Thought this E28 brake upgrade thread might be of use!

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sohlman

Post by sohlman »

Here is an article i have written for the BMW Car Club magasine taking an exspanding on the information that was currently out there plus using my own exsperiences. Enjoy

E24 Brake Upgrades
Information also valid for E28/E32/E34/E31


It has been for some time that I have wanted to write an article of this nature. Most of the information that has enabled me to complete the job has been obtained from the US Web site www.bigcoupe.com . The rest of the information along with personal experiences has been used to write this article.

The first main point is: why upgrade your brakes?

Most modern cars have great brakes, but older cars brakes are often less impressive. You may want to do track work, which requires significantly better brakes. If you plan on modifying your car the first thing you should do is sort out a decent set of stoppers that can deal with the extra performance. Another reason for upgrading is that you are not satisfied with your current set up.

Personally I found that the brakes on my six were unsatisfactory, I wanted to possibly do some track work in the future, and I definitely wanted to modify the performance of the car significantly. So my decision to upgrade was easily justified. My main problem was finding out what was the best option.

What are the main factors that affect brake performance?

On this one I go with the theory bigger is better. Pad material affects braking as does disc type, but pad size, piston size and power and disc size are bigger factors that can help brakes. Another factor is disc thickness. The wider the disc the more applications it can deal with before it heats up to a temperature that is beyond it?s working range. Heat is probable the biggest factor that kills brakes and induces brake fade. So having a wider, bigger discs and a larger calliper aids the braking system in cooling as well as retardation.

Another factor that can affect braking performance is brake fluid. Again, like the rest of the system, as more and more heat gets into the fluid eventually a point will come where the fluid boils, and then you have no brakes, although this is difficult. However old fluid absorbs water and lowers the boiling point, so fresh brake fluid is very important.

The last factor that can affect the braking system is brake lines. Old brake lines may swell under braking resulting in a softer pedal. So there is a good case for replacing these when doing a conversion. There is also the option of a stainless steel brake line which is much stiffer which leads to a more direct pedal feel.

What are the braking options available?

There are actually a huge number of options for upgrading the brakes on an E24/E28. The easiest and cheapest option is to get an uprated set of pads, but the performance difference may not be any better than the genuine BMW pad. There are also performance brake discs that can be bought with drilled and vented rotors, which will improve retardation, but there may be a bigger limitation and that normally comes down to calliper and disc size. If you really want a significant improvement then you need to look at uprating the size of the callipers and discs. Now doing this does not have to be expensive.

Now obviously there are big brake conversions out there from the likes of AP racing, Brembo, Willwood and others, and these usually come to ?1500 - ?3000. There are however a huge number of BMW options that can get close to the stopping power of these systems for a lot less money.

A big point to note is that BMW is a big fan of part sharing so many other models share the same parts and parts can be interchanged. Consequently brakes can be fitted to an E24 that also fit and E28, E31, E32, E34. There are however some considerations that have to be made.

Let?s look at the standard brakes for comparison?

Early E12 > 1982 based sixes have a dual system with two master cylinders and four pot callipers at the front. These were the same fitted to the M535I e12 M car and are considered a good system. There is even a brake balance controller in there.

E24 1982 ? 1986 cars had a single master cylinder mounted on the passenger side connected to the brake pedals via a bar that runs across the bulk head. The system also has a brake accumulator or brake bomb that pressurises the system giving massive power. The callipers are single piston units with 282x25mm discs.

E24 1987 ? 1989 cars had the master cylinder on the same side on the driver?s side and does away with the brake bar. Consequently the brakes have a much firmer feel. The callipers and discs are the same size.

E24 M635csi 1984 - 1989 had the same basic system as above depending on year, but had four piston callipers at the front and 300x30mm discs. These were significantly more powerful then the standard system.

All post 1982 sixes shared the same rear discs and callipers which are 284x10mm and the callipers are also found on the E30 325i.

