Still More Brake Musings.....

[Dan Sarandrea (Phila)]

Seems like there are several brake threads going right now, so I'll jump in with something I have been considering.

It's a given, based on what Bernice and other long-time Xers have posted, that replacing the stock 34mm bore rear calipers with 38mm rear calipers from the FIAT 125, 132, and the Lancia Montecarlo/Scorpion is a very beneficial mod to make, enhancing front-to-rear braking balance and overall braking performance.

Unfortunately, sources for OEM versions of these are drying up, and the aftermarket item that is being sold by, for example, Mr. FIAT on eBay, leave a lot to be desired in their execution of the parking brake mechanism part of the caliper. TonyK recently posted his difficulties with such calipers, noting that the parking brake bits on the aftermarket caliper were substandard and negatively affecting actual braking performance due to adjustment issues.

I was curious about the possibility of machining the bore of the stock 34mm caliper out to 38mm, keeping the factory quality parking brake components but meshing them with the 38mm unit's major rebuild kit, which would supply the 38mm piston plus seals, dust boot, and o-ring.

My machinist buddy says that the boring operation is pretty simple, the time consuming part would be coming up with a satisfactory way to secure the caliper to the Bridgeport table with an eye toward repeatability, which might or might not require the fabbing of a jig of sorts.

The whole idea depends upon the availability of sufficient quantities of major rebuild kits for the 38mm caliper, as the kits would be the source for the 38mm piston. I don't know of a ready supplier of these

 

[ng_randolph]

My understanding from reading the earlier threads, is that the problem is with the piston and piston internals, rather than with the caliper housing. Perhaps boring up 34 mm stock calipers to 38 mm would not be needed.

From TonyK's thread, it looks like stock piston internals are the same for 34 and 38 mm, so those bits would transfer over. I think FiatFactory pointed out that the after market pistons used a C-clip rather than the OEM bent wire spring clip to hold the piston internals in place. This would likely mean that the internal grove in the after market pistons would not fit the OEM spring clip. Perhaps all that is needed is to enlarge the groove in the after market piston? This would have to be done with some precision, so as not to alter any clearances in the mechanism once assembled. Chucking a piston in a lathe would certainly be easier than making a fixture for the whole caliper.

 

[Dr.Jeff]

Unfortunately, sources for OEM versions of these are drying up

Dan, nice write up as always. I fully agree the lack of availability of components from other models is a big issue (here in the US). In addition to the ones you mention, several other models have also been cited as potential donor parts but all have the same limitation in the US. I'll add a further concern to that; the quality of "re-manufactured" or "rebuilt" components is often horrible, so even if you find something it likely won't be much good. Not to mention shipping costs these days. Your concept is interesting. Have you been able to confirm there is sufficient material to bore without creating other issues?

On the notion of Euro models vs US models, I always get a kick how we (US) want the Euro stuff and guys in Europe seem to like the US stuff. Over the last few years I've seen a huge trend of guys coming over from Europe and buying up US vehicles to ship back. Isn't the worlds largest gathering of classic US vehicles in Sweden I believe? Guess we always want what we can't have.

 

[rocco79/138]

I am hoping they(euro peeps) are looking for classic pre 74 cars. I had a '74 Corvette which I think had less power than my X...
Nobody but nobody is looking for a solid Chevy Monza... I always cringed every time I read the "styling changes will be made to fit the NA market" when reading about some great looking euro model...
Turns out most of what was sold as "performance parts" were little more than stock euro parts.
I had two Scorpions and somehow ended up with one rear caliper. I ran it on my 86 and only found out while rebuilding a complete set this '79.
The 34mm seal will tell every time! There should be plenty of room the remove the additional 2mm around the outside. The calipers were/are identical on the outside and all the inside bits are the same too. I just rebuilt one of each and except for the seal I would not have been able to tell them apart.
I won't take them apart for some time but from what I remember could you not have 38mm pistons made while modifying the calipers? All the bits would play just fine and the Scorpion rebuilt kit are easy to get as well.
Regards

 

[Dr.Jeff]

could you not have 38mm pistons made

That might be a realistic approach to Dan's plan. I've seen lots of aftermarket pistons offered in S/S, as direct replacements for older vehicles that often suffered rusted "steel" pistons. So there may be sources willing to make them at a reasonable price. Or they might even be available already? Here's one UK source that offers a long list, do any match the requirements? http://biggred.co.uk/caliper-piston

