Brake pedal firm after driving up incline.

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Brake pedal firm after driving up incline.

Postby AussieAnth on Mon Oct 08, 2018 6:39 am

Had a situation recently on a week long trip in NW Vic desert country. Was driving up a long steep sand dune. Got to the point where tyres dug in and I wasn't going to make it, so I hit the brake quickly. Brake pedal was really firm, and I had to push much harder than usual to get it to engage. Anyone had this before or explain why it might have happened?

I use to have an 08 BT-50, and something very similar happened on a much longer gradual climb that got too steep in clay to progress. Slammed my foot down twice on the brake and the pedal wouldn't budge. Ended up rolling back down, clipping a stump and rolled it 3/4 of a turn onto its side. Once we flipped it back, the brake worked fine.
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Re: Brake pedal firm after driving up incline.

Postby RHKTriton on Mon Oct 08, 2018 7:06 am

Does your vehicle have traction control?

I'm thinking whether the traction control possibly causes depletion of the brake boosters reserve?

Alternately, heavy TC action could be heating up the brake fluid.
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Re: Brake pedal firm after driving up incline.

Postby AussieAnth on Mon Oct 08, 2018 7:12 am

Yep I've got a 2013 GLX Manual. Hadn't been doing much heavy work leading up to that attempt. Turned stability control off. I'd been driving about 20min of flat sand tracks leading up to that spot, but had the engine off for probably half hour before attempting the climb.
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Re: Brake pedal firm after driving up incline.

Postby Bitsamissing on Mon Oct 08, 2018 8:20 am

I am not a mechanic... so this is just a mental exercise on my part...

A firm pedal and difficult braking indicate a loss of power assistance. Power assistance comes from the reservoir of stored vacuum in your brake booster, and the vacuum is generated by the vacuum pump on the engine.

Vacuum is stored in the booster to ensure there is at least one good power-assisted stop available following an engine failure.

If say there was something affecting your vacuum pump or the hose to the booster during the long steep climb, you should still have had enough stored vacuum to provide assistance when you hit the brakes near the top. That makes me wonder if there was something allowing the stored vacuum (in the booster) to deplenish (an air leak) during the climb. I can't suggest what that may be though...

It may be an interesting exercise to pay attention to how long your stored vacuum lasts during ordinary usage. Normally if you leave your vehicle sitting for a couple of days, if you come back to it and put your foot on the brake before starting it, the pedal will be very firm because the stored vacuum has dissipated. Leave your foot on the brake when you start it and the pedal will drop down under your foot as the power assistance kicks in. If you leave the car sitting for only half an hour however, when you come back to it the brake pedal should feel like it normally does when driving. If it doesn't, that may indicate an air leak in the booster... an air leak that may get worse under certain conditions... like a steep climb up a sand dune...
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Re: Brake pedal firm after driving up incline.

Postby RHKTriton on Tue Oct 09, 2018 8:07 pm

Just read through your bit bitsa.

There may be a cracked/loose vacuum line between the engine and body or chassis. This could be opening when the engine is under load and moves relative to the bodywork.
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Re: Brake pedal firm after driving up incline.

Postby msrlo on Wed Oct 10, 2018 5:09 am

Do you have a dual battery set up. Myself and someone else on here had a similar issue and it turned out to be a kinked vacuum brake hose
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Re: Brake pedal firm after driving up incline.

Postby AussieAnth on Thu Oct 11, 2018 7:43 am

msrlo wrote:Do you have a dual battery set up. Myself and someone else on here had a similar issue and it turned out to be a kinked vacuum brake hose


2nd battery is in the back so that won't be it.

I do have a secondary fuel filter in that same space with extra hoses, and loads of extra 12v cabling feeding to the factory battery so I will look. Any tips on how to identify the hose that might be kinked?
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My MN & ML Triton WORKSHOP MANUAL page on DropBox. Take a look.
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Re: Brake pedal firm after driving up incline.

Postby msrlo on Fri Oct 12, 2018 5:15 am

just follow the steel hose from the brake booster to the passenger side, when it goes to a rubber just check its not bent and it doesn't have kinked much
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