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· Master Story Teller & Fabricator
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Discussion Starter · #1 · (Edited)
I just made an awesome discovery! Adjustable TH180 auto tranny vacuum modulators! I had heard rumors about such a thing existing, but in 40 years of automatic Opeling and modulator buying I have never seen one. And, on top of that, there seem to be several types with different color stripes on them. If you have an auto tranny Opel with a Combo cam, you'll notice that your tranny shifts horribly at the wrong times because Combo cams drop your vacuum in the manifold a LOT. You might want one of these. Here's why I want one:

I had a 45DCOE single side draft on my 2.4 engine and the engine and tranny performed and shifted perfectly. REALLY perfectly. The engine stared and ran like an FI car and the tranny shifted perfectly and almost imperceptably and at the right time. I then installed a 45mm twin throttle body with fuel injectors and FI and now it won't shift at all unless I take my foot off the gas. Same size carb/TB, but totally different tranny shifting. Now, the 45DCOE carb had 38mm venturis restricting the air flow, but the throttle body doesn't have venturis, so all 45mm worth of air can come in with no restriction.

I put vacuum gauges in all my cars. They let me monitor if I have a vacuum leak forming and I get big fun watching the needle swing when I step on the gas and they help you manage your fuel economy a bit. Under normal, casual, acceleration your auto tranny should upshift at about 2700 rpm. If you floor it, it will shift later in the 3000's. If you really floor it and keep the pedal to the floor, it will shift in the 4000's. Under very light acceleration my tranny isn't shifting well up into the 3000's and I discovered that I have to take my foot off the gas for a secondor two to get it to shift. Downshifting occurs normally. So I started watching my vacuum gauge, with my new FI and TB's, and under very light acceleration I have basically zero vacuum and as I get up into the 3000+ rpm range and it's still not shifting and I ease off on the pedal a bit, when the vacuum rises to about 5Hg the tranny finally shifts. When idling or cruising at a steady speed down the road, vacuum is usually at between 10Hg-15Hg's, maybe as high as 20Hg's, this is the perfect, normal, vacuum for ANY car when cruising at a steady speed on a flat road. I never monitored the vacuum during shifting when I had the carb, so I have no idea what it was.

So, what does this all tell me?

I have a very low vacuum situation during casual acceleration that is causing my tranny not to shift and if I raise the vacuum just a little bit by easing back on the gas pedal just a little bit and increasing the vacuum, it does shift.

So, what can I do about it?

I found adjustable TH180 modulators! You can find adjustable TH350 modulators, but adjustable TH180 ones are hard to find. Why else would they be adjustable if not for the purpose of adjusting them to be more or less sensitive to vacuum?

Now, I have found several types on Ebay with part numbers of 5182 and 5183 and others identified as having blue or purple stripes on the outside. Only one of the adjustable types actually listed the adjustment range as "66-75Kpa" part number "JVM-5182". I have no idea how many different types there are, there might just be the two blue and purple stripe ones or maybe others. The stripes may mean different vacuum ranges. I don't know which type is best for my needs, I'm waiting for a seller to tell me which is best for my very low vacuum situation. I will update this thread when I find out more.

Edit: I have now found SIX types of TH180 vacuum modulators, with 3 different color stripes and each of those in either one stripe or 2 stripe variants, and I have found contradicting ads saying whether they are adjustable or not. Holy Cow, what a can of worms!

If any of you excellent Internet sleuths can find the answer, many Opelers could benefit from this knowledge. Your help greatly appreciated!

Here is a pic of the "normal", non-adjustable, TH180 vacuum modulator I just took out of my car:

Gas Wood Auto part Automotive wheel system Button

Door Wood Fixture Gas Door handle


Here is a pic of a TH350 adjustable modulator. It is not compatible, it does not screw in:

Auto part Metal Cylinder Gas Titanium


This is a pic of a blue stripe, adjustable, TH180 one with a screw adjuster in the vacuum hose outlet:

Handle Household hardware Jewellery Button Dead bolt


This one appears to have a green stripe/lettering:

Liquid Font Rectangle Chemical compound Fashion accessory


This one has a purple stripe

Circle Magenta Wire Auto part Jewellery


Oh boy, I just found other listings that contradict previous ones. It appears that some modulators have 2 stripes and others only have one. Some say that one stripe ones are adjustable and some say they aren't.:

One blue stripe listed as non-adjustable:
Household hardware Liquid Gas Electric blue Auto part


Two blue stripes, adjustable

Serveware Font Circle Metal Fashion accessory


Two green stripes, listed as non-adjustable

Wood Font Metal Fashion accessory Auto part
 

· Master Story Teller & Fabricator
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Discussion Starter · #6 ·
Okay, in the first link, if you read further I bought the type Wrench bought and it turned out not to be adjustable. Also, that thread was from 10 years ago.

