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twodoorgaz

importance of servo size with disc brakes?

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Hi folks. Hoping someone can educate me a bit here.

I’m about to place my next order with Heystee for a disc brake swivel kit for the front of a SWB series Land Rover - this time for my father’s vehicle.

The series Land Rover in question is a later SIII, fitted as standard with a servo assisted pedal box.

The vehicle is in the middle of a chassis swap And has been neglected for decades, so I’m planning to renew the brake system wholesale.

I’ve already bought a set of front calipers and backplates from a 200TDI ninety. These use the same 10” rear drums, but have slightly different rear cylinders - so, in order to keep a near stock brake setup - I’ll be using the same discs/calipers/master cylinder/wheel cylinder and shoes/drums as a factory 200TDI defender - all new or recon. No issues there.

but the servo itself is causing some confusion.

the factory SIII used a 6” servo. The factory 200TDi 90 used an 8” servo. You can get a defender pedal box to fit, but we’re not keen on it as it needs a bit of a mod and doesn’t have the right look.

 

that leaves two options - using the factory 6” servo with the complete 200TDI 90 brake setup... or doing the same thing, except splashing out for one of Heystee’s custom 8” servos that fit onto the series pedal box.

the issue with the latter is cost (they’re 3-4x the price of a standard LR servo and also spares availability - if I ever need to replace it, then it leaves me reliant on one manufacturer - something I’m not keen on.

 

so my question is: does the servo size have any impact on the braking performance/functionality or just in the pedal effort? If it’s just effort and if the pedal will still feel “right” then I’ll stick with stock and save our money.

 

i notice that North America Overland - one of the people that fit these kits, seem to use standard servos with a “late SIII/early Ninety” master cylinder. Heystee push you towards vented discs, which I don’t need.

 

could anyone advise? Thank you.

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You should keep in mind that the 88" is lighter than the 90" you're comparing it too.. I al absolutely convinced that the 6" servo will be plenty good enough. On my 80" I have a Heystee kit as well, and without servo. There is so much bite in the discs that I dont really need a servo now, but when I was running drums I retro fitted a servo to be able to lock up the wheels

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Why is an 88 so much lighter than a 90?

I'd have thought the cast iron engine block should weigh more, and the galv on the chassis would weigh the same as the extra 4 inches of steel in the 90.

How much does a 90 weigh?

 

Screenshot_2020-03-08-08-34-33-898_com.brave.browser.jpg

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I'm not at that stage with my build, but I do have a defender and a series pedal box. Want me to dig them out? The servo may swap over.

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Well the engine block is also cast on the 200 only difference is the head, but then theres the turbo, IC etc.. anyway the main weight difference lies in the suspension system, coilers are a lot heavier. Just look at your own specs, not even a stripped down 90" weighs 1300 kgs

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When I converted my 110CSW from rear drum to rear disc, I retained the existing servo & master cylinder, my servo is the small diameter but thicker front to back, I haven't had any braking problems. using the same servo on a lighter vehicle should give you good stopping power.

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1 hour ago, Soren Frimodt said:

Well the engine block is also cast on the 200 only difference is the head, but then theres the turbo, IC etc.. anyway the main weight difference lies in the suspension system, coilers are a lot heavier. Just look at your own specs, not even a stripped down 90" weighs 1300 kgs

Good point, the coils do require a lot of heavy bracketry that the more elegant leafsprings don't require.

No wonder Landrover ditched the system. Not sure the air systems are any better, mind.

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Posted (edited)
3 hours ago, Gazzar said:

I'm not at that stage with my build, but I do have a defender and a series pedal box. Want me to dig them out? The servo may swap over.

Thank you, but think that Terri-Anne has it all covered on her website (power brakes for series Land Rover) - the servo can, just about be made to fit by changing the forks, but it looks a bit odd (this one is intended to be a bit stealth).

 

pending no big changes in opinion, I think that the above is the reassurance I needed to stick with the factory servo and the 90 master cylinder coupled with the correct 90 calipers/rear cylinders and the various valves etc.


now just need to visit the vault of, ever more valuable spare parts I have, to pick out the bits to sell to cover the Heystee kit.

 

thank you!

Edited by twodoorgaz

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I would be less worried about the brake servo, and more about the master cylinder: in theory, the master cylinder used in the drum setup is different from the disc setup; This is to do with residual pressure in the system when not applying the brakes. The drum setup has some residual pressure in the system, the disk setup has n't or has very little.

Of course, people have swapped and changed the brakes around and had no problems. But something else to consider. Also master cylinder diameter is probably different. You can just try the setup you are planning and see how it works. There is always this: https://www.mcgillmotorsport.com/brake-products-brake-residual-valves/

What is heystee suggesting?

 

Daan

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There seems to be quite a bit of confusion about swapping to a coil sprung servo. I've recently been through the same process.

