MOT and brake force

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

User avatar
chinkostu
Posts: 1180
Joined: 24 Sep 2014, 09:41
Location: cheshire
My Cars: N Xantia 1.9TD SX
03 Fiesta 1.4 Zetec
x 30

Re: MOT and brake force

Post by chinkostu »

citronut wrote:
chinkostu wrote:
if you ever need to work on that car again, take a look at the bar that runs from the back of the booster to the pedal (across the top of the bulkhead)

theres a 13mm locknut that you can use to adjust the pedal travel. chances are they've nipped it out so theres a bit of free play in the brakes. Both my Saxo's had iffy feeling brakes until I adjusted them.

this is a Xantia we are talking her Mr chinkostu,
they do not have servo assisted brakes like the Saxo does, and the usual fault on the Saxo is the linkage at the bulkhead seizes up

I was referring to the saxo ;) ;)
Stu

Cars
1995 Xantia 1.9TD SX in (faded) Red
2003 Fiesta 1.4 Zetec in GREEEEEEEN
2001 206 1.9 LX
2001 Saxo VTR
1999 Saxo 1.1 East coast
1999 Punto :oops:
1996 306 1.8 XN Auto :?
1996 Fiesta 1.3 #-o
citronut
Posts: 10937
Joined: 29 Apr 2005, 00:46
Location: United Kingdom east sussex
My Cars:
x 92

Re: MOT and brake force

Post by citronut »

citronut wrote:
Stickyfinger wrote: and what causes it ??
maybe an uninitiated MOT tester
Regards, malcolm.

current ride a BX 1.7 TZD estate
1986 MK1 BX 1.9na D Auto(in Mothman Andy's stable )
layed up roppy 1.9TD XANT estate, now gone to meet her maker
purple and lilac metalic 2CV(VIOLET)registered to her in doors
1972 DS special been layed up aprox 31 years
citronut
Posts: 10937
Joined: 29 Apr 2005, 00:46
Location: United Kingdom east sussex
My Cars:
x 92

Re: MOT and brake force

Post by citronut »

chinkostu wrote:
citronut wrote:
if you ever need to work on that car again, take a look at the bar that runs from the back of the booster to the pedal (across the top of the bulkhead)
citronut wrote: this is a Xantia we are talking her Mr chinkostu,
they do not have servo assisted brakes like the Saxo does, and the usual fault on the Saxo is the linkage at the bulkhead seizes up
chinkostu wrote: I was referring to the saxo ;) ;)
sorry bud it certainly did not read that way to me anyway's :-D :wink:
Regards, malcolm.

current ride a BX 1.7 TZD estate
1986 MK1 BX 1.9na D Auto(in Mothman Andy's stable )
layed up roppy 1.9TD XANT estate, now gone to meet her maker
purple and lilac metalic 2CV(VIOLET)registered to her in doors
1972 DS special been layed up aprox 31 years
User avatar
chinkostu
Posts: 1180
Joined: 24 Sep 2014, 09:41
Location: cheshire
My Cars: N Xantia 1.9TD SX
03 Fiesta 1.4 Zetec
x 30

Re: MOT and brake force

Post by chinkostu »

citronut wrote:
chinkostu wrote:
citronut wrote:
if you ever need to work on that car again, take a look at the bar that runs from the back of the booster to the pedal (across the top of the bulkhead)
citronut wrote: this is a Xantia we are talking her Mr chinkostu,
they do not have servo assisted brakes like the Saxo does, and the usual fault on the Saxo is the linkage at the bulkhead seizes up
chinkostu wrote: I was referring to the saxo ;) ;)
sorry bud it certainly did not read that way to me anyway's :-D :wink:
I worded it poorly ;)

if you read it, i do say "both of my saxos" :rofl2:


regardless, i don't think theres any linkage adjustment on a xantia :lol:
Stu

Cars
1995 Xantia 1.9TD SX in (faded) Red
2003 Fiesta 1.4 Zetec in GREEEEEEEN
2001 206 1.9 LX
2001 Saxo VTR
1999 Saxo 1.1 East coast
1999 Punto :oops:
1996 306 1.8 XN Auto :?
1996 Fiesta 1.3 #-o
c.morewood
Donor 2023
Posts: 1041
Joined: 05 Nov 2004, 14:38
Location: Kemnay, Nr Aberdeen, United Kingdom
My Cars: '00 Xantia 110 bhp Hdi SX Estate 65K "W"
'99 Xantia 110 bhp Hdi SX Estate 310K SORN "V"
'98 Xantia 1.9TD SX Estate 150K Sold "T"
x 47