The second link isn't giving me anything on Ebay and the guy never used it. I suppose with some searching I might be able to find that particular adjustable TH180 modulator, but where's the indicator that it is for an Opel. The adjustable modulators came out after our cars were made, so I would think that any part number linking an adjustable TH180 modulator to an Opel is questionable.

So the questions are:
Of the 6 that I found, and I've found some with no stripes at all, so there may be more varieties, how many are adjustable and how many are fixed?
If there are multiple fixed ones, do they come in different vacuum actuation variations?

And the BIG question:
Which one of the adjustable ones would be best for my needs?

I don't need stock non-adjustable modulators, I have 2 of them, neither of them has stripes.
 

· Master Story Teller & Fabricator
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Discussion Starter · #7 ·
I just checked with Gil and he doesn't know anything about these adjustable modulators or that there are multiple different kinds.

I also checked Amazon for modulators to see if they were cheaper and found ones with no stripes, stripes in unusual places, one pic that said, printed on the modulator, "Made in the USA", but the ad write up says "Made in China", etc. So, probably stock photographs that have no relation to the actual product and the usual mostly Chinese rip-off krapp that you can't trust one bit on Amazon.


I seem to recall hearing that "manifold vacuum can be affected by spark timing". Can anyone confirm or deny this?
 

· Master Story Teller & Fabricator
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Discussion Starter · #8 ·
I know that the answer to all this will never come, so I bought three $40 ones that were all supposed to be adjustable in green, blue, and purple striped varieties, two with double stripes, all with different part numbers.
 

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Discussion Starter · #12 ·
Different level of what is the question. The stripes obviously mean something, but what is that something? I haven't found anyone or any place that can give me an answer.

Are certain colors for large engines, small engines, powerful, weak, big displacement, low displacement, high rpm, low rpm, etc.?

Almost none of the sellers indicate what cars they are for. Some sellers said this particular type was for Holdens, Commodores, etc. ; Another seller's particular one was for a specific Peugoet ; Another said it was for Post Office Jeeps and Chevettes ; Another said specifically for a Suzuki Vitara ; and another said "For all 4, 6, and 8 cyl vehicles".

Which one do you choose for a jacked up 2.4?

With nothing to go on, I had to use the shotgun approach and buy them in all the colors.
 

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Discussion Starter · #15 ·
Can you make up a test jig that you can apply vacuum to one and see at what level it activates. With your setup, ones that trigger at higher vacuum levels wouldn't work.

Shouldn't your torque curve determine the shift points? Shifting when torque is low would make the car feel flat. I'm not sure how you would match your torque curve to the vacuum profile.

At this point it's all a big guessing game. I noticed that my tranny was waiting until about 3500 rpm to upshift for about 2-3 weeks before I started my FI project. Then when I started driving the car with the new FI it wouldn't shift at all unless I eased off the gas pedal a bit, which would bring the vacuum up from zero to 4-5Hg's, then it would shift as normal.

Is something wrong with my tranny? The modulator? Vacuum leak somewhere? Some quirk of too much spark advance causing low manifold pressure? Throttle bodies too big? It's anyone's guess.

I just completed a serious vacuum leak search and destroy mission and replaced all my hoses, modulator, head-to-manifold gasket, TB-to-manifold seals, etc. I did find some looseness of the hose at the modulator. It could be as simple as that being the cause. But I want to hedge my bet and look into the adjustable modulator thing. I didn't think they existed, but then I found that MOST of the TH180 modulators for sale are now adjustable and there are multiple different types.

I suppose I could cook up a rig to test them and I am curious, but I can't imagine how to make a test rig to do it .
 

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Discussion Starter · #19 ·
It's been over 40 years since I worked in a transmission shop, so I don't remember what the color codes are. For some reason I'm thinking black is the lowest spring rating, but don't hold me to that. What I can tell you is what the color code refers to. It's the spring tension in the modulator. The stiffer the spring the more vacuum required for the shift and the lighter the spring the less vacuum required. But regardless the spring rate the adjustment works the same way on all. There is another spring behind the adjustment screw, so backing the screw out lowers the required vacuum and turning it in raises the required vacuum for the shift.


OH! THANK YOU SO MUCH! That was my next dilemma that I was going to post about. I had no idea which way to turn the screw to adjust it for my needs. Two of them have arrived so far, third one is on the way.

Now, with all 3 versions in my hands, which color and combo of stripes would likely be the best to use for my needs? I know that you probably don't know off the top of your head, so this is just a general question that remains for someone to find the answer to.

