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Brake bias adjustment question
dome - 23/2/16 at 10:14 AM

Hello all.

My new to me Locost has a very stiff brake pedal and locks the back brakes before the fronts. First port of call is to try and adjust the bias. I don't appear to have a conventional pedal box though...




Can anyone advise how to adjust this? Is it simply a case of turning the threaded rods to suit?

Thanks in advance.

Brian

loggyboy - 23/2/16 at 11:16 AM

There should be a spherical bearing within the tube of the pedal. It should slide up and down that tube which is controlled by rotating the threaded bar.
The principle should be that bearing will act more strongly on the m/c nearest to it.

https://www.rallydesign.co.uk/balancebar.php

mcerd1 - 23/2/16 at 11:22 AM

It should also have locknuts' or similar prevent the adjustment changing itself...

loggyboy - 23/2/16 at 11:26 AM

quote:
Originally posted by mcerd1
It should also have locknuts' or similar prevent the adjustment changing itself...


Technically that's required for IVA, id the car is registered you shouldnt need them, (unless there is evidence the bar is turning by itself)

mcerd1 - 23/2/16 at 12:08 PM

How permanent the thread locking is for the SVA/IVA has changed a bit over the years - but I've never seen anyone suggest you didn't need any thread locking on a bias bar

Bolts under any kind of dynamic loading will work themself loose eventually without something to stop them
For some bolts that could just be a high torque, but that's not going to be suitable for this type of application, besides the last thing you want to find when you have to stand on the brakes is they don't work as you expected.....

loggyboy - 23/2/16 at 12:12 PM

quote:
Originally posted by mcerd1
How permanent the thread locking is for the SVA/IVA has changed a bit over the years - but I've never seen anyone suggest you didn't need any thread locking on a bias bar

Bolts under any kind of dynamic loading will work themself loose eventually without something to stop them
For some bolts that could just be a high torque, but that's not going to be suitable for this type of application, besides the last thing you want to find when you have to stand on the brakes is they don't work as you expected.....


I don't know what you would lock against - all parts need to move freely. Ideally it should be connected to bias adjuster that would ensure its kept from spinning.

adithorp - 23/2/16 at 12:29 PM

quote:
Originally posted by loggyboy

The principle should be that bearing will act more strongly on the m/c nearest to it.



Looking atthe picture it appears that the bias is adjusted towards the right hand master cylinder currently. If that is the rear circuit then adjust it the other way untill you get the balence right with the front'slocking first. If the right cylinder is the front then adjust it even further to the right; However if you run out of adjustment you'll need to start looking at the master cylinder bore sizes and possibly changeing them.

The brakes pedal feel will always seem solid/hard compared to a tin-top with a servoand take a bit of time to adjust to. This may or may not be made worse by master cylinders choice. Smaller bore cylinders will give softer feel, requiring less pedal pressure but at the expence of more travel.

dome - 23/2/16 at 12:59 PM

Thanks guys. Right is front, left rear. I'll have a look and see if I can adjust it.

dome - 23/2/16 at 07:12 PM

Well, I had a bit of a play with this today. Adjusting the threaded rod doesn't seem to have an affect-there doesn't seem to be a spherical joint inside it. I ran out of light today but will strip it down at some point and investigate further-I see the likes of Merlin sell adjusters.

The best I managed to do was adjust the rods going to each master cylinder, this helped a bit but it's still locking the rears first.

View from the top.



I also discovered I have a leak from the front stainless hose under pressure which is less than ideal. I shall have to find out what calipers I have to locate a replacement, can anyone help identify these?



