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post #1 of (permalink) Old 09-03-2006, 10:37 AM Thread Starter
 
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Jeep suspension on ford shaking

Hey guys, I hope you'll be able to help.

My cousin and I have put a jeeps suspension onto his ford escort. Me have welded the leaf spring brackets onto his chassis and have made sure that the wheels are straight, inline with each other and that the distance between front and back wheels are exact.

The problem is that when we drive, the whole front diff shakes from left to right and gets pretty bad. The whole car shakes and we have to try slow down slowly. Im not talking about bad wheel balancing, im talking about feels like the cars going to roll! That is at about 30 - 40 km/h and when the diff was horizontal to the ground.

There are lines in the inside of the CV joints. (Im sorry, but i dont know what these lines are technically called). So, when the lines are vertical, the wheels will only turn left and right, instead of the wheels also turning slightly inwards and outwards. If I havent explained that accurately - you know when a mercedes turns at a sharp engle, you can usually see the wheels are not vertical, they are an an angle to the ground.

So....we set those lines to vertical, and the problem has gone away, well mostly, BUT the diff is now at an angle where it is not parrallel to the ground and is nearly in line with the drive shaft. How can we sort out this problem, so that we can have the diff horizontal and that the car doesnt drive like a raging bull. Someone mentioned steering dampers??

Was hoping to add a pic but the PC aint so happy
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post #2 of (permalink) Old 09-03-2006, 12:53 PM
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Re: Jeep suspension on ford shaking

Welcome to the board!

What you're describing is commonly referred to as "Death Wobble" and you're on the right track to solving it. The effect of the wheels tilting in towards the direction of turn is caused by the caster angle. If you draw a line through the eyes on the end of the axel, the line should be tilted forward at the bottom, backward at the top. That's positive caster, and you want about 3 to 4 degrees of tilt. If the line is too close to vertical or tilted the other way, forward at the top, it can lead to death wobble.

You adjust that by how the spring perches are welded to the axel tube, in the case of a leaf spring suspension, and by the attachment points and lengths of the links if it's coil sprung.

How the differential sits is another matter that affects the U-joints in the driveshaft. If both U-joints on the driveshaft are of the same type, then the pinion shaft on the differential should be approximately parallel with the output shaft of the transfer case, or pointed slightly downward. If the rear driveshaft U-joint is a double-cardan constant-velocity joint, then the pinion shaft should be pointed upwards directly at the rear joint.

Death wobble can also be caused or exacerbated by looseness in the suspension or steering linkage. Make sure that everything is tight by having your buddy rock the steering wheel back and forth until the road wheels just start to steer. Then you check every connection in the system, from the steering shaft through the steering box all the way to the wheels. Any lost motion can allow death wobble or make it get worse and worse once it starts.
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post #3 of (permalink) Old 09-03-2006, 09:54 PM
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Re: Jeep suspension on ford shaking

In this case, pictures of your suspension, axle, etc. would help a whole lot.
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post #4 of (permalink) Old 09-04-2006, 11:29 AM Thread Starter
 
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Re: Jeep suspension on ford shaking

We're working on the car on saturday. I'll take some photos then and attach them.
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post #5 of (permalink) Old 09-05-2006, 02:21 PM Thread Starter
 
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Re: Jeep suspension on ford shaking

Hi Jim,

I appreciate your input. I am glad that there is a name for it and that it looks to be fixable.

There are somethings in your reply that I don’t understand though and would really appreciate it if you could help me with these before we get going on it again on Saturday.

Firstly…

"If you draw a line through the eyes on the end of the axel, the line should be tilted forward at the bottom, backward at the top. That's positive caster, and you want about 3 to 4 degrees of tilt. If the line is too close to vertical or tilted the other way, forward at the top, it can lead to death wobble."

What are the eyes?

and also….

"How the differential sits is another matter that affects the U-joints in the driveshaft. If both U-joints on the driveshaft are of the same type, then the pinion shaft on the differential should be approximately parallel with the output shaft of the transfer case, or pointed slightly downward. If the rear driveshaft U-joint is a double-cardan constant-velocity joint, then the pinion shaft should be pointed upwards directly at the rear joint."