Re: MOT and brake force

Post by c.morewood »

I'm with you Malcolm .. just discovered he's about 23 and dosen't know a lot about hydraulic Citroens...
So I've read that the best way to test Xantia rear brakes is either a lot of weight in the back or suspension on high?
I'm wondering if thats correct so I can pass it on to him.. need to have a word about the travel and what force and efficiency he's expecting to see from the brakes.
I've heard he's quite a fair chap just uninitiated with the hydraulics.
Any thoughts from you guys about the force required/expected and efficiency expected from the brakes?
Chris
Tesla Model 3 LR DM AWD Blue White
'00 Xant 110HdiSX Est 83K "W"
'99 Xant 110HdiSX Est 320K "V"
'98 Xant 1.9TDSX Est 150K "T"
'97 Xant 1.9TD 20k Est
'94 Fiat TipoTd 40K

'85 BMW K100RT 330K Garaged 26yrs '80 Honda CB250 twin Superdream
User avatar
xantia_v6
Forum Admin Team
Posts: 9052
Joined: 09 Nov 2005, 22:03
Location: France or NewZealand
Lexia Available: Yes
My Cars: -
1997 Citroen Xantia V6 (France)
1999 Citroen XM V6 ES9 (France)
2011 Peugeot 308 CC THP 155 (NZ)
1975 Jaguar XJ-S pre-HE (NZ)
x 825

Re: MOT and brake force

Post by xantia_v6 »

The MOT brake machines compensate for axle weight. I had a xantia that failed on rear brake efficiency by a few percent. I took it home, put 200kg of concrete in the boot and took it back.... the brake efficiency was just the same. In that case I think the problem was the "performance" brake pads fitted by the previous owner did not have much grip when cold.
superloopy
Posts: 3306
Joined: 30 Mar 2005, 03:25
Location: United Kingdom
My Cars:
x 18

Re: MOT and brake force

Post by superloopy »

How is it then that the rear brakes silver up with a fully loaded car and dont seem to do anything when not loaded? How can the machine simulate the axle weight?
Mike

Xantia Activa Dante Red MK1 (96) 121k - SORN, to be broken
Xantia Activa Silex Grey MK2 (98) 120k -SORN, ditto
Xantia V6 Silex Grey MK2 (98) 95k - non-runner
Xantia TD Storm Grey MK1 (95) 95k - non-runner
citronut
Posts: 10937
Joined: 29 Apr 2005, 00:46
Location: United Kingdom east sussex
My Cars:
x 92

Re: MOT and brake force

Post by citronut »

as far as i know the axle weight is calculated by VOSA's computer not through the rolling road/brake tester, as the car is logged on for the MOT through VOSA' s
data base,
because older cars that may not be on the data base the MOT tester has to either ask the person presenting the car, or try to look it up on a wall chart
Regards, malcolm.

current ride a BX 1.7 TZD estate
1986 MK1 BX 1.9na D Auto(in Mothman Andy's stable )
layed up roppy 1.9TD XANT estate, now gone to meet her maker
purple and lilac metalic 2CV(VIOLET)registered to her in doors
1972 DS special been layed up aprox 31 years
superloopy
Posts: 3306
Joined: 30 Mar 2005, 03:25
Location: United Kingdom
My Cars:
x 18

Re: MOT and brake force

Post by superloopy »

Thats my point. The fact that the rear axle requires 'extra' loading is lost to the majority of testers these days who will dial in the book values. Proof that the brakes need loading is surely that the disks themselves are very lightly used otherwise. Also explains why you cant properly bleed the rear brakes without the axle being loaded.
There is no pressure in the system otherwise so makes sense to me that without any loading the brakes are not effective resulting in marginal values. Chuck the extra weight in .. thats what i do if only to silver up my disks!
Last edited by superloopy on 19 May 2015, 13:29, edited 1 time in total.
Mike

Xantia Activa Dante Red MK1 (96) 121k - SORN, to be broken
Xantia Activa Silex Grey MK2 (98) 120k -SORN, ditto
Xantia V6 Silex Grey MK2 (98) 95k - non-runner
Xantia TD Storm Grey MK1 (95) 95k - non-runner
User avatar
Stickyfinger
(Donor 2016)
Posts: 10411
Joined: 28 Mar 2013, 21:05
Location: Somset my lovleee
My Cars: Xantia V6 ACTIVA 3ltr 24v Manual p1
Xm 2.1TD Ph2 Exclusive
AX, little Daffodil
SAXO White Mk1. Sally
x 1280
Contact:

Re: MOT and brake force

Post by Stickyfinger »

In an EMPTY car, when on the road, the movement/ "throw" of the car loads the suspension constantly as does body roll etc, this will not be happening on a "static" body even if it is weight loaded as the system is self leveling.....I do not fully understand why weight when static on a roller would change that state ?