Cheers

Brian

loggyboy - 23/2/16 at 08:19 PM

Its probably seized in the shaft. Full dismantle job.

rusty nuts - 23/2/16 at 08:33 PM

While you have it stripped it might be a good idea to drill and tap the trunnions on their top to fit a couple of grub screws as locking devices, also what bore master cylinders do you have? If one is larger than the other make sure it's fitted the rear brake circuit , the smaller to the front as it will generate more pressure
.

alfas - 23/2/16 at 09:36 PM

ususally the brake hose, caliper side, does have a conic seat, not a flat seat with copper washer. that might be your problem in terms of leakage.

for the stiff pedal:

there is no servo in such cars, but if the pedal is hard and the brakes do not to seem to work without unusual pedal force than master cylinders might have the wrong size (bore)

dome - 23/2/16 at 09:44 PM

quote:
Originally posted by alfas
ususally the brake hose, caliper side, does have a conic seat, not a flat seat with copper washer. that might be your problem in terms of leakage.

for the stiff pedal:

there is no servo in such cars, but if the pedal is hard and the brakes do not to seem to work without unusual pedal force than master cylinders might have the wrong size (bore)


It's actually leaking from the hose itself, where it goes into the union. I have some new Mk2 Escort hoses on order which will hopefully fit, if not I'll get some made up. The copper washer was put on by me to see if that cured the leak, I'll remove it when I fit the new hoses.

Looks like I'll be stripping down my shaft this week then to try and sort the bias box out! I'll check out the size of the master cylinders too.

Thanks for the input guys.

adithorp - 23/2/16 at 11:35 PM

Master cylinders might have the bore size on the casting. Common sizes are 0.75", 0.7", 0.625" (0.875+1" also available but rarely seen on a kit)

loggyboy - 24/2/16 at 07:54 AM

Calipers are ford 'M16' BTW.
Very available. From mk1/2 escorts and capris.

alfas - 24/2/16 at 06:05 PM

if you think about purchasing replacment calipers and you need new brakes hoses anyway, why not fancy a weight saving upgrade:

http://www.hispeccalipers.co.uk/ul4m16.html

dome - 27/2/16 at 06:05 PM

Hoses still haven't arrived but I stripped down the pedal box today.

Here's what I found...






Where there should be a spherical bearing there's actually just this rod so no adjustment is possible Threaded M10 and with a 25mm diameter. I'll need to have a look and see if it's possible to swap this for a spherical bearing. Suggestions welcome!

P.S. My calipers are brand new so they'll do for a while yet!

nickm - 27/2/16 at 07:48 PM

Hi
If you look for "bias bar" in Rally Design or Car Builder Solutions, and others you will find a new one approx £25, the spherical bearing should slide L to R in the pedal housing and tilt up and down like a see saw when in the pedal you may also have to polish up the inner housing to allow this nice easy movement.
My pedal has the housing made of steel which is part of the pedal and then a nice polished up inner lining tube which the spherical bearing sits inside, i think the item above has that nice inner as part of the kit.
Llight pressure is enough to make it move in its lining which is how its supposed to be.

Nick M

gremlin1234 - 27/2/16 at 08:00 PM

quote:
Originally posted by domeHere's what I found...
Where there should be a spherical bearing there's actually just this rod so no adjustment is possible
thats not a balance bar, its a method to push two cylinders the same amount with one pedal.

[Edited on 27/2/16 by gremlin1234]

dome - 27/2/16 at 08:48 PM

quote:
Originally posted by gremlin1234
quote:
Originally posted by domeHere's what I found...
Where there should be a spherical bearing there's actually just this rod so no adjustment is possible
thats not a balance bar, its a method to push two cylinders the same amount with one pedal.

[Edited on 27/2/16 by gremlin1234]


Yep. Once I replace the leaky hoses on the front I'll try it as it is-it has passed SVA/MOTs with this setup so it may be set up to work correctly. I can get my local garage to test the brakes too. If I'm not happy with it I'll convert it to a balance bar.

alfas - 28/2/16 at 12:01 AM

passed sva/mot means nothing

those institutions check if the brakes work....but it says nothing about balance, force needed for pushing the pedal etc.

we are talking about brakes here...one of the main safety devices in a car.

rusty nuts - 28/2/16 at 08:07 AM

quote:
Originally posted by alfas
passed sva/mot means nothing

those institutions check if the brakes work....but it says nothing about balance, force needed for pushing the pedal etc



Don't know how you came to that conclusion because when the brakes were tested during my cars SVA test a brake pedal pressure gauge was fitted and the individual
Brakes tested until they locked up with the pedal pressure recorded at the same time . This is how the brake bias is tested , it covers balance as well as bias. At one time in the early 70s there was talk of measuring pedal pressure for the MOT

big-vee-twin - 28/2/16 at 09:01 AM

I went through IVA Friday and they check the balance and also pressure applied by attaching a sensor to the testers foot.

