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Discussion Starter #1
I have a 96 Cobra with 4.10 gears and an abbott ERA speedo calibrator. The car surges when cruise control is on.

I've seen mention of this in other threads. Is there a solution?

Thanks.
- Jim
 

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I just ordered a set of 4.30 along with the ERA myself. Are all cruise controls affected or just some? I am looking forward to hearing the responses to your post.
 

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I've got an Abbot with 4:10s in a Cobra. The only flaw I've noticed is that when going down very steep hills at highway speeds it tends to slow down too vigorously once the speed starts creeping up. It then has to speed back up, eventually overspeeds and over-decelerates again .... and so on. It seems to work correctly under all other conditions. I don't think that's a problem with the Abbot. I think it's the speed control computer itself.

Possibly significant details:

The Abbot is as close to the VSS as it could be and still be inside the vehicle. They said to keep the wire length (from VSS to Abbot input) to a minimum.

The speedo gear is a 21 tooth rather than the OEM lesser tooth count gear. Long story, but I discovered for myself that the 23 tooth bastard gears are NOT a long term solution and couldn't find the original when it became Abbot time so I went with the biggest legitimate gear available. That leaves the Abbot making a smaller electronic compensation. I don't know how these compensator things work internally in fine detail but some other posts I've seen make me wonder if "maybe" that's part of why mine ended up relatively well behaved.
 

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I'm not sure I can help with the Abbott, but I designed the SpeedCal and we currently have a "test group" with a new software load to try and address this specific issue. Hopefully some units will be installed this weekend and we will have some results.

That being said, I absolutely agree with both points Rick brought up. The closer the unit is to the VSS sensor the less chance to pickup noise on the signal which may induce jitter on the ERA output. The idea for the 21 tooth gear was excellent in my opinion to try to keep the electronic compensation to a minimum. In fact if you use the ground wire which goes to the VSS sensor as the ERA ground you may reduce the noise even more.

Another thing you may try if you could is just swap out VSS sensors with a friend if there's one available. If the sensor itself has a drastically asymetrical (distorted) output it could possibly cause problems for the electronic adapter.

And lastly are you absolutely sure you dont have an intermittant power problem to the unit? Take a look at the heart beat LED. It should be a nice steady beat pattern with no abrupt changes (I think...).

Let us know what you find out...
 

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I have the same issue with my 4.10-geared, Abbott corrected, '96 Cobra. It's not a big deal (for me), but it is noticable - mostly when going up or down a hill. As long as the terrain is relatively flat, there is no problem at all. I don't think the problem has anything to do with the Abbott though. I think it's the way the cruise control responds to speed signals from the computer. Basically, the cruise senses that it needs to make an adjustment and overcorrects because of the 4.10 gears. It attempts to adjust the throttle for what would be appropriate for the stock 3.27 gears. Since you have 4.10 gears, that amount of throttle input causes too much of a correction. It speeds up too much, senses that it needs to back off a little, backs off too much, senses that it needs to speed up a little... etc. etc. etc...

There was some talk about this a while back - and I think someone had a fix - some way to slow down, or moderate the input from the cruise control unit I believe.

Sorry I can't be more help. Maybe someone who knows more will chime in.

Good Luck,
 

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TriBlk... I just recieved a new SpeedCal a few days ago to install in 98 Cobra with 4.10's and T 45. Are you saying it would be better to use 20 or 21 tooth speedo gear VS the stock 19? Would you also say it would work better with 3.73's VS 4.10's? I am familiar with the DM site for coming up with the dip switch settings.
 

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TriBlk....I've been reading your post about SpeedCal for a while, and have another question to ask you. Since you've done the math about the gear corrections.

I notice when you plug in the stock 3.27 rear, around 810-815 tire RPM, 7 tooth drive gear , from stock Cobra setup (96-98), in the Ford formula, you get a number like 18.5-18.6 teeth, and yet Ford uses the 19 tooth speedo gear. Most mags said the bone stock 98 Cobra speedometer was very accurate. If that is so, then when you change rear gears, one needs to go with a tire/wheel combo that nets out a number a little under the 20 (for 3.55), or little under 21 (for 3.73), or little under 23 (for 4.10). Or use a correction device like yours.

