Rear wheel lock up

[JON1D]

Jon. Just had all the brakes checked on the rolling road, all passed with flying colours. Feed is good off master cylinder. I think i put a 25 series in the car with new replacement reservoir.

That's good news and reassuring. A big tick and nothing to worry about now. 

[Julesdm]

Adjustable valves will not pass IVA

Yup thats why i didnt do it back then in 2021

[johnnyoz]

Adjustable valves will not pass IVA

[Julesdm]

Your rears should only be 25% braking power and 75% front.
I would check that your front discs are working on a rolling brake test. Friendly MOT station can check it.
Check the feed is correct off the master cylinder as you say for front and rear feed.
Which master cylinder are you using?
ROVER MK3 200 or Rover 25 SERIES (1995-2005)

Jon. Just had all the brakes checked on the rolling road, all passed with flying colours. Feed is good off master cylinder. I think i put a 25 series in the car with new replacement reservoir.

[Julesdm]

I've got an adjustable proportioning valve (willwood I think) you can have for £25
Simon

i have PM'ed you

[GDCobra]

I had exactly the opposite issue with mine, fronts would lock up prematurely limiting the overall stopping power.
Obviously the only solution was to increase the power of the rears (the idea of pressure reducing the front circuit did not apeal to me).  I converted the rear brakes to outboard using 4 pot Wilwood calipers.  At the same time I added a Wilwood reducing valve to the rear line in case I'd overdone the power increase.

It's important to understand that the type of valve I've used does not simply reduce the pressure across the full range, it drops the pressure only after the line pressure has reached a threshold, wihch is what is adjustable.
This means at lower pedal pressures the rears still 'see' full pressure but under heavier braking, and hence weight transfer, the rears are toned down.  Works well for me.

[Simon]

I've got an adjustable proportioning valve (willwood I think) you can have for £25
Simon

[johnnyoz]

I had tha same problem with my RAM.I found a new old stock Ford Mondeo brake proportioning valve on ebay and fitted it into the rear brake feed pipe.Worked like a charm.

[JON1D]

Your rears should only be 25% braking power and 75% front.
I would check that your front discs are working on a rolling brake test. Friendly MOT station can check it.
Check the feed is correct off the master cylinder as you say for front and rear feed.
Which master cylinder are you using?
ROVER MK3 200 or Rover 25 SERIES (1995-2005)

[Chris]

You should able to get inline restrictors for your rears, this should stop the issues that you are having .
The rears as most know do not need anywhere near as much braking force on our cobs .
The SR that I own has the xj rear set up with just the single discs and is perfectly capable for my purposes,
with four pot calipers and vented discs up front, no restrictors necessary.
 
Chris.

[Julesdm]

Just intrigued to know if anyone else has had the same experience.

The car failed at IVF because the rears locked up under heavy braking before the front. Got over this the second time by inflating and deflating tyres to induce a front lock up as advised by AK.

I did check the plumbing to the master cylinder as some say on some forums there is a slightly different pressure on each outlet. Whether this is true is debatable.

Had to break hard in the autumn in warm dry conditions to miss a T bone scenario where some idiot pulled out in front of me. Travelling probably 40mph rears locked up and car began to twist, released brakes to straighten up and then hit them again.......lots of melted rubber on the road and smoke to boot. A proper butt clencher!

This weekend pre MOT for the new season,  i though i would change the brake fluid and swap the outlets over on the master cylinder. To try and address the problem.

Took her for a quick spin. Braking hard the car performed, however, rear wheel lock up depended on the type of road surface (smooth v worn).

I had this situation once in an Astra Mk2 i owned, came around a bend to find a dustbin lorry parked up, hit the brakes and the rear end came around like a hand brake turn!!! Not amusing....i do not want this to happen in the Cobra.

Seriously considering a brake proportioning valve.

Has anyone else had this issue, is it normal, based on how light the car is.....

Thanks Jules

Driving an AK which i built in 2020/21.