1 Series (E87) Tarmac rally car build by Mefmotorsport

[is-si]

I've been way too busy lately and not been on here much.
There shouldn't be anything wrong with a 4 pot on the back, but I've no idea how you could work out how to compare a 350 disc +single pot caliper V's a 300 disc +4 pot caliper

For reference we've got:
Front: 325+2x36mm+2x40mm piston caliper - .625 m.cyl
Rear: 295+2x28mm+2x30mm piston caliper - .70 m.cyl

and from an old catalogue, early E30 Gp A would have had:
Front: 330+2x38mm+2x42mm piston caliper - .625 m.cyl
Rear: 280+4x36mm piston caliper - .75 m.cyl
Not sure if or how prodrive modded this set-up.

Quite a brave move to change that many things at once, I've done it myself and been mentally tormented that I didn't really get hold of the culprit
Anyway roll bars are a defo-yes, more castor can't do any halm, and I think we've talked about spring rates previously after O.pk. Your car does seem very low and static. I'd pick it up and experiment with rake too. If you've got your corners wt's I can take a look and see how we compare
J.

[mef]

Thanks for the input regarding the rear brakes, I have decided to go with a 304mm x 25 rear disc and a Lotus Elise 2 pot front caliper (made by AP Racing). I have done a lot of homework and this seems like the best solution that will fit the hub mountings with a specially machined mounting bracket for the radially mounted calipers. This caliper seems to be adequate and easily available. The required mounting bracket is fairly straightforward to machine. I will go ahead with this combination and see how we get on.

OK about castor angle on the front struts, thats fairly easy to achieve, I will do that last.

Martin

[mef]

Some progress with my rear brake downgrade:

original M3 E90 rear discs, 350mm x 24 = 8.9Kgs

New AP Racing CP3047 discs & home machined alloy bells 304 x 25 = 4.3Kgs



A worthwhile saving of 9.2Kgs and loads more to come when I weigh the new Elise alloy calipers in comparison with the heavy steel BMW single pot sliding caliper and bracket!

I hope the originally superb hydraulic handbrake works as well, might need to tug it harder!

[mef]

The Elise 2 pot calipers turned out to be 3kg each lighter than the original BMW E90 M3 single pots, so thats another 6 kgs saved, plus 2 Kgs from removing the handbrake shoes and mechanisms all adds up to a total weight saving of around 17Kgs with the new rear disc & calipers. Weight saving was never really the mission but very worthwhile!

On the downside I weighed the replacement M3 E90 diff and got a shock. I knew it was heavy but never thought it would be as heavy as 44Kgs, Yikes! But there's no way around this one, it has to stay!

The Elise 2 pot calipers have 44.4mm pistons, slightly (6% CSA) bigger than the 43mm ones of the original single pot ones. I dont think that will cause too much of a problem. Hopefully the smaller diameter disc and smaller pad area will reduce the rear braking power sufficiently for a better balance between front & rear and I will be able to move the balance bar to a more neutral position, rather than fully to the front.

Here's the new 304 x 25mm AP disc in place and the Elise 2 pot AP Caliper.



Martin

[mef]

Today I was speaking to Alan at Questmead (mintex brakes) about my rear brake conversion. He said that he'd used the very same callipers on Colin McRaes Mk2 escort which is good news! I also found out at the weekend that Mike English has the same ones on his Mk2, so maybe I'm going in the right direction with this!

Today I had some spare time ( no works faults to attend), so refitted the new rear diff (filled with 1.2 litres of lucas 75w140 synthetic lsd diff oil), I also modified the drain plug to take a temperature sensor. Fitted the new 13mm rear anti roll bar and did some More work on the rear brake conversion parts, nearly there!ii

[donald]

Hi Martin,
do you know what failed on your diff yet and what are you using for a handbrake? Is a cable operated system still required?
I,m looking at getting a bit more rear braking on my car as I can't get enough rear bias with my current set up.
Donald

[mef]

Donald, it looks like it was probably my own fault, I never checked the oil since I got the whole rear subframe from a breaker, it came straight off a car. When we drained it on the event in Belgium we only got around 0.2 litres, so one whole litre was missing. It wasnt running dry but it ws certainly very low.

