Rear Bag Question

jbird97

jbird97

Registered
Ok guys, I know this might be a repeat question but I haven't found it. I've been trying to figure this out since last fall. Last fall I swapped on the cobra r's and the smaller diameter tires. Which made the gap in the wheel well huge. The car was level before and level after. I lowered the front and it was looking good. I hadn't gotten to the back yet to try lowering, when the tires on the front dry rotted. While I was waiting for new tires to come I put stock back on, but I had sold two of my stockers to the guy down the street. So I had to drive around with the the cobras on the rear and stock up front. The overall diameter of the fronts was larger so the front rode higher during this time. The new tires came and got the Cobra's back on, and now the back was tucking (never lowered the back) and the front had a gap just like when I originally switched from stock to cobras. My thought was that the car had gotten used to the mismatched wheels and it was filling the bags accordingly, and that over time it would readjust. That didnt happen. I tried playing around with the suspension a little but nothing worked. Well I put the car away for winter up on jack stands and didn't try anything with the suspension, I was hoping that with all of the wheels fully extended the suspension would be level when I pulled it out. Well I pulled it out today and its the same as before, but the back is tucking even more. I'm thinking about trying to do the opposite of lowering the rear, to bring it up a bit. The bags do lift the rear a tad but nowhere near where it should. Are my bags gone, and need replaced? Or is it just something else weird? I'm a little tight on money right now, so I'd rather not start throwing money at parts till it gets fixed. Any ideas?
 
The sensors have no clue what tire, rim or size or tire/rim are on the car. It does level the car but it does NOT level it relative to the ground. It levels based on the position of the upper or lower control arms. If clearances allowed you could put tractor wheels on there and the ride height sensors would no none the better. However different size tires can give the appearance that the car is lower or higher than it should be since the wheel well clearance will change, but the hub will still be in the exact same relative location.

Just need to get those sensors right and you will be fine. Remember to lower the front you raise the bottom on the sensor up. But the rear you do to it exactly what you want the rear to do - lower the sensor to lower the rear or raise to raise up.
 
Yea I did the front, just never got to the back. Wouldn't the larger stock tires, put the hub higher then the rear hub, by half the difference in tire height? I just thought that had something to do with it because the back dropped after having the two seperate sized tires on there. BTW I looked for the kink you found and no luck, its straight through there for me.
 
The hub never changes position, no matter the tire or rim size. Larger diameters just mean the wheel well clearance is reduced.
 
Ok, well I guess I was thinking wrong, guess the bags just went bad when I had the seperate wheels on there, weird coincidence. I don't think its a sensor issue, because all I touched was the front, and when I did, it worked. If my bags are bad, would it cause a cel? I don't have any popping up.
 
So what is exactly the problem. You have 4 matching Cobra rims and matching tires, right? And when installed you lowered the front of the car to close the gap but never touched the rear sensor. Now you take it out and the rear wont go up?

The sensors are set to a certain height. These three critical sensors are all the info the air-ride gets. If the rear will not inflate enough to rear the proper height, the message center will give a "check air ride" error. If you are not getting any errors the system is working within spec. If the rear is low, all that needs to be done is to raise the sensor a bit.

Just remember the rear ties will cut closer to the wells. Measure the rocker panel to the ground to get a better idea on how level the car is. From a distance and ONLY looking at the wheel wells the rear will always look lower.
 
unity said:
So what is exactly the problem. You have 4 matching Cobra rims and matching tires, right? And when installed you lowered the front of the car to close the gap but never touched the rear sensor. Now you take it out and the rear wont go up?
Click to expand...

Yes, and when I had originally put them on, and dropped the front by adjusting the sensors, it sat like this:
9dac569a.jpg


Then the front tires dry rotted, they were old and came with the wheels, the other two I had already replaced. While I was waiting for the tires to ship from tirerack I had to drive around with the stock wheels/tires on front. When I finally got the new wheels and put the Cobra's back on, the back was tucking the wheels. Instead of having the gap that you can see in the pic. The gap on the front had increased compared to before. Now they are tucking even worse. I know adjusting sensors changes ride height. But I did nothing to the rear, they aired up just like in that picture before, and now they are tucking in the wheel wells. You can feel the car angling backwards sitting in it. I don't have any cels, or messages in the message center. Would I be right to guess that just for some reason my bags went bad at the same time as me having the mismatched wheels on?