BMW Braking options

Front
Model Disc Size Piston Size Wheel size required
E24 / E28 628, 635csi 282x25mm 1x57mm 14?
E24 / E28 M5,M635csi 300x30mm 4x40mm 15?
E34 525,530,535 302x22mm 1x60mm 15?
E34 540 / E32 735, 740, 750 302x28mm 1x60mm 15?
E34 M5 3.6 315x28mm 1x60mm 16?
E31 850 pre 1993 324x30mm 1x60mm 16?
E31 840 post 1993 324x30mm 4x42mm
BREMBO 17?
E31 850csi / M5 3.8 345x32mm 4x?
BREMBO 18?

The other option is the master cylinder. The 6 series shares the same master cylinder on all post-1982 models and has a bore of 23.81mm. When uprating brakes it is necessary to upgrade to the E32 master cylinder, which has a 25mm bore size to prevent pedal drop.

Rear
Model Disc Size Piston Size Wheel size required
E24 / E28 All Models 284x10mm 1x36mm 14?
E34 525, 530, 535 300x10mm 1x38mm 15?
E34 540, M5 300x20mm 1x40mm 15?


So what?s the right option for you?

Road use does not require the same braking needs as track use and some options may not necessarily be better in the driving seat. If you want better brakes without spending a fortune I would recommend fitting the E34 540 750 front callipers and the E32 master cylinder. For around ?200 - ?250 these parts can be purchased from a breaker?s yard, and then you require discs and pads which will cost no more than your standard items. If you have a 1982?1986 E24 with the brake bar then I would recommend braided hoses which are available from Goodridge and cost around ?100.

One easy fix for M635 / M5 owners who suffer from regular front brake warping is to fit the E34 540 rear callipers. This will improve the brake balance and will give much better wear as it will take the pressure off the front brakes.

If you want a set up for fast road use then I would recommend going for the rear E34 540, M5 callipers and you could possible look at getting the M5 fronts instead of the E32 750 callipers although these are much more expensive and discs will be three times the price of the 750 discs. With this set up you will keep the standard brake balance of the car, but will require the larger master cylinder, as the pedal drop will need to be countered.

For regular track work then I would suggest going for the E31 850 single piston or 840 Brembo set up. This set up is very powerful, but you need the vented 540 rear callipers otherwise you will have a very dominant front brake balance. The cost of this system will be around ?350 for a pair of callipers and discs are ?150 each with pads costing ?50+. For reference the later model seven series has Brembo callipers, which look the same, but have different mounting holes and so won?t fit, so make sure you specify 8 series brakes.

For racing use the 850csi M5 3.8 Brembo?s are excellent, but are very hard to come by. They also may be a little large for homologuing in race series such as the Khumo as the largest wheel size allowed is 17? Therefore at this stage you might consider going for a complete AP race set up. You would probable have to pay ?800 for a pair of these callipers and the discs are ?200 each. An AP racing set up would cost around ?3000.

How easy are they to fit?

With all these brake options no modification of brackets is required. I am no mechanic, but any competent mechanic could fit an entire brake system if you were to change everything in one day. The only advice I would give is that using a pressure bleeder is recommended and will save a lot of time when bleeding all the brakes as you will have taken everything apart.

What is the difference in the driver?s seat?

Speaking personally I have fitted two big brake conversions to my 6. The first involved fitting the 750 master cylinder and 840 four pot callipers. After the initial bedding in process I started to test the brakes. The power of the brakes was superb and the retardation from naughty speeds verged on the winding. Seat belts would start to feel obtrusive and would cut into you. However I found the system had less feeling in traffic at very slow speeds. I then removed this system to allow my 16? Alpina to be fitted and then installed the E32 750/ E34 540 front callipers and E34 540 rear callipers. This felt no different at slow speeds to the standard set up, but had equal retardation at naughty speeds to the Brembo set up. However the car felt if anything more stable as the brakes pulled both the front and rear of the car into the tarmac and the car now does not suffer from train tracking under braking. I now feel that I never have to try to stop for any danger that may present itself. Just recently I fitted Goodridge braided hoses and this sharpened up the pedal giving about 15% more feel over the original hoses and about one-inch less travel.