As an example, from 3.27's to 4.10's is a little over 25% change, but from 19 to 23 teeth is a little over 21% change. That 4% difference in change (to get an accurate speedometer) has to be made up for with a larger tire circumference, a correction device like yours, or just be aware your speedo is off 4% with stock 25.7" tires. A lot of us are using 25.9-26.1" circumference tires now anyway, which takes up about half of the 4%, so we are a little closer to being accurate. I'm not so picky about speedo accuracy that I worry much about being 2-3% off, but I wonder if I am figuring this correctly. Of course, I need to replace my 23 tooth for sake of durability. Thanks for your responses.
 

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Ralph, yes I was agreeing with what Rick speculated about changing to the largest available Ford gear to try to minimize the problem. I'm just speculating there (since I dont know exactly what is happening in the Abbott...) but it does make sense to me. When you change the rearend to steeper gears, you have to slow down the VSS period to compensate. If an electronic adapter has any significant noise at its input it can multiply that noise when it compensates for the gears (unless they do some time averaging or something but I doubt that they do a great deal if any of this.) If you change as much as you can with the driven gearing, and the noise is in fact electrical and not a distorted sensor output, then it seems you could run a chance of not multiplying the noise as much to get to the same compensation value, IE the noise/jitter is smaller on a percentage basis in the compensated signal.

On the Ford math, I honestly have never looked at it. It never really factored into the SpeedCal product development. However it sounds like they do a lot of "absolute calculation" IE for a given tire size, drive gear, etc... you need this exact driven gear for the speedo to be correct. It sounds like they had specifics in mind for this table. Again, I've never seen it but could this be leftovers from the EEC-IV days and the cable speedos? But for the ratios you listed, I got numbers that are very close to what you listed for the 3.55, 3.73, and 4.10 scenario. However, for the 23 tooth gear please remember that it is not a Ford gear. In order to do ratio math you assume the gear pitch is the same. That's not necessarily the case with the 23 tooth gear as I believe it is a Mopar gear? However its probably very close.

In your last paragraph about th 3.27 to 4.10 change again you get to within 4% with the gear change alone. I wont argue that either. If the gear doesnt get chewed up and thats close enough for people then that is obiviously the cheapest option and I say go for it. On 96-98 cars I dont ever remember telling people they HAVE to use an electroic adapter. I try to always list the option of a driven gear also.

In your previous post about a different driven gear, remember I was trying to help out with the Abbott case speculating that it MIGHT help in that case. I'm not bashing the Abbott, I'm just trying to throw out ideas of what might help. In the case of the Abbott, I'm on the outside looking in just like you guys... Of couse having more detailed knowledge of how the SpeedCal works I dont think there's a big advantage to changing out the gear. I would just say drop in the electronic adapter and see how it works. With either adapter I think the chances are small you will have a problem. And as for what gear range you can go to without having a problem... currently that's unclear to me.

There's a very easy way to tell if its the cruise or not. Right after you do the gear swap and before the electroic adapter is installed, just drive it! Of course drive in enough so that you're sure everything is ok but that should tell you if its the cruise or not. I would really encourage this to the people running 4.10+ gears. Then add the electronic adapter. If it starts getting nervous then I would suspect the culprit is more in the calibrator.

Ralph, if it causes you any problems drop me a line.
 

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I think Poe is right

The cruise control is tuned for the stock power and gearing. It probably uses a simple PI regulator. By changing to 4.10's, we have effectivly altered the characteristics of the system so the tuning of the regulator is now wrong.

I have the same symptoms on my car. One interesting thing to check is are there any supercharged, stock geared cars out there that have seen similar symtoms with the cruise control?
 

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Yes but...

A change from 3.27 to 4.10 is a 25% increase in loop gain or about 1.9dB. I admit is possible that this could pertubate the loop and will in fact eat into its stability margins, I have in fact speculated that in other threads. However, if someone at Ford designed a control loop that is that sensitive to external disturbances or loop variations, they should be publicly shot... IMHO...
 

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With 4.10's and supercharger and 23 tooth speedo gear, my car experiences some of the cruising surges Rick explains about. It's OK on flat terrain, but in hilly country it seems to under and over compensate. And this is before I install the SpeedCal.

I hadn't thought about just starting with a 21 tooth as Rick mentions. That would correct for about half of the change mechanically, and then the SpeedCal could do the rest. Are their any negatives to doing that? The 21 tooth is a Ford part and durable.
 

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I wouldnt think so Ralph. Let me know if you need some help dialing in the switch settings. Basically all you need to do on the calculator is make sure you change to driven gear teeth settings.
 

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Thanks for the offer. But I think I can figure it out. I've already changed the switches for a 19 tooth and 285X35X18 tires and am just awaiting installation. I'll just insert 21 in the menu.

