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jpboost

Member Since: 13 Apr 2021
Location: Gatwick
Posts: 377

2014 Defender 110 Puma 2.2 SW Keswick Green

Braking issue, probably hydraulic?

I'm experiencing some weird behavior in my bitsa/working 1972 Series 3.

There are two, linked, symptoms that popping up on a more frequent basis. Not every time I drive it, but where it was very occasionally, it's now probably 1 in 3 times I drive it. They are relating to braking pedal issues, and rolling resistance...

Some more details:

Occasionally, when I'm driving my Series 3, the brake pedal will go really, really hard.
It's not completely solid, and really standing on it makes the brakes operate, but it's very very different suddenly.
Then, just as suddenly, it'll go back to normal. Sometimes this is after a few of applications of the brake (i.e. a few corners later), sometimes after 10 minutes or a good few miles later. There doesn't seem to be any consistency in how long it lasts for.
The pedal is right at the top of it's travel.

While the pedal issue is happening then the car also feels like it's laboring. It's almost like the handbrake is on. This also clears the moment the brake pedal frees up.

It's got a 200tdi in it, sitting on Disco axles. Still leaf sprung, but with standard disco disc brakes all round. It runs the original master cylinder, and no servo. The handbrake is disc converted, and works fine. it's correctly adjusted, and not binding.
Overall it's a nice setup and when not doing the above, it works really really well and has done for years.

I originally thought it was a sticking brake caliper, but even after driving a while with the issue, none of the wheels feel hot (or certainly no particular wheel feels warmer than the others). And it comes and goes so quickly, so this seems unlikely to be the problem. It also doesn't pull left or right.

The engine seems totally fine, so I think it's just having a tough time to overcome the resistance when the issue is happening.

Perhaps one of the flexi brake hoes is breaking down internally? they look fine, but in the past I have had some weird behaviours from a clutch flexi hose internally breaking down, so I'm always aware that they can look fine but be causing problems.

Other than the above, I think that only leaves the brake master cylinder..

In the absence of any other ideas, I think I'll do the master and flexis in one go, just to minimise the amount of times I have to take it apart and bleed the brakes.

Any other ideas from the group before I start buying parts and taking it to bits?

Thanks

Jon

8th Nov 2024 3:04pm

TexasRover

Member Since: 24 Nov 2022
Location: Paris
Posts: 1086

2002 Defender 110 Td5 DCPU Chawton White

Normally when you don't apply the brakes there is an open path from each caliper through the master cylinder to the brake reservoir. Once you apply the brakes and the MC plunger moves it closes this path and starts building pressure.

Maybe your brake pedal is poorly adjusted with the plunger slightly engaged closing this free path even when you dont apply the brake. As thing heat up a bit the pressure cannot escape putting a slight pressure on the system causing some braking and when you try to brake you are immediately pushing against pressure.

There are adjustment options in the linkage and there are some documented dimensions you can check, but I would start with checking if there is any free play in the MC pushrod and check if fluid can flow freely. On modern cars it all just fits right, on Series/Defenders some fetteling might be required.

One other thing is that there are different brake systems and while the MCs can be interchangeable it is not necessarily a match. You have drum brakes in different sizes, disc brakes - normally not, and then you have single and dual systems and power assist or not. The fluid volumes and pressures required to make each of them work right are different so you need to make sure you have the right MC for your brakes or else you have too much fluid and low pressure or too little fluid and too much pedal travel

8th Nov 2024 4:19pm

jpboost

Member Since: 13 Apr 2021
Location: Gatwick
Posts: 377

Hmm, that's an interesting bit of information. Thank you.

I'd not considered linkage etc, as it's been working well in this setup for 5+ years, but it's worth me checking.

Master cylinder size/bore is a bit of an odd one. I swapped from drums to discs all round, and I fully expected to have to change the master for exactly the reasons you mention.
But when the axles went on, I connected everything up to the original hydraulics (to get a baseline of how it felt, pedal travel etc) and it was absolutely spot on.

8th Nov 2024 4:50pm

Gareth

Member Since: 12 Dec 2011
Location: Woodford
Posts: 1110

+1 for the pushrod to master cylinder adjustment. You need a bit of free play. The intermittency of it says that’s the cause. If it was a mismatch of components I’d expect it to be more consistent. 2021 Defender 110 X-Dynamic HSE D300 MHEV
1966 S2a 109 aka Betsy

8th Nov 2024 4:55pm

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