What are the U joints and pinion shaft?

Sorry if these questions seem trivial but I am not familiar with this.

You don’t by any chance have a diagram of how this is done?
Thanks again for your help.
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post #6 of (permalink) Old 09-05-2006, 03:21 PM
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Re: Jeep suspension on ford shaking

on the ends of the Axle housing you have these:


Top and bottom both have holes in them. these are the eyes Jim speaks of

and read this for Driveline 101
http://www.4crawler.com/4x4/CheapTri...line-101.shtml
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post #7 of (permalink) Old 09-05-2006, 03:53 PM
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Re: Jeep suspension on ford shaking

"What are the eyes?"

If you look at the ends of the axle from underneath the vehicle you will see that there are an upper and a lower eye on each side. They have holes about an inch - around 25MM - in diameter into which are pressed the upper and lower ball joints. When the wheel steers back and forth it turns on the ball joints.

It's impossible to get an exact reading of caster from them, as the only precise surface is the inside of the hole, which you can only access by removing all of the outer components. What you can do is get a combination angle protractor and level. (The attached pictures are of a Starret instrument. They're expensive, at around $80 US, but similar ones can be found for half that price.) Make sure that the car is sitting on a level surface. Put the flat surface of the instrument across the upper and lower eyes and rotate the level until the bubble is centered. Then the instrument will show you the caster angle, or the caster angle plus 90 degrees, depending on the instrument.

You want to perform that exercise on both the front and the rear of the eyes, and on both sides. Write down all the readings, and then do it again. after several tries you should be coming up with the same answers every time. Then you will know that you've developed a good and repeatable technique.

Professional shops have instruments of various kinds that attach to the wheel and measure the caster quite accurately, so you can always take the vehicle to one, but for your purposes so far, if you're careful, you should be able to get the angle to within a degree, and that's good enough. You're not building the space shuttle here.


"What are the U joints and pinion shaft?"

The pinion shaft is the input shaft of the differential. The U-joints are the Universal Joints that connect the pinion shaft to the drive shaft, and the drive shaft to the output shaft of the transfer case.

The engine sits a little lower in the back, and everything that's bolted to it is tilted the same way. So the transfer case output shaft angles slightly downward to the rear, and slightly upward towards the front. If both U-joints on the front drive shaft are the same kind, the pinion shaft should be approximately parallel to the transfer case output shaft, which is parallel to the engine crankshaft.

If the rear U-joint of the front shaft is a double one, it's called a constant velocity joint. In that case the pinion shaft of the front differential should be pointed right at the double joint. Any deviation from the proper alignment will cause vibration in the shaft. Two or three degrees is insignificant, and it has a lot to do also with the length of the shaft and a lot of other factors.

If setting the caster angle conflicts with a proper pinion shaft angle, get the caster right first. If you then get a drive shaft vibration, there are ways to deal with it.
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post #8 of (permalink) Old 09-09-2006, 01:06 PM Thread Starter
 
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Re: Jeep suspension on ford shaking

Thanks guys. We worked on the car today and have sorted out the problem. Thanks a ton!

Perhaps you could help with another topic we are trying to solve?

We are looking to make the front slip diff, run permanent diff lock?
I have heard that there is something you can weld on the front diff to make this possible?

Thanks in advance
McGav
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post #9 of (permalink) Old 09-09-2006, 04:56 PM
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Re: Jeep suspension on ford shaking

Down inside the differential carrier are four bevel gears, about 50mm in diameter. If you weld them to each other it will permanently lock the differential.

But if you plan to drive the car on a hard surface, don't do it. It will become almost impossible to steer and wear the tires out in nothing flat. There are better options, although they cost a lot more.
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post #10 of (permalink) Old 09-10-2006, 03:21 PM Thread Starter
 
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Re: Jeep suspension on ford shaking

What option would you suggest? Welding the diff for prmanent diff lock definitly looks like a no go between the consenses.
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