Technical 500 rear brake wear

[Franko500]

I took Franko to another show today. The Darling Buds of May Classic motor show held in the fields next to the original setting from the series.
It was a great turn out however the fine drizzly rain put a damper on things!


This was Franko's longest run so far about 26 miles each way.
I kept him off the motorway and kept to the A/B roads. He is quite happy driving at 30-45mph.
On the way I noticed a noise coming from the osr wheel. I have heard it before but usually when I am coasting on going round a bend. It disappears when the brakes are used so I presumed it may be a slightly distorted drum.
When I got home I dismantled the rear drum to find its not so much a distorted drum but the edge of the leading shoe is rubbing on the inner face of the drum.

I have checked the original set up and everything is correct including the lower spring inside the lower plate.
I have taken the grinder to the shoe to remove the excess metal thinking maybe the shoe is too wide. reassembled and its still rubbing.
Tried adjusting the lower metal plate to adjust the tension on the lower spring so as not to cause the shoes to pop out so much but still no difference.
Any suggestions before I go ordering a new set of drums & shoes?
The photos show the wear to the outer edge of the leading shoe and also one of the set up when I took the car apart originally.

 

[Vitesse]

Before you put the drum on Sean do the shoes sit flat on the back plate? That lead shoe must be popping forward off the back plate when you put the drum on. Does it show even wear on the brake shoe where that rubbing is or is it still to new to show?

I would imagine if it was the drum you would get the same wear on both shoes.

Are the back plates and drums new as well? I would try swapping the shoe over with one from the other rear wheel and see what happens.

 

[Franko500]

By tweaking the lower plate it released some of the tension on the lower spring which pulls the shoes out of their proper position. So I managed to get the shoes to sit correctly before putting the drum on, however there is still some springiness there which can make the leading shoe pop out slightly.
There is some wear on the edge near the back plate on both shoes so I think there is some uneven wear.
Here is a diagram of what I imagine is happening - slightly exaggerated for demonstration purposes.
Both back plates are the old ones, no wear was present and the locating pegs were both still round and showing no wear.
There's not a lip on the edge of the drum, although they are not what I would like to say "Smooth". So maybe I am thinking they are worn and causing the shoe not to sit correctly within the drum.

 

[fiat500]

I'd guess it's a combination of slight wear on the backplate, brake-shoe pivots, slightly over-sized internal sockets in the repro friction washers on the new shoes and strong pull-off springs. All that may be conspiring to literally pull the shoes off the posts.
I have wondered if the backplates can be modified to retrofit the the steady pins that I think are fitted to later 126 and subsequent Cinquecentos etc.
I have a front brake that I suspect has the same problem.
I also wonder if the wheel bearing needs adjustment on mine.

 

[Vitesse]

By tweaking the lower plate it released some of the tension on the lower spring which pulls the shoes out of their proper position. So I managed to get the shoes to sit correctly before putting the drum on, however there is still some springiness there which can make the leading shoe pop out slightly.
There is some wear on the edge near the back plate on both shoes so I think there is some uneven wear.
Here is a diagram of what I imagine is happening - slightly exaggerated for demonstration purposes.
Both back plates are the old ones, no wear was present and the locating pegs were both still round and showing no wear.
There's not a lip on the edge of the drum, although they are not what I would like to say "Smooth". So maybe I am thinking they are worn and causing the shoe not to sit correctly within the drum.

Yeah I reckon that is what happening and the spring is pulling it forward as per your diagram. The inside of my drums are far from perfect TBH, so I wouldn't think it was the drum to blame.

It does make me wonder whether the self adjusters aren't working properly, added to the fact that you did think you had some issues when you initially bled them?

Have you tried the old driving backwards and forwards and stamping on the brakes a few times. The faster the better, don't be shy.

I must admit I can't really get my head around how these self adjusters are meant to work?

