Yet another rear disc conversion....

[EuropaTC]

Firstly, apologies to those who clicked on this topic expecting a fully documented "how-to" because at the moment it's just a pipe dream, but hopefully it will become reality in the near future.  The idea of the thread is to share with you guys the pitfalls, dumb mistakes and "doh" moments as I try for this conversion. I'll aim to update this topic every day or two with whatever progress (or not).  It should work, it might not but hopefully the thread will prevent anyone else making the same mistakes. Feel free to chip in when you see me going astray.....

To start off, the background;

I don't need a rear disc conversion and I doubt anyone really does for a road car. But I want one and as my dad used to say "you'll keep fixing that car until it's broken", so I'm going to have a go.

For those not involved with the Yahoo group, there have been numerous debates on this topic, several conversions and even a spreadsheet model produced for the braking system. For anyone considering this modification, I would urge you to read up on these references;

http://lotus-europa.com/manuals/index.htm            (several fully documented conversions)
http://groups.yahoo.com/group/lotuseuropa/files/    (you need to sign up to the Yahoo group for access)

I'm at the point of starting now, so this first post is what I've assembled so far;

Renault Scenic rear calipers with handbrake mechanism.
MGF 240mm rear discs, 10mm thick.
1/4" mild steel plate.

And here's the first "doh" moments......

1. I doubt this will fit with 13" Cosmic Alloys. Simply dropping the disc & caliper inside the wheel shows there's not enough clearance due to the internal section of the rim casting. This may or may not be a problem with other alloys, but I will measure the installation clearances once complete so we will know for those of us with 13" steel wheels.  Fortunately I have a set of 15" wheels sitting ready, just in case this happened.....

2. The discs have the correct PCD for the Europa hubs, and a very neat top-hat section which suits the installation. The "doh" is that the internal diameter of the disc top-hat is too small and the hubs need approx. 1mm grinding away to fit properly.

to be continued......

[EuropaTC]

Update #1

The car has reverted to kit form and is in pieces, so there's no turning back now !  So far I have ground the hubs to clear the MGF discs, which amounted to probably less than 1mm taken off the edges. Both hubs were then drilled & tapped to allow the discs to be bolted into place with M5 stainless countersunk screws. This isn't essential as the wheel will keep everything together but it does make things easier to have a single assembly unit to deal with over the next stages.

Once this is done you can mount the hub/disc and start to see what clearances you have. By just placing and wedging the caliper in the position required we then get confirmation that the existing Cosmic wheels aren't going to fit once this conversion is done. I've uploaded a picture of where the wheel catches the caliper. This could be solved by wheel spacers but I'm not so keen on that idea and will move to 15" wheels. (14" would also work, it's only just touching the rim)

These wheels are 13x5J Cosmics and it's an internal rib which causes the problem. I don't know if the OEM Lotus alloys have the same section casting so this may not be an issue with other wheels, or even 5.5" section rims if they have a greater offset. Steel wheels will probably be ok (the Elan uses a larger rear disc with 13x4.5" steel rims and no clearance issues) Once everything is finally mounted I'll take dimensions which should answer that one.

I've started fabricating the first bracket using 1/4" mild steel plate. The caliper locating part is fairly straightforward and I used the caliper itself as a drilling template. For the hub part I used the brake backing plate as a template for drilling the holes and laboriously chain-drilled the large hole for the axle. It seems to fit ok, now all I have to do is join them together keeping everything parallel and square.

Now there's a challenge, you don't normally see me with "welding" and "accurate" in the same sentence  .......

to be continued............

[Bainford]

Cheers Brian. May the force be with you.

[EuropaTC]

Update #2

Day 3 and there's good news and there's not so good news.   

The good news is that one caliper is mounted and looks ok. The not so good news is that I obviously took my eye off the welding rod during the second bracket and as a result it's got some distortion.  I'm working with hand tools and my measurements and alignments are by vernier, spirit levels and a lot of "well, that looks right", so I can't be 100% but I think the second one is about 0.010" out. Whatever it is, it throws the caliper mount off a nice square 90deg angle.  Not so much really, but it just looks a bit "off" compared to the other side.  And so I started work on a 3rd bracket.

Assuming everything works at the end, so far I'm very pleased with the components now I can see it coming together. The caliper sits very close to the hub carrier which does make the bracket dimensions quite critical, but on the other hand it's so compact that it will be a very strong and rigid set-up. 

The pictures today were taken during the bracket fabrication process to give you an idea of how I approached it.  I used a square section tubing to clamp parts together at 90deg, and then spirit levels to check for parallel between the hub carrier plate and the caliper mounting portion. This is fairly simple and does appear to work ok, it's fairly obvious when you can see the bubbles all aligned and you just tack it in place. After welding I also checked with a vernier gauge, in theory this should give you measurements  to within 0.001", plus or minus whatever my personal measuring error is.

The other shots are the best caliper mounted which looks better in the metal than in the photo, it's not easy to get a good photo from inside the wheel arch.   For the final shot I put on a wheel to check how much clearance there is - lots !!!

to be continued.....

