New build - Poor Brake Feel, Pedal not returning

[Purplemeanie]

Hi All, I hope I can impose on your collective wisdom again and sorry for the long post...

I have a new build (by me) 420R with uprated 4 pot front brakes. The 420R also comes standard with the uprated master cylinder. I am through IVA and on the road but am finding the brake pedal feel is not as solid as I remember from test drives, and the pedal doesn't return to the top of it's travel. I have 160 miles on the clock... so open to the fact that this will get better... however...

I'm concerned that with the pedal not returning to the top of it's travel, after pressing the brakes, the brake lights will stay on. I've adjusted the brake-light switch as much as I dare so that the brakes only stay on occasionally now, but I'm worried that the brake lights will stay on and people following me don't appreciate that I'm braking again. I've had a couple of near misses already - or is this normal for people to rear-end a Caterham!

The brake pedal drops about half of its full travel with a solid push, and feels spongy (in non-assisted brake terms).

The tech at Williams reported that I probably had air in the system and bleeding them should get the pedal firmer and it should then return to the top position after pressing the pedal.

But... I've now bled the brakes 5 times. I've used the tried and tested: undo nipple, press pedal, close nipple, pedal up, repeat. I also bought a pressurized brake bleed system as used by the tech at Williams. Have used the pressurized system 4 times now.

The next piece of the puzzle is that the brake pedal feel is rock solid if the handbrake is slightly on.

So, having read various posts (though still not sure quite why) I have also slackened off the handbrake, taken the rear calipers off and wound back in the pistons. As part of this process I tipped and banged the calipers endlessly in the hope that any air pockets would be dislodged. I then fitted the calipers and pumped the brakes to set the pistons and reset the handbrake... no change.

My current theory is that for some reason the rear brake pads are coming too far off the discs when there's no pressure on the brake pedal... partially applying the handbrake will push the pads closer to the discs and pre-engage them for when the pedal is pressed - hence a firm pedal in that situation.

Any suggestions gratefully received. I have the club Novices Trackday booked for end of April and clearly keen to make sure I have great brakes by the time I get there.

Thanks in advance, John

[SM25T]

Rear calipers. Leave handbrake cable fully slackened off after you wind pistons back in. Press hard on brake pedal a few times to allow the self adjusters to do their thing. Only then adjust the handbrake cable. If you pull on handrake before pressing pedal it will mess up the self adjustment. Front calipers ... you have mounted them with the bleed nipples at the top ? Have heard of some being mounted upside down before ! Pedal not returning ... does it return if you loosen cap of MC ? Have you got the pedal return spring fitted ?

[Purplemeanie]

SM25T, thanks for the reply...

I already did the rear calipers. Handbrake slackened off completely. Wind pistons in. Pumped brake pedal - big and repeated pushes to reset. Only then re-adjusted handbrake.

Do I wind pistons clockwise on both sides? I saw a post saying to do clockwise on both sides but rewind kit comes with left and right versions.

Front calipers are fitted with bleed nipples at top - yes.

I'm pretty sure the pedal does not return still if MC cap is off. What's happening there if it does? I will try that this evening though.

Pedal return spring: Where is that fitted? Is it in the MC assembly or on the pedal assembly somewhere? The pedal returns fine to about 1 inch from the top of its travel - but I guess that's the pressure in the lines perhaps doing that.

Update: thinking about this. Can't see that it's anything to do with the MC and/or pedal. If the handbrake is on (slightly) then the pedal returns perfectly and with good feel. It's got to be something to do with the rear or else the handbrake would make no difference.

 

[elie boone]

What is the make of the pressurized bleed tool, i use an old reservoir cap with a hole in it and a gun to pressurize the system works everytime. Did you test the mastercil disconnected from the pedal if it comes back to his stop ? are the notches on the rear piston lined up with the pad ?

[ChrisC]

Do you have standard brakes, or the 4 pot uprated?

Given its been throught IVA and PBC, I guess no one is expecting a bleed problenm.   If you have standard 2 pot AP radial calipers at the front, CC may have changed the brake pedal to a high effort pedal during the IVA test.   Did you present the car at the IVA?   If that's the case then it could just be adjustment of the clevis and the master cylinder.  Mine had loads of slack, and no return spring to hold it up.  

Update, Just looked at your blog, 4 pots and you presented, so no change to the brake pedal :(. Worth checking for slack on the clevis, but not holding my breath. 