By James Sohl
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Brucey
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Post by Brucey »

This is a really nice article James;

if you are open to a little constructive criticism, it might be a good idea to make it clear that the E12, E12/E24 brakes don't interchange with the later E28 parts much at all. Also, the E12 brakes have an unusual split;
-one master cylinder works half the front brake pistons, the other works the other half at the front, plus the rear brakes. Thus the bias adjuster doesn't have exactly the same effect as it does on other cars.

I shall read it thoroughly and inwardly digest....

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
UKDaveJ

Post by UKDaveJ »

Nice one James, will be having a good read through that! :D
sohlman

Post by sohlman »

Brucey wrote:This is a really nice article James;

if you are open to a little constructive criticism, it might be a good idea to make it clear that the E12, E12/E24 brakes don't interchange with the later E28 parts much at all. Also, the E12 brakes have an unusual split;
-one master cylinder works half the front brake pistons, the other works the other half at the front, plus the rear brakes. Thus the bias adjuster doesn't have exactly the same effect as it does on other cars.

I shall read it thoroughly and inwardly digest....

cheers
Constructive critisism is a good thing. When i wrote the article i was not aware if anything at all was or was not interchangable. So thus i left the E12 off the list. However i am told rear brakes are interchangeable. I was told by a CSL owner.

James
six

Thanks!

Post by six »

Well done, James.

Keep up your writing!


IC
Lymond

Post by Lymond »

Great article, I was just researching this because I plan on upgradung this summer.
Which master cylinder would you use, I know there are a couple different ones for the e32, would you happen to have the part # or model the master cylinder comes from?
horsetan

Post by horsetan »

That was very very readable. And none of the usual spelling errors, either :wink:

Lymond wrote:....Which master cylinder would you use, I know there are a couple different ones for the e32...
750i or 750iL
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Post by Brucey »

horsetan wrote:That was very very readable. And none of the usual spelling errors, either :wink:
-ah you say that, but the pedant in me feels driven to point out that for brakes, 'caliper' is the spelling I am more familiar with.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
horsetan

Post by horsetan »

Brucey wrote:
horsetan wrote:That was very very readable. And none of the usual spelling errors, either :wink:
-ah you say that, but the pedant in me feels driven to point out that for brakes, 'caliper' is the spelling I am more familiar with.
Please re-read my post. I wrote:

(*pedantic mode*)

"none of the usual spelling errors"

(/*pedantic mode*)

That is not the same as saying there weren't any spelling errors :lol:
UKDaveJ

A tad harsh me thinks!

Post by UKDaveJ »

Found a few in the first sentence!

"Here is an article i have written for the BMW Car Club magasine taking an exspanding on the information that was currently out there plus using my own exsperiences."

But this matters not, what's great is that James has written a damn fine article & should be very proud of it. :D
horsetan

Re: A tad harsh me thinks!

Post by horsetan »

UKDaveJ wrote:Found a few in the first sentence!
There ye go! :lol:
sohlman

Post by sohlman »

I am allowed a certain amount of poetic license. It comes with being Dyslexic.

Just enjoy my spelling errors and laugh.

Thats what i do.

James
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Post by Brucey »

-we all have our little foibles; despite horsey's and Dave's remarks your article appears to me (mind you my spelling and grammar are not perfect either) to be fine apart from the spelling of 'caliper'. 'Calliper' is a word I think but isn't normally used for brake parts.

BTW I have had a stab at putting some science to your recommendations- see below;

Brake Fundamentals;

There are a few fundamental things about brakes that affect their performance, which are described below. In addition to these, there is the issue of heat dissipation, and furthermore one can add 'feel' which is much less easy to quantify; of this, more later.

