servo on rear drums as well as front discs???

[wibble_puppy]

thank you so much for that long and clear explanation, lovely Packedup

I guess you could say that an unladen van has "a very light rear" unless BG or another LCV person can enlighten me?

[bigginger]

Nope, full agreement, and the stiff springs aren't much help for keeping the rear on the road unladen either... I'd still rather servo all 4, but am willing to be convinced otherwise too

[Willie]

This has been an excellent use of the forum, all sides giving reasoned views.

[wibble_puppy]

yeah, it's been so good for learning stuff

I have been mulling over the posts so far and I have another pig-ignorant question, in two parts:

(part 1):

If you fit a servo to the front discs only

and if the purpose of a servo is to reduce the leg effort required to exert a certain amount of pressure on the brakes

then how much leg effort will you end up needing? That required for the fronts? That required for the rears? or something in between?

and (part 2):

whatever the answer to part 1, does this mean that you might be applying too much or too little pressure to one or other sets of wheels?

does that make sense? if not i will have another hack at it

grateful wibble xx

[aupickup]

a servo does not give you more power for breaking, it is just less effort, whether on the front or both

[wibble_puppy]

hiya aupickup

is that a reply to the second part of my question?

[aupickup]

yes i guess it is
i have had a servo with disc brakes and it is definately worth while in my opinion
makes it less effort to stop

[wibble_puppy]

yeah, definitely going to replumb mine in - just a question of whether I apply it to the rear drums as well as to the front cylinders

<edit: make that "front discs" >

[picky]

wibble,

to get a definate answer on whether to servo all the brakes or just the front I think you would need to either simulate it in a computer, or plumb in the servo with several brake bias valves, so you could in effect turn off the servo effect on the rear drums. (I am not entirely sure of the plumbing in this but I am sure it is possible) Then you would have to do lots of emergency stops and find the combination that gives your car the shortest stopping distance

If you were to servo all four, and then find that the rears lock before the front, I wonder if fitting a brake bias valve to the rear would serve as an adjustable pressure reducer??

All of the top of my head, hope it makes sense!!!

[bmcecosse]

Yes - adjustable pressure limiter valve is the way to go - almost all modern cars have these - linked to the suspension so as load increases so does braking at the rear. So - the easy way to do this is just to servo the fronts, risk is the rears may not be doing all the braking they could - but it will be relatively safe with no chance of rear wheels locking early. More difficult is tp servo all four wheels - risk now is that rears may lock up early (very nasty) before the front wheels are doing all the braking they can. Solution then is to add a pressure limiting valve in the line to the rears. Personally - if I was fitting a servo - I would just use it on the front discs.

[Willie]

Juliet, the whole purpose of fitting a servo is to reduce the amount of pedal pressure needed to achieve the maximum braking effort. The effect of this over a typical journey means that you have had to apply much less effort to control the car which obviously translates into being less tiring, especially in your case. I would estimate that the servo reduces the necessary pressure by 30-35%. Couple this with the discs and you will eliminate brake fade to all intents and purposes. Only if you have cooked the drum brakes down hill etc and have arrived at the traffic lights with no effect when you press the pedal will you appreciate
this!

[jonathon]

We must have fitted over 50 sets of discs to otherwise standard minors,and have always servo'd all four brakes. You are upsetting the original balance by adding only front discs, but we have not yet had any problems with the rears locking up before the fronts.
We have fitted over 40 front discs and either Ital or Escort axles the latter running 9" wide 2.8 drums, we still servo all four brakes and have never experienced problems with this set up, what the larger brakes of the Ital and Escort do offer, is a restored balance in braking

[Willie]

Iwondered where you were Jonathon! Crikey, 9" wide 2.8 drums?

[bmcecosse]

Surprised it needs ANY front brakes with rear anchors that size!

[jonathon]

OOPs missed the comma 9",( diameter) wide( as not the standard RS 2000 narrower ) 2.8 capri drums . Sorry chaps

[Matt]

Errm the truck in my sig pic has 14" dia x 4"width drums on the back, trust me you need front brakes too ;) it weighs about the same as a minor but stopping from 40 mph is a bit scary!

[IslipMinor]

Please see the next post - somehow managed to submit when I meant to preview!!

Where's it gone?? There were two, now there's just this one!

It was obviously there as there is a quote from it, very strange.

I will re-post and hope.

[Matt]

:s

[alex_holden]

(fitting the Wolesley 9” drums is not so effective!!). Yes, larger diameter drums, but much smaller wheel cylinder bores, so not as much braking effort for the same line pressure.

Doesn't that just mean you have to push the pedal a bit harder to lock the wheels? Having previously driven an unservoed Series Land Rover (which I'd upgraded to the larger LWB drums), I'm less worried about that than I am about fade. How does the Riley 1.5 9" front drums/late 7" minor rear drums combination fare in this model?

I find modern cars are often so over-servoed that it's difficult to brake lightly.

[Matt]

But thats probably because we are used to unservo'd brakes...