I have a spare bias bar with bearing and clevises if your interested never used, £20 posted its the Rally Design one.

[Edited on 28/2/16 by big-vee-twin]

mcerd1 - 28/2/16 at 09:44 AM

quote:
Originally posted by dome
quote:
Originally posted by gremlin1234
quote:
Originally posted by domeHere's what I found...
Where there should be a spherical bearing there's actually just this rod so no adjustment is possible
thats not a balance bar, its a method to push two cylinders the same amount with one pedal.

[Edited on 27/2/16 by gremlin1234]


Yep. Once I replace the leaky hoses on the front I'll try it as it is-it has passed SVA/MOTs with this setup so it may be set up to work correctly. I can get my local garage to test the brakes too. If I'm not happy with it I'll convert it to a balance bar.


The problem is you don't know what's been "fixed" or "upgraded" since the SVA and experience tells me that not all cars that pass an MOT should have done....

alfas - 28/2/16 at 03:04 PM

quote:
....

The problem is you don't know what's been "fixed" or "upgraded" since the SVA and experience tells me that not all cars that pass an MOT should have done....


thats what i wanted to say......


majority of cars me and my mates have bought in the past 10years would not have passed another MOT straight after purchase, even those cars passed the MOT a few days before...and i´m not talking about stupid little details...some of the cars had really severe faults.

anyway...back to the thread.

dome - 28/2/16 at 06:12 PM

quote:
Originally posted by alfas


thats what i wanted to say......


majority of cars me and my mates have bought in the past 10years would not have passed another MOT straight after purchase, even those cars passed the MOT a few days before...and i´m not talking about stupid little details...some of the cars had really severe faults.

anyway...back to the thread.


Agreed, I'm under no illusions about the MOT test nor some of the work carried out by previous owners. The pedal setup looks original though, hence it being worth trying the car when the front brakes are fixed and getting it tested by my tame garage. I'm also going to remove the plumbing for the hydraulic handbrake as I'll never use it.

mcerd1 - 29/2/16 at 08:58 AM

Its quite likely that the car was originally built using a single master cylinder (either from the donor car or a similar one, there are loads of threads on here about picking the best one)
Then its likely that this was 'upgraded' at the same time as your hydraulic handbrake was added, both of these would have failed an SVA test
Not that it helps you any, you're still going to need to sort it one way or another...


The bias bars you can get from the likes of rally design are pretty cheap so my vote would be to fit it now and save alot of messing about with the current setup - it'll also give you more flexibility for any brake upgrades you may want to fit later


Did you ever manage to find any clues to the master cylinder sizes that have been fitted?

If they aren't different sizes then they probably should be, if they are different then there is a good chance someone's plumbed then in the wrong way round...

the size is often marked on the sides, 5/8" [0.625] and 3/4" [0.75] are common for quite a few cars, the smaller one should be connected to the front brakes as per the comments above

If they are the wrong way round then correcting this would go a long way to sorting the problem, but without the bias bar for the fine adjustment you'll be very very lucky if its 100% right



[Edited on 29/2/2016 by mcerd1]

adithorp - 29/2/16 at 10:23 AM

There's absolutely no point putting that back together; You'll only have to do it again.

The slight leak from the calipers will not be significant enough to account for the imbalance (it'd have to be pouring out). You need a proper balence bar. You'll have to set it by trial and error as set of MOT brake rollers won't give that, due to not having weight transfer (at IVA/SVA it's a much more complex test and they do a calculation for the F/R balance). Starting with the bearing dead centre will give the same balance as before. Slightly to the front cylinder will be where you probably end up.

Angel Acevedo - 1/3/16 at 03:17 PM

Dome.
If I were you and have access to a lathe, I´d turn the "Bushing" to the Pedals tube diameter and reassemble.
Then go testing for balance at a private road.
If you run out of travel, then switch cylinders as stated somewhere above.
HTH

Edit to correct OP Name.

[Edited on 3/1/2016 by Angel Acevedo]