Iso-clamp Axles

As I've been struggling with getting the rear end of my Gremlin aligned, I've attempted to find out some more info regarding the iso-clamp axles that started to be used in the late 70's. Unsurprisingly, I didn't find a whole lot of discussion about them, so I thought I'd write up a post with some information I've seen mentioned, as well as my own observations and points I plan to get more information on. If anyone has anything to add, please do- my hope is that this can serve as a resource to anyone else that is trying to figure out how to deal with this setup after decades of wear and corrosion have been inflicted on it.

First, the main difference I've found to be the biggest hassle with the iso-clamp design is that the axle perches have large oval voids to act as a guide instead of the center pin bore of previous years. This makes reverting to the previous arrangement (where the perch is placed directly on the center pin of the leaf pack) into either a slight inconvenience or a serious problem, depending on your toolset and experience with modifying able housings.

The rubber-up is, of course, that the isopads have long been out of production and use a unique shape for the certain boss on the pad's top surface. There are no aftermarket replacements available, and similar pads for other makes (such as those from Prothane) require some shaping to fit (removal of centering material or chamfering the top sides). Even if these parts are used, further work has to be done to ensure alignment with the axle perch since the bosses are not similarly keyed.

One option that I've seen people recommend when someone brings up their having an iso-clamp setup that needs servicing is to replace the perches with ones of the older style. In my case, I don't feel that my welding skills are adequate to do this work and be confident that it's acceptable to have on the road with other drivers nearby. Since I limit my welding to non-structural parts, and my budget won't allow for taking the work to be done at a shop, I've been trying to make due with the system as it is.

To address the centering of the axle perch, I cut an oval plate and drilled a center pin hole, then tacked it in the oval of the leaf clamp, followed by cutting a small tube to run through the center of the pad and hole in the plate. Basically, I filled in the oval opening that the leaf clamp had and drilled a centering hole in it. That helps to ensure pad, clamp, and pin alignment, and the axle sits on the leaf clamp in the same way as it had before.

I've seen people mention a possibility that the iso and non leaves may not be interchangeable, though I'm not sure if this is something that's been confirmed. I'm going to look into this in further detail, since it's been a while since I measured my springs.

Aside from the serviceability aspect of the design, there have been a number of accounts I've read where people described the iso-clamp design as being detrimental to the life of the leaf packs, due to the rubber being a collection point for dirt, salt, water, and all the road stuff you don't want to have your (presumably) bare steel springs packed in. I'm curious as to whether or not the polyurethane pads will have similar problems, but I suspect not, since they won't suffer the same kind of increased porosity and breakdown that rubber will. Again, this is just speculation; I don't have any real info to back that up..

From what I've observed, the shock mount plates seem to be more prone to warping as time goes on. There have been a number of these plates that I've seen that have severe banging on the u-bolt sides. Whether this is caused solely by the pads breaking down, or if it's a combination of that with the bigger center void in the shock mount plate is something I've had in mind. That's not to say the previous years didn't see similar problems, so for all I know, there could be no real difference.

I plan to give the poly pads a shot and see how they do, though if they turn out not to work as well as hoped, I'm considering cutting a spacer plate of a similar thickness to take the place of the top pad so I can keep having the benefit of the leaf packs being somewhat captive, as well as keeping the height consistent in the rear. I haven't seen much about taking this route, but I can't think of any reason it wouldn't work (though I'm far from an expert in this, so take that for what it's worth).

So that's what I've got. Most of this was stuff that you can get by searching around online and/or getting under your car for a while. Hopefully this is useful info to someone.

If you have any interest...I still have a limited number of sets of 4 of new iso-clamp rubbers original from old dealer stock...I would like to see these get put to good use by someone who has these cars...Everything I had that used them is gone now so they are no longer needed here...4 rubbers for $40 plus 13.80 to 48 states if you want a set....Bob Reno in Fort Payne, Alabama

I had no idea that AMC used Iso-Clamps on any Gremlin - until this moment, I thought it was only a Concord/Spirit thing.  Is your Gremlin a 78?  That to me would be the only year that iso-clamps could show up.  My 77 Gremlin (258/4speed) that I bought new in 77 definitely had the traditional axle spring perch/pin/directly to leaf spring with no rubber isolator.  My 73 Gremlin is traditional spring clamps as well. It's my 80 Concord (saggy springs and all..) has the Iso-Clamps. Please understand I'm not doubting what you have - I'm just trying to learn.


Edited by 73Gremlin401 - May/26/2018 at 7:35pm

73Gremlin401:. No worries. Yep, I definitely have the iso-clamp setup in my '78. From what I understand, it may or may not have been an "all the time" setup. As Bob mentioned, and the parts catalog for '73-'78 indicates, the Pacer had them as well though what looks like all years. That said, I was briefly doubting that this axle was the one that the vehicle originally came with. This was mostly due to parts catalog ambiguity and things that had been done by a previous owner. The '78 TSM, however, describes the iso-clamp system as appropriate for the Gremlin, Concord, Pacer, etc, so was probably in wider use that year than it had been in '77.