New diff now fitted after inspection and cleaning out then 1.2 litres of 75W140 LDS oil. I also fitted a temperature sensor in the drain plug so I can keep an eye on diff oil temp on my X dash.

I must admit though, I'd always thought that the old diff had a lot of backlash, the new one has minimal so maybe the other was worn when I got it.

Lesson learned!

Regarding the handbrake, I spent most of yesterday modifying my rear pads in the new Elise AP rear calipers such that my existing handbrake cable pulls them together and gives the effect of a rather poor mechanical handbrake, enough to satisfy the Scrutineers, not good enough to pass an MOT!

I welded tabs to the outside edge of the pads backing material, pics to follow.

It looks convincing!

Martin

[mimtbr]

I would also like to know what failed in the diff.
You guys both went the stock M3 210mm diff path. Currently thinking of installing a 2010+ Chevrolet Camaro SS 218mm diff with clutch plate limited slip. It's all aluminum and has 32spline x 36mm input like our bmw. The diff it's self is very close in size to the 215mm open diff.

Hi Martin,
do you know what failed on your diff yet and what are you using for a handbrake? Is a cable operated system still required?

[mef]

All the teeth were stripped from the crownwheel and pinion. I think the oil level was very low, my own fault as I forgot to check it.

New diff fitted now and I noticed it has a lot less backlash than the first one had from the beginning so maybe it will be better.

I notice you can get a 210 CWP in 4.45 ratio from a guy on ebay in Germany (Marcus) He says they are stronger than the standard ones as they are hardened and shop peened motorsport CWP's from BMW Motorsport (his mate works there) £700 delivered to UK. If I was to change to one I dont know which way to go, ie a 3.85 as per now or get a 4.45 and change my Tractive drop gears to compensate. It seems that the CWP is the same for an E46 M3 and the E90 M3 even though the diff casings are different.

Martin

[gartrac]

Martin

Keep the 3.85 it's stronger believe it or not

As the ratios get lower the pinion gets smaller so you have less teeth in contact at any given time

I would say you are correct with the diagnosis of low oil by the sound of it the diff overheated and literally melted the teeth

All 210 internal are the same except the early ones had smaller crown wheel bolts

From memory early ones had 1/2 bolts later ones 14mm, yours will be 14mm

Peter

[mef]

OK, thanks Peter, Yes, I had an idea that a higher ratio, ie 3.85 had a better crownwheel/pinion teeth count and was therfore stronger and also less expensive as I dont have to buy another pair of Tractive drop gears ratios too!

I emptied the new one, cleaned it out and re-filled with 1.2 litres of Luas oils 75W140 oil which is stated as being suitable for clutch plate type LSD's, hopefully this will be the same as Castrol Syntex 74W140?

So, I will stick with the new replacement road going E92 M3 diff and se how we get on. I have seen some discussion about the Motorsport M3 variable road diff being not so good/too slow acting for rally cars, not sure how true this is, maybe a proper fixed torque plate LSD would be better for me?

Cheers,

Martin

[gartrac]

I think it's all down to personal choice if the M3 Diff works for then leave it alone

Should you not be happy with it and want something a lot more aggressive then try a plated LSD with a 4 plate conversion from this guy

http://www.driveandtraction.blogspot.co.uk/

No machining required, uses 4 plates with no bevelled washers apparently this is how ZF built them for competition use

Not for the faint-hearted

Peter

[mrfuzzyfelts]

I think it's all down to personal choice if the M3 Diff works for then leave it alone

Should you not be happy with it and want something a lot more aggressive then try a plated LSD with a 4 plate conversion from this guy

http://www.driveandtraction.blogspot.co.uk/

No machining required, uses 4 plates with no bevelled washers apparently this is how ZF built them for competition use

Not for the faint-hearted

Peter

There horrible to drive with like this, much better to do a 4 plate with machining the end cover to fit. Then you can leave the bevel washers in.

