MOT Fail - Handbrake Efficiency

[TheDan]

Hey all,

Probably a bit of a weird one...

My Z4 just failed its MOT on "Parking brake efficiency below requirements". The weird bit of this is that I replaced the handbrake shoes, springs and full mechanism in July and replaced the rear brake discs a couple of weeks ago.

Surely with both of the friction parts being reasonably new (and no cables being snapped) the handbrake should operate perfectly?

Apparently, it was only just a fail at 14% vs a 16% efficiency target, but I am not sure what this percentage is denoting.

Let me know what you think and whether this could be fixed with a simple adjustment of the shoes.

 

[bigwinn]

I literally just replaced mine- I noted that the adjusters needed backing off 100% and the wheel was tuning with minimal binding; one click and it would have been rubbing too much

Didnt adjust the handbrake itself as that was the extent of working/not working

And the old ones I took off were metal faced no friction surface!!!

 

[brillomaster]

probably need to bed the handbrake shoes to the new discs, similar to bedding in brakes.

slow speed, apply a bit of handbrake (not enough to lock the wheels) and repeat a few times. should work a lot better after that.

 

[enuff_zed]

If you fitted all new shoes and discs, is it possible that they've just bedded in a little and maybe slightly glazed the shoes?
I think efficiency is based on actual stopping power, not the amount you pull the handle, unless it's right up round your ears and still not gripping enough?
Maybe simply whipping the discs off and roughing up the shoes would get that 2% back?

 

[enuff_zed]

If you fitted all new shoes and discs, is it possible that they've just bedded in a little and maybe slightly glazed the shoes?
I think efficiency is based on actual stopping power, not the amount you pull the handle, unless it's right up round your ears and still not gripping enough?
Maybe simply whipping the discs off and roughing up the shoes would get that 2% back?

It seems [ref]brillomaster[/ref] is another member who can type faster than me. :roll:

 

[TheDan]

Thanks all, I will try to rough the surface up with some sandpaper a bit and then make the adjustment to the shoes. Hopefully this will get me what I need.

When adjusting the shoes, do you guys have any advice for number of "clicks" to back off from fully binding?

 

[Rucky]

Not doubting your skills but when setting up the Z4 handbrake with new shoes / discs when carrying out the adjustment the cable service lock under the handbrake lever has to be disconnected with a long handle screw driver, Its a pain cos it means taking the trim out to get at it but its the startung point. That way you get maximum leverage when the shoes are correctly adjusted.

Better to leave it in gear and not use the handbrake as I find the shoes rust onto the drums overnight when its wet,

Otherwise - as suggested - use the handbrake when moving once a week just to keep the drums clean.

I fins Pelican parts how tos very good info - like this
https://www.pelicanparts.com/techarticles/BMW_Z4M/92-BRAKES-Parking_Brake_Adjusting/92-BRAKES-Parking_Brake_Adjusting.htm

 

[TheDan]

Not doubting your skills but when setting up the Z4 handbrake with new shoes / discs when carrying out the adjustment the cable service lock under the handbrake lever has to be disconnected with a long handle screw driver, Its a pain cos it means taking the trim out to get at it but its the startung point. That way you get maximum leverage when the shoes are correctly adjusted.

Better to leave it in gear and not use the handbrake as I find the shoes rust onto the drums overnight when its wet,

Otherwise - as suggested - use the handbrake when moving once a week just to keep the drums clean.

I fins Pelican parts how tos very good info - like this
https://www.pelicanparts.com/techarticles/BMW_Z4M/92-BRAKES-Parking_Brake_Adjusting/92-BRAKES-Parking_Brake_Adjusting.htm

I was actually about to ask about this. I made the adjustments to the handbrake shoes (after changing the discs) without releasing the cable tension, ie not engaging the service lock. Does this mean I likely have slack in the cable that I should sort out? I assume the fix for this is to engage the service lock and then adjust the handbrake shoes?

But otherwise I do park it overnight with the handbrake off and the vehicle in gear.

Thanks btw for the advice Rucky.

