XHD springs on Fifth Avenue

Cambo

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I was wondering if anyone here has had success with E-body XHD leaf springs on an M body?

My plan was Firm Feel spring hangers with the MP XHD leaf springs, using some B body shock plates I have.
The ride height is the main concern, I am assuming that the E bodies had less weight over the rear than the M's, but maybe I'm wrong.
Also, would it be correct that if I were to use the B body shock plates versus the iso-delete kit, this may actually raise the car because I'm not using the shock plates on top like I would with the iso-delete?
I'm looking to get it to sit at a factory level or just slightly higher, at the moment the passenger spring is getting weak and not holding up its part of the deal.

Any advice is appreciated!
 

BudW

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I don’t have any firsthand experience, but I know others do have.

Suspension: Chrysler Leaf Spring Dimensions - 1960-1989 this link has some dimensions you might want to look at, before making a purchase. There was another web site that had even more spring dimensions to it, but couldn’t find it on a quick search.

The front segment is from the alignment bolt of leaf spring to center of front bushing. Rear segment is leaf spring alignment bolt to center of rear (shackle) bushing.

The one inch overall shorter length is not a big deal, and that might be fixed using adjustable front spring hangers, maybe. The two inches to front segment is a bigger deal and may require driveshaft modification, possibly.

I have ridden in cars with those XHD springs and they don’t allow for much pampering to ye ole kidneys.
Is there a reason you are wanting to use those springs?
BudW
 

Cambo

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Thanks for the reference, good to have.

The main reason I was thinking E body springs was that (according to Firmfeel), you can use their leaf spring hangers made for FJM's that allow you to use the 57" E body springs. This would give me more choices and possibly lower the cost. Driveshaft modification is not a problem if I need to.

From my internet perusing it seemed that the XHD's are pretty popular among the muscle car crowd, being a little more firm than stock with only a slight rise in ride height. I'm not sure exactly how this would translate to a Fifth Avenue, I don't mind the ride a little firm but I would like to keep my kidneys!

Back about 20 years ago I remember slapping a few truck leafs in the F/A I had then. It was a little rough, I really want to make things right this time.
 

BudW

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Muscle cars need more “spring” to prevent leaf spring/differential windup under heavy acceleration. To achieve this, on 440 HP and Hemi's Chrysler had added a leaf on one side rear (drivers side, I think) and two half leaves on the other side. On top of my head, I can't remember which side.
The XHD springs are “beefier” version of the 440 HP/Hemi springs, if I recall correctly.

They were not made to increase ride height or carrying capacity, per se, but to prevent axle windup which effects driveshaft angles and so forth.


If you are concerned with ride height, I recommend either reuse existing springs or use the five leaf spring version.

Leaf springs will sag over time. It just happens – but a spring shop – or even yourself if you have access to a stand-up hydraulic press you can re-arc the springs yourself.
20tonhydraulicshoppress2.jpg

Its not that hard, just time consuming.

Another way to raise rear of car ½” is to get rid of the Iso-Clamp system and use older Chrysler shock plates.

To many people, having more “spring” in rear without a reason for needing more “spring” makes an un-satafactory ride. Now if you are going to tow with car or have a high performance car, then it makes more sense.
BudW
 

Cambo

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I have never tried re-arcing springs before, but I like the idea. We have a 40 ton press at the shop that should do the trick.

I would really like to keep the "couch on four wheels" feeling with this car, but improve handling where I can.
I don't see it heading to the Nurburgring any time soon, though.
 

BudW

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Sounds to me eliminating the Iso-clamp and re-arching might be all you need.

There are You-Tube videos as to how it's done and it can be done at home.
Would recommend a new center bolt and spring pads when spring is apart, though.

Now, if you are dead set to get E-body XHD springs, I don't want to stop you, but I think the above will be more cost effective and all-in-all less work.
BudW
 

LSM360

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If you buy a new set of M body Police five leaf springs, you will see quite a lift and increased stiffness in the rear of your M. I bought a new set for one of my Police cars that already had a set of five leaf springs stock, but they were worn. The car was lifted quite a bit just with the new springs. So going from four to five, and new, I think you'll see quite a difference.

I could not find any shops in my area that re-arched springs. And, you're not starting out with five leafers any how.
 
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89.Fifth

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I will tell you that years ago I bought a set of 5 Leaf Springs with +1" arch on them. Both the ride and the handling were so much better because of the improved suspension angles (roll center as it was told to me) and that's what I plan to do again on my current car.

78-757 Leaf Spring Assembly
 

Dr Lebaron

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I've always had my leafs re arched and added another spring.
There's a bunch of places here that still do that.
Harry's Spring Service has been around forever.
 

