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Anyone upgrade to the "race" rear brake caliper setup?


KnifeySpoony

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My car is mostly a track car, I really only drive it to/from the track. I had considered this upgrade for maximum performance during my 420R build last year, but decided to see how the stock setup was. I found it a little over-braked in the front, but upgrading the rear pads to DS3000 has pushed the bias rearward enough that I am happy with the braking performance. However given my recent issues with interference between my rear calipers and watts linkage arms (https://www.caterhamlotus7.club/forum/techtalk/rear-brake-caliper-contacting-radius-armwatts-link), I am thinking about this upgrade yet again. Presumably the lower profile rear calipers won't have any interference issues. I'm OK with the handbrake delete (I'm in the US and in my state the car will never be inspected again). This setup seems to need a proportioning valve, although my calculations of brake bias don't seem to suggest the bias moves all that far rearward compared to the standard setup. 

I'm wondering if anyone has done this upgrade, or driven one of the R300/420R race cars with this setup and can comment on performance. I have never plumbed brake lines, and I would have to get the appropriated line flaring tools etc, but it seems not too difficult to learn. Also I would need to decide on a cockpit-mounted prop valve vs one in the engine bay (much easier to install). Wondering if the easy adjustability is really necessary, as I won't racing in the race.

 

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  • 2 weeks later...

I have the earlier version  of solid discs and ap racing calipers and a spot handbrake caliper(mot compliant once a year!!!). The earlier version was developed on Vauxhall race cars running slicks they then changed to vented discs (front vented disc on the rear) for a performance improvement( wear or retardation??).  I run it on my 21 which is 695 kgs which is enclosed due to the bodywork and runs around 400deg c . I intend to upgrade to vented discs due to high pad wear on the existing setup. If you change you will need new uprated hubs, ears, caliper spacers, calipers, disc spacer, specific rear discs ( as front but bigger internal dia) and if you wish to run on the road a mechanical handbrake caliper / mounting. The rear track will increase by approx 25mm. Hope this helps. Dave

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The caliper is a CP5119 with 44.5mm pistons (unless the Caterham piston spec is something different somehow). The standard Sierra rear is a 42.8mm piston, so minimal increase in size. The rotor does go from 232mm to 254mm, so there is some additional torque there. I'm kinda surprised it needs a prop valve tbh.

 

https://caterhamparts.co.uk/15252-thickbox_default/brake-caliper-rear-race-10-lh.jpg

 

https://apracing.com/race-car/brake-calipers/formula-car-range/2-piston-fia-f4-cp5119

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Its a Hi Spec spot caliper . Not very effective. I looked into this a few years ,you need a lever ratio of approx 15/1 for a good mechanical handbrake this system along with a modified hand brake lever was about 9/1. To get a higher lever ratio the caliper installation required redesign. This problem has been visited before E Type Jag ,Lotus Elan  these types of design would provide adequate leverage put packaging might be the issue. Willwood might be worth a look. Dave

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  • Area Representative

'However given my recent issues with interference between my rear calipers and watts linkage arms' - Getting back to the original issue I cannot understand how this is occurring ?

Or am I missing something obvious.

Seems to be an expensive & time consuming way of trying to get over a simple problem.

I know that inboard movement of the caliper during pad wear creates a decreasing clearance but not to the extreme.

The clearances on my R400 are fine as is the rear anti roll bar connection to the de Dion ear. Later cars have a different connection setup of the AR to the ear which if the adjustment is not correct causes interference with the inside of the rear wheel.

The only time that the Watts Linkage & calipers would cause an obstruction is if they have both been assembled incorrectly. 

Are the caliper spacers correctly fitted? Are the linkages assembled correctly though this is almost impossible not to do correctly?

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The problem arose after changing my DeDion ears from 1.5 to 2.0 deg. This apparently brought the calipers in closer to the linkage. Before the upgrade there was no contact. I'm not sure how/why Caterham sells the 2.0deg plates if they cause this issue, but I guess Caterham gonna Caterham. 

related thread: https://www.caterhamlotus7.club/forum/techtalk/rear-brake-caliper-contacting-radius-armwatts-link

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If CC endorse the 2.0 degree ears by having them on sale then they either are not aware of the problem, ignore it or have an 'easy fix'.

Of course the cheapest & easiest course of action is to revert to 1.5 degree ears........

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  • Leadership Team

Re #22  Are you aware as to whether there's a contact issue with the 2 degree ears if using standard radius arms rather than a Watts link setup?  A swap to radius arms might be the easiest solution to your problem and you definitely wouldn't be the first to go that route, myself included.

Stu.

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I ran this setup years ago for a while, combined with the AP uprated front calipers. It was the best brake setup I've ever had on the car but the handbrake caliper is hopeless and just kept eating itself. I gave up in the end and moved to a 2 pot Hi-spec rear caliper, it's effective in terms of ultimate braking performance but the pedal feel has never been as a good as the AP setup.

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