They did my mates and the whole internals are now scrap as its worn in a funny way :-S why i dont know!

[mef]

Traction Control

I've been busy wiring up the BMW abs sensors to the DTA ecu to allow me to have full traction control.

From what I've heard and seen this works extremely well so seeing that its an available facility in the DTA S80 ecu I thought I may as well take advantage of it!

I found out that you have to use certain kinds of BMW abs sensors, not all will work, some of the newer ones are far too clever giving out pulses even when the vehicle is stationary so they can determine wheel rotation direction! No good for an aftermarket motorsports ecu.

I was told that I needed BMW 1 series, standard 118d front sensors but at the rear, specifically those from a 1 series 123D model so these are the ones I aquired. These are 2 wire devices, not like the earlier E30 7 e36 3 wire devices. They are not hall effect sensors or even VR sensors like used on many other cars. They are current operated devices that require a 12v or 5v supply and the output is taken accross a 120 ohm resistor in the ground circuit. The resultant signal is only small, typically a 0.5V square wave across the 120ohm resistor.

http://www.ebay.co.uk/itm/251046832443? ... 1497.l2649

Then I had to build 4 channel convertor which converts the low level current signals from each sensor to a 5V square wave signal suitable for the dta S80 ecu, the same signal that you get from a normal hall effect sensor.

The circuit for this uses an LM393 dual comparator chip, 2 required to make the 4 circuits, I can publish the circuit if anyone's interested.

So, I have now fitted the 4 abs sensors to the hubs and routed the cables back to my little convertor box, and connected the outputs to the dta ecu inputs. Now all I have to do is to install a switch to enable traction control, also one for wet/dry settings and a variable control to set aggression level.

I tried just one sensor first, this works the speedo in the X Dash via the CANbus signal from the DTA ecu. I had to change the pulses from the sensor from 5 that I had previously to 48. The DTA Swin software is superb, I could easily confirm by looking at the software on the laptop that 1 wheel rotation equated to 48 pulses. The speedo now works perfectly and consistantly unlike previously!

Castor angle

Meanwhile I decided to make a change to the front suspension to increase the static castor from the standard setting, hopefully to add a further 2 degrees of castor angle. This entailed moving the strut top-mount fixings backwards by 20mm. (thanks to John Coulson of "BRUVS" for the advice)

Not so easy as I had to re-drill the topmount holes in a completely different orientation to allow this to be possible, also I had to cut off excess material from the alloy top mount and re-drill and re-tap one of the M8 fixing holes. I've done 1 side now and it looks like its worked out fine, next is to do the same to the other side, it should be a lot easier now I know exactly what's required.

Pics to follow.

Martin

[mef]

I decided to change the gearbox oil and whilst draining the oil I happened to notice that one of the nuts was missing off the gearbox drive flange, where it connects to the propshaft via the Guibo coupling. In fact the other 2 bolts were also loose.

Weve checked these a few times since I used to have problems with these coming loose back in the Escort Cosworth days (1995) but they've never shown signs of coming loose at all. I found that the Guibo coupling is knackered (was brand new when I built the car and have only done half a dozen events).

It looks like the Guibo has bee winding up like Lotus Elan & Hillman Imp driveshafts, there are marks where the bolt heads have hit the propshaft flange on windup. The bolts have become severely damaged where they have been rattling about in the flanges. I was wondering if the diff failure could have caused these bolts to come loose as there was a severe vibration before the diff actually failed.

Anyway, a new one is now required before the event next weekend at Anglesey Circuit, also some new bolts and locknuts.

Martin