[Bainford]

Looking good, Brian. The mounting is indeed quite compact which will impart rigidity (and keep accumulated unsprung weight in check). I can appreciate the difficulties in keeping fabrications perfectly square.

[YellowS4DHC]

Brian,
Once again, you are blazing a trail to be followed here.   

If possible, could you include a pic or two of the finished bracket?  And maybe annotate it with approx dimensions? That would be a great gift to us planning our own project.

regards
Rick

[YellowS4DHC]

oops,

Brian, I forgot to ask what are those 15" wheels in the picture of your earlier post?  Are those off a late model Lotus or aftermarket?  I'd like to learn more about those wheels, they look like they belong on a Europa.

Rick

[EuropaTC]

Once again, you are blazing a trail to be followed here.   

Sadly Rick, there's no trail-blazing here, I'm following a path already well-blazed and with a few signposts along the way        A UK member of the Yahoo group (Richard) completed this conversion several months ago and it was from him that I had the recommendation for the calipers I've used.  I don't know Richard well, but he comes across as a competent & practical engineer which is what gave me confidence to try this particular modification.

If possible, could you include a pic or two of the finished bracket?  And maybe annotate it with approx dimensions? That would be a great gift to us planning our own project.

Yes, that's already in the camera, I just have to spend some time with photoshop to transfer the dimensions.  My plan is to produce a PDF file with more detail than this thread which I will slot into my workshop manual to remind me of what I've done and why, plus where to source spare parts in the future. When I'm happy the modifications work on the road, I'll post that file in the technical section as a completed project because whether people go this way or not, it's helpful to have as many ideas as possible when planning these things.

The wheels ? Another "Richard" one.  I was considering fitting Elise S1 wheels to my car as I just happen to have a spare set in my garage, when Richard posted that MGF  wheels are the same PCD as our cars.  The Elise rear wheels are 7x16 so you need even lower profile tyres to get the same radius,  but these MGF ones are 6x15 all round so the tyre profiles look more suited and tyre options are greater than with 13".   I've had them on the car before but if this mod works then they'll become a permanent fixture I think.   

Brian

[YellowS4DHC]

Brian,
I don't mean to hijack your thread, but where might one look for MGF wheels on this side of the pond?  Any UK  vendors come to mind?

Rick

[EuropaTC]

I can't help with US based suppliers I'm afraid, I suppose there must be importers over there but suspect the wheels wouldn't come cheap if you bought new. Over here they are because there are lots of MGFs and many are reaching the age when they get scrapped so there's a healthy secondhand market. I bought mine from Ebay for £160 delivered and that included 2 new/2 worn tyres and was considered "expensive" ! 

The PCD is correct, as is internal clearance on my TC, but be aware that as a modern wheel they are not a simple bolt-on swop. They use 12mm studs with larger wheel nuts and I've been running with those for a while now as I drilled out the Cosmics to take the larger stud.  These wheels won't fit with standard Lotus/Triumph wheel studs. (or at least not easily)

Brian

[Bainford]

One may have to sleeve the stud bores on the MG wheels with steel sleeves. Looks like there is plenty of material around the stud bores to support this. If one was to retain the 3/8" Europa wheel studs, it would be important to ensure that the overall diameter of the new tire/wheel package is not significantly greater than the stock Europa package, so as to not over stress the small studs. Just a thought.

[EuropaTC]

Update #3

Well, we're almost there folks.  At last both calipers are mounted, the handbrake actuators have been modified and moved to allow a smoother cable operation and new brake pipes installed.  Yesterday I made a new handbrake cable which fits much better than the OEM one, which is now too long for the job.  So how did it all go ?

The caliper brackets proved much more of a problem than I'd expected and underlines the fact that you really need machine tools to make these things inside any acceptable timescale. They looked good to my first measurements but during final inspection after mounting everything firmly I found I had differing disc to caliper body clearances at the front & rear of one caliper, which meant it was slightly twisted. 

It's not visually noticable but a vernier gauge sees everything,  so I ended up with a tedious process of measuring the caliper/disc clearances and hand filing the mount in-situ to get it right. That is slow work but you get there in the end.

And of course we've had a few more hiccups along the way. Because I was mounting/dismounting the brackets so often during the final adjustments I  ended up stripping the threads of 2 holes in the aluminium carriers, so there was another pause whilst I fitted helicoils to the carriers.

The pictures today are close ups of the bracket design, I used the 2nd one (the one which distorted) for these photos so it's unfinished, but the only differences are that I ground the welds smooth and finished the profiles off a touch neater. The dimensions are only of use for this specific caliper and disc combination, but they do give a feeling of what's involved.  The mounting holes for the hub carrier bolts were taken off a paper template made from the drum brake backplate, so again there will be some approximation in the dimensions.  I can't stress enough that if you do this sort of thing,  don't take my measurements as gospel truth but make your own templates ! (the TC & TCS are different anyway I think ?)

