Rear brake pressure limiter

[MikeNash]

Last night I had to brake my Traveller REALLY hard on a wet road as some idiot slowly pulled out a few cars up into the A3 traffic just south of the M25. By the time everybody had worked out what was going on we'd all used up our braking distances and things were desparate. Luckily he then shot off. However, I noticed that when braking, while the rear wheels locked up (with much smell of burning rubber) the front wheels were still rotating, and since then I've wondered whether anyone has thought about, or fitted, a pressure limiter to the rear brakes. Also, is this the reason some fit servos to operate only on the front brakes?
Regards, MikeN.

[Cam]

The problem is that the rear end of the Minor is very light and the front heavy. This is probably why your rear locked up first. I have never had the problem personally. Fitting a limiter (like the minis have) would improve matters though I guess.

[rayofleamington]

The thing about emergency stops is that the rear of the car becomes VERY light. Therefore the rear wheels lock with a lot less effort than normal.
The front of the car becomes more loaded therefore it is harder to lock the fronts.

The situation is different when braking 'normally' and the late Minor set up with 8" twin leaders on the front and 7" singles on the back is prety well balanced for most situations.
If you reduce the braking at the rear to remove this problem in hard braking, the front brakes will get more use in normal braking and are likely to get hotter - that's the last thing you want before doing an emergency stop!

Just my humble opinion though - others may see it differently

[ColinP]

I agree with Ray, In the dry, I've been able to lock the front wheels on my 2 door (1098cc), with the rear wheels not locking.

Obviously that's going to change in the wet, and with different loads.
At that level of stopping, there's all sorts of things involved - tyre pressures, tread patterns, age of tyres, load balance, etc etc.
(maybe worth checking all the brake adjusters? - I tend to adjust the fronts more often than the rear - the fronts do wear faster).

If you put in a pressure limiter, what happens when you have a full load in the back?

The only car I had which worked well for that was a Citroen GS, where the rear brake pressure was taken from the rear suspension which was height controlled (at lots of psis).

Colin

[rayofleamington]

The only car I had which worked well for that was a Citroen GS, where the rear brake pressure was taken from the rear suspension which was height controlled (at lots of psis).

That's a really neat idea! I was wondering how a system could work that controlled brake pressure based on weight loading on the rear wheels, but I couldn't think of a good way (other than modern ABS)

[ColinP]

Yeah,

The whole GS (and ID/DS) concept was to use the high pressure oil for the suspension (height controllers front and rear), use the high pressure for the front discs, and then use the lower pressure from the rear suspension leveller for the rear discs.

I ended up with the rear discs not working (driving unloaded most of the time - and "gentle" braking).

It also required a separate set of pads on the front for the handbrake (front handbrake on inboard discs - made for a lot of "rock).

Nice suspension & great power brakes - I could lock all 4 wheels from 50 mph in a straight line - but ultimately very complex and expensive to maintain.....

Colin

[bmcecosse]

The real problem here lies with your front brakes - they are not working well enough - get them checked out. If you can find a set of Wolseley 9" drums for the front brakes then I can tell you that you certainly won't have this problem ! If you really want - I can sell you a nos brake pressure limiting valve - but it's not the answer to this problem. You should be able to lock ALL FOUR wheels on a dry road. Any that don't lock are not working properly.

[Alec]

Hello Mike,

I tend to agree with Bmce. particularly as the road was wet, it shouldn't have been to hard to lock all four.
Incidentally, I remeber reading an article of a driving seminar by a scandinavian rally driver (maybe Hannu Mikola) who commented that most people just do not brake hard enough.

Alec

[bmcecosse]

Indeed - you really need to stamp on it ! Modern cars of course have something called brake force assist - in an emergency there is a booster system that hammers the brakes on - and relies on the ABS to stop the wheels locking. Mikola was more into throttle than brakes as i remember - awesome to watch on down hill forest stages on The Scottish rally !