I am now convinced that spark timing and other factors related to manifold vacuum are the root cause of my tranny's reluctant shifting. I had not connected a vacuum compensation hose from my regulator to the manifold on my FI project. I did this yesterday and now the car drives much better, revs past 3000 and 4000 without issues, and even shifts better. The vacuum in the manifold seems to have now increased. I had also done major regasketing and hose replacement to make sure that vacuum leaks weren't a factor. It's still not perfect, but the shifting has improved to almost acceptability. Shifting 1-2 is still not happening when it should, if at all, but the shift 2-3 is almost dialed in. Downshifts are no problem.

I fully realize that my desire for an adjustable modulator probably isn't really needed, but maybe it is, due to the high compression of my engine. I bought the 3 adjustable modulators to give me options to help me deal with my issues and make the car work properly as I work through some issues.
 

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Discussion Starter · #21 ·
There is no need for you to get one of these adjustable modulators, they are only used for special circumstances. The only conceivable need for one of these would be if you installed a Combo cam on an automatic Opel. The Combo cams lower the manifold pressure and can cause the auto trannies to shift prematurely. I only know about the Combo cam thing, I don't know what the situation is with "racier" cams. Generally, guys with the "racier" cams have stick shifts, so the premature or, in my case, late shifting isn't an issue.
 

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Discussion Starter · #22 ·
I'm adding the post below from another thread because it applies to this thread:

From Knorm:

<<< Also here’s something to help you figure out the shifting issue with much more validity than my cursory knowledge of auto transmissions. >>>

https://shop.ukrtrans.biz/wp-content/uploads/catalogs/TH180.pdf

Font Line Parallel Document Letter


Font Line Parallel Document Letter


More from Knorm:

<<< So now about your vacuum modulator. You probably need 15inHg to operate your modulator acceptably. So if you are seeing 14inHG when you test 3000rpm NO LOAD on your car you have an issue. If you are seeing 15-20 like me you have no issue. The modulator works by reading the vacuum signal. When it see a large load (low vacuum) it will shift to a lower gear. When it sees a low load (high vacuum) it will shift to a higher gear. There are different modulators available for the GM180 that have different spring pressure and shift differently. There’s also an adjustable one out there.

Now to the quoted comment:

What that is referring to is the intake valve closing AFTER the optimum point of rotation.

You can try check your lash while the engine is running with the vacuum gauge plugged in. I generally adjust my valves while running and looking at a vacuum gauge so I can experiment and obtain the best vacuum at idle. You may have your intake valves too tight, but I kind of doubt it. The hydraulic lifters are pretty forgiving.

I’d check your cam timing first since we know your engine has been milled. kwilford and Mike Meier have both written stuff on that procedure I think. You may have bought firstopels timing system back in the day too. If so visit that thread and put it to use.

I would highly recommend eliminating the cam timing variable before spending time getting messy and trying anything else. >>>
 

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Discussion Starter · #24 ·
I did some research and it seems that a company called Rostra is the primary manufacturer of the various types of these. This is their website link to the page that lists their TH180 adjustable modulators:


Rostra lists 3 types as being available, although several more may be out there. The 3 I ordered have arrived:

Metal Nickel Household hardware Gas Auto part


That's great, but I still don't know what the vacuum range on any of these are and which would be most appropriate to try out first. It's yucky to remove them and screw in a new one because tranny fluid comes pouring out and I'd really like to only have to do this once with the most likely candidate. So I found a PDF on the Rostra site that lists their modulators, here is the page that lists the TH180 ones:

Font Parallel Pattern Number Rectangle


If you look in the Technical Data column you'll see FC and ADJ, I figure that the FC ones are Fixed and the ADJ ones are Adjustable. Notice that the first one is Blue and is spec'd for 69-70 Opels. After the FC's and ADJ's you see numbers, which I guess is the vacuum range. Now, I don't need the Blue Fixed one for stock Opels, I need one that can deal with whatever my problem is, which I figure is caused by low vacuum. Since the Blue Fixed one says "15-16" and the Blue Adj. one says "15-17", I figure that there isn't much difference between them. The Dual Green has the lowest numbers at "9.5-11.5" and the Dual Purple is somewhere in the middle at "12-14". Dual meaning: 2 stripes. So, I have the 3 types.

Which do I try first?

FYI: I think my reluctant tranny shifting is something caused by my throttle bodies, or valve adjustment, or valve timing, or spark timing/misfire, or something other than a problem with the transmission and that the problem is temporary until I find the culprit. Keep in mind that my tranny shifted better than any auto tranny GT I have ever driven over 40 years and it's a rebuilt auto tranny with new belts and stuff inside and I've never abused it, I very much doubt that there's anything wrong with the tranny, it's something external causing the shift problem. I bought these modulators in case I DON'T find the problem and I have to treat the symptom and not the cause.
 