 

[the hobbler]

To call them 'self adjusters' is a bit of a misnomer. They are really 'friction holders'. The idea is that the wheel cylinders are stronger than the friction exerted by the friction washers, so push the shoes out, to make contact with the drum. The springs have only enough tension to JUST pull the shoes away from the drum when you take your foot off the brake pedal. After a little bit of retraction, the spring becomes weaker than the tension of the friction washers--the shoes don't retract anymore.
The original 'adjusters' were capable of being overhauled--you held one side by the flats on the adjuster, unscrewed the other side of the adjuster (with a factory tool), took the adjuster apart, fitted new friction washers and spring and screwed the parts back together--tight. This was in the days when the brake shoes were obtainable without the adjusters--you transferred and overhauled the old adjusters and fitted them to the new shoes---you had to be a proper mechanic in those days!

 

[Franko500]

I feel that the 2 springs holding the shoes together are too strong and this is the main cause for holding them off the back plate.
They were the original springs and so I kept them as I thought they would be better than reproductions.
Maybe I could file the holes in the shoe to release some tension on the spring?
Yes Tony I tried the braking in reverse tactic.
They also passed with flying colours in the MOT so they must be working!

 

[Vitesse]

Oh ok I understand now Tom.

 

[Vitesse]

I feel that the 2 springs holding the shoes together are too strong and this is the main cause for holding them off the back plate.
They were the original springs and so I kept them as I thought they would be better than reproductions.
Maybe I could file the holes in the shoe to release some tension on the spring?
Yes Tony I tried the braking in reverse tactic.
They also passed with flying colours in the MOT so they must be working!

I changed the springs last time I refurbed the brakes and used repro springs. They were really hard work to get on compared to the old ones. I could barely get the shoes back onto the back plate because the springs were so tight. They even broke my spring puller in half.

If it were me I would try swapping the shoes and springs from one wheel to the other and see if the problem moves. A pain in the butt but at least it may give you an idea.

 

[fiat500]

The MOT advised that I changed the rear brake drums and the brake-light switch.

I'm pleased to report that the drums are a notable exception to the copy reproductions are poor (C.R.A.P.) rule. Although, from the packaging these are not specifically for the middle or early years Fiat 500s and have a slightly different construction, this is all to the good. From the design it appears that they will keep out dirt and moisture better, possibly cool better and there is certainly a chunkier casting where the wheel bolts screw in.
MAL_1999 by Peter Thompson, on Flickr

Having had a few thousand miles to stretch the new springs, the whole job was much easier than the last time. Although the linings were hardly worn at all I obviously replaced them, one of the friction washers was broken and one drum was badly scored at one part of the diameter.

I had to bleed the brakes after fitting the pressure switch and was amazed to see how discoloured the brake fluid had become in the two years and so kept going until it all ran clear.

 

[Dorisinblue]

I had exactly same problem with my 500F rebuild. I changed the shoes and springs and eventually the drums also. Still had the rubbing issue.
Eventually I made up a 1mm spacer from sheet metal with 4 holes for wheel bolts and the big hole in middle to fit over bearing housing. I fitted this between the drum and the hub. In effect this moves drum 1mm away from the shoes.
I also fitted slightly longer wheel bolts to compensate.
Fixed the problem and brakes seem to work fine although I plan to revert to normal setup after a few miles to see if brakes have "settled" into correct position.

 

[stevehg]

Peter, were they the metelli drums from axel? They look like the ones I used to replace my rears, and as you say they look better quality than the existing ones.

cheers, Steve

 

[fiat500]

Peter, were they the metelli drums from axel?

cheers, Steve

They were.

When removing the old, I didn't see any signs of the misaligment problem which started this thread.

I'm pretty sure that if the adjusters are working properly, the shoes will self-align back onto the pins when under load

Later Fiats always had and have the little locating pin halfway down the shoes,which are to prevent this happening. It wouldn't be too hard to modify them for this.

 

[fiat500]

There you are, Roger NZ already has them..