions, I can't see how it can have a part to play if you take your foot off the gas entirely.

It's a pretty primitive transmission. Are your thoughts possibly based on later more sophisticated transmissions?

I'll stop at the tranny shop on the way home from work tomorrow and see what they have to say.....
 

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Welcome John
Nice info and thanks for your input on the matter.

I think that Gordon saw this picture in the FSM.
Text Passive circuit component Circuit component Diagram Font


So the question can you tweak the modulator spool valve with a adjustable vacuum
regulator valve? I believe that you can within some degree.

To answer your question Gordon about how to adjust the vac. mod.
Take a test drive noting the shift speeds(mph)
Only turn the screw 1/2 of a turn at a time.
IIRC - IN = raises shift points, OUT - lowers shift points.
After about five or six test drives and adjustments. You might find a sweet spot
that you can live with.
 

· Opel Key Master
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I don't know why you feel you have more vacuum now with this engine. Did you ever check it before and after. Why would you restrict the vacuum...the modulator under torque load sees about 0" of vacuum at this point. Acording to the manual it requires about 16" of vacuum to bypass the spring pressure...but it is also working against vehicle speed regulated at the govenor. I don't think by closing off a line is going to restrict inches of vacuum. Its like an air line...if I squeezed it...line pressure isn't going to change until air is allowed to escape...then it would slow it down...but the amount would not be measurable at these small amounts. You would need a more sofisticated valve to perform this idea I would imagine. Gordon...your hard headedness is getting in the way of an engineered technology...get you a new kick down cable and properly adjust it. Then if you are having issues of early shifting..maybe it is something with the valve body. I always wonder what these tranny guys consider a "rebuild". I have seen too many old school fixes/shortcuts to call a tranny rebuilt.
Keith
 

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I have rebuilt a number of Opel Trans. and ( Later GM and etc. ) and you need the detent cable working correctly for shift timing . Adjusting the vacuum modulator will not fix your concerns . HTH
John
 
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To add to this : On the Opel trans. (TH-180) ,the detent valve is activated by the downshift (detent) cable which is connected to the carburetor linkage. When the the throttle is half open,the detent valve (being pulled by the cable ) is actuated, causing a part throttle downshift at speeds below 50 mph. When the throttle is fully opened, the detent valve is "AGAIN" actuated causing the tranmission to downshift. The idea that the detent cable is used only for wide open throttle downshifts is incorrect.
To fix your problem you must a good working detent cable , adjusted correctly for you to enjoy your ride .
( DAN knows I hate to type but I wanted to be clear on the operation of the detent cable ) HTH
John
 
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· Master Story Teller & Fabricator
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Discussion Starter · #26 ·
Okay. I'll defer to higher authority.

Okay. I'll defer to higher authority. But, I'm gonna try both ideas because I'm hardheaded. Also, because trying the adjustable modulator is a lot cheaper and easier and because it's very name says what I've been hoping for: adjustable modulation(ie. adjustable shift timing).

My car was converted from a stick to an auto, so I'll have to find someone with the cable stop bracket from the motor mount crossmember of an auto GT or make one. I had bought a brand new cable from OGTS when I made the car 3 years ago because the rebuilt tranny I'd gotten was missing it. I had it routed properly, but not hooked up to anything. Shortly thereafter I started having tranny leak puddles. My brand new 35+ year old cable had gotten brittle with age and the outer housing cracked in numerous places. Chopped it and plugged it and goodbye cable. It's pretty tight in that area in a GT and a new cable may involve a partial drop of the motor to do a good job of installing it. And disconnecting carb and selector linkage, the driveshaft, possibly the exhaust, etc.

That's a lot of potential work considering that two tranny shops told me this week what the Service Manual implies: It's a just a passing gear cable.

You're saying that the cable get's pulled a certain amount by half throttle, and causes something to happen, then after getting pulled some more at full throttle there's even more effect. That implies that it's mutli-position or is infinitely variable. I've had 3 auto GT's. Pull on that cable and you downshift immediately. You even hear a pop happen in the tranny.

Still, if you're right, I now have to find the correct baseline adjustment, since the Service Manual is wrong. I also remember, from trying to adjust them in the past, that the cable can only pull the rod inside the tranny maybe an inch max and that if you make the cable start to pull too soon the cable stops your foot pedal before the throttle linkage is maxxed out putting all your foot pressure on the ball end of the cable, easily tearing it off.

Gosh, I wish I wasn't the only guy with an auto GT debating this issue. Don't any of you guys have an auto equipped Opel with a working cable and can tell us how you have yours adjusted?

This problem isn't that serious guys. It's easy to live with. I just wanted to see if I could finesse it a bit.
 

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IIRC, John worked on Opel's at a Buick dealership back in the day.

I have never paid attention to the cable adjustment in my Ascona wagon. But if things go according to plan the TH180 will be sitting on the ground this summer.
 

