99Hawk120

Just completed a rear swap yesterday (well, actually this morning) using drum brake axles in a disc rear. The ONLY difference appears to be the outer diameter of the flange the drum/rotor mounts to.

The drum axle has a larger flange, so you'll have to machine it down until the rotor fits over it. We put the car in low gear and used a bench grinder on a laundry detergent tub to grind it down. With it in gear, you don't have to worry about grinding the axles out of balance. Besides, the axle flange was noticeable out of round before we started and now is less so.

We ended up having to machine approximately 0.3" off the diameter of the flange, which as you might guess, took a while.

JAY87GTA

Wow, that's cool. How long did it take you to think of the laundry tub idea? Good stuff, thanks for the info man.

ANDYZ28

During my research into this question. I have discovered that with "certain" brands of rotors modification of the axle is not required!

99Hawk120, what did you do about shiming the caliper backing plate to center it (the caliper) on the rotor?

Thanx,ANDYZ28

onebad82z

iTrader: (7)

I bought brass shim stock (flat sheets) from a local tool supply store in varied thickness(like .001" to .037"),paid around $25.Made a template of housing end out of cardboard,transfered this to the shim stock and made several shims out of the brass in different thickness,and then trial fit everything together till I got the required clearance from the caliper bracket to the rotor,about .060" on both sides of the rotor.This took repeated assembly and disassembly of the axle,rotor,and bracket,very time consuming,but I did get it finally.Driver side was more of a pain than passenger side for whatever reason and also required more shims to get it into spec.Just remeber to fully torque all bolts when trial fitting,the clearance changes when torqued,learned that the hard way after I thought I was finished with one side,torqued it and realized clearance was all screwed again,RRRR!Start over.Hope this helps someone out.

AlkyIROC

Aftermarket axles don't have that problem. They fit both.

ANDYZ28

I noticed that the GM shims are made of steel.

AlkyIROC

Aftermarket axles don't have that problem. They fit both.

onebad82z

iTrader: (7)

Yes the GM shims are made of steel,I chose brass because it is much easier to work with,and can be found much easier in such small sizes(.001"-.010").Also I would like to credit Daniel Burk and his third gen hobbyist page http://www.ws6transam.org/fcar.html for the idea originally of using brass for this reason,his is the page that got me thinking of doing the 1LE swap 2 years ago,made me realize it was possible,got the link to his page on F-body.com,which is now down I beleive?Then a while back seeing ANDYZ28 posts about the GM supply of caliper cradles and such dwindling down to nothing made me realize to get this project on the road before I miss out on the parts I would need.I got one of the last sets of front brackets left in existance..thank you ANDYZ28 for the heads up!I also give ANDYZ28 much credit for his site,very informative posts,and willingness to help out every time I emailed him with a question.Without these two guys and their help I would have spent alot more and just bought a Baer kit.Instead I did the swap entirely myself in my garage and am very pleased with the performance of the 1LE system.Thank you both very much,more pride in your car when you can say"I did it,I didn't have to buy it and bolt it on".This is what this hobby is all about.

ANDYZ28

I am in the process of having these now long discontinued axle shims manufactured. Their are a total of four shims required. Each one is a different thickness. I will keep you posted.

99Hawk120

I didn't shim the backing plate at all. The calipers were centered on the rotors without any shims.

(edit)

I thought of one other thing. Since the calipers are a floating single-piston design, shouldn't they be self-centering to a certain extent? The mounting bolt simply passes through the caliper and mounts to the backing plate, leaving the whole caliper free to slide side-to-side.

I suppose if you're worried about it running out of room to one side or another, but there should be a decent amount of tolerance built into the system as-is.

camaro6spd

The shims better not be a outragious price like the hindge pins.....I don't need AeroSpace Nuts for a door hindge. A nylon with Red locktight works fine.

ANDYZ28

Well sort of! If I have learned pne thing on this board. I don't sat anything unless I can prove it and support it with a bible sized book of facts.

So, I will comment on this later when I have some documentation to post.

But I will say that the procedure to shim the disc brake backing plate is quite involved and precise. Their is a reason for this.