[RogerRust]

I had a front brake that kept loosing its adjustment. Eventually I realised that the problem was that the yoke that the snail sits in. It had worn smooth so on braking it unwound abit at a time simply got a new pair of them replaced the offending item and now have a spare, as the over side it was ok.
Now I can do four wheel skids at will!! I replaced all the brakes with a set from the Morris Minor Parts Centre in Raynes Park. That was one of those jobs that escalated and ended up replacing the rear hub oil seals and bearings for good measure. Still should be good for another 30 years - I hope

[MikeNash]

Thanks for your comments.
Re Citroens and their automatic load adjutments - yeah! I had a Xantia the best car I've had. Superb ride and brakes - until it went wrong and then what a cost!
Re ColinP's comments, they've made me check when I last looked at the brakes and its coming up for 10k miles! I'm surprised they've gone so long without trouble and ashamed I've not done a bit of proper checking. Thanks fo the reminder.
Re 9 inch front drums BMCecosse, I've been tempted but I'm told that getting new cylinders and shoes is difficult. Is this so? Are they going to be difficult to get bits to maintain?
One day I'll fit a pressure gauge to the brake system to see what pressures we get. In the meantime I'm glad I moved a while ago to radials! Regards and thanks, MikeN.

[rayofleamington]

Re 9 inch front drums BMCecosse, I've been tempted but I'm told that getting new cylinders and shoes is difficult. Is this so? Are they going to be difficult to get bits to maintain?

Cylinders are pretty rare, so with a bit off effort (changing the length of the rectangular hole and moving one of the fixing holes) you can convert to Minor cylinders... Which is what I'm planning to do with my set (in about 2 years when I've got some free time coming up )

[TerryG]

I have just read "minor matters" and found a set of wolsley 1500 drums in the parts for sale section if you are looking for a pair (I can copy you the ad if you dont get the mag)

[wanderinstar]

BMCEcosse has fitted Minor cylinders to Wolseley front brakes and there is a set of Wolseley brakes in Parts for sale. They do work a lot better than Minors.
Ian.

[MikeNash]

Thanks Wanderinstar & TerryG for pointing out the advert on the Wolseley brake bits that I'd not spotted.
Have bought them! (Thought I'd put in this note last night but its gone astray.) You know, this internet lark and the webby sites are (a) worth their weight in gold (b) an education and (c) jolly good fun. Even if I cringe sometimes for the rubbish I've written. Regardsagain andhanks to all, MikeN.

[Multiphonikks]

Can I just point out folks that locking one's wheels is not a good idea.

I may sound a bit pompous but perhaps learning to cadence break would be far more effective

If you need to stop in a hurry and you're using standard brakes:

Touch your brakes firmly and wait for the front of the car to dip.
Then, release the brakes, and wait for the car to 'bob' upwards.
When the car then 'bobs' back down at the front again, re-apply the brakes. The extra 'weight' (though of course the car doesn't gain it rather that the weight of the car is acting lower on the suspension and thus is pushing harder on the road) will help the front wheels gain traction and stop you.

Now, before anyone says... I know the original post was about rear-wheel lockups. I'd suggest checking each drum. The front brakes on a minor are designed to be far more effective than the rear. Are you sure that all the adjustment cams are working and are at the correct setting? (Again, not wishing to teach my grandmother to suck eggs so please forgive if I'm stating the obvious!) :)

[bmcecosse]

Err - in an emergency - as we gather this was - the just stamp on the brakes good and hard - then you can sort it out with cadence braking if there is time - but the main thing is to get the brakes ON !

[aupickup]

i have servo assisted front discs and would not be with out them now, having driven many minors in the past with normal drums.

my van does go fully laden a lot of the time and it is peace of mind and body for these to fitted.

i know they can be expensive , but what price are our lives PRICELESS.

[Multiphonikks]

[quote="bmcecosse"]Err - in an emergency - as we gather this was - the just stamp on the brakes good and hard - then you can sort it out with cadence braking if there is time - but the main thing is to get the brakes ON ![/quote

BMC, That is the MOST dangerous thing you can do! (Especially if it's wet)

Brakes should be applied with even pressure. Stamping on them suddenly and quickly will most certainly cause the wheels to lock.

Having seen several accidents in my few years of driving caused by people stamping on the brakes and also being the victim of wheel lock caused by ME stamping on the brakes, I'd say learning to pump/cadence brake is essential for anyone in a classic with drums. It's not difficult to learn and most driving schools these days will either show you (at a refresher course) or actually teach it as part of the regular tuition!


Minors on standard wheels and tyres have a very small footprint. It's essential when driving them that the wheels don't lock.

Nikki

[aupickup]

thats true