 

[Rucky]

I believe that is where your problem lies then, follow the Pelican service procedure (unless you have a BMW One) and I think your problem will go away - yes it does mean backing off the hub adjusters.

 

[TheDan]

I believe that is where your problem lies then, follow the Pelican service procedure (unless you have a BMW One) and I think your problem will go away - yes it does mean backing off the hub adjusters.

Yep will follow the Pelican guide tomorrow then (gets dark so early now). Do you mean back off the adjusters on the shoes before or after pushing in the service lock? Or doesn't it matter?

 

[Rucky]

You probably won't be able to release it without backing off the adjusters first. There needs to be a bit of play. It's a pita , as is working the adjusters through the stud hole but with a focussed head torch a thin screwdriver and some patience it's all doable. Good luck.

 

[GuidoK]

Base adjustment procedure from bmw is that you first lock the lever adjuster unit.
So remove the trim around the brakelever and push back the spring until the spring perch locks into the hook.
I use a tyre iron here for that but whatever works, you can see the little hook grabbing the slot in the perch:


(I don't remember if the hand brake lever has to be put in the down position again after locking the spring perch)

Then (on the wheel/handbrake itself), turn the setting screw until it's impossible to rotate the wheel anymore.
You can do that through a bolt hole from a wheelbolt you remove
Back down 9 clics/teeth on the setting screw. (bmw says 9, pelican says 8, I wonder if that makes any difference; 8 clicks for sure gives more brake power )

So this is the base setting for the z4.
It might need fine tuning

 

[enuff_zed]

So remove the trim around the brakelever and push back the spring until the spring perch locks into the hook.

Is this done with the handbrake lever up or down?

 

[colb]

Lever in down off position and cable lock engaged, use adjusters in the drums, back off if you cant get the cable lock to engage. Back off the adjuster then wind them up so the drum locks on, back off until there is no friction on the drum, usually anything between 7 and 9 clicks. Mine was adjusted like this and I ended up once the cable lock was released with three clicks to lock the brake shoes on. Passed MOT ok like this. I did deglaze the shoes before doing the adjustments by taking the disc drum off and cleaning the drum surface with some emery cloth to roughen them up.

 

[Zulu4]

This has been a very useful thread. Thanks.

The E85/86 handbrake system seems to work by very strange mechanics and dark magic.
I wonder why BMW didn't just use the brake pads & discs for the handbrake like most other modern cars.

 

[GuidoK]

Is this done with the handbrake lever up or down?

If I remember correctly the perch is very difficult to reach with the lever down.
But I made that picture over 11 years ago :lol:

 

[GuidoK]

I wonder why BMW didn't just use the brake pads & discs for the handbrake like most other modern cars.

Afaik most RDW cars that don't have an electronic handbrake use an inner drum on the rear discs as a setup like bmw.
There are high performance cars that sometimes use a separate little caliper for just the handbrake.

 

[TheDan]

My service lock seems way more inaccessible than the guide on Pelican... I can't seem to get anything onto it to push it in.

It also doesn't budge with the handbrake raised only slightly

 

[Zulu4]

I wonder why BMW didn't just use the brake pads & discs for the handbrake like most other modern cars.

Afaik most RDW cars that don't have an electronic handbrake use an inner drum on the rear discs as a setup like bmw.
There are high performance cars that sometimes use a separate little caliper for just the handbrake.

Thanks. Strange how I've not come across this method before.

My VW Phaeton (AWD) was designed around the same time as the E85. It has disc brakes all round and uses a cable system to pull the rear pads on for parking (admittedly via a small footbrake). Mrs Wife's Mk1 Ford Kuga AWD had discs all round and used a handbrake & cable to act on the rear pads. Same with our old FIAT Stilo.

 

[TheDan]

After much swearing and cut up hands I managed to get the service lock pushed in. I then adjusted the shoes as per Pelican's instructions and put it all back together (and released the service lock).

The handbrake now only pulls 5 clicks up and is pretty firm at 3 clicks. The holding power was only slightly improved, but after a few 10 to 0 stops with the handbrake it seems to have improved a bit more.

MOT re-test this afternoon so fingers crossed.

Thanks all for your help on this