Brake Pedal Travel?

[BrettJ]

I've just driven my car for the first time and the brake pedal seems a bit long. It travels about 5 cm before stopping and the front wheels locking up. Is this normal and if not what is the average travel for an upgraded MC with 4 pot calipers?

[7 wonders of the world]

No

[Jonathan Kay]

Does it feel as if there's any slack/play before it does anything?

And is the pedal firm or spongy when it does take effect?

Fluid level OK in the reservoir?

And do you know when the fluid was last changed?

Jonathan

[aerobod - near CYYC]

Hi Brett, only a few mm of travel in my upgraded MC with 4-pot calipers before the pedal becomes very firm.

Likely there is air in your system that requires a re-bleed. The rear calipers are hardest to bleed and really require them to be tilted upwards. I normally just remove one of the slide bolts and tilt the caliper so that the bleed nipple is higher, but still keep about a quarter of the caliper piston in contact with the pad to stop it being forced out while bleeding.

The front calipers also have to be bled from both inner and outer nipples, if you hadn't already realised that.

The other issue may be that the handbrake adjustment on the rear brakes is off if you have the single piston floating caliper, the pistons have to be wound in (always clockwise), calipers installed and foot brake pressed until the pedal is firm, before activating the handbrake self adjusters.

[Nigel B]

I struggled with this issue for about eighteen months with my 420R (uprated master cylinder, but standard front calipers).

I tried all manner of different approaches to brake bleeding, but the pedal still felt 'spongey'. Eventually, I fitted Caterham's 'high effort' brake pedal, at the advice of a specialist. 

That sorted the problem, the pedal now has a very short travel & a positive feel. Far better for heel & toe.

[7 wonders of the world]

Bret when you say driven for the firsr time is that after winter lay up or it she new to you...?

Is the pedal just 'springy' or will the pedal 'pump up' and become firmer with less travel on repeated applications ('spongey') if the later then re bleed as James advises, if the former one thing worth checking especially if work has been carried out is it could be the rear pads are not located in the piston, the pads have a 'pip' o then which requires the pston to be set in the correct place in order it locates in the corresponding slot, this gives a very springy brake if set incorrectly

[Beagler]

Can I ask, what is the "high effort brake pedal". Is it this,

https://caterhamparts.co.uk/pedals/1248-brake-pedal-high-effort-imperial-cars.html

[paul richards]

Yes it is, but the one you have linked to is for an imperial chassis not metric. 

[Nigel B]

#7   Yes, although I used the metric version. (I think your car is metric too?) It essentially means the pedal travel is reduced, but more foot pressure is required. Although, in practice, I can't say it seems to require much more effort than the standard pedal. You quickly acclimatise.

I was convinced my long pedal travel was caused by air in the system. I asked for a second opinion from DPR Motorsport & they advised me that 'they're all like that' & suggested a high effort pedal. 

It's strange, because my last Caterham, a 2002 live axle car, had a much shorter pedal travel as standard. The 420R with the high effort pedal fitted, feels to me very similar to how my old car felt.

 

[Beagler]

[Beagler]

Spoke to CC to see if they recommend a high effort pedal to go with my 4 pot caliper and lager bore M/cyl upgrade. He advised that very rarley do they need it and that I should bed in the new pads and discs and rebleed the system and the pedal should come up and be firmer. This was my thoughts so thats what I'll do then reassess.

[ChrisC]

Brett, as you can see it's either, as designed, a bleeding issue, an undetected leak, the brakes need bedding in or a combination of all four.

Are you planning PBC before IVA, if you are then I would leave it the tech to decide, they have seen plenty of examples and will know if it's right or what's wrong.  If on the other hand (and I wouldn't recommend) your just going to drive to IVA before PBC then it might be worth getting a second opinion beforehand. 

Once it's passed IVA and the they have bedded in a bit you can make a decision. if you don't like the feel and want a firmer pedal, it's a simple procedure to change. 
 

My brakes to begin with had a firm pedal, but didn't bite as desired.  On the way to the IVA I had plenty of time to work them, fairly hard to the point I could smell them, to gain the pass.  From that point they have improved further.  I have confidence in them.  If I did more track work then I think I would go with the firmer pedal, but understand anyone taking that option for road uses.

[BrettJ]

Thank all, this is a new build and I wasn't aware of the issues with the rear calipers. I think I'll bleed them again using aerobod's technique.

@ChrisC, yes I will be presenting it myself for the IVA test before it goes to PBC.

[ChrisC]

Hi Brett, then I strongly suggest you get a second opinion on the brake pedal.  The bake test during IVA is I think the hardest part to pass, there is little if any leeway or allowance for new braking components, yet no way of bringing them up to performance.   Have you attended a local club night? You could reach out to a local owner and even compare 420 pedal feel.  It will tell you what you need to know.  The performance will come, but the feel needs to be right. 

