Author Topic: Yet another rear disc conversion (grand finale !)  (Read 2902 times)

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Offline EuropaTC

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Yet another rear disc conversion (grand finale !)
« on: Tuesday,October 01, 2013, 12:58:09 AM »
Hi folks,

There's not a lot to write here, most of it has been covered in the thread in the Garage section, but I've posted here with 4 PDF files which collate all the relevant data for anyone else planning to go down this route.  I have lots of photos and sketches so if anyone is contemplating this type of project and something isn't quite clear, I'll be happy to send over more photos of any particular stage.

Part 1 is details of the basic components, calipers/discs/cables
Part 2 is hubs & discs & the start of the caliper brackets
Part 3 is putting it all together, plus handbrake cables
Part 4 is final installation pictures and caveats on this specific conversion.

Brian

Offline Bainford

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Re: Yet another rear disc conversion (grand finale !)
« Reply #1 on: Friday,October 04, 2013, 08:05:09 AM »
Thanks for doing this, Brian. It is very much appreciated. I'll be attempting something like this eventually, but it will be a ways down the road yet. A lot of other things to take care of first. Have you had a chance to road test yet? I'm interested to get your impressions of the set up in service.
The Twin Cam plays the symphony whilst my right foot conducts the orchestra. At 3800 rpm the Mad Pipe Organ joins in.

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Offline EuropaTC

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Re: Yet another rear disc conversion (grand finale !)
« Reply #2 on: Friday,October 04, 2013, 09:34:54 AM »
yup, it's been road tested a lot over the last few days, strictly in the scientific goal of research you understand...    :)

What's it like then ? Well, it's ok.

You're no doubt now asking "only ok" ?

Well, it's not mind-blowing.  I don't suddenly feel that I've transformed the braking system into a 21st century icon, but there are subtle differences.  Some are silly, like the car now stops noticably quicker when I'm reversing down the slope out of the workshop and the parking brake is now like the ones on "real" cars.   I've got the brake pedal half decent now and it might be imagination but I think it's improving more as the new rear pads & discs settle in. The contact pattern on the rear discs looks good with a full, even depth of contact and after a few miles you can see where it's biting.

I do think the rear braking is taking a greater part in stopping the car and although it is still possible to lock the fronts on our gravel drive, I haven't managed to do so on the roads yet. (it's very quiet around here as far as traffic goes, so that's not as hooligan-like as you might be thinking).   I seem to recall reading that drum brakes have slower reaction times than discs, so maybe that's the main reason as they're all coming together at once ?

There are other factors in the mix though. I also changed the wheels and bought some new tyres last month, all of which improve braking as I've gone from 175/185 70 series Dunlops to 195/205, 50 series Toyos, which I've had on other cars and quite like. 

Brian

Offline EuropaTC

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Re: Yet another rear disc conversion - The Epilogue
« Reply #3 on: Saturday,October 19, 2013, 10:00:42 AM »
Hi again folks.

Ok, I suppose you’re wondering “I thought he’d finished that little job ?” and in one sense you’re right. The car has been running with rear discs for over a month now, and I’ve been slowly tackling the niggles as I came across them.

The first was what I considered to be excessive travel on the pedal, and the initial attempts caused me to fit 2psi residual pressure valves to both circuits which rather surprisingly did make a difference but the pedal travel still didn’t match the original calculations. It was around 1/2” too much, which doesn’t sound worth bothering with but was bugging me. With full application the brake was noticeably below the accelerator pedal which it hadn't been before,  so it boils down to "if it feels wrong, it probably is wrong" - a confidence thing.

I was going in circles so I moved on to the next job, which was to fit a flexible pipe just before the calipers so that I could swing the sliding component up to replace pads in the future rather than dismantle the whole system.  There’s nothing significant here other than selecting the shortest flexible I could find which will allow enough movement.  In normal service it doesn’t move or vibrate and just acts like a fixed line. 

