Front Caliper Fittings: Banjo Vs. Bundy Pipes

[DreamsOfA26R]

Hello all,

I understand that there are two types of fittings that connect the flexible brake hoses to the side-input front brake calipers; there's the hard, buddy pipe style attached to the caliper mounting bolts, and the banjo fitting that connects the flexible hose directly to the caliper. Is one of these styles better than the other? Are the two systems interchangeable? It seems that my car has the banjo bolt style currently and given that I'm replacing the old hoses I want to ensure I put the best, most performance oriented of the original type systems in the car.

Thoughts?

[StressCraxx]

Neither is better than the other. Both work well when installed correctly. Do buy the good service kits and expect to replace the pistons with new. Use the hard chromed steel pistons, they will last longer than the aftermarket stainless because the hard chrome surface is much harder and more resistant to fretting corrosion.

[DreamsOfA26R]

Hard choked over stainless? Once again you've come to my rescue with details I hadn't even thought to consider. Given how rusty the calipers are currently the idea of stainless really was enticing, but if the chrome is stronger and comparatively corrosion resistant then it seems the better choice!

[2cams70]

If you go back through previous topics I’ve had a rant about this and various noted people have disagreed. I would not put stainless steel pistons in my calipers if there was an alternative more like the originals. No OEM caliper manufacturer has ever used stainless steel as a material for caliper pistons as far as I’m aware. To me that says something. What type of fitting you need to connect to the caliper with is entirely dependent on the caliper design - you can’t interchange. Seems a bit of an odd question. I’m not really sure where you are coming from.

[gjz30075]

The banjo fitting is one less potential leak point. ie, the flex line goes straight to the frame mount whereas
a hard line into the caliper requires a joint to a flex line going to the frame mount.

[Craven]

Early S3 front caliper, side entry used a banjo adaptor on the caliper end to fit a flexible pipe with similar straight connector both ends, that is caliper to chassis.

[RichardHawkins]

2 Cams,

There must be a reason why hard chrome appears to be the industry standard. When I was in my 20’s I worked in the hydraulics section for my employer, and if I remember correctly all piston rods were hard chrome plated. Later in the mining industry piston rods on earth moving machines were also hard chrome.

I thought I would ask professor Google, but can’t find an answer. Sometimes the answer is we have always done it this way, or it’s cheaper. Working on the assumption that the manufacturers probably know best I have stayed with hard chrome but would really like to know why?

Richard Hawkins

[StressCraxx]

I'm glad to hear some owners like Type45 have had success with stainless pistons. The key issue is the integrity of the chrome oxide layer on stainless which is only about a micron thick. If one drives the car frequently I believe one will find the fretting corrosion will occur. Rubber grease will help for a while until it is gone, but it also attracts grit on the atmospheric side with speeds up the mechanical fretting process.

I have had lots of experience with dynamic gaskets rubbing on 300 series stainless, all the way up to Hastelloy C276. These materials have good resistance to pitting corrosion when the oxide layer is present. The soft rubber gasket gently rubs the oxide layer away leaving the remaining iron exposed to pitting before more chrome oxide can form. 300 series stainless is usually 18% chrome, 8% nickel. Type 316 is the same with about 1% molybdenum. The remainder of the alloy is iron 73-74%.

One solution was using a plasma sprayed chrome oxide coating over the stainless gasket mating surface. This method works really well and we can reuse the part without having to recoat the surface. We frequently used hard chrome on shaft surfaces if that is what the client specified. Will either work forever? Sadly no. Corrosion never sleeps. Please find below a link to some technical documents on fretting corrosion.

https://www.sciencedirect.com/topics/en ... 20products.

[2cams70]

Stainless pistons are probably fine on hobby cars but OEMs don’t seem to use them on road cars for some reason and I very much doubt that reason is cost - after all you can get stainless fasteners these days for much the same price as regular steel fasteners. Plating - especially chromium is expensive these days because of environmental factors that now need to be considered.

On the topic of hoses and seals swelling - this should never occur if the correct grade of rubber and the correct grade of fluid has been used. Seals wearing yes - swelling no. If you have swelling something is wrong that isn’t related to age or mileage.

[nmauduit]

any thoughts on other caliper piston materials, e.g. Al alloy which are offered for some applications ( or Ti ? ) or even ceramic if any ?

As for fluid I'm still with silicone based on my street car (or motorcycle), a pain to purge the small bubbles but once done I find the feel ok (250°C boiling point to keep in mind for track days).

[patrics]

Hi,
Girling / Lucas did try stainless pistons but the piston rollback (desirable) was inconsistent compared to chrome plating. Also knock-back was a problem which is always a issue with opposed piston calipers and flexible suspension.
The original chrome plating was rubbish as there was no copper base layer but at least they were round. Having said that, these days unless you know the quality of the chrome plating you are probably better off with stainless – it would be good if they were machined at top of the tolerance so that the seal nip was higher.
Anyway if you have issues with inconsistent pedal travel you know the possible causes and it might only become an issue if you have high suspension loads like on a race track.
The rear pistons in stainless won’t be a problem because the volumes are very low.
Stainless pistons will help, but it still doesn’t cure the basic problem with sticking pistons as it is the iron caliper housing which tends to rust and swell.

Regards
Steve