I now need to change from roof mounted carriers (591’s) to my towbar carrier as I have changed cars.

I’m totally convinced that when I used my towbar carrier before the exhaust fumes contaminated my brakes (diesel fumes on the discs) as they were fine on the roof but they lost their bite, squeel and feel very spongy. Has anyone else though the same and if so what have you put over the discs and calipers so stop this happening? To make it worse my new car has an exhaust on each side so I need to cover both the front and back.

Any help would be welcome.

Ta

oh right your exhaust fumes passed your seals and created air pockets in your brake system to make them spongy ? or did the fumes magically turn the pads into the consistancy of sponge ?

thats some good exhaust gasses.

Exhaust deflectors?

just put a poly/tin foil bag over them if your feeling really paranoid

I think your imagination is getting the better of you…

now, now. The diesel particals have got on to the disc and contaminated the pads, hence the lack of power and spongy feel… 🙄

I always found that commuting in traffic made by BB7s very squeely. All it took to improve them was to get them really hot once a week or so.

see, I’m not going mad!

Lack of power – credible symptom of diesel/crap on the disc
spongy feel – not credible symptom of diesel/crap on the disc.

it’s more likely traffic film on the pads.

The spongy feel might be me pulling the lever harder to get them to work.

I’m running XTR Trails which as we all know dont have power issues.

Disc brake cleaner? Nice solventy stuff should get rid of the buildup I would have thought

We drove down to the Alps with all bikes in the van, but Pete-Poddy’s Pitch on the rear mount (something to do with weight distribution, and the Pitch weighing as much as a 2.2 diesel engine or something…)

His bike, and therefore brakes, were covered in road and diesel shite, and really needed a good scrubbing before he could mince down the Pleny….

So, your idea isn’t all mad!

DrP

never noticed this with my diseasal but then i have down pointing pipes and brakes above bumper level so maybd it goes down and doesnt float up again until behind the rack.

Do notice the bike collects more road filth out back though.

Is there a similar issue with petrol on startup with unburned fuel?

I’ve known of this happening, bike on boot rack and brake over exhaust pipe looses performance.

’tis the diesel practicals contaminating the pads / rotor.

I thought you were talking about he rear discs on your car getting contaminated at first. 😳

It’s not a problem I’ve ever experienced with my towbar mounted rack TBH but if you’re that worried I’d have thought the cheapest option would be a deflector as recommended above.

If you use 99RON/Shell VPower you’ll get better braking performance.

Just as I though, any suggestions on what to cover the dics with to stop this happening again?

Nope sorry, just the black stuff!

what to cover the dics with to stop this happening again?

Bonnet de douche (….Rodney). You know, the disposable ones you get in hotel rooms.

I’ve not had this problem, but last time we popped the bikes on the rear rack and drove on the motorway to our destination the both of us had issues with squealing brakes. We put it down to salty spray / road grime getting onto the discs, not diesel fumes (I drive a petrol car).

its more likely to be the diesel/petrol film that is on our roads and in the rain this sprays up behind you.

never wondered why cars get dirty rears and the rest of the car can be clean …. thats aerodynamics at work.

not really as I always put my bike on the rack the facing same way (due to the way it was strapped on 😯 ) and it was only the brake nearest the exhaust that was affected, but now I have an exhaust at both sides…… h-mmm

Take a clean rag and bottle of meths / disc cleaner, and wipe the discs before riding?

I do that after every ride now, even thought the bikes travel in the back, just to minimise pad contamination; not had noisy brakes since I started.

Remove your brakes before transport and put them back on after? It only takes a minute or 2.

In terms of the rotors, clean them with brake cleaner or isopropyl alcohol before putting the brakes back on.

ISTR a comment yonks ago about a hot exhaust causing a tyre to explode. Is it possible you cooked a brake hose?

I have the same issue as the OP.

I have a car with roof rack for bikes, and I have a van with rear carrier.
The brakes always squeal like a banshee after carrying them on the van.
Rather than exhaust fumes, I put it down to general road grime. The sort that makes the boot of your car more dirty than the roof or front.

Always carry mine on a tow bar mounted rack, had both a new car with twin exhausts and an old Diesel with one smoking exhaust and still the only time my brakes are ruined is from the salt and grit from winter roads

Carrying bikes on the back is a good way to get them absolutely covered in salt, grit, rain and general road filth.

Watch a car going down a wet motorway and see the spray covering everything on the back. That’ll wreck brakes far more than the exhaust gases from your car (although that won’t help either when thrown into the mix).

You can buy full bike covers that still accommodate the bike rack, they’re quite expensive but they do keep the junk off and also stop prying eyes seeing exactly what you’re carrying.

Actually the muck that accumulates on the back of cars are mostly deposits from exhaust rather than stuff kicked up off the road. Exhaust fumes are fuel rich, loaded with unburned fuel particles, even on so-called lean burn engines, so it is entirely plausible if the position of the exhaust pipes is right combined with the turbulent air at the back of the car then fuel deposits can accumulate on the discs. I’d just take a can of brake cleaner with you to clean the discs off before you ride. Far easier and less fiddley than trying to cover the discs. But i doubt exhaust deflectors will be that effective due to the turbulent air behind the car.