The basic variables are;

1) Brake pedal leverage; how much is the pedal force multiplied by the leverage of the pedal to give a resultant at the master cylinder?
2) What fluid pressure arises for a given force on the master cylinder? This depends on the master cylinder piston area.
3) What is the servo-assistance factor? The brake servo will act to multiply the pressure in the braking system.
4) What is the clamping force produced by the caliper? This depends on the piston area.
5) What is the frictional coefficient of the brake pads?
6) What is the effective radius of the brake disc? This depends on both the disc size and the piston diameter.

How does this affect a 6er brake swap?

Fortunately several of the above variables are, for our '6er upgrade' purposes, fixed, or at least only have a few possible values. So, for a 100lb pedal force;

1) Pedal leverage; this is approximately 4:1 with an E28 pedal box, so this gives ~400lbs force at the master cylinder.
2) Master cylinder area; 23.81mm dia gives 0.69 sq in, and 25mm diameter gives 0.76 sq in. Thus pressures of 580 psi and 526psi respectively. Note the smaller master cylinder produces a higher pressure in the brake lines.

Item 3) Servo assistance; this could be anything from x2 to x5, but it will be fixed on E28 systems by the hydraulic booster pressure. Since brake systems don't normally run much over 1000psi I shall assume its x2 for the sake of argument. Thus line pressures become 1160 psi and 1062psi respectively.

Item 5)- standard road pads usually have a frictional coefficient of about 0.3, but ones suitable for the road could go up to 0.5. Below I have assumed 0.3.

Items 4) and 6) retarding forces; standard master cylinder ( larger master cylinder);

taking James' list of suggestions;

Model Disc Size Piston Size Eff. piston area eff. disc radius retarding force at wheel
E24 / E28 628, 635csi ('82-) 282x25mm 1x57mm 3.95 sq in 112.5mm 563lbs (516)
E24 / E28 M5,M635csi 300x30mm 4x40mm 3.89 sq in 130 636lbs (582)
E34 525,530,535 302x22mm 1x60mm 4.38 sq in 121 671lbs (614)
E34 540 / E32 735, 740, 750 302x28mm 1x60mm 4.38 sq in 121 671lbs (614)
E34 M5 3.6 315x28mm 1x60mm 4.38 sq in 127.5 701lbs (642)
E31 850 pre 1993 324x30mm 1x60mm 4.38 sq in 132 732lbs (669)
E31 840 post 1993 324x30mm 4x42mm 4.29 sq in 141 671lbs (696)

rears;

E24 / E28 All Models ('82-) 284x10mm 1x36mm 1.58 sq in 124 248lbs (227)
E34 525, 530, 535 300x10mm 1x38mm 1.76 sq in 131 292lbs (267)
E34 540, M5 300x20mm 1x40mm 1.95 sq in 130 319lbs (292)


From the above it is clear that up to 30% more front braking effort is possible by going to bigger discs and caliper piston area, by (say) using early E31 front brakes. However, with the original master cylinder, the pedal (at a given force) will be about 10% longer because of the larger caliper pistons. A similar percentage increase in the rear braking force is also possible, and contributes very little extra to the pedal travel because of the smaller pistons, giving a total of about 15% extra pedal travel if both front and rear brakes are changed. In practice this is about the same difference as would be retrieved by fitting braided steel brake lines in place of the OE rubber ones.

With the larger master cylinder retarding forces are about 8% less, but pedal travel (for 100lbs pedal force) will be similar to an OE set-up even with the bigger calipers.

Note that overall pedal feel may not be so greatly different if (say) the retarding force and the pedal travel both go up at the same time- the pedal may go down as far (albeit with less force) for the same retardation, unless the early E28 brake linkage is changed or braided lines are fitted.

All being equal, a 10% increase in brake disc size gives at least 20% increase in heat dissipation from the discs; this will make a big difference to the chances of brake fade. On the minus side these discs are also heavier, unless they are thinner too (as with the stock E34 fitment).

