90 300TDI Poor Brake Performance. Help needed. What can I Upgrade?

Hi, I have a much loved 1998 S Reg 300TDI (no ABS) 90 that keeps having my MOT tester complaining about poor brake performance. Apparently, it only achieves 51% which bearly passes the test. To be honest, I can press hard on the peddle and make the tyres skid so how much more braking power is needed but there you go!???

So, since this issue started occurring over four years ago I have changed:
1. Brake Bias Valve
2. New Rear Calipers
3. New Rear Disks & Pads
4. New Front Disks & Pads ( Pads were Mintex but now Apexi)
5. New Front Stainless Steel Pistons

My mechanic, (who I've drafted in on this issue), agrees there is nothing else that can be done and the vacuum being created is fine for the servo.

So to the questions.
Can I change the servo over to the double ABS style servo to gain more power?
Is there a bigger disk, caliper and pad set out there that I need?
Should I just sack off the MOT tester? ;-)
Looking for genuine help please guys n gals.

Not helpful.. but...
That's odd - I have the same year and model. When mine was tested in April I could not lock up the brakes under any circumstances.
Still passed though, with an advisory about thin pads. I've since put new callipers and pads all round and it's much better, it'll lock up if I push hard enough.
Question is if you can lock up on 51% wtf would happen at 100%? Sounds scary!

Hello and welcome btw

If you're locking up on 51% could it be that your tyres are not very grippy. Are you running off-road tyres?

Hi, Current tyres are Kumho mt kl71 and previous were BF Goodrich KO2 so wouldn't have thought they would be an issue.

If your FRONT brakes are locking they can't be any more efficient. The rears shouldn't lock up, this would be a bad thing.
Is the mechanic using brake rollers or a tapley meter?

Can they get reliable efficiency testing on rollers? I thought you have to remove one of the props first otherwise you are trying to test all four corners with only two on the rollers?? My tester only uses a Tapely meter on my landy.

Wimblowdriver said:

Can they get reliable efficiency testing on rollers? I thought you have to remove one of the props first otherwise you are trying to test all four corners with only two on the rollers?? My tester only uses a Tapely meter on my landy.

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Prob use the decelerometer as they have old technology equipment/rollers
The new type have 4x4 settings so they can test very accurately on a 2 roller system.
I have an Mitsubishi evo rs all mechanical plated diffs & my tester does it on the 2 rollers.
We also tested it on the G meter he said the brakes are outstanding.

He also done my 90 recently & never said anything about the brakes so they must have been good

Could stick some Brembo's on the front

The MOT tester is very old school so I bet he is using old rollers. I have heard about a Tapely Meter before. To be honest I would have thought that with more and more 4x4's on the road the DVLA would have insisted on an MOT station having the correct equipment. I think I'll just move on to another testing station. I'm happy that it's pulling up okay so bugger it, lets see what a new tester thinks. Fingers crossed for the 10th of August....

PukkaPicka said:

I'm happy that it's pulling up okay so bugger it, lets see what a new tester thinks.

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I should think so too. Bestaluck mate

Hopefully it's just the test station as you say. If you're even close to locking the fronts I'd say your brakes are effective enough to pass the test easily. With new calipers, discs, pads and a new servo my 1985 90" reached 79% on the front axle. That dropped down to 69% after a couple of years. The new servo made a big difference - previous to this I was also just passing, although I definitely had seized front calipers.