But it was during this stage that I finally solved the pedal travel problem and as usual, it wasn’t rocket science it was something I should have seen earlier but had missed.

You may remember I’d switched the inlet & bleed ports round because the caliper was designed to mount as vertically, but to get it on the Europa it needed to be either vertical leading or horizontal due to the spring/damper assembly.  The handbrake meant horizontal mounting which placed the inlet at the top with the bleed nipple below.  Clearly a problem for bleeding, so I’d just checked both holes had tapered seats and swopped them over as shown in the attached photo.

And that was mistake #1 (actually it’s more like mistake #101 ! )

Now that I had the calipers on the bench working out the new flexible connections  I finally realized that they’re actually different sized ports, and doing the go/no-go test with some drill shanks I reckon the original inlet is 3mm with the bleed port 1mm less. Yep, should have seen that before, but I didn't.

From my 40yr old physics I don’t think this would affect the pressure behind the caliper piston & hence clamping force on the disc, but it will affect the rate of flow into the caliper as the smaller hole is acting as an orifice plate, and hence speed of application.  A marginal effect I’m sure, but not knowing enough about the physics I’m left thinking that the designer must have picked differing sizes for a reason otherwise why drill 2 different sized holes ?

So I reversed the ports to OEM, which meant that to bleed the system properly I needed the calipers partially dismounted and moving on the (new) flexible hoses.  More hassle....

But hey, guess what ?  I started with the caliper static and the bleed nipple uppermost, but for some reason I decided to manipulate it during the process and was rewarded by another slug of air bubbles coming out.   I can only guess that previously swopping the ports in combination with the mounting position, I’d somehow managed to lock some air inside the calipers which didn’t come out with normal bleeding.  But surely the excess travel couldn't be something as simple as a bubble of trapped air ?

But it was you know.  The end result is that travel at the master cyinder stroke has dropped by over 5mm and total pedal movement is now roughly 1” from start of application to full lock-up. Maybe a touch more because it’s difficult to measure accurately down the footwell, but it’s significantly less than previously and a great confidence boost.

All that trouble over a bubble of air....  just like it says in all the books. Who'd have thought....    ;)

Offline StrawberryCheesecake

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Re: Yet another rear disc conversion (grand finale !)
« Reply #4 on: Friday,May 22, 2015, 03:32:26 PM »
Very interesting. I need to do this at some point, as the car came with 4 calipers, rather than drum rears.

The renault calipers look very much like Mk2/3 golf ones. Will have to measure up at some point. Interestingly, Mk4 golfs have a caliper the same size that's made of ally rather than steel - mucho unsprung weight saving, and they're less prone to seizing. I'll compare the spare calipers that came with the car to the Mk4 golf ones I have lying in a scirocco Mk2, waiting to be fitted... and report back at some point.

Offline EuropaTC

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Re: Yet another rear disc conversion (grand finale !)
« Reply #5 on: Friday,May 22, 2015, 10:10:39 PM »
I think you might be right on the Golf calipers. It's too long ago now for me to be positive, but at the time of the conversion I was doing a lot of internet surfing for images of potential calipers and came to the conclusion that the Renault ones I used were a fairly common design.  I've kept an interest in such things and although I doubt I'd throw these away just yet, the idea of an aluminium body does appeal.

The current status is only slightly changed from the previous photos. I ended up junking the first, short flexible hose I selected and have ended up with a longer braided hose which has a smoother path and as much flexibility as you can imagine should I need to remove & manipulate the caliper when bleeding.

It's a year or so on from the initial project and if I'm honest, the greatest gain from the whole exercise has been getting a handbrake that actually works and is no longer a concern when going for the annual MoT test. I realise that sounds crazy, but as "the handbrake, yes or no ?" used to bug me every year at the test, for me it's been worth all the effort.

Brian
« Last Edit: Friday,May 22, 2015, 10:20:38 PM by EuropaTC »