The other bit of progress was to wire up the handbrake. The OEM cable is, as suspected, far too long for this job and so I made a new one.  The nipples are soldered into position and shown in the second photograph. I made the nipples from mild steel rod, 8mm with a 3mm hole for the wire and a 5mm drill in the upper part to allow the wire to be splayed out before soldering in place.  I don't know if that's the way they are made, but my logic was that you're not relying on the shear strength of a soldered bond between the wire and a straight hole as you would be if it was just soldered into place. If you wanted to pull out the wire now, not only would you need to overcome the shear bond but also somehow compress and pull the splayed end through. I think I'd need to eat a lot more spinach to do that trick....   

[YellowS4DHC]

Brian,

regarding the front to rear misalignment on one of your caliper brackets.  How far off was it?  If it were only a few thou off (say, no more than .010"),  couldn't you just shim one or the other bolt holes to get proper caliper/disc alignment?  Alternatively, you could just let differential pad wear make the misalignment moot after 500 miles or so.  Since you brought out the file, I assume it must have been too large for either of those approaches.

When I did my rear brakes some time back, I noticed (but did not measure) an apparent misalignment between the RH brake back plate and the hub face.  This was very evident once the brake drum was mounted on the hub.  I initially thought that the brake back plate was distorted but that didn't appear to be the case (or at least it wasn't the sole reason for the observed misalignment).  For some reason, it appears that the mounting plane of my hub carrier is not perfectly parallel to my hub mounting face.  Once my shoes were bedded in, it's not a problem and I didn't sweat it back then because I always figured I'd dump the drums anyway.

Later, as I was thinking of rear caliper bracket fab at some future date, I realized I'd need to adjust for any lack of parallelism between the hub face where the rotor would mount and the hub carrier which would define the orientation of the caliper bracket.  It sounds like I'll probably be doing just as you, bringing out the file to tailor each bracket for each side.

I don't know the standard mfg tolerance for the parallelism between the pad and rotor for modern brake systems; do you know what that is?

regards
Rick

[EuropaTC]

Hi Rick,

It was only a few thou, and I couldn't tell until I started to measure everything after finally torquing up the hub nut. The picture shows where the problem lay, the gap wasn't the same across the front/rear of the caliper. As you say I did consider leaving it and letting the pads accommodate it, but knowing it was out and that I could fix it just didn't lie well in the end. I'm guessing that with modern machining and the assembly being metal/metal interfaces with no paint or gaskets, they aim for +/-0.001" ? Disc run-out is given as 0.004" in total so they obviously work to finer tolerances than they did when making the panel gaps in the bodywork...   

Anyway, it's all together and this weekend I've been chasing a problem with excessive pedal travel which may or may not be as a result of the conversion. I'd calculated it would be a touch more as the 34mm rear piston is obviously more than the drum brake cylinder, but I wasn't happy with the amount of pedal travel because over here you can fail your annual test if the mechanic feels there is "excessive pedal travel". And I really don't want to get into arguing that one next year.

What was really bugging me is that the Elan has the same m/cyl with discs all round and even has bigger front caliper pistons, but has a much better pedal feel. The TC should be tighter with smaller front calipers, but it wasn't.

I've improved it now and it feels acceptable, but during the process I contacted Richard (the guy who's also done the same mod) and asked if he'd had problems in this area. We're running different systems, he's with s/circuit & servo whereas mine is d/circuit & no servo, but yes, he'd had the same issue. We had a remarkably similar "possible solution list" and fortunately he'd gone down his and found an answer, which turned out to be a residual pressure valve to keep 2psi in the system at all times.

The theory is that on some layouts there isn't enough hydrostatic head on the m/cyl to keep the system under slight pressure and so your first press is restoring this before braking occurs. Mostly it's not a problem and you never notice it, but maybe with the adoption of larger rear pistons we're on the limit of what a 0.7" bore m/cyl can cope with ? I have no idea but I'm going to try the pressure valve this week to see if I can get it the same as the Elan. It could be the answer because as you know the Elan has a higher m/cyl mounting, and on mine the remote reservoir is even higher as I moved it from underneath the carbs. But the remote on my TC is probably a foot lower ?

I've rambled on for long enough so I'll close by saying I've got the workshop notebook up here now and am slowly compiling the details into a single file. If I can convert that into a pdf I'll post it in the "technical articles" section so the group will have all the specifications of the parts used, the costs and what I think I'd do differently if tackling it again.

Brian

[Bainford]

That's a good looking set-up, Brian. Interesting comments on the excessive pedal travel. I would have assumed that one of the advantages with four wheel discs is significantly reduced pedal travel. A firm pedal with little pedal travel and good control over brake modulation is what I would be looking forward to. However, the low mounting position of the Europa master cylinder is a curiosity, and I have pondered this previously. Though I haven't taken measurements, it looks almost as though the M/C fluid level is as low as the front caliper bleed point, which would seem quite wrong, so I assume that it has to be slightly higher. I'm very interested to know how the residual pressure valve works out. Will this result in accelerated pad wear, and will it pose any problems with pushing the piston back into the caliper during brake service? Just thinking out loud here...