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Discussion Starter · #1 ·
Yes, this requires some machine work but for those who have the equipment or can think out of the box on how to make this mod this should work just fine.
Anyone that has a really large TB like a 90mm may be experiencing a VERY sensitive cruise control. May car cannot maintain a steady speed without bucking the car pretty violently while trying to maintain a steady speed. The reason for this is b/c the cruise control motor is programmed to pull the cable at a specific rate in order to maintain the proper speed. When installing a larger TB this same amount of pull rotates the throttle blade the same amount however b/c the TB is so much larger a higher volume of air is going into the motor which makes the car accelerate a lot faster than before.
I've experimented with making the cable connection on the TB bracket up to 3" from the throttle blade pivot point and it still didn't help and making it longer than this would only cause interference with the fuel rails.

Solution: There is a pulley inside the cruise control and turning this pulley down to a smaller diameter prevents the cable from being pulled as far. This modification 100% solved this issue. See pic of what I did.
1072517



Also, on my car which uses a custom throttle blade bracket the cruise control connects to the stud on the TB bracket approx .500" from the throttle blade pivot point and I currenly have room to go longer to soften the acceleration rate a lot more but right now I don't see the need for it. This mod worked so well that the car was a complete joy to cruise around in.

KS
 

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Nice find!!

what is the size of this wheel?

I think i could 3d print it.
 

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Discussion Starter · #3 · (Edited)
Nice find!!

what is the size of this wheel?

I think i could 3d print it.
About 1.5" in diameter.
My car is a 2002 GT so I'm not sure how other years compare but the theory should work.
I thought about modeling it up and buying a printed one but decided to try filling the cavities with epoxy first and see how it would machine. It was slow going but came out great. I held it with a 3/8" collet on that D-shaped boss in the photo.
3D printing should work. There are features that are required, like that triangular hole on the left side which holds the end of a spring, but I can't see any feature being that critical. The motor is designed to take up any slack in the cable so it doesn't need to be precise. The pulley is a press fit onto a shaft that has a flat on one side. I bought a few junkyard controllers so I can take them apart and see how it worked, and just in case I needed one, but things worked out as hoped.

For anyone that has the ambition this is a simple mod.

ks
 

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Nice! Mine has the same problem. I had looked into changing the gain of the cruise amplifier, but this seems easier and I won't have to climb under the dash to dig out the control unit.
 
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Discussion Starter · #5 · (Edited)
Early on I really thought making the cable connection point on the TB bracket longer would solve the issue but after 5 different designs it didn't make as much a difference as I thought it would. The last attempt was crazy long at 3" and it didn't make much difference. That's when I decided to see what internal mods to the motor could be done. I knew making a smaller diameter pulley would have an affect but not this much. Especially since the cable now connects 1/2" instead of 3" from the throttle blade pivot point.
This is one thing that had really depressed me about driving the car b/c I use the cruise everywhere in town and on the highway and to have the car feel like a POS when driving made it really depressing. Now it's such a nice machine to simply jump in it and drive.


ks
 

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About 1.5" in diameter.
My car is a 2002 GT so I'm not sure how other years compare but the theory should work.
I thought about modeling it up and buying a printed one but decided to try filling the cavities with epoxy first and see how it would machine. It was slow going but came out great. I held it with a 3/8" collet on that D-shaped boss in the photo.
3D printing should work. There are features that are required, like that triangular hole on the left side which holds the end of a spring, but I can't see any feature being that critical. The motor is designed to take up any slack in the cable so it doesn't need to be precise. The pulley is a press fit onto a shaft that has a flat on one side. I bought a few junkyard controllers so I can take them apart and see how it worked, and just in case I needed one, but things worked out as hoped.

For anyone that has the ambition this is a simple mod.

ks

thank you, should be easily printable.....

I'll hit a local wrecker, and grab a sample to CAD up.
 
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I look forward to your results to Indy. I may upgrade to larger than 75mm TB at some point and this is super helpful.
 