However, in the above calculations I have assumed that the pads have a coefficient of friction of 0.3. If (say) 0.5 pads were fitted this would give 67% more retarding force even with a stock set-up. You don't get something for nothing here; the chances are that both pads and discs may wear faster, and initial 'bite' may be completely different (although this will vary with pad type). However it is a very cost-effective way of improving your brakes, particularly if a more heat-tolerant compound is selected.

Its worth noting that once the disc and caliper piston sizes are set, so is the brake balance on an E28 set-up. The only variable left to play with is the pad compound (frictional coefficient) difference between the front and the rear.

With grippier tyres, the extra grip can only be exploited under braking if the bias is shifted to the front brakes a bit; this can only be sensibly achieved by changing pads or front brakes. Given that road tyres may have a frictional coefficent of 1, but race tyres could go up to about 1.6, it is likely that both pad type and brake size would have to be changed to make the most of race tyres. A sticky road tyre (say 1.25) would require changing one or the other, but not necessarily both.


Overall, I would draw the following conclusions;

1) Fitting braided hoses, better quality brake fluid, and better brake pads will provide a very cost-effective brake improvement, and allow retention of standard wheels.
2) If track use and/or much grippier tyres are contemplated, upgraded front brakes (with appropriate pads) would be very sensible, so as to retain both appropriate brake balance and fade resistance.
3) Pedal 'feel' will vary considerably with the various component combinations that are possible, but note that changes to brake lines and pad type will likely have as much effect as changes to calipers and master cylinders.

cheers

addendum; I realised later that I made two errors in the above; 1) a small one; the assumption I used for the disc effective radius is wrong, causing a small error, 2) the retarding forces are per pad, so the total retarding force is exactly double the numbers quoted per wheel.

D'oh!.....
Last edited by Brucey on Wed Jan 18, 2006 10:41 pm, edited 1 time in total.
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UKDaveJ

Post by UKDaveJ »

What an interesting read, superb work Brucey! Most impressed with what you & James have written. :D
six

Much Appreciated

Post by six »

Yes, both these brake write ups are highly readable and informative. Certainly they should find a more prominent home in the Tech Articles section.

Thanks again.

IC
UKDaveJ

Post by UKDaveJ »

Couldn't agree more!
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Up rating brakes

Post by ron »

Great articles from both Brucey and James.Just a couple of comments.
Fitting a 750i m/c to a r/h drive Highline requires new brake lines as the
lines come out on the other side of the m/c.
750i rear calipers are the same as 540 but the 750i discs don't fit as the
the top hat measurement is larger.
HTH Regds. Ron.
They are ALWAYS rustier than you thought!!!!!!
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Post by Brucey »

E12 front brakes; 4x40mm caliper, 280x22mm disc.

I may experiment by fitting E34 discs, and the above calipers together with special adapter plates. This should give M6-esque brakes, but lighter discs.

cheers
~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Post by sharkfan »

My M635 has (fitted by the PO) the E34/E32 discs with the standard M635 four-pot calipers - the PO said someone had recommended the set-up to him and he believed the different discs had reduced fade and improved feel - any thoughts?

I wouldn't know any different but the Sohlman has been in both of my sixers and seemed to think the brakes were ok - the 635 has newly replaced hoses and ATE powerdiscs - and perhaps a little better than the standard set-ups

HTH

Sharkfan.

BTW James - excellent article and pretty much covered angle 8)
Chris Wright

Post by Chris Wright »

Here is a response Sohlman made in another thread about his articule above. I thought I'd include it here for easy reference:

-----------------------------------------------------------------------------
Sohlman wrote:

All brakes mentioned in my article will bolt straight on. As mentioned late 7 series brakes look the same as the E31 8 series brakes, but the mounting bolts are in different locations so won't work. The 850csi/M5 3.8 Brembo's are beasts and are overkill for the six. Bear in mind thy were designed for a car running close to 400bhp and weighing nearly 2 tons in the case of the 850csi.