One thing...I've been putting all kinds of combinations in the menu for the settings, and I can't tell how the setting numbers correlate with percentage gear and tire changes. Do the numbers go up and down arithmetically? Maybe they don't. Is it just a series of 0 and 1's? I know nothing about programing.
 

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the gears will take a guarenteed .5 second of ur time.

I have a 98 Gt with the mods listed in my sig., when i put the 4.10's on i went from a 15.2 to a 14.8. and i do alot of highway driving. u will be fine with the 4.10's, u'll be kiking urself in the azz if u don't. my buddy's '00gt (automatic) has 4.10's and he went from a 14.6 to a 14.1 on street tires so u can see the difference with the gears.

there is lots of talk about the loss of top end mph, and the loss of gas mileage, and everything else bad that people say about 4.10's, but the simple fact is that they r a great gear to have (highway or street) and i have not seen any of those negative factors since i've had them. i still can & have gone 140mph (@4K rpm's)with the gears so i know the top end crap is *BS*
 

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Ralph, yes the switch settings are a binary constant which feeds directly into the VSS period multiplication algorithm. Basically the steeper the gear, the larger the constant value.
 

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Discussion Starter #17
Everyone,
Thanks for all your posts!

Rick,
The what I am calling 'surging' is exactly the symptom you describe. However, I get slow speed-up-slow-down cycles on flat ground, uphill, or downhill. But, with 3.73 gears and no electronic compensator the criuse control was rock solid - no fluctuation. I don't think there is a problem with it. I don't know if the mechanic changed the speedometer gear when he changed the ring and pinion or not. I think it originally had a 23 tooth gear. The speedo read about 2% fast. I'm assuming I still have the 23 tooth gear.

TriBlk,
Thanks for the info. I didn't realize that noise was the problem. The wires do seem to be quite long in my installation. Long enough that I can remove the black box out to the front of the passenger seat to set the switches. The ground is attached to a bolt right near (or on top of) the shifter.

If noise is the problem could some kind of shielding be used on the pickup wire? I could try changing the ground (if I could find the VSS ground wire). Since Rick and others seem to have the same problem even with short wires would it be worth it ffor me to rewire?

I do not have an intermittent power problem. The light you describe blinks steadily.

You mentioned swapping out the VSS sensor. Is it likely that a bad sensor would work OK with the 3.73s, but surge with the 4.10s and Abbott? If so, I might be able to get one to try. How would I get to the sensor? With my installation I see the white wire just 'disappear' down through the shifter boot (cut down boot used with pro 5.0 shifter). I can't see the source of the wire.

Thanks again, everyone.
- Jim
 

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AUmustang65, I was just speculating on what might be happening I really dont actually know. I do know on the SpeedCal noise on the input signal can cause symptoms just as you are describing but in our wiring we send the ground wire with the signal wire. It sounds like the input wire already goes down to the VSS signal as it is just below the shifter. The other wire on the VSS sensor is the ground wire.

About the sensor itself. What I'm speculating is that the sensor isnt bad, it just may have distortion properties which get aggrevated by the electronic adapter. Again, this can happen in the SpeedCal but we are testing new software which eliminates the possiblity of this happening. The sensor is held in the tranny by just one bolt. Remove the VSS connector, remove the bolt and slide out the sensor. Be sure that the sensor you swap in has the same gear on it. Also, if you decide to try this dont go buy a sensor for this. See if you can borrow a buddies.

Sorry man, but this is difficult to troubleshoot by remote control. I have limited knowledge of the inner workings of an Abbott so without actually wrapping my hands around it its gonna be difficult for me to be of more help. Good luck though! Keep us posted if you figure it out.
 

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tirefyre, It looks like you're already running 4.10's so I would guess that you've already got it solved... If not. There are two options for a 96-96.

1. Change out the driven gear. Someone will have to post how close that gets you. I honestly dont commit those numbers to memory.

2. Use an electronic adapter. In that option the two most commonly used on this board are the Abbott ERA (which is also sold by Hyland) and the Dallas Mustang SpeedCal (which is also sold by Brothers Performance ). I designed the SpeedCal so I will not give a preference for obivious reasons...

As an update on the cruise control issue with Abbotts and SpeedCals, I've heard from 5 of my 8 guinea pigs. All have reported success to date with the new software load. Its still preliminary and I've asked that they drive it a while and get back to me. Also, I know there we're some 4.10's in there but not sure if there was any steeper gears. I know of one guinea pig who is running 4.56's but hasnt posted back to me yet...
 
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