71 Mustang front shocks are destroying top bushings

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71BossPrototype

Well-known member
Joined
Oct 11, 2010
Messages
91
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3
Location
Wisconsin & Florida
My Car
1971 Boss 351 (Med. Metallic Blue and Argent)
1971 Boss 302/351 (Ford's singular regular production 1971 G-code Car, Grabber Yellow and Black)
I am restoring a '71 fastback and wondering if anyone ever had this kind of problem? I am just finishing putting together this 71 project car, which I purchased in pieces. The car came from the P.O. with all new front suspension pieces including upper a-arms and lower control arms, springs, etc. Most of the pieces were decent looking but typical off-shore stuff, and from about 10 years ago. The springs were painted blue, and I have no idea who made them. They were tough to compress, but fit into place well.

Anyway, my problem is that whether I use the new KYB shocks that came with the project, or a pair of cheapie standard replacement shocks that I picked up (but specifically for 71 mustang) the top rubber bushing compresses when I raise the car, and the top steel washer actually cuts it like a cookie-cutter. That is, the top washer starts to cut right through it, and even the underside of the top rubber is also cutting itself through the hole in the shock tower cap. However, when the car is not lifted, and is just sitting on the ground, the A-arm is straight out and level with the pavement.

When the car is raised the last 3 or four inches of lift necessary to get the tires off the ground, the bushings flatten out like chewing gum into little flat tires! I have tried several different size and thickness of bushings, with the same results. The bushings are ruined after one lift with the jack.

Also, when the car sitting without jacking, the shock is fully extended and there is really no travel left to allow any upward movement of the body beyond the resting position. It isn't in any bind at that point, just has nothing left for upward movement or bounce.

Any help would be appreciated. I have not yet had this car on the road. Just trying to get to that point -Andy

 
Sounds like the body is twisting an putting a heavy load on the rubber. Are you jacking like the instructions under the rocker or torque box? If you are jacking under the front suspension arm you are way overloading the bushing. Normal suspension travel does not lift the car off the ground. Try jacking under rocker where they show the notches or torque box and should not be an issue again.

David

 
Sounds like the body is twisting an putting a heavy load on the rubber. Are you jacking like the instructions under the rocker or torque box? If you are jacking under the front suspension arm you are way overloading the bushing. Normal suspension travel does not lift the car off the ground. Try jacking under rocker where they show the notches or torque box and should not be an issue again.

David
Thanks for the reply! There's no twisting here at all, as I am lifting the whole front from the center of the cross-member until both tires are up off the ground. It would be the same as raising the car on lift, as you would still completely unload both springs to their full travel as limited by the shock, when the upper arm moves down. It's like the springs have way too much pull when they are decompressing, or the shock needs a lot more travel? Frustrating.

 
I know what you are talking about. I was wondering the same thing too on my car. I have the original suspension,springs etc. I replaced the front and rear shocks with the KYB gas adjust shocks. The piston travel is a lot shorter than the ones I took off. When the car is jacked up from the front and the wheels are off the floor, it's flattening out the upper bushings.

I never remember having an issue when I jacked the car and put it on jack stands with the old shocks.

I did a little comparison after I installed my shocks. It seems they make different shaft lengths. Check it out. go to advance auto parts online and search for shocks that fit your car. Look at the specifications tab and see the compressed length and the extended length.

You will see that they are not all made the same. I will someday change mine but will be looking for the longest length version when I do.

http://shop.advanceautoparts.com/p/monroe-oespectrum-passenger-car-shock-absorber-5823/19710806-P?searchTerm=shock+absorbers#fragment-2

http://shop.advanceautoparts.com/p/kyb-front-gas-shock-343156/19170405-P?searchTerm=shock+absorbers#fragment-2

http://shop.advanceautoparts.com/p/kyb-front-gas-shock-kg4504/19171011-P?searchTerm=shock+absorbers#fragment-2

 
Unless you're related to Bo and Luke Duke from Hazzard County, I would probably err on the side of a shorter rather than longer shock.

Although I haven't had any exposure to shocks on our cars, I would think too long of a shock (not saying a little over length would work) may allow the control arm to hit metal to metal at extension. I may want the top bushings taking the shock of over extension (when jumping a creek running from 'ol Sheriff Coltraine :) . Conversely, it (may) bottom out the shock itself (internally) before hitting the snubber on the coil spring cover on full compression if too long.

A bit of experimentation and measuring may go a long way with this subject. I don't think I've ever heard anybody ask about it.

Wonder how much, if any, optimal shock length will vary from car to car.

Wonder what the production road racers from back in the day did to find shock absorber zen.

Or even the "stock appearing" drag racers of today...

Good topic, I like it. Makes me go hmmmmm.....

 
Is the engine in the car?

What is happening is the extended length of the shock is shorter than the rebound (extension, unloaded) position of the front suspension. So when you try to raise the car, the force from your new, unknown coil spring is trying to pull the nut and washer through the shock mounting rubbers.

The springs will sag with time and use so the problem should lessen. Seems weird though, when I took my car apart the upper control arms would sit on the frame rail with no load on the front end and the shocks would stick out the top of the tower. What I'm saying is there should 't be a way that your condition should occur. I'll snap some pics of mine over the weekend, I think I still have the shocks somewhere...

 
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I don't think the extended length of a different shock is going to make the condition worse by bottoming out on the frame rail. The front strut bar and stabilizer link will help support the suspension and if it did touch , it's not going to hurt it. Unless you are jumping a creek and your suspension is unloaded but then you might have a bigger problem than being concerned if your control arm is touching your frame rail when you land it. :p

The extended length range on just those links that I posted are between 12.2", 12.625" and 13.9" They are specifically made for the "73" in those examples. I have not tried comparing the other model years but I found it interesting that there was a wide range in the length. I'm not sure why there are such differences. I've never come across that before and thought if you needed shocks for your car they were all the same in length.