I run with 540 front and rear calipers. They work with 15" or above wheels, they are simple and were designed for a car running 286bhp and 1650kg's so are more than up for retarding the six. They do a great job and if anything give the six slightly more rear braking then stock, but if you consider that the rear discs are the same size as an E30 318is/325 that weighs 250kg's less and has less power they are somewhat lacking and a reason why the six sufferes from front brake warpage. Most modern cars run a 60/40 braking split were as the six is over 70% balanced to the front. I have stock pads and discs from BMW and the are great. The pads need one application to warm up properly, but bite well from cold. I would say that the six can brake as well as my fathers E39 528 and my e46 320 coupe and if you have driven these cars the brakes are excellent. Standard six brakes are not even close to these cars.

Previously i had the 840 4 pot bembo's on which did not fit over my purchase of 16" Black centred wheels although they will fit over the 16" flat centred Alpina's. These were amazing at 100mph+, but at 10mph and below they were like an on/off switch. These were then sold to a friend who has them on his racing M635csi and the brakes are killer. Nothing in the championship has out braked him.

For a road six i think the ultimate would be to go with some e34 M5 3.6 /850 pre 1993 front brakes and some E34 540/M5 rear brakes. The rears are the biggest that you can have and the fronts are large single pot callipers and are easy to fix if they go wrong. However pricing wise because the brakes are shared with the Mcar there is a premium over the 540 set up which in 95% of situations will be no better. This set up will require 16" rims.

For track work or show posing the 840 Brembo's at the front are great. They look nice and are sizable, but for road work are not as good as the E34 set up at slow speeds. Bit of a trade off, but when pressing on they will not fade and are excellent. Just watch out whats behind you as you might need a new rear bumper and some time with th physio. They are that good.

The 850csi/E34 M5 3.8 brakes are just insanely big. They are not as good looking as the smaller Brembo's and will ideally require 18" rims as the 17" rims are so close you can't fit wheel balance weights. However if ultimate braking is required these are the ones. However buying them is very exspensive. New discs are ?200 each plus pads at ?140 each pair. If i had a 350bhp six then i would consider these. But you will also need upgraded bushing and control arms as you wil just destroy them when you put the anchors on.

Don't forget when making a conversion of the brakes you will be asking more of the master cylinder and will need to upgrade to an E32 750 one to counter the difference.

Hope this all helps

James

-----------------------------------------------------------------------------

Here is the thread it is from:
viewtopic.php?t=2648&highlight=brakes
Last edited by Chris Wright on Mon Dec 21, 2009 5:21 pm, edited 1 time in total.
wokke

Info oin 850CSi front brake callipers

Post by wokke »

the 850CSi/E34-M5-3.8 front brake calipers use pistons of different diameter:
2 x 40mm and 2 x42mm. Same as the E32-750 EC/JAP version 4-piston calipers that go with 324mm rotors.

Cheers
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Post by BUELLRIDER »

I have been looking for better brakes and here is some to look at. OK the pics ar not here I will try again.
1981 635 German FRANKEN6ER gray market RIG, 1988 635,91 Nissan 240SX , 1993 Harley 1340ccFXR Super Glide, 2000 M2 Buell 1200cc.
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Post by BUELLRIDER »

Left to right ,e12 ,e28, e34.
Attachments
ROTORS.jpg
ROTORS.jpg (429.25 KiB) Viewed 56029 times
Bobby& rotor.jpg
Bobby& rotor.jpg (591.39 KiB) Viewed 56032 times
ROTORS.jpg
ROTORS.jpg (429.25 KiB) Viewed 56033 times
Rotors2.jpg
Rotors2.jpg (573.42 KiB) Viewed 56034 times
1981 635 German FRANKEN6ER gray market RIG, 1988 635,91 Nissan 240SX , 1993 Harley 1340ccFXR Super Glide, 2000 M2 Buell 1200cc.
alpinacsi

Post by alpinacsi »

if that e12 rotor was off your car; you have/had a serious problem. Pad should be making contact to the OD of the rotor and if it was really only 7/8; it was not contacting with the complete pad surface.
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