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MG Midget and Sprite Technical - Is this brake line route ok plus other queries

I've run the rear brake line through the tunnel and wasn't sure about gearbox clearance. Does it look ok? Also which front brake line comes off the front/ top of the 4 way? Does the master cylinder pipe go around the front or rear of the pedal box? My stripdown pictures aren't as clear as they might be! Also, has anyone tested a hydraulic brake light switch? I tried this with a bicycle pump (floor one) but got no continuity, but it may need much more pressure.


Bill Bretherton

I was planning to set up a test rig with a pressure gauge and connect it to my compressor, as I have a lot of brake light switches.

Another lockdown project.
Dave O'Neill 2

Bill

The frogeye rear brake line ran underneath the car, the Spridget ones (certanly MK111 Sprite onwards) were inside the tunnel but it doesn't really matter. The brake pipe comes out of the MC and goes down the left hand side of the pedal box (when viewed from the front), crosses over the bottom of the pedal box and into the 4 way
Bob Beaumont

Thanks Bob, that's what I suspected.

Dave, interesting. Looking up typical brake line pressure (100's of psi) I'm nowhere near with a bike pump but maybe a compressor would get high enough to operate the switch.
Bill Bretherton

Bill,

this is my layout which I think is similar to what Bob has described.
It's a MkIII btw.



Jeremy MkIII

" Looking up typical brake line pressure (100's of psi) "

Hmmm, higher than I thought.

Maybe I'll just use a spare master cylinder.
Dave O'Neill 2

I understand that brake line pressure can be up to 400psi, though perhaps that is just for modern servo assisted cars, I don't know. I doubt therefore that a standard compressor will give enough pressure.

Why not set up a simple test rig using a brake master and single pipe to a two way connector to take a bleed nipple and the pressure switch to be tested.
GuyW

Bear in mind that the switch has to operate even with minor braking to illuminate the brake lights to warn those behind you so should operate at a low pressure, no point in it just working in an emergency stop situation. Judging by the many I follow these days the driver touches the brake pedal as a security blanket thing but doesn't actually slow the car, whether that is a pressure switch or switch detecting pedal depression like the 1500 IIRC I don't know.
David Billington

Thanks Jeremy.

Maybe a compressor might trigger the switch then.
Bill Bretherton

Yes I guess so David. What I had in mind though is that quite light foot pressure on the pedal will produce quite a high pressure in psi in the pipe lines because of the small diameter of the pipe compared to the master cylinder bore plus the mechanical advantage of the brake pedal itself.
GuyW

Guy,

The pressure generated in the master cylinder by the force on the piston and its area will be constant throughout the system so the force at the far end is only down to the area ratios, fluid flow losses in a normal brake system being negligible.
David Billington

One thing to remember about moderns is that they have mechanical switches which don't depend on hydraulic pressure, just movement of the pedal.
Martin

Bill, as you can sort of see in Jeremy's pic, the 4-way seems better mounted in X position rather than +. It then allows the pipes to go off in their respective directions a bit more naturally with shallower bends.
David Smith

The PO had the brake pipe in the tunnel on my Mk1V it was rubbing the prop. I re-routed it in the lip along the bottom.
L Langley

Yes I had an unsecured brake line in the transmission tunnel that strayed on to the prop or UJ but it was easily sorted by installing a P-clip.
Nigel Atkins

David, thanks, a good point.

L.L., Nigel, Putting the brake pipe in the tunnel has been discussed, particularly amongst Frogeye renovators, and the consensus seems to be it is preferable. I've used 3 P clips so should be ok but I was more concerned about the gearbox snagging on it during installation.
Bill Bretherton

I have had a brake line through the tunnel on my '71 Sprite for 25 years with no problems. They do need to be well fastened though, to stop them wandering about and getting friendly with the prop shaft!

Now I have done my Frogeye the same.
Bill, on the photo, pipe feed and exit to n/side brake are the horizontals, rear from the bottom and outlet to o/side from the top. Pressure switch is operated via the relay.


GuyW

Thanks Guy, your picture is very helpful. Currently bending front end brake pipes.
Bill Bretherton

Bill, you'd have to be very ham-fisted with the gearbox installation to do much damage, even the outfit that originally installed my g/box conversion didn't - but they did leave the brake pipe loose in the tunnel.