Unloaded suspension before I overhauled and detailed it. Note: the control arm is touching the frame rail.

2ds4bpt.jpg


Loaded suspension after overhauled. I don't have a picture of unloaded suspension after the overhaul but I can say it's not much different than in this picture. The shock travel is shorter.

w0i347.jpg


 
:chin: I can be wrong but:

There is too much upward pressure from the springs because there is not enough weight in the front of the car, I just suspect the engine(weight) is in the car but no radiator / front bumper / battery / fenders / hood / or ...

(see picture 1: rubber/empty engine bay)

I have now KYB in use and have NOS front shock absorbers as spare parts, the seller said that its original for your car... what do you think about Motorcraft shock absorbers versus KYB? (see pictures)

 
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I think you have the wrong springs in the car myself. and I think mjlan's explanation is right as well as Terlingua_RS's observation about shock extended length which will affect total available travel. If the springs aren't stock, then the shocks need to be compatible and I think they are not at this time.

Stock 73 springs I removed were 16" long uncompressed and .67 in in diameter (and 40 years old)

Replacement 1.5 drop springs were .77 in diameter and only 13" tall uncompressed. I would expect an acceptable spring would come pretty close to falling within those general parameters more or less.

While it is a few hours work, you could pull the springs, measure them to see how they compare, cut off whatever seems appropriate after you have them free and reinstall.

 
Shock travel (extended and compressed length) is independent of the spring free height and rate.

 
A couple years ago I started to have issues with my upper bushings disintegrating within months of installing them. Whatever the compound is that makes up replacements from Advance Auto, etc. it was not very elastic and would fall to pieces in a couple hundred miles.

Purchased these 2 years ago from Summit. http://www.summitracing.com/parts/ens-3-8106g

They're polyurethane and work very well.

 
Thanks for all of the great advice and thoughts on this! Since posting this here and on the VMF, I have had several people relate the same problem on their cars. I agree that it has to relate to the amount of downward force on the shock at the point it runs out of travel when the car is fully raised, since a longer travel would allow the spring to further unload before pulling on the top bushing. Since the upper arm is fairly level when springs are compressed, the spring height (under full weight of car) seems good, or a little to much while new. The poly bushing is a good idea, and several have posted they are using these with no similar problems. Still, I suspect the shock length and springs are not right, as Jeff and others suggested. I'll try to post some photos this weekend. Thanks!!

 
:chin: I can be wrong but:

There is too much upward pressure from the springs because there is not enough weight in the front of the car, I just suspect the engine(weight) is in the car but no radiator / front bumper / battery / fenders / hood / or ...

(see picture 1: rubber/empty engine bay)

I have now KYB in use and have NOS front shock absorbers as spare parts, the seller said that its original for your car... what do you think about Motorcraft shock absorbers versus KYB? (see pictures)
I would appreciate it if you would measure the full extended length of those original motorcraft shocks and post the result. -Andy

 
At one time there were blue 1 inch drop 620 rated front springs

They were very stiff

 
:chin: I can be wrong but:

There is too much upward pressure from the springs because there is not enough weight in the front of the car, I just suspect the engine(weight) is in the car but no radiator / front bumper / battery / fenders / hood / or ...

(see picture 1: rubber/empty engine bay)

I have now KYB in use and have NOS front shock absorbers as spare parts, the seller said that its original for your car... what do you think about Motorcraft shock absorbers versus KYB? (see pictures)
I would appreciate it if you would measure the full extended length of those original motorcraft shocks and post the result. -Andy
Total length = 38.50cm

 
:chin: I can be wrong but:

There is too much upward pressure from the springs because there is not enough weight in the front of the car, I just suspect the engine(weight) is in the car but no radiator / front bumper / battery / fenders / hood / or ...

(see picture 1: rubber/empty engine bay)

I have now KYB in use and have NOS front shock absorbers as spare parts, the seller said that its original for your car... what do you think about Motorcraft shock absorbers versus KYB? (see pictures)
I would appreciate it if you would measure the full extended length of those original motorcraft shocks and post the result. -Andy
Total length = 38.50cm
THANK YOU! for taking the time to measure and post the photo. I will compare it to mine, and report back. (Now I have to find a metric ruler....dang...LOL!) Thanks again. -Andy

 
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bi10yf.jpg


z71wo.jpg


Although it doesn't look it, the tape is lined up with the top end of the stud.

The KYB Gas Adjust measures 37.5cm from the end of stem to bottom of the mounting plate (and 40 cm to the end of the mounting studs, but the studs don't really add anything to the effective length of the shock.) So, it would appear the KYB's are at least as long or a little longer than your Motorcraft shocks, which looks to be 36.6cm to the bottom of the mounting plate. You can also see that the length of travel is about 3.75" or 9.5cm.

I guess that rules out the shocks as the cause of the problem, leaving the bushings, the springs or some anomaly in my frame/suspension. I am going to try the poly bushings first, till I get the car on the road for a few hundred miles. If that doesn't work, I will look for a different set of springs. Thanks again for all of the kind input from everybody. -Andy

 
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Andy: one thing to check is the diameter of the upper shock mount holes. I once had a situation where the shocks were leaning outboard and they wore the opening out to egg shape. The also made a hell of a squeak as they rubbed which always sounded like it was coming from under the dash. Drove me nuts for a few years before I finally figured it out. I purchased new repro's to replace the originals when I changed over to roller bearing spring perches which has the added benefit of keeping the coil spring an shock perfectly aligned.

IF you had a similar condition, the over-sized opening may not be holding the bushings in place as they should. Just a thought.

 
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