[Purplemeanie]

Thanks for the reply Chris. I'm thinking it may be that I didn't reset the handbrake adjuster correctly on the LHS. There isn't much slack in around the clevis. I wasn't keen to just wind up the nut on threaded rod into the master cylinder.. that seemed a bit crass.

I think I'll have another go at resetting the handbrake auto adjusters when I get a chance.

Update: hmmm.... having done a more specific search on here it seems that Clockwise is the right way to windback both LH and RH rear calipers. Still looking for suggestions.

[Purplemeanie]

Elie boone, thanks, 

I have the notches set correctly yes. I wouldn't have been able to get the pads into the calipers if the notches weren't upright.

I didn't test the MC disconnected from the pedal. That's a good suggestion though if my theory below doesn't work.

The bleed tool is off amazon. I don't think it's that. It provides plenty of pressure to push fluid through the lines and out of the bleed nipples. I've been reading up on some people who think pressurizing is not as good as vacuum - and I've bought a vacumm system just in case to try if all else fails. The theory being that a vacuum causes air bubble to become larger and exit where they're stuck, not sure that it will make that much of a difference but clutching at straws now. I don't think its that now though.

Current theory is that I didn't reset the LHS handbrake adjuster when I wound it in clockwise. I may try counter-clockwise and see if that works any better. Any advice on correct windback direction for RH and LH would be appreciated.

Update: hmmm.... having done a more specific search on here it seems that Clockwise is the right way to windback both LH and RH rear calipers. Still looking for suggestions.

[SM25T]

Clockwise both sides. Never anticlockwise .... ask me how I know !

[shn7]

Whilst all the above sounds like the problem relates to the rear brakes do the current uprated front calipers have each 2 bleed nipples and if so have you bled both?

[Purplemeanie]

Good point Steve. But yes, bled inner's and outer's multiple times.

John

[Jim 123]

With the pedal not returning to the top of it's travel how far short of full return does it achieve? If it doesn't fully return what happens if you lift the pedal back up with your toe?

[Purplemeanie]

Hi Jim, thanks for the questions, it falls short by about an inch or so. If I lift it back up with my toe then it stays up. It probably falls short 50% of the time (but dependant on how hard I prod - a vigorous prod tends to bring the pedal all the way up) and about one in ten now it falls short enough not to turn off the brake lights (which I've adjusted the brake light switch as far as I dare).

Again, it doesn't fall short and is rock solid when the handbrake is partially applied. If I sit stationary in the car, apply handbrake and push the pedal - then the pedal remains high and solid even when the handbrake is disengaged. Only after some time and prodding does the pedal eventually drop.

Did that answer your question?

[Jim 123]

A couple of things that you may not have considered............ Is it worth checking that the master cylinder return springs/pistons are not sticking a little when the pressure is taken off, and that the cap is venting properly?  Also, is the top of the brake pedal set in the highest resting position relative to the available threads on the master cylinder plunger?  From your recent IVA are there any clues in the recorded brake efficiency readings?

[Purplemeanie]

Thanks Jim. Some research needed into those points.

John

[Ian Mackenzie]

Following on from Jim's point... I have a high ratio pedal and uprated master cylinder and the push-rod did fowl the bulkhead, so it is worth checking that the master cylinder push-rod is not rubbing. There is a shim that can be inserted to prevent this....https://caterhamparts.co.uk/fittings/6304-high-effort-brake-pedal-shim.html?search_query=shim&results=28  This may be the case as well for you if you have the high ratio pedal. In the short term you could pack with a washer and test...

Once this is OK, then reset the rear caliper....

Hope this helps...

[Purplemeanie]

Thanks Ian. I'll check that out.

[Jim 123]

PM sent.

[Geoff Brown]

The culprit to me seems to be the master cylinder.

The pedal should always return to the 'off load' position.

Check the alignment of the piston ram in the pedal box. Too much of an angle could cause the sticking. I had to realign my R400Ds ram at the connection with a very thin washer to prevent too much angular deflection when the brakes were operated. This was to prevent DOT 4 weeping passed the end seal!

Otherwise the seals in the master cylinder could be the  cause of the problem either swollen or rolled in the cylinder. As the car is a new build exchange with CC should be no problem. (Ha, Ha).

 

[Purplemeanie]

Thanks for the suggestion Geoff. I’ve got a busy holiday weekend to investigate all this. But great to have so many suggestions after I was thinking I’d got to the end of what could be wrong.