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Home > Technical > Tdi vs Td5 brakes - what's the big difference?

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donmacn

Member Since: 07 Nov 2017
Location: Nth Scotland
Posts: 1829

Thanks Retro,

ABS Servo above - yep - I hadn't taken a close look at it until now, but certainly the M/C is different as are the mounting bolts at the rear. My question was more about the principle of using a different/bigger servo, and which one might be a 'bolt on' job. On the other hand, given that there's so much good stuff being said about standard brakes in good nick, that's a better target for me - try and identify the fault and fix that.

Thanks for the suggestion of trying the brakes minus servo. Simple idea - but it hadn't occurred to me! I did this on the way into work just now. With the hose off, I can hear the pump sucking air, and I can feel it on my finger tip. I don't have the experience to know if it's strong enough or not, but it's definitely working.

Without the servo - 20/25mph on damp tarmac - I can stop the car OK, though it does take a reasonable amount of effort. I wouldn't say it was 'very difficult' - so I'm taking that as a good sign, that the actual lines, calipers, discs and pads are in good nick.

With the servo reconnected - I can feel a significant difference, so it is doing something - but I wouldn't say it's a "startling" difference.

Tried again, seeing as I was there - 25mph/damp tarmac/empty car - slam on the brakes. No sign at all of the wheels locking up. So, as you say, "something going on there".

Did the 'servo test' - engine off; press the pedal a few times to use up the vacuum; foot on pedal till it's hard; turn on engine. The pedal does absolutely nothing. Doesn't drop at all. (Conventional wisdom says this is the servo not working - but as demonstrated above it is definitely doing something.)

If I then lift off, and press again, the pedal drops a lot and then continues to slowly drop. Does this suggest a M/C leak, where I'm then getting servo assistance to press the M/C plunger and force fluid past a leaky internal seal?? Donald

1994 Defender 300Tdi 110 SW - owned since 2002 - 230k miles and going strong
(The 'rolling restoration' or tinkering thread: http://www.defender2.net/forum/topic58538.html )
2000 Range Rover P38 4.0L V8

in the past..
RR classic - fitted with 200Tdi
1984 RR classic - V8 with ZF auto box
1993 Discovery 300Tdi

not to mention the minis and the Type 2 VW camper...

4th Aug 2020 9:34am

sako243

Member Since: 08 Jul 2014
Location: Wales
Posts: 1185

1994 Defender 110 300 Tdi CSW Alpine White

Sounds very much like what had happened to mine. The servo has a diaphragm inside if I remember correctly and this had partly broken / disconnected.

When you do the pedal pumping test it probably puts the diaphragm in a particular position such that the vacuum has no effect. However once running then it can hold a partial vacuum and does appear to do something. I took a punt and for £75 from Bearmach got a replacement (STC442) and the difference was astounding. Due to the diaphragm partially breaking it was a gradual process so hadn't quite realised how bad they had become.

For the sake of under a hundred quid I'd get another one in and swap it over. Worst case you'll end up with a spare. Ed
82 Hotspur Sandringham 6x6
95 Defender 110 300Tdi

4th Aug 2020 9:41am

roel

Member Since: 08 Aug 2009
Location: Lelystad
Posts: 2039

I did the what you call servo test i.e. pump a few times and then with the foot on the brake start the engine. I didn't feel anything either. So I didn't think that is a 100% test especially if you have the uprated brakehoses.

However you pedal should be hard and stationary. It should nog go down.
This could be air or a leak somewhere. Roel

1984 90 2.5 na Diesel - RR V8 (1994-2001)
1997 Camel Trophy Discovery 300TDI (2001-2009)
2005 G4 Discovery III 4.4 V8 (2008-2018) It's gone but it still hurts.
2003 90 Td5 (2009-now)

4th Aug 2020 11:50am

MaxRPM

Member Since: 15 Jan 2013
Location: South Staffs
Posts: 1114

Changed the alternator/vacuum pump on my TD5 90 yesterday and the brakes are now really good, just in time to get it MOT'd again!

5th Aug 2020 11:26am

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