[Catgraham]

Does anyone know off hand what the lever arm lengths of the high effort pedals are?

The pedal on my 2001 chassis looks standard, and I suspect it probably is (it's definitely not the chunky high effort pedal 77198A referenced above), but it doesn't line up well with the master cylinder. The distance from the pedal pivot axis to the master cylinder axis is 2", whereas the lever arm on the pedal, from pivot to clevis pin is 2 3/8". The clutch pedal is 2", but is a cable pedal. Both pedals are 7 1/2" from pivot to pad.

The original owner overcame the alignment issue using a cut-price version of the CC wedge shim - leant on the master cylinder to bend the pedal box until the pushrod lined up with the hole in the pedal!!

Graham.

[Jonathan Kay]

Comparison photo.

And a measurement... but I'm not sure which type it is...

Jonathan

[Catgraham]

Thanks Jonathan. 58.4mm sounds near enough to mine, so I'll assume it's standard. Still too high for the master cylinder though!!

Would be handy to know how much longer the high effort pedals are....

Graham

[Jonathan Kay]

Doesn't the photo show that?

Jonathan

[Catgraham]

Ah, yes, sorry - had to brighten it up a bit to see what was going on.... It does show the high effort pedal as being a good bit longer, probably 8 - 10mm.

My pedal is much like the standard one in the last photo, but when compared to the first photo does appear to be a bit longer in the top part. Hard to say, really, and there is a lot of years between them... Still don't like the pushrod alignment on mine though!

Graham

[ChrisC]

Are you supposed to fit the shim to remove the angle?

https://caterhamparts.co.uk/fittings/6304-high-effort-brake-pedal-shim-use-with-30b045a.html

[7 wonders of the world]

Yep

[Geoff Brown]

Irrespective of which pedal or caliper is fitted when the brake system is fully bled the pedal should be very firm with only a couple of mm travel caused by mechanical lost motion.

It can take extensive bleeding & a lot of fluid to finally reach a satisfactory pedal feel.

Post diff refit I fitted new rear pads, bled the brake system at least three times using 1.5 litres of fluid. The last bleed only extracted tiny bubbles for a short time. The pedal feel was the best I could attain but over about 50 miles running in the pads the pedal feel was absolutely solid.

When I built the car a painstaking bleed was carried out & from memory I used 2 litres of fluid during three bleeds.

A good test after bleeding is to sit in the seat & apply constant pressure to the pedal. If all is not well you will be surprised how far the pedal will travel.

Unfortunately 'they all do that sir' is not far from the truth but with a bit of patience the problem can be overcome.

 

[Nigel B]

I spent eighteen months repeatedly bleeding the brakes on my 420R, using every method & trick I could find & pushing many, many litres of fluid through the system & I still had a long, mushy feeling pedal. 

It really did feel like air in the system, but I still felt suspicious that, that wasn't the case, because after the initial couple of bleeds, no further air bubbles emerged (not even tiny ones) & after each bleeding session, the pedal felt exactly the same, with no incremental improvements.

I asked two Caterham race teams for their opinion on the brakes at the beginning of last year, when they were doing work on my car & they both said the pedal feel/travel was very good for a 420R.
 

Eventually I fitted a 'high effort' pedal, which halved the travel & much improved the feel.

[ChrisC]

Two things you will find in the archives of blatchat when bleeding the rears, is one jiggle the handbrake as the pedal is down, and two tap the caliper with a rubber mallet as the pedal is down. Both help to find that elusive last trapped air bubble.

[7 wonders of the world]

Whatever calipers you are running on the rear WILL need to be partially or fully removed for a clean bleed since CC opted to mount the rears in a horizontal orientation, the Sierra and VW and be swung by removal of one bolt in order to get the nipple to the highest point. personally I remove the sierra ones as the nipple is angled, removal permits getting it vertical, I use a suitable piece of oak floor board between the pads - naturally this procedure can be impeded by the rigid rear brake pipes CC insist on using. tapping calipers with the hammer shaft will encourage bubble to exit too.

I run HiSpec 2 pots on the rear, these AP rear and Willwoods again all need removal.

I start with new fluid that's been stood for 2-3 days and slowly fill the master cyl then using nothing more than gravity, working from furthest to nearest and inner then outer on 4 pots, short length of clear hose over the nipple into a bottle and just crack the nipple no more than 1/2 a turn - the bled from this alone is 99% and probably 4-5 pumps per corner with SWMBO in the hot seat.

Don't do what I've seen done many times and shake the bottle of fluid - it's brake fluid not a strawberry milk shake.!!

fluid wise for normal road ATE Typ 200 has one of the highest boil points and is a sensible price too - 1 ltr from empty will get a solid brake.

.Track fluid will offer higher boil points naturally there is a price penalty though.