Girling Rear Mechanical Brake Dust Gaiter / Boot

Designed to replace the rubber dust cover / gaiter / boot of the rear brake assembly of a friend's Lanchester car, as the rubber in the old gaiters had broken down and just crumbled away. Apparently the Girling mechanical brake assembly can be found on all sorts of classic cars from the 1920s to the 1980s!

Rubber replacements can be bought for about £38 (inc P&P!) for a pair of them (https://www.designdevelopmenteng.co.uk/shop/Girling-Mechanical-Brake-Expander-Rubber-Boot-p389433922) but for a few pence you might find this design durable enough at least for an emergency replacement, and depending on how the TPU lasts, hopefully permanent! 

I tried two wall thicknesses (0.4mm nozzle) in Shore95A TPU (Eryone Transparent, as that's the only TPU I have in stock) and it was a bit too firm and would be difficult to expand the narrow end to pass over the brake rod's end-eye. Single wall thickness with spiralised wall turned out to be surprisingly tough but much more stretchy and does pass over the end-eye especially if you lube it well and stretch it on the end of narrow-beaked pliers as you're applying the gaiter to the brake rod. 

There is a constriction in the design to fit the groove in the brake housing, but ideally use a ziptie to reinforce the connection once it's in place. Likewise the narrow end is designed to be not too tight for easier fitting over the end-eye, and could benefit from being ziptied in place so I've added a decent length of narrow end, this can be cut shorter if desired.

Printing - important settings:

TPU of course, nothing else is likely to be of any use! Shore95A seems ok, softer might be better if you've got it available.

0.4mm nozzle is great. 0.2mm layer height is great.

Bottom layers = 28 to ensure the groove-locating section is printed full thickness and not spiralised.

Infill = 15% but probably irrelevant as it's mostly just one wall.

Print speed 10mm/s first layer, then 20mm/s, worked well with this TPU and the print time was about 30mins so no real need to print faster.

Adhesion = Brim about 4 lines, outside only, brim line width 0.5mm (=initial line width 125%), this is really needed to stick the model to the build plate. I tried adding a flange instead but this made the base unstretchable and a bit tricky to fit to the brake mounting block. The brim gives you a little bit to get hold of with snipe nose pliers if you need to, just be a little careful not to rip the brim, lubricate the assembly well before fitting and ease it on gradually working around the edge.

Temperatures - on my Elegoo Neptune3 Pro and with the Eryone TPU this was 205C nozzle temp and 0C build plate (no heating) on PEI textured stock plate, TPU can bond extremely well to PEI and even damage the surface, I find Eryone's TPU adheres very nicely to my PEI with no heat at all, and removal after printing is very nice - adheres well but not too much.

TPU is very compatible with oils and grease, and so should be great in an application like this where lots of grease is very desirable for lubricating the mechanical parts and to help keep out dust and dirt and water etc.

Please let me know in the comments how you get on with this model, and upload your makes :o)

UPDATE - Now fitted. The clear TPU is remarkably see-through isn't it? I've reprinted them in black to be fitted later for better “authenticity”! The published STL has a longer narrow neck bit than the one in the photo.

If this model saves you a few bob, please visit… https://www.buymeacoffee.com/gigabeast :o)