Severe Wobble
 

Hello all - All my winter projects are completed. I re-did the fromt suspension, fixed the steering and replaced the rear springs. I am having a major problem....I took the car out today for the first time to get gassed up and go for a test ride and as soon as I hit the road and went over 10 mph the car started to shake very hard. I could not tell where it was coming from? The car drove fine before I did the mods I mentioned above over the winter. I have a feeling it is shaking because of the new rear springs. When I put thie springs on - it lowered the car by several inches. I did not think anything about it at the time, because they were heavy duty springs, but do you think because of the height difference my U-Joints are causeing the problem or maybe the driveshaft itself. How do I check the dirveshaft - I want to start to rule areas OUT as the cause. U really don't think it is the trans or the front end. It vibrates and shakes just as much when coasting (which is what I did all the way back to the house).

Where should I start and what should I look for....As a positive note - the car steers great, spedo now works and the new shifter and trans are great....

Hope someone can help!

TJ

Basics OK?
 

Please forgive me for getting down to basics. Are the front wheel bearings adjusted properly, no looseness allowing wobble? Lug nuts all tight?

The rear end should not be lower for any reason unless you added lowering blocks or springs with a modified "eye", i.e. mid eye, reverse eye options. New springs normally raise it some from the old sagging leaf springs position. Rear shackles also need to be in good shape, but that usually hurts cornering more than anything.

Balancing a drive shaft needs to be done at a drive train specialty shop. Now would be a good time to replace u joints if they are 5 yrs. old.

Still, there must be something way off to cause shaking at speeds 10 mph and above. I'm not sure what that could be.

Rev

Jack it up or put it on a lift. Start car and put it in gear. Inspect, from a safe distance. Do this with the rear on stands, and off stands. That gives two different loads on the suspention. I could see the pinion angle being off if the springs were way diff from stock.

Maybe found the culprit
 

I believe I have found the cause....I put the car up on jacks (like it was suggested) and started it up , put it in first gear and watched the drive shaft. It was loping very bad and shaking. I checked the U-Joints at the rear and they were literaly falling apart. That was the cause, so I bought new U-Joints, but have not installed them yet. Here is the question....

The new springs were not stock at all - 5 leaf heavy duty and lowered the car several inches. I am sure this effected the angle the driveshaft connects to the rear. If so and I install new U-Joints am I going to have this same problem??? I still have the original springs but do not want to put them back unless I really have to. Is there a way to make this work. It is also possible that the U-Joints were just bad to begin with. If I install the new ones and put the drive shaft back on - should I be able to tell from spinning it? It would seem that if it spins freely without any obstructions that it will be OK.

Thoughts...and thanks for the advise.

TJ

Asuming the springs are for a Mustang than the total lenght should be correct. Meaning the driveshaft isn't shoved into the tranny.

Pinion angle is hard to explain. The angle off of the tranny should be equal of angle from the pinion. Don't quote me but I think yours should be around 7 degrees negitive pinion angle. Leaf spring cars use more angle. The more rigid the suspension the less negitive angle you'd need. This is figured by measuring at different points. Probably best to let a shop do it. Although it can be done in your driveway.

I think since your car has been lowered the pinion angle may be less than needed. Because the pinion would be higher up into the chassis making less angle. When you stomp the gas the pinion gear tries to climb the ring gear. (Front of rear raises.) You will definately get vibration from severe angle changes. And could cause U-joint failure. If your U-joints were old anyway, it probably didn't take much to kill them.

I think I confused myself.

Going to try again
 

Well - I am kinda glad it was just the U-Joints and not something more serious. I bought 2 sets of joints and I figure I am going to try it again with the new ones. If they fail - then it has to be the new springs (difference in height) and I will put the old ones back on and install the other set of U-Joints and be happy (Not). I know that the height of the car has something to do with it...Thanks for explaining the angle stuff. I am not sure how to make it good again other than by putting the old springs back on. I will let you know what happens this weekend. I suspect that if they are going to fail - it won't take much and will happen rather quickly. Good thing these were cheap....only $7.00 .

TJ

if your pinion angle is way off and you have to change it, Chassis engineering sells aluminum shims just for that purpose. They fit between the spring and the rear housing. Depending on which way you put them they will either increase or decrease the angle.

Problem Fixed
 

Hello all - for those not reading about my latest Battery Problem - I replaced the U-Joints and all is good again. I guess they were just ready to go and the timing was just right. Easy fix. Trans works great - If anyone needs advice on rebuilding a 4 speed toploader - give me a shout.

TJ