12 replies to this topic

[Clip]

I just came across this fix in another mini forum so it’s not my idea, but I think it’s worth shouting about as I have not read about this fix anywhere before (apologies if it has). 

The simple fix to get my brake pedal full and not having to double pump to get a full pedal every time was by putting a bar (I used a length on 30x30mm timber) to put pressure on my baked pedal just where the pistons would be moving out. The OP suggested leaving it overnight, but I only left mine a few hours as I had to take the car out, but bingo, even after that short time, I had a  nice full pedal! 

Edited by Clip, 25 January 2023 - 08:18 AM.

[mbolt998]

How does that work? I assumed you always had to pump realistically unless you keep adjusting the drums and don't drive fast so they never get hot.

[Clip]

I pretty sure it’s just for disc brake systems. I used to do this with my bikes, especially the Aprilias which always seemed to be an issue with bleeding (I use to cable tie the front brake lever on overnight). But I don’t think it is an air/ bleed issue for the mini, as it was with the bikes. I think it’s more a repositioning of the disc brake pistons so they don’t retreat as far back every time you take your foot off the brake. I’m guessing that’s what it is as my brakes were not spongy, which would indicate air in the system. Hope that makes sense. 
I will still need to keep my rear brakes constantly adjusted too.

Edited by Clip, 25 January 2023 - 10:14 AM.

[whistler]

Strangely enough I've recently had this problem with my 66 resto after fitting 7.5" discs. A small pump and there's a full pedal. Don't have that problem on my wife's '83 with 7.5" discs or my '89 with servo master, so what is causing this problem on the mk1 with disc conversion?

[Clip]

Strangely enough I've recently had this problem with my 66 resto after fitting 7.5" discs. A small pump and there's a full pedal. Don't have that problem on my wife's '83 with 7.5" discs or my '89 with servo master, so what is causing this problem on the mk1 with disc conversion?

I don’t know, but mine is a ‘62 and only hade the problem since fitting the discs too. Maybe it’s something with the new callipers or the type of seals that are used, can’t think of any other reason as the issue is definitely with the disc brake setup and the pistons returning too far into the calliper. 

[KTS]

possibly new seals 'grabbing' on the pistons causing them to pull away from the brake pad when you take your foot off the pedal

 

the issue may disappear after a while as the pads bed in, or you could try taking the pads out (one at a time?) and replace with an old worn pad or similar (you must have something in place to stop the piston popping out) and pump the brakes a few time to get the pistons to travel a bit further and lubricate the seals to see if that improves things

[Ethel]

If you hold the pedal down you're isolating the reservoir and, by extension, atmospheric pressure from the resting brake circuit.  Consequently the only way for the pressure to adjust is by the caliper pistons. Most likely, the calipers will lose heat & contract: the fluid pressure will be increased & push the pistons outwards, so there's less slack to take up next time you brake.

 

Not sure there'd be any lasting benefit, the discs still need to push the pads back to avoid binding.

[sonscar]

I thought it was the shape of the seal and groove that retracted the pads?The disc pushing back the pads I know as pad knock off,and is less than desirable.Might be wrong,Steve..

[MiNiKiN]

possibly new seals 'grabbing' on the pistons causing them to pull away from the brake pad when you take your foot off the pedal

 

 

It is a feature of these square shapped seals to slightly pull back the piston, not a bug. It's ensuring necessary clearance between pad and disc.

 

I just came across this fix in another mini forum so it’s not my idea, but I think it’s worth shouting about as I have not read about this fix anywhere before (apologies if it has). 

The simple fix to get my brake pedal full and not having to double pump to get a full pedal every time was by putting a bar (I used a length on 30x30mm timber) to put pressure on my baked pedal just where the pistons would be moving out. The OP suggested leaving it overnight, but I only left mine a few hours as I had to take the car out, but bingo, even after that short time, I had a  nice full pedal! 

 

I too do that on difficult to bleed brakes. The work principle could be somehow according to the following thesis:

I think that applying the brake for a longer period of time (overnight) increases the pressure in the brake system (this is self evident so far).
But any air trapped in the system experiences greater buoyancy under pressure and therefore tends to move slowly up through the pipework. It'll escapes from the master cylinder the next time you release and apply the brake. My2p

 

[nicklouse]

Just lure the seals go use the car sorted.

What the bar “trick” does is give the seals time to move on the pistons so they don’t retract the pistons as much.

We used to do similar on disc brakes on MTBs to get a firmer action for the fussy customer who could not wait for the pads to bed in and the pistons to settle.

It works but is not needed if everything is set correctly.

[Clip]

As this is a common issue with disc brake conversions, I can’t help wondering if there’s something in the design of the after market ones. It would be interesting to hear from anyone with 4 pot or genuine callipers to see if they have the same issue.

[Clip]

I should add that as of this morning when I drove, the brake pedal did not feel quite as high as when I first did it, so suspect it may not be a lasting solution. 

[timmy850]

I rebuilt my calipers with new seals and used the red rubber grease. The seals were tight & withdrew the pistons back so far that the brake pads rattled if you poked them

I removed the pads, then slowly worked the pistons out to make sure they were lubricated by brake fluid. I didn’t push the pistons all the way back in before putting the pads in, I left them out slightly so it was a snug fit. With some heavy use they eventually wore in so the pedal was improved