Thanx,ANDYZ28

ANDYZ28

Well, OK. With an attitude like that of camaro6spd
I won't even bother with getting the shims made!

The price for the hinge pins must not be all that bad. I'm sold out!

OH well,ANDYZ28

99Hawk120

I'll be interested to see what you come up with. Like I said, from my understanding the system is effectively self-adjusting (within limits).

There may be a reason for everything, but in some cases what was a good reason for GM is not necessarily a good reason to the end user. I've run into that enough times.

What's more important, IMO, is that I ran through all three Helms Manuals I own (84, 87, and 91) and didn't see anything about shimming the backing plates. Again, perhaps GM did that from the factory, but I want to know why before I waste my time chasing down a bunch of shims. Hell, maybe it just means you won't be able to quite use all of the brake pad, which would be a big deal for some people, but not for me.

onebad82z

iTrader: (7)

The shims go between the backing plate and housing end to center the caliper bracket to the rotor,not the caliper itself.There will be no mention of it in repair manuals because this procedure was done at the factory and all consumers had to do was change pads and rotors,why would they have to pull a backing plate off?Set it and forget it deal.Trust me,like ANDYZ28 said,this is a necessary step in the conversion,maybe you just lucked out.I know if I didn't shim my driver side,the bracket would lock against the rotor when all was torqued down,shimming was absolutely necessary.

99Hawk120

Right, I know where the shims would go. However, your statement that the backing plate locked against the rotor makes no sense when you consider that you can only shim the backing plate TOWARDS the rotor. Or were you saying that you had to remove the old shims?

At any rate, assuming no interference between the caliper backing plate and the rotor--which if, in fact, you did have, could only be fixed by removing pre-existing shims or shimming the rotor--I don't see the point of really worrying about it too much. The caliper backing plate really only determines the absolute inboard and outboard "stops" if you will, since the caliper rides the mounting bolts rather than being securely attached to them.

Once installed, the caliper (with pads installed) will then self-center to the rotor (assuming new or evenly worn pads) as the pedal is depressed. This how floating-style disc brakes work! The force of the piston will slide the caliper over until even (or close to even) force is applied by both brake pads.

The absolute position of the caliper on the slide pins can be changed by shimming the backing plate, yes, but that should only be an issue if the caliper runs out of "self-adjustment" room. And with the pads removed, the caliper has quite a bit of inboard to outboard travel that I don't see it as an issue unless your axle assembly is REALLY off.

99Hawk120

Well, over the weekend I did some more inspection of the brakes on my friend's car. I still couldn't figure out why you were making such a big deal about shimming the backing plate.

Then I went over and looked at MY car (the 84) and figured it out.

The rear we installed in the 92RS was an 86 rear with a torsen take-off posi from SLP. The posi was replaced because I grenaded the original, which was a 26-spline unit. Not having any 28-spline axles around except for the ones that were in the original rear on the 92RS (28-spline open/drum 2.73), we ground those down and then moved them over to the disc brake rear.

Here's where I think you got confused. The axle we put in was an 86 with the 82-88 style rear disc brakes. These calipers do NOT have a carrier--in other words, there is nothing that sits over the rotor that doesn't move. If you remove the caliper, the rotor slides right off. IIRC, the standard (non-1LE) front brakes also have no carrier.

MY car (the 84) has the '89-'92 style brakes on it, and I can easily see why the position of the backing plate is critical. If it's too far in either direction, the caliper carrier will rub on the rotor. So, you need to shim the backing plate to center the caliper carrier over the rotor (again, the position of the caliper shouldn't matter, since it's a floating design).

I think, in the final analysis, you can conclude the following:

1) '82-'88 disc brakes do not require any shimming of the backing plates except in the most extreme circumstances.
2) '89-'92 disc brakes must have the backing plate shimmed in order to approximately center the caliper carrier over the rotor.

Oh, and just in case you are curious, I didn't have to shim the brakes on my car either; but I did carefully inspect them to make sure it was close to the center. But they're on a Ford 9" rear, so who knows what the actual measurements were--I think you're right, that was a case of "getting lucky".