You can fit a type 50 Defender pedal box and servo to a Series but you will need some mods. The top of the servo tower may clash with the bonnet and it can easily be trimmed away for clearance. The pedal needs to be slightly shortened and reangled to match the Series but the biggest issue will be the need for a significant wing / mudshield cut, the Defender pedal box sits the master cylinder much further forward.  I made all  the mods then decided I  didn't want the additional  cuts.

 

You cant just bolt the type 50 servo to the Series tower, stud pattern dosnt match. I needed to made an adaptor plate about 15mm thick to place the Series pedal in the correct position and you will need to turn up an adaptor to link the Series pedal to the fork end of the type 50 servo and also slightly reduce the thickness of the existing bush in the Series pedal. Next problem is  clearance around the steering box,  its going to  be tight and I  cant say for sure if  its  going to fit, I did  some  steering mods at the same  time so  mine isn't standard,  at the very least you will  need to  rotate  the column  on the steering box.  Its  worth noting that  the larger servo that Haystee supply is designed for a left hand drive vehicle, it has a cutout on the servo  flange presumably to  clear the steering box,  off course its on the  wrong side for a right hand  drive vehicle.

I  can link you to another  website where I compared the two  pedal  boxes.

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Additionally, Soren fitted a remote servo, so avoided all those issues :)

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2 hours ago, Bowie69 said:

Additionally, Soren fitted a remote servo, so avoided all those issues :)

Yes I did indeed, but as I said now I'm running without any servo and braking is so much Better than it was with servo and drum brakes so thats why I'm convinced the standard booster is more than adequate for an 88"

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Did this 20 odd years ago...….. sort of.

Fitted 90 axles to a series 3. Drum braked rear axle. Used the standard series servo and master cyl. Used silicone fluid too. Brakes were and are absolutely fine. Still got the vehicle but its looking a bit forlorn now.

Also towed some big trailers with it. No issues that I can recall.

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Posted (edited)

Thanks guys - this is incredibly useful.

So, having had a quick scan through the various parts books my plan would be:

pedal box: SIII (got)

servo: SIII pn STC1816 (got)

master cylinder: early Ninety pn NRC9529 (need)

G-valve (stops rear brakes locking): early Ninety pn NRC8215 - with correct angled bracket (need)

calipers: early Ninety pn RTc3168/9 (got)

discs: early ninety, non vented pn FRC7329 (got but will replace)

rear wheel Cylinders: early ninety pn RTc3168/9 (got bit will replace)

rear backplates: early ninety pn RTc3166/7 (got)

rear shoes: RTC3171 (got but will replace)

Cuprinickel pipes, tees, clips, brackets, mud shields, switches, etc will all be new and generic.

Plus the Heystee swivel kit and hubs.

So, everything is from the exact same model year of Land Rover Ninety, except for the servo and pedal box which will be from a late SIII- does this sound about right to give a factory-feel pedal?

Edited by twodoorgaz

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I did this on my 109.  SIII servo pedal box (original to the vehicle), Discovery 1 servo and master cylinder, with an 8mm adaptor plate between the servo and pedal box.  That lined the clevis pin holes up between pedal and servo input fork and allowed for the different bolt pattern.  Just be wary that the axis of the studs on the servo are not 45degrees, and if you drill the holes at 45 degrees on the adaptor, the master cylinder reservoir will slightly canted to one side (not enough to make any mechanical issue, just aesthetic.   http://www.nickslandrover.co.uk/braking-sorted/

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I have an early Defender servo on my 109 with the 10-15mm spacer & fork adapter, works lovely. I fitted a 110 master cylinder on the grounds that the balance etc. should be about right, and it certainly seems to be.

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For what is it worth.....

I have a SWB Series III (sort of) with a 200 Tdi (fully dressed) with both front & rear discs (ZEUS Conversion)

Standard Series III servo and never any problems.

Brakes work very, very well.

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Guys - thank you very much. Think I’m all set to start cracking on with getting the last of the bits

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Posted (edited)

Not all cars fitted with disc brakes had aservo fitted. My Renauly R8 had disc brakes all roung no servo it also had a single line brake master cylinder. The size of the master cylinder is more important

 

 

Edited by mmgemini

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For reference, my setup:

2020-03-14_16-31-11.jpg

Series 3 pedal box, Defender servo + 110 master cylinder, Wilwood 4-pot callipers + 310mm discs all round, far more braking than grip :lol:

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Yes I'm hoping to be doing this using the Heystee kit, was hoping to fit both front and rear kits but think Heystee have stopped doing the rear disc conversion now so will just be doing the front conversion instead :(:)

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This is the same setup in an Series 3, type 50 servo, Series master cylinder with a standard wing cut.  Also  pics of  the adaptor plate.

610211405_Picture015.thumb.jpg.4f9831fc87d75e736409241dcaefd187.jpg

IMG_2017.thumb.jpg.0dadf2da7df9f63fe8350d0fa70fdfad.jpg

IMG_2019.thumb.jpg.502531b1c85234f0d8f68fe82b77cb38.jpg

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