Z4-forum.com

Quite a number of BMW owners, of all different models, complain about the brakes on their cars, and look for upgrades, including fitting expensive aftermarket BBKs (Big Brake Kits). There are a few very cheap and simple mods that you can do to improve the OEM brakes as well as uprating the brake pads, using DOT 5.1 brake fluid and fitting braided brake hoses. One thing you can do is fabricate brake ducting so that a constant supply of cold air can cool the brakes thus considerably improving the "duty cycle". I've already written about this here: http://www.z4-forum.com/forum/viewtopic ... 34&t=38775

Additionally you can also replace the OEM guiding bolt rubber brake bushings with solid brass bushings. In the part diagram below, you can see that the guiding bolt, Part Number 34 11 1 157 041 (part 6 in the diagram) fits within a rubber bushing with end cap (parts 7 & 8 ) which are inserted into the brake caliper (2 per caliper)




The photo below shows the guiding bolts removed from the front calipers and you can see how the bushes can only touch the brake caliper in 2 places in their housings and that the bushings can easily be deformed under relatively light finger pressure. Obviously, the brake calipers can easily move in 3 dimensions with such bushes when, ideally, they should move laterally, only.




The solution is to fit solid bass bushings as shown below. Part Number 34 11 1 157 041 is used on virtually all BMW cars, so this mod will work on all Z4s.





I already have a set of these bushings on another BMW car for over 7 years now and had no problem with them at all. I wanted a set for my Z4MC but they are only available from a few suppliers in the USA, who always insist on selling the brass bushes with the guiding bolts, which bumps the price up, and coupled with import duty and handling charge fees on top of freight charges, they prove to be quite expensive. Recently, I discovered a trader on eBay who sells the brass bushes and required circlips WITHOUT the guiding bolts, and who will accept offers on the listings, so that you can buy them for less than £18, the threshold at which import duty and handling fees are levied. Here's a link to these items: http://www.ebay.co.uk/itm/Brand-New-Bra ... fc0&_uhb=1

The only downside of this mod is that the bushes need lubricating from time to time, whereas the OEM bushes are maintenance free. I have seen cases where the OEM rubber bushes have been destroyed by the heat generated on trackdays, so the brass bushes should allow more heat dissipation by conduction through the metal bushes, thus assisting with cooling of the brakes. The fact that the solid bushings restrict movement laterally, only, prevents twisting of the calipers and ensures that the brake pads wear evenly.


Fitting the brass bushings is as easy as fitting new brake pads. You simply need to remove the caliper using a 7mm hex bit to undo the two guiding bolts







Here's the caliper removed.





Then take a large screw driver and push the rubber bushing out from the inside.




With the bushings removed, clean the holes inside the caliper and test fit the brass bushings. The bushings need to be able to slide and rotate freely.



Put lots of copper grease around each brass bushings before inserting from inside the caliper. Then attach the circlip around the groove on the bushing on the outside end.






Once the two brass bushings are fastened in the caliper, the brake caliper can then be refitted. Put lots of copper grease on the smooth part of the guiding bolts but avoid getting any on the threads.




Once the calipers have been refitted, you will see how the spring (Part 9 in the diagram) limits the movement of the caliper to sliding on the guide bolts.

Looks like a great, easy mod!

It's disturbing how many ways BMW designers have softened our cars, which we need to undo in order to have a real driving machine.

Any lubrication recommendations? What and how often?

bcworkz wrote: Any lubrication recommendations? What and how often?

High temperature copper grease is the stuff you want to use. Some people suggest lubing them every 6 months but I've found that you can leave it longer than that especially if the car isn't racking up huge miles. If you're a hands-on owner, it's no big deal to lube the pins whenever you remove the wheels and to lube the outsides of the bushes whenever you check or change brake pads.

I was recently thinking of such a mod to my brake system, but did not yet take the time to source a reliable vendor for the guiding bushings.
I guess that will be my next investment ! (well, i also need a set of braided hoses...)

Excellent write up! I am impressed with the condition of your cars struts and calipers...........very clean.

FAB! Combined with decent pads and braided hoses and DOT 5.1 (works wonders) should capitalise on these improvements.