Rustyroger

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My 5th Avenue also sits down a little at the rear.
On various GM cars i have cured this by putting small coil springs inside the originals, surprisingly it brought the ride height up to spec but didn't affect ride comfort noticeably.
Of course this won't work with cart springs, another fix I've used successfully is using air shocks. Especially useful for cars used for towing, as this car will be.
What is the iso-clamp, and how do you eliminate it?. How does this help?.
Only been on this forum for six weeks, and I'm much bettr informed about all things M Body (and other Mopar cars of the same layout and vintage). :)

Roger.
 

BudW

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I would think finding a pair of leaf springs and shipping then across the pond would be cost prohibitive.

Air springs work, but the body mount piece of sheet metal (crossmember), doesn’t like the extra stress of air shocks. I have seen that rear upper shock mount fail on several cars that had air shocks installed. Where it fails is almost always where the body mount connects to the frame rails – and generally is not an easy fix.

The red circles are the (only) places the body mount attaches to frame rails (or anything, for that matter). The blue line/blue arrow is where the upper shock bolts are at.
FM Frame.JPG

If a person was top reinforce that upper mount, I would find a way to attach the mount to the trunk pan on top as well as weld in struts to the lower half of that mount. What happens is that part starts to twist in place until it separates from the frame rails.

Now, I have seen it happen a few times and only with cars with air shocks. I’ve not seen it happen with normal shocks. I have also seen several cars with air shocks without troubles.

If I was dead-set on using air shocks, I would reinforce that mount – or also for extreme usage (all out road racing).

- - - - -
What I would do is inspect the area, if OK, then leave it alone. Then take your original 4-leaf leaf springs and get them re-arched and additional leaf installed at same time, at a spring shop.

That way you are set and ride height has been increased to whatever you desire.

Removing the Iso-clamp will also raise the car up by about ½ inch (13 mm) or so.

The first picture is from ’72 parts book, I think.
Iso-Clamp.JPG

The second pic is from ’82 parts book.
Iso-Clamp B.JPG

The second pic, item # 22 is the rubber biscuits that insulate the road and makes the car fleet soft. Also item # 21 is the weak link. If it breaks, then that corner of car is dragging the ground.

Firm Feel makes a delete kit that reuses some existing hardware (reuse old shock absorbers).
ISO delete kit.JPG


I recommend finding some ’60-72 shock plates (and new U-bolts). Some people are making them new. They will require different shocks because of the rear attachment is different. The shock length is the same. Just look for say ’70 B-body rear shocks and they will fit fine.
Shockplates1.jpg

Aftermarket New
shock plate.jpg

Used

If using the older shock plates, you will need to have “normal bolts” re-installed (when getting old springs re-ached at spring shop) instead of the Iso-clamp wide version (they will reuse old bolt – which won’t work with older shock plates).


To recap:
In my opinion, it is worth the effort to get rid of the Iso-clamp system using either older shock plates or using one of the aftermarket kits. You may need new shocks as well and going through the effort of springs and such, it makes sense.

I would prefer you not to use air shocks – but I can’t stop you. Raising the rear ride height via springs make a lot more logical sense and afterwards – you might not even need air shocks. If still considering air shocks, look into reinforcement of the upper shock plate (crossmember).
BudW
 

lowbudget

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ESPO has the iso poly biscuits in stock for 65.00 plus shipping for the 4 of them. I guess I know what I'll be doing this days off. Oh well I need to go to the city and pick up a 67 Charger gauge assembly I'll get my springs re arched then.....unless some one can tell me how to re arch them myself. (Bud W)

What really sucks is if I do my new to me 84 I will have to do my 87 also. I put overloads on it to stiffen it up. Hopefully it will stay warm up enough to do it in 2 weeks when I get home.

I need to quit reading this forum at work and finding new projects for my days off......
 

BudW

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I have done them myself. You will need some clamps and a press.
Plenty of YouTube videos that be better to watch - than to have me explain.
Spring shops have a specially made press which is slick to use.

A lot of details on Jeep leaf springs, but the same exact process as FMJ cars.

In summery
If doing yourself, find a flat floor, garage or driveway. Lay spring down and make a chalk outline on one side of spring. This is your baseline.

If raising rear of car up say 2” (or whatever your goal is) then once done, your spring will be 2” taller from your baseline on the ground.

Using clamps, take spring apart. New metal bands are available, as well as bolts. Sometimes you can reuse both.

Each leaf will need to be bent separately. Put spring in press and bend it every 2-3 inches or so. You are not bending it much – and it takes a while to figure out how much to bend it.

Once you have your “grove” down, it goes fairly quick.
Getting to the “grove” takes a bit of time and seams awkward - to a certain extent.
BudW
 
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