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Discussion Starter · #25 · (Edited)
I found some more info about adjusting these gizmos that puts it in simple terms:

Question:
"I did a search and found that to make my TH400 shift later I need to tighten the flathead screw in the vacuum modulator clockwise. Is this a micro-adustment or does it take full turns to get a significant difference? For example, the secondary valve spring in a Quardajet is a micro-adjustment -- every 1/8th to 1/16th of a turn makes a huge difference. Is the vacuum modulator that sensitive, or does it take 1/4, 1/2, full turns before a change is noticed? I know trial-and-error would give me the answer, but since I don't have a space to work on it (street parking and scissor jack) I'd like to have a baseline to save time before I jack the car up-and-down a dozen times. "

Answers:
"From the Summit Adjustable Vacuum Modulator instructions...."To adjust the shift points of the transmission, disconnect the vacuum hose. With a flat blade screw driver turn the screw on the inside of the modulator end clockwise to raise the shift points and firm up the shifts. To lower the shift points turn the screw counter clockwise, this will also soften the shifts. Only turn the screw two full turns at a time, reconnect the vacuum line to the modulator, and then test drive the vehicle. Re-adjust if necessary." "

"Modulator adjustment doesn't make it shift harder. You have to modify the valve body for that. Adjusting the modulator just changes the shift points or rpm at which the transmission shifts. (ie: holds in a particular gear for either a longer or shorter period of time.)"

"The Modulator will make the shift happen by engine VACUUM... The way to set the modulator is by driving slowly without using much acceleration and allowing the VACUUM to do the shift and set the screw in the modulator for that transition point I set mine about 25MPH.... Once you romp on the gas pedal then the "detent" or "kick-down" cable over-rides the vacuum modulator for the 1-2 shift... Then it is in the governor and valve body for the 1-2 shift........Programming this requires dropping the valve body more times times till you get it where you want...but this will change with temperature and RPM......that is why many use a floor shifter in manual mode so you can shift at your ideal spots where torque is peaking.. "


So, what I'm gleaning from this handful of comments and the quote from the Summit site:
1) To make the tranny shift later, turn the screw clockwise.
2) To make the tranny shift earlier, turn the screw counter-clockwise.
3) Only turn the screw 2 times on your first adjustment attempt, drive, and readjust as necessary.
4) Do your driving tests at low speed/low throttle of about 25mph. Too much throttle will make the tranny shift later than "normal".

In regards to how many screw turns to adjust them and how many turns you can do before you can't adjust it anymore or it falls apart, below is a pic of the 3 modulators I received and the screw positions when I received them. There appears to be at least 4 turns of adjustment possible and possibly several more. Read my comments in the pic:

Camera lens Cameras & optics Lens Camera accessory Circle
 

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Discussion Starter · #26 ·
One thing that I am going to look into to solve my shifting problem is the possibility of inserting the venturis from my 45DCOE carb into the throttle barrels. The car shifted GREAT with a 45 DCOE on it, but now it shifts like crapp with 45mm throttle bodies. So what is the difference between the two? The DCOE has venturis/restrictors in the barrels, the TB's do not. The TB's are 45mm all the way through, the 45 DCOE had 38mm venturis in it, effectively giving it a 38mm passageway. If I slip the venturis into the TB barrels and it fixes the problem.....well......that's what the problem is: My throttle bodies are two big to let my tranny shift normally. I really should install, say, 40mm throttle bodies to mimic the 38mm venturis. That would be the simple answer, but there might be other factors involved, if this works. Venturis increase the velocity of the air through the carb after the venturis. Maybe the increase in velocity will improve the engine tranny performance with the TB's.

I'll find out.....
 

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Discussion Starter · #28 ·
I did my hydraulic lifter 1/4 turn looser adjustment and I'm now at 1/2 of a turn preload. I think I found a lifter that was partially collapsing or compressing too easily.

I took it for a drive and it did seem that the tranny was more willing to shift without me taking my foot off the gas, but still nowhere near right. So I installed the purple stripe 12-14 Hg adjustment range one and screwed in it's adjustment screw 2 turns. I should have then been close to 12 Hg.

Hooray! My tranny shifted without me taking my foot off the pedal! Although good, it was shifting a little too early and I came home, parked on the lift, raised it, and unscrewed it one turn. I should be close to 13 hgs, but who knows. When I do another test drive I'll find out if I've got it just right.

The Conclusion:
Adjustable auto tranny modulators work! It fixed my problem or at least the symptom of my problem. Good enough for now. Now I can just focus on the engine FI tuning without the tranny complicating matters.

🤩
 
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