Also Unity the new wheels and tires have an overall diameter shorter than stock by about an inch and a half. Im almost certain that changes hub position by half that difference. Considering you can raise a vehicle with larger tires, which changes the hub position to the center of height of the tires.

I don't know how you tell that you have bad bags. The rear does raise slightly when you start the car, but barely at all. The fronts air up fine. Would that be a sign that the compressor and all the system is working fine, and just maybe theres a crack in the rear bags that is leaking air?
 
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jbird97 said:
Also Unity the new wheels and tires have an overall diameter shorter than stock by about an inch and a half. Im almost certain that changes hub position by half that difference. Considering you can raise a vehicle with larger tires, which changes the hub position to the center of height of the tires.

I don't know how you tell that you have bad bags. The rear does raise slightly when you start the car, but barely at all. The fronts air up fine. Would that be a sign that the compressor and all the system is working fine, and just maybe theres a crack in the rear bags that is leaking air?
Click to expand...

You need to understand better how the system works. Its simple but people do over think it. I thought it was more complex too until I worked on it.

The compressor fills the bags until the sensor says "ok, this is about right". Then it stops. The system checks the sensors every 45 seconds to make sure they are reading within the ride height window. That window is a tolerance that the sensor can be in, about a half inch or so.

So sensors read the distance between the frame and a control arm. Thats all. No matter what size tire you put on the distance between the frame and control arm will always be the same, or shall I say the air ride want to keep that distance the same. The center of the hub will ALWAYS be the same distance from the wheel well lip because the control arm to frame distance is kept within that small ride height window.

True that a larger wheel will raise the vehicle off the ground higher, but at the same time the wheel well clearance in reduced because unless the sensors are adjusted, the hub is in the exact same spot.

If you are not getting an error, everything is fine. You said you had it on jacks, this is not the best idea since it hangs the suspension and compresses ALL of the sensors. Its very possible the rear sensor slid.

When you fire up the car the front and rear usually raise from park/highway height to drive height. Thats about an inch increase in height. If the rear goes up and no error comes up, all is well. If you look in your rear view mirror and start to see the rear end lowering slowly or it does so when driving you have a leak. But the compressor will run often to keep the rear end in the "height" window.
 
Ok thanks. I never had a car with air before this, I guess I was assuming it worked differently than it did.

The car was up on jack stands during winter, but the problem was happening before I put it away for winter.

I'll check the rear sensor to see if it moved at all. Though from how you're describing it, I think my bag(s) are just gone.
 
If the bags are gone, the compressor will run a lot to compensate for leaks. The only way rear bags can go bad are if they leak. If the compressor can not keep them at height it errors out.

Also, if they leak bad the rear end will usually end up pretty dang low when sitting over nite. When the car is off the air-ride system keeps working but I think thats for an hour or less. Then its off so the rear can sink. But if you fire up the car and the rear just goes up a little. Then its the sensor that needs adjustment.

So from what you say, the rear bags sound fine.
 
Hmm, ok, I'll try adjusting the sensor and see if it works. If it does cool, I don't have to pay for new bags. I'm just confused as to how it got that low in the first place. Oh well, hopefully its the sensor and not the bags. Thanks for all the help Unity, I know it can get frustrating trying to explain something to someone who's not getting it. I'll let you know if its the sensor. I won't be able to play with it until Thursday though, I have school all day tomorrow.
 
Lol, I feel like an idiot. Unity you were right, it was the sensor. Apparently it had popped off the ball clip thing, so it was just hanging there. I somehow missed it in my trouble shooting. Clipped it back on, and it aired right up. Thanks Unity and sorry about the hassle.
 
No problem. And now you have a better understanding of the system for future trouble shooting! Its all good, glad it was a free fix.
 
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