 

[fiatfactory]

Boring the caliper from 34mm to 38mm might be pretty simple, a lot more difficult would be the machining of the seal groove, which isn't square on the bottom... it has a chamfer on the front edge to tip the square section seal up a little at one end (this is what makes the piston retract)

Given the time involved to bore / cut a suitable seal groove... and the cost of suitable pistons... surely this is going to add up to the approximate cost of new calipers anyway...cost is the biggest hurdle for most people (not the availability)

SteveC

 

[Dr.Jeff]

cost is the biggest hurdle for most people

Although the cost of existing options in the US isn't good either. See this listing for used Uno Turbo calipers; no assurance that they are even rebuildable, but if they are then add that cost plus the rotors, pads, etc:

http://www.ebay.com/itm/fiat-128-un...ash=item3f809a6678:g:uNEAAOSw2xRYPYzW&vxp=mtr

And this listing isn't much different, rears only but at least new. Double this cost for the other side (separate listing), without the pad carriers, brackets, etc, etc. Interestingly they appear to be only 30mm ?:

http://www.ebay.com/itm/FIAT-UNO-1-...962363?hash=item4649265fbb:g:ji8AAOSwOyJX-3bZ

 

[kmead]

As the calipers are in fact standard Girling units, one can look at other cars that use the Girling caliper such as the VW Golf which uses a 38mm piston in its rear calipers. The likelihood of the mounting points being the same from an Uno Turbo Girling caliper to a VW Girling caliper is pretty high.

Getting the brackets could be half the battle as the calipers are likely the same across Girling designs. Clearly would need verification but interesting nonetheless to consider.

https://www.kartek.com/parts/volkswagen-girling-38mm-rear-disc-brake-calipers-right-hand-side.html

 

[Rupunzell]

Surprising how few Turbo Uno front caliper sets are available today as Fiat built an awful lot of them.

As mentioned before, problem with current Fiat 500 front calipers are the 54mm pistons. This is enough to significantly alter brake balance of the system in the wrong direction of excessive front brake bias.

The problem is not with getting alternative parts to fit, the problem is to get the proper parts to work as needed, then fitment becomes the challenge.

The idea of using 38mm VW Girling calipers is much preferred to boring out the 34mm calipers then sourcing pistons to match. Added benefit to the VW Girling rear calipers, they are a modern design pin floating calipers which are FAR better than the old Fiat slider design. One more added benefit, a variety of brake pads should be available at reasonable cost due to the sheer number of VWs on the road world wide.

Boring out the 34mm calipers is quite do-able. It will require set up tooling and fixture to be built to secure both LH & RH calipers into the machine tool's table. Seal groove shape can be made by grinding a specific grooving tool as needed, this is a very common machine shop operation. 38mm pistons can also be made as needed. Stock Fiat-Lancia piston is chrome plated steel for durability. Stainless steel can be used, but know the surface finish can be an issue as the OEM Fiat-Lancia chrome plated pistons are quite smooth with a specific surface finish and the chrome plating does reduce friction while promoting proper square cut seal performance.

There is a desire to find a easy way to modify the stock brakes on the exxe to gain something, reality is the problem is far more complex than most would want to believe or accept. What is important when considering any brake system change is the actual effort and cost involved mixed with a realistic understanding of what the results of these changes might be. No wishful thinking, be realistic with what is possible.
Do respect the original design as the brakes as delivered on the exxe does work well, very well when they are in good condition.


Bernice

 

[Rupunzell]

Very typical FWD rear brake caliper. Weight distribution of a FWD chassis is mostly opposite of a mid-engine chassis. Weight up front is why the rear caliper piston diameter is much smaller than the front brake calipers.

Bernice

And this listing isn't much different, rears only but at least new. Double this cost for the other side (separate listing), without the pad carriers, brackets, etc, etc. Interestingly they appear to be only 30mm ?:

http://www.ebay.com/itm/FIAT-UNO-1-...962363?hash=item4649265fbb:g:ji8AAOSwOyJX-3bZ

 

[kmead]

Alfa 164 rear calipers are 38mm and would have the right clocking for a rear caliper on an X for the handbrake cable to interact with it.

We might even get lucky and find that the mounts holes are in the right place since it is part of the family.

Makes one wonder if the SAAB 9000 rear calipers might also be the same as the Lancia Thema, Alfa 164 and the SAAB 9000 were all on the one platform.