Technical Front Brakes

[The Whitakers]

Morning All


So in usual fashion there is a problem and after a scary moment of insufficient brakes I thought I had better take a look....


So to close off some of the 'traditional' Q+A's


Yes I have gone backwards at Mach scary pant speeds and hit the brakes many times to no avail.....


The springs are old springs and do not pull the shoes back in. I have had the drum off and pushed the shoe to the far extremities of adjustment, marked them and left them overnight and they are still in the same position....


So I started looking a little closer...…


The locating pins on the back plates are not worn so I gave them a measure and then measured the holes in the brake shoe adjusters, there was nearly 2mm difference! so I refitted the shoes and got Mrs W to press the brakes slightly (without the drum on) and you could see the shoe and adjuster moving significantly but because of the play the adjuster wasn't taking up the slack and adjusting. I got Mrs W to keep pressing the brake pedal to see if I could observe movement in the adjuster and the amount the shoe had to move outwards (which was far more than it would be able to if the drum was on) was madness. to take up the slack in the difference of hole to locating pin and then that of the adjustment spring meant that potentially the shoes would only adjust once the linings had worn away!!


So to prove my theory I got the sleeve from a rawlbolt and cut two 14mm lengths from it and tapped it over both pins on the back plates. this meant that the shoe adjusters fitted snug onto them. Mrs W jumped into the car and started to depress the pedal and like magic the adjusters started to work within a few mm's of travel. Brilliant I thought! then in true style the next problem occurred...….


Because the hole in the brake shoe adjusters is conical for the first 15mm'ish the force of the conical shoe adjuster on the pin was causing the shoes under the stress of the main shoe release springs to pull out of situ and angle away from the back plate, this also happened with the drum on also. It was at that point that I noted that the shoes do not have the usual pin/spring and cup retaining set up to hold them against the back plate like most drum set ups have.


SO! before I start entering a black hole of brake issues has anyone got any input on the following please...…


1, MotoBambino list brake shoes for the 500N/D and then also for the 500/126 so do I have the wrong shoes - are the pins different sizes? This confuses me as they only list one back plate (L/H and R/H) and one drum to fit all?! so why the different shoes? they then do a brake over haul kit that fits the F/L models.....


2, Has anyone ever retro fitted the pin/spring and cup shoe retaining set up before?


Back brakes are fine BTW but are just let down with the amount of movement the fronts have.....


Rob

 

[Toshi 975]

I have a pair of NOS front brake backing plates here so I measured the locating pin diameters just in case it’s relevant. Looking at them I thought 8mm for sure but they measured 0.345” , a bit over 5/16” - 8mm which surprised me.
They are for sale should it be of interest

 

[Toshi 975]

Also got other assorted new and used brake parts

 

[the hobbler]

I have found that some of the 'pattern' shoes are manufactured with slightly thinner linings than the original Fiat version. MBG have had some shoes made (for the 500) for them by a major brake shoe manufacturer to the original specification. This might help.

 

[fiat500]

I have found that some of the 'pattern' shoes are manufactured with slightly thinner linings than the original Fiat version. MBG have had some shoes made (for the 500) for them by a major brake shoe manufacturer to the original specification. This might help.

Having read Rob's The Whitakers very detailed and well thought-out analysis of the physics of his problem, it sounds like the standard? linings he has fitted already are too thick in the circumstances, given that the self-adjuster pivots are worn. So thicker linings will not cure this; only new or unworn backplates or some way of permanently sleeving or repairing the pivot pins will cure it. A very enlightening bit of information. Thanks Rob.

 

[The Whitakers]

Having read Rob's The Whitakers very detailed and well thought-out analysis of the physics of his problem, it sounds like the standard? linings he has fitted already are too thick in the circumstances, given that the self-adjuster pivots are worn. So thicker linings will not cure this; only new or unworn backplates or some way of permanently sleeving or repairing the pivot pins will cure it. A very enlightening bit of information. Thanks Rob.

Hi Pete, for clarity the linings I have fitted are actually thinner than one of the old shoes I took off 12 months ago. Only by 0.2 of a mm but still thinner. The self adjuster pivots aren’t worn at all it’s the hole in the self adjuster on the New shoes that is far bigger Than the shoes I took off.

I need to get an image hosting account so I can post pics, they tell a thousand words!

 

[fiat500]

The self adjuster pivots aren’t worn at all it’s the hole in the self adjuster on the New shoes that is far bigger Than the shoes I took off.

...I see, so the problem is crappy repro parts again.:bang:

I think I once saw it written that obviously there had to be small amount of slack in the self-adjuster fit in order to let the shoes back off a smidgen after the friction part keaves the linings right against the drum. This would be essential, especially when new; otherwise the brakes would bind. But it sounds like yours are out of spec.

The original linings had reusable friction adjusters which were possible better made? As there must be a lot of stress placed on the inner part of the adjusters and the pivots there is unlikely to be any sort of tube with a wall thin enough and yet still hard enough to either line the inner part or sleeve the posts, but that's the only solution I can see other than getting shoes with a tighter fit on the adusters.

I think you've probably nailed why so many people report poor "bleeding" of their brakes.

 

[the hobbler]

Other than Middle Barton's brake shoes, a make that I have used very succesfully is "Metelli". These are marketed by "Autodoc.co.uk" and at the moment are only about £9 a set (+carriage). I have used this company a number of times and have had no problems with them

 

[Vitesse]

Other than Middle Barton's brake shoes, a make that I have used very succesfully is "Metelli". These are marketed by "Autodoc.co.uk" and at the moment are only about £9 a set (+carriage). I have used this company a number of times and have had no problems with them

That’s an interesting site Tom. Their prices in comparison to other main Fiat 500 suppliers are really cheap and they do seem to have quite a lot of parts for classics. For example a dynamo from autodoc was (because they don’t currently have it in stock) £69.48 + £15 p&p. Ricambio in comparison will sell you a recon dynamo for £335.88!!!!!!!!

 

[the hobbler]

Maybe I am very lucky, but whenever I have wanted an alternator or starter over-hauled on my engine (or for colleagues) I take it down to my local 'electrical repair' company (small, family-run) and they overhaul the units for about £40 + vat.

 

[lazylobster]

That’s an interesting site Tom. Their prices in comparison to other main Fiat 500 suppliers are really cheap and they do seem to have quite a lot of parts for classics. For example a dynamo from autodoc was (because they don’t currently have it in stock) £69.48 + £15 p&p. Ricambio in comparison will sell you a recon dynamo for £335.88!!!!!!!!

I'm dubious of these sort of sites as they advertise but don't have. However, this site seems a winner and lots of options and cheap prices.


thanks Tom!

 

[fiat500]

I'm dubious of these sort of sites as they advertise but don't have.

I've had the air-filter and plug leads from Autodoc...the latter didn't include the king-lead and they were a bit long. I got a water-pump for my van which was almost £70 cheaper than a UK seller.

What I do is to add Fiat 500 items to an order for maintenance or repair items needed for the modern cars in the household and I stock up in advance. I don't see these sellers being at all useful for most things other than commonly expendable items.

 

[The Whitakers]

Other than Middle Barton's brake shoes, a make that I have used very succesfully is "Metelli". These are marketed by "Autodoc.co.uk" and at the moment are only about £9 a set (+carriage). I have used this company a number of times and have had no problems with them

Just on their site now, A set will be ordered...….

 

[The Whitakers]

Interesting to see the slight variations in sizes between them all too....


Marelli ones are out of stock typically...….