I'm ordering at Turner Motorsports one of the following days, and will bring the goods back to Belgium in 2 weeks. I don't mind ordering additional sets for other forum members - you'll just have to cover the list price + shipping BE -> your place.

Reviving an old thread as I'm thinking of doing this soon. Do the end caps fit on the brass bushings and is it worth doing F+R or just fronts?

Scooba_Steve wrote:Reviving an old thread as I'm thinking of doing this soon. Do the end caps fit on the brass bushings and is it worth doing F+R or just fronts?

The end caps don't fit on. Just put a smear of copper grease over the exposed ends. If you want maximum effect you should use them F&R because the problem is the same at both ends.

Thanks for the info both, I'm looking at calliper refurb on the front hence the question. I've had judder when the brakes get hot on track hence the rebuild and thinking of doing this at the same time. I'm a little concerned about not having an end cap though and also the rear bushes look different on RealOEM.

Scooba_Steve wrote:I'm a little concerned about not having an end cap though and also the rear bushes look different on RealOEM.

Looking at RealOEM or BMWfans, it shows Part Number 34 11 1 157 038 in the parts diagrams both front and rear as the "Repair Kit Guide Bush" and Part Number 34 11 1 157 041 as the "Guiding Bolt". Both these parts are used almost universally across the entire range of BMW models past and present. I've not found the lack of an end cap a problem. When I installed the first set I covered the exposed ends with some clear silicone sealer, which was allowed to set before use of the brakes, as makeshift end caps. I've not bothered with this after last replacing the pads and lubing the pins and bushes. I've had no problems at all but the cars are not used as DDs. There is a noticeable difference to the brake pedal feel and pad wear is very even.

So what about as a DD like mine is? It's not a big job to get the calliper off when I change wheels, every 3/6 months to clean and lube? Does the end cap keep much out?

Scooba_Steve wrote:So what about as a DD like mine is? It's not a big job to get the calliper off when I change wheels, every 3/6 months to clean and lube? Does the end cap keep much out?

I use copper grease on my solid bushes on both the outsides and insides against both the calliper and the pins. Because copper grease is relatively thick, any contamination that gets on the pins will stick to the exposed parts only and will not travel along the length of the pin inside the bush. If the pins were lubricated with a liquid, such as oil, then contamination could spread. When I've cleaned my pins and bushes, they remained well lubricated and were not filthy, but then again, I use Yellowstuff pads which don't create lots of filthy brake dust. If you like tinkering with your car, then keeping the bushes and pins in good clean condition is no big deal, but for someone who doesn't DIY, then these wouldn't be for you.

An excellent write up.

UPDATE

I fitted these bushes nearly 3 years ago and I did a track day a couple of days ago so I thought it would be timely to blow all the dust out of the discs and re-lubricate the pins in the bushes for the second time since they were fitted. This was a simple job and the pins and bushes were like new.

Whilst I was doing this I decided to take a few photos to show the way these solid brake bushings work, as demonstrated by the wear on the pads. The photos are of Yellowstuff pads from the N/S calliper, and those from the O/S are exactly the same. As can be seen, the wear is even across the entire width and length of both pads and the thickness of the outside pad is almost identical to that on the inside pad. I measured the total thickness of the pads and backing plates with a digital micrometer and there is no more than 0.6mm difference at any point between the two pads. Clearly the solid brake bushes do their job as designed and keep the pads parallel to the face of the disc. These pads were fitted at the same time as new OEM discs and the combination have done a total of 7k miles with around 120 laps of The Ring (approx 1,500 miles) + 1 track day at Donnington (150 miles) + fast road use.

The discs now measures 27.99mm in thickness and look perfect. Before I fitted them, I put them at the bottom of our freezer, under all the frozen stuff, and left them in there for a month. I did this in the hope that they might benefit from some kind of cryogenic treatment after reading how BMW produced their high-powered F1 engines in the 1980s, by leaving engine blocks buried under snow.

I use DOT 5.1 brake fluid (Comma = Halfords' best) and have stainless brake lines and auxiliary cooling ducts (see: viewtopic.php?f=24&t=38775) and I find the OEM brakes superb and never had a problem of brake fade.