Guys, thank YOU!! Really appreciate the help and all the suggestions.

I gave up and took the car to a certified LR service shop, who by some strange incidence is located in building next door to the MOT centre where I tried to pass a week ago. They checked the brakes and took it to the same MOT roller, and somehow got the front brake to show a higher efficiency than when the MOT guys did it on the same roller a week ago - before 65%, now 75%.

The rear brake efficiency was the same. For the rear brakes they said the problem was in the rear brake calipers. I want to thank Kermit_RR and Tottot for calling it. When I told this to the mechanic who's been working on my Defender for the past 4 years and has become my friend by now, he was somewhat in distress as it was him who was telling me for some time that the calipers are fine.

From what I've read here, I also will replace the rear pads and the flexi brake hoses. I'm also thinking about replacing the front calipers and flexihoses.

I hate to be that person who asks stupid questions, but I've been doing that long enough and will allow myself to do it once more:
do You think that the difference between the cheapest calipers like here https://www.paddockspares.com/smc500110-rear-caliper-new-rh.html and the OEM ones here https://www.paddockspares.com/smc500110g-rear-caliper-new-rh-ap.html are worth the price difference - for 4 calipers the difference is gonna be 200 euros, so I'd only like to go for the more expensive ones, if You say it's worth it

Stock_90_TD5_SW said:

I hate to be that person who asks stupid questions, but I've been doing that long enough and will allow myself to do it once more:
do You think that the difference between the cheapest calipers like here https://www.paddockspares.com/smc500110-rear-caliper-new-rh.html and the OEM ones here https://www.paddockspares.com/smc500110g-rear-caliper-new-rh-ap.html are worth the price difference - for 4 calipers the difference is gonna be 200 euros, so I'd only like to go for the more expensive ones, if You say it's worth it

Click to expand...

I would split your current ones, clean them up, and rebuild with new gallery seals, genuine piston seals, and stainless pistons, will give you a far better result than buying new ones, will last longer, be cheaper, and is not difficult to do yourself. I have done both of mine by following the write-ups available on the forum. I could find the one I used if you decide to go this way.

Britpart calipers are ok these days and reasonably priced

£28 Caliper will work just fine.

glad to hear you got to the bottom of it
I too would be inclined to clean up the existing caliper if its serviceable, cylinder walls no scored or pitted etc. definitely new seals, pistons if they can't be cleaned up nice and smooth. a bit of discolouration is OK

Good you know the problem.
A hint for those on standard [ not stainless pistons ] If your truck only does a low miles each year change the pads anyway at least every other year. This keeps most of the piston in the caliper cylinder where they do not rust. If you wait for the pads to wear thin a lot of the piston is exposed and corrodes. Corroded pistons pushed back in to fit new pads stick or soon destroy seals.

I know a photo of a part will be "non contractual" but those two calipers are identical, wouldn't be the first time a blue box/bag contains a decent name part.

tottot said:

Good you know the problem.
A hint for those on standard [ not stainless pistons ] If your truck only does a low miles each year change the pads anyway at least every other year. This keeps most of the piston in the caliper cylinder where they do not rust. If you wait for the pads to wear thin a lot of the piston is exposed and corrodes. Corroded pistons pushed back in to fit new pads stick or soon destroy seals.

Click to expand...

I like that idea, I barely do 5000 miles per year, and new pads are a lot easier and cheaper to fit than faffing around with calipers.

Guys, I'm back with some good and bad news

In short, I had a problem with my rear brakes being very weak from the moment I've bought the truck 5 years ago, but the front was so good that I passed the MOT 4 years in a row. Then I replaced all four discs and pads and the brakes got worse.

My go-to mechanic said it was not the rear calipers and we replaced the brake valve that divides pressure between front and rear axles, no significant change.

Took the truck to a certified dealer - they said it's the calipers.

I asked for Your helped here and was advised to replace the flexi hoses as well. Replaced the rear calipers, flexis, rear pads and pad retaining bits, the front caliper pistons with their rubber seals..... and threw the brake master cylinder in the mix to make the outcome more solid, as it was relatively inexpensive compared to the servo and the vacuum pump

The efficiency got up from 23% to 29% on the rear and the front is now back to 74% from the 64% on the previous attempt. I passed the MOT with the average of 54%, but in my book that means that it was not the calipers as the rear brakes are still very weak. Replaced the brake fluid of course and the mechanic swears there is no air.

Are we left with two last possible suspects - servo and vacuum pump? Or does anyone think there could be some less expensive part still to be tried before going for those

Thank You again for all Your help! Respect to You for not letting a fellow human suffer on his own!!!!

Have the brakes bedded in, after changing pads it may take a week for them to bed in and become fully effective, I changed my front pads a few weeks ago and they were crap for the first few days then improved and now perfect again.

Thanks, Scooby, but do You really think that while changing the calipers and pads increased the efficiency from 23% to mere 29%, but the breaking in of the pads will increase the efficiency to over 50%? I somehow doubt it:|

Ok

Mine always went for a brake test on the road, never went on the rollers. As long as it passed the decelorometer test, that was job done. There is no averages, percentages or individual settings. Mine maybe the same as yours, no way of telling.