· Old Opeler
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Modulator & Kickdown Functions

The modulator (vacuum controlled ) is responsible for downshift on light throttle application. When the manifold pressure drops below the threshold due to engine load the modulator will open a valve that can cause the transmission to downshift. Once manifold pressure has increased above the threshold the modulator closes the valve and the transmission can upshift. The manifold pressure drop at 3000+ rpm is typically not sufficient to cause the gearbox to downshift. The kickdown switch/cable is used to open a similar valve at full throttle regardless of engine load.

Note that the kickdown cable moves a spool that cuts off the Modulator controlled oil supply line to over-ride that function and force kickdown.

Because the Modulator spring pressure also controls the point at which the light throttle loads change-down occurs the adjustable spring pressure Modulator valve allows this actual point to be adjusted.

The confussion arises when people consider the Aisin-Warner type auto trans; in which the oil pressure is modified by the Throttle Valve cable (looks the same and hooks up via cable to the trottle ...) - The TH180 Kickdown cable does not modify oil pressure it is 'just' a kickdown cable so no harm comes to the trans from high or low oil pressure when it is disconnected (I think!).
 

· Master Story Teller & Fabricator
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Discussion Starter · #32 · (Edited)
I bought the adjustable modulator that Dan gave me the link to. About $40 bucks with the shipping. When it comes, I'll pop it in and tinker with it's range of adjustment and some test drives and see if it makes the Opel automatic transmission experience more enjoyable.

I'll post the range of results.....
 

· Master Story Teller & Fabricator
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Discussion Starter · #34 · (Edited)
Non-adjustable

I bought and received the "adjustable" modulator. Couldn't see any way to adjust it. No allen, slot, or phillips head anywhere. Looking inside the holes on either side you just see a flat metal surface. Ended up getting the number of the manufacturer and talked to their head engineer. He pulled a few off the shelf and lo and behold they weren't adjustable either. This caused great turmoil at the company since all their advertising stated that they were adjustable. Returned the modulator.

Tried the c-clamp to restrict the air and it worked like a charm. I'll stick a 1/4 turn ball valve in the line and make my own adjustable modulation.
 

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... Looking inside the holes on either side you just see a flat metal surface. Ended up getting the number of the manufacturer and talked to their head engineer. He pulled a few off the shelf and lo and behold they weren't adjustable either. This caused great turmoil at the company since all their advertising stated that they were adjustable. Returned the modulator.
Ugh, you got to love it!
 

· Old Opeler
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Vacuum Modulator Operation

Found my Holden Trimatic Service Manual - same trans TH180

Note: Modulator pressure between the spools of the control valve will have no effect on the shift patterns since the spools have equal areas.

Coast 2-1 Downshift

If, with the transmission operating in second gear, the accelerator is released, the modulator pressure will return to zero with the spring(s) the only force opposing the line and governor pressure at the shift valve. At approximately 8 mph governor pressure will have reduced to a value such that the spring(s) can move the shift valve to the downshift position, opening the second clutch circuit to exhaust at the shift valve bore. Oil leaving the second clutch will unseat the ball check at the clutch dump valve to provide a rapid exhaust of the second clutch oil. With the second clutch circuit open to exhaust the accumulator spring will move the 1-2 accumulator piston up against its stop.
 

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Well, I was going to chime in about the "adjustable" modulator but I was hoping you might have better luck than me. I went through the exact same thing last year. I have pretty good connections with the local napa and they were kind enough to order me three different "adjustable" modulators before we all determined that the manufacturers advertising must be wrong.
As far as the shifting issues. It has been almost a year since I have driven my GT. It is an original auto car however the original trans was long gone. I actually built one from a manta/ascona th180 and parts from another fiat spider trans, also th180. The shift lever still is on the wrong side of the case for the GT and so that causes a whole bunch of other issues. I do have the detent cable hooked up and adjusted. I have a weber carb and can't remember that causing any issues. I will post follow up when I get it out this year and drive it some more.
 

· Master Story Teller & Fabricator
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Discussion Starter · #38 ·
Well, like I'd said, my issues with the shifting happening a little too soon during acceleration and downshifting a little too late during deceleration weren't debilitating, but they were just enough to be annoying. I don't have the standard "tree" coming off my manifold. I used plumbing fittings to form a T with one side going to the brake booster and the other to the modulator. The diameter of the outlet going to the modulator is probably 3 or more times the size of the stock one. Just like you can blow/suck more air through a fat straw than a skinny one, I figured that my larger diameter was altering the normal shift profile. I restricted the air and both the upshift and downshift issues normalized.
 

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Just thought I would follow up on the modulator thing even though I see you fixed it. I have found an adjustable modulator. Interestingly enough it is the one sold by GIL et al. at OpelGTSource although they do not advertise it as such, go figure.

I ordered it last year (as I had doubts that the one on the manta trans that had sat in a trailer for possibly decades would be functional) but never installed it because surprisingly enough my frankentrans seems to be working flawlessly so far. I took a look at it today and it does have the adjusting screw on the vacuum side inside the port.

It is a BWD brand part #vm501.
 
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