Is there an effect on the system if the front wheels are not rotating ?
How does suspension movement/loading effect pressures in the brake lines/system valves ?
Alasdair
Activa, the Moose Rider
3x C5x7 Steering racks and counting
superloopy
Posts: 3306
Joined: 30 Mar 2005, 03:25
Location: United Kingdom
My Cars:
x 18

Re: MOT and brake force

Post by superloopy »

Try bleeding the back brakes without any load. It cant be done. Something to do with opening valves which i dont fully understand. Putting suspension on high as has been suggested has the same effect as loading the rear. No doubt someone will have an explanation for this.
Mike

Xantia Activa Dante Red MK1 (96) 121k - SORN, to be broken
Xantia Activa Silex Grey MK2 (98) 120k -SORN, ditto
Xantia V6 Silex Grey MK2 (98) 95k - non-runner
Xantia TD Storm Grey MK1 (95) 95k - non-runner
Gibbo2286
(Donor 2020)
Posts: 7170
Joined: 08 Jun 2011, 18:04
Location: GL15***
My Cars: 2006 C5 2.0 Litre HDI VTR Automatic Estate.(now sold on)
Currently Renault Zoe 2014 ZE
x 2500

Re: MOT and brake force

Post by Gibbo2286 »

Here you are fellas, work it out for yourselves :) http://www.citroenet.org.uk/miscellaneo ... ics-1.html
Man is, by nature, a lazy beast, he does not need twice encouraging to do nothing.
superloopy
Posts: 3306
Joined: 30 Mar 2005, 03:25
Location: United Kingdom
My Cars:
x 18

Re: MOT and brake force

Post by superloopy »

Gulp! It does mention brake force and load though across the axles. Anyone able to make sense?
Mike

Xantia Activa Dante Red MK1 (96) 121k - SORN, to be broken
Xantia Activa Silex Grey MK2 (98) 120k -SORN, ditto
Xantia V6 Silex Grey MK2 (98) 95k - non-runner
Xantia TD Storm Grey MK1 (95) 95k - non-runner
User avatar
xantia_v6
Forum Admin Team
Posts: 9052
Joined: 09 Nov 2005, 22:03
Location: France or NewZealand
Lexia Available: Yes
My Cars: -
1997 Citroen Xantia V6 (France)
1999 Citroen XM V6 ES9 (France)
2011 Peugeot 308 CC THP 155 (NZ)
1975 Jaguar XJ-S pre-HE (NZ)
x 825

Re: MOT and brake force

Post by xantia_v6 »

citronut wrote:as far as i know the axle weight is calculated by VOSA's computer not through the rolling road/brake tester, as the car is logged on for the MOT through VOSA' s
data base,
because older cars that may not be on the data base the MOT tester has to either ask the person presenting the car, or try to look it up on a wall chart
Quoting from the tester's manual

Code: Select all

For Class 4 vehicles the ATL system will automatically weigh the vehicle and this presented weight will be used for the brake efficiency calculations.
citronut
Posts: 10937
Joined: 29 Apr 2005, 00:46
Location: United Kingdom east sussex
My Cars:
x 92

Re: MOT and brake force

Post by citronut »

Northerner wrote:Thats my point. The fact that the rear axle requires 'extra' liading is lost to the majority of testers these days who will dial in the book values. Proof that the brakes need loading is surely that the disks themselves are very lightly used otherwise. Also explains why you cant properly bleed the rear brakes without the axle being loaded.
There is no pressure in the system otherwise so makes sense to me that without any loading the brakes are not effective resulting in marginal values. Chuck the extra weight in .. thats what i do if only to silver up my disks!
i have always understood you are ideally meant to present the car for an MOT unladen,

all my customers cars i take for MOT's i virtually never have a problen on the brake rollers unless there is an actual fault with the braking system,

like on a conventional suspended car with a compensator valve on the back axle, they do not test if the valve is operating on an MOT, but just make sure the lever arm is not seized/stuck
Last edited by citronut on 19 May 2015, 13:45, edited 2 times in total.
Regards, malcolm.

current ride a BX 1.7 TZD estate
1986 MK1 BX 1.9na D Auto(in Mothman Andy's stable )
layed up roppy 1.9TD XANT estate, now gone to meet her maker
purple and lilac metalic 2CV(VIOLET)registered to her in doors
1972 DS special been layed up aprox 31 years
Post Reply