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For the people with 93 and older fox bodies they use a vacuum powered servo not an electric motor servo. The vacuum servo doesn't have the wheel.
 

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Aaah of course. Thanks for the SMH moment. Was surfing this section and left my brain in the 90’s.
 

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For the people with 93 and older fox bodies they use a vacuum powered servo not an electric motor servo. The vacuum servo doesn't have the wheel.
plan b time
 

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I asked over on another forum where there's a thread with Cruise info, including wiring diagrams. It looks like it might be possible to change the gain by inserting a resistor in the wires connecting the cruise control amplifier and the speed control servo. Restricting the vacuum like would help by adding a delay, but the total throttle movement would eventually occur. This might slow the oscillations, but probably wouldn't stop them. I guess someone could try it.
 

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The servo matches set speed, and I think slowing it down may help prevent over shooting and hunting for the target speed. The servos don't target a programed throttle opening for a specific speed. If they targeted a specific amount of throttle opening there wouldn't be any way to adjust for engine wear and variances in performance. There are probably some preset PID settings programed in the control module, if you could change them it may solve the problem. I don't know how you could do that, but slowing it down may make it easier for the control system to achieve target.

Actually the system doesn't know how fast the vehicle is going in miles per hour.. When you push the set button it looks at the frequency and amplitude of the speed sensor and then targets that.
 

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The servo matches set speed, and I think slowing it down may help prevent over shooting and hunting for the target speed. The servos don't target a programed throttle opening for a specific speed. If they targeted a specific amount of throttle opening there wouldn't be any way to adjust for engine wear and variances in performance. There are probably some preset PID settings programed in the control module, if you could change them it may solve the problem. I don't know how you could do that, but slowing it down may make it easier for the control system to achieve target.

Actually the system doesn't know how fast the vehicle is going in miles per hour.. When you push the set button it looks at the frequency and amplitude of the speed sensor and then targets that.
I say we try different methods and compare notes. I'm actually unsure how a low-vacuum engine like mine will work with the servo. I don't even have cruise control cable connected, but this thread reminded me that since I'm still using the OEM VSS for my digital dash that there's no reason the cruise shouldn't work, even though I'm running a Holly ECU.
 

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I don't have cruise on my car , so it makes it hard for me to do any testing. If you have a low vacuum engine there are 12v vacuum pumps that you could use in conjunction with a vacuum reservoir. Several diesel trucks used them from the factory and there are also aftermarket ones available. Use it along with engine vacuum with a check valve. The engine would provide the volume and the pump would increase the level of vacuum kind of like a 2 stage air compressor.

Dorman makes one part #904-214
 

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There are three wires that control the servo. I think adding two resistors might slow it down slightly. It's worth a shot, but i have no idea what values to use. I'd say try starting with a 25-50K ohm resistor and see if it makes a noticable difference. It would need to be installed on 2 of the 3 wires that power the actuator. This would all be an experiment of course.

Wire colors did change, so i don't want to quote which wires. The diagrams are all in my other thread on that other Forum
 
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Here's the page from my Cougar/Tbird electrical/vacuum manual. Wire colors may vary compared to your vehicle. Possibly inserting a resistor into the VAC and VENT wires as this should slow the modulator from applying vacuum or vent to accelerate or decelerate the car. The 50k pot sees movement of the actuator via the wiper (Y/R) feedback wire, so the amplifier might increase output if it doesn't see the actuator moving fast enough, but hopefully the slower action will mimic a smaller TB and oscillate less (rapid speed up/slow down that infuriates those who have added larger TBs.) Hopefully I have time to play with this. I'd have more time if someone knows how to fix the defective radios in the MK3 Focus. :rolleyes:

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😂 thx tho!
 

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Discussion Starter · #20 ·
Here's a long shot but what year trucks(?) came from the factory with a 90mm TB?
Could their cruise control units be cannibalized and assembled to the Mustang units in any form?

ks
 
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