The copper brake pipes are robust so you'd have to fairly careless to do much, perhaps if the pipe was freer it would give more and then secure once the box is in.
Nigel Atkins

According to Paul Hunts MGB site, it can take as little as 50 psi to operate the brake light switch.

Here’s an adaptor that I made some time ago. Its only use so far has been to remove some stubborn calliper pistons. I shall press on with the test rig.
Dave O'Neill 2

That's good news Dave, I shouldn't have mentioned the (assumed) high psi requirement!

The first picture is offside front brake line - is the bend too tight (in terms of bleeding)? I found it difficult to route through the tiny gap.

The second picture is nearside front. Does the line go round the base of the shock absorber or over it ( to get to the cross member)?

Also, I found I had to loosen the flexible hose brackets to fit the hoses i.e. they won't thread through - is this normal? Seems a strange design.






Bill Bretherton

Bend is cosmetically unpleasing but not to tight.

Coiled pipe often gives wrinkly runs but for route and bends what you could do is make a pattern with some thick stiff wire as that'll also give you an idea of the lengths of each pipe run to save wastage and cutting too short.

Sorry don't know, or can't remember (more likely don't know) about your other two questions.
Nigel Atkins

I had a feeling that the pipe went around the damper rather than having a tight bend in it.

Dave O'Neill 2

I forgot to attach the pic of the adaptor earlier.

Anyway, here it is with a few other bits attached.

I knew that broken dual gauge would be useful for something.

I haven’t got time to do any more with it at the moment, as there are a few more pressing jobs to attend to. I will start another thread when I get it up and running.


Dave O'Neill 2

Be interesting to see if it reaches the 'N' rarely does on my gauge.











Wot meds? :)



Nigel Atkins

Nigel, thanks, I am using stiff wire patterns but it's difficult to be precise. Pre-cut terminated lengths from an Automec brake line set.

Dave, will look forward to seeing test. Is that an airline to 3/16 compression adaptor?
Bill Bretherton

Bill,
if they're pre-cut then they will follow their route for length. Do they not show details of routes or shapes. I remember picking up their book at their stand at the NEC and (I thought?) it had some details but I can't remember what (I might be off on Fantasy Island or misremembered again though). Perhaps routes/shapes are in some other publication (WSM?).

I did think their prices were high and didn't like the coiled sets. Now this might just have been a one-off at the show as there was a young lad on their stand and the two chaps were busy but one of the display ends didn't look straight - but perhaps that was done on purpose as a demo of how not to do it.

Good practice, where possible, to check and test fit ends before routing and bending pipe anyway.

Sod's Law you will always see, or be told of, a better route after you've fully fitted.
Nigel Atkins

Bill, this is the route I took around the n/s damper. Coming from across the front cross member at bottom left of photo.
As I made up my own pipes I maybe had a bit more flexibility about routing, not being constrained by a preordained pipe length.

Second, slightly wavey looking pipe is the fuel line.


GuyW

Thanks Guy, that's what I thought it probably was.
Bill Bretherton

Guy,

Is yours a later car, mine is a frogeye and I have a memory the brake pipe passed under the damper lever arm to get to the flexible pipe support. When I fitted the LA damper replacement I moved the connection to the later position as yours is due to the body bracket precluding the standard frogeye pipe routing.
David Billington

David, mind is a Frogeye, but I have renewed all of the piping so was able to select my preferred route. I didn't like The look of the original routing beneath the moving arm, thinking it potentially liable to dsmage.
I know the route I have isn't as original, but prefer this. Perhaps I should have made this clear to Bill, but I don't think he is after a concourse original standard either.
GuyW

Not even close to concourse! It's BRG for a start! Well I'll use points initially (sorry Nigel) but will use an alternator and electronic tach (which it came with and I've renovated). I've also changed from stud windscreen (original as it's a 1958) tonthe later one. So the brake line routes don't need to be original (disc at front as well).
Bill Bretherton

well done Bill, I am a points man myself!
Bob Beaumont

Bill,
as long as you're car's not holding me up in anyway you can use matchsticks for the spark if you want. :)

Do be careful about the quality of the CB points and condenser/capacitor though if you want to restriction your points fiddling.

Always remember on a tour an Elan Sprint went by me, nice to see a car driven in the way it was designed for, but I passed him a mile up the road as he had his bonnet up in a layby, twin points IIRC. I prefered the relaxed pub stop myself.
Nigel Atkins

This thread was discussed between 15/04/2020 and 17/04/2020

MG Midget and Sprite Technical index

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