Common solutions are:
- relocate stock booster
- use smaller booster
- booster delete
Relocate stock boosterEdit
The stock E30 booster and master cylinder can be used if the firewall is drilled to mount the booster about 1/2 inch further to the left. There may be complications on RHD cars, due to the brake pedal linkage. How to move the booster:
- mark your new holes and what the curve will be for the center hole
- tap each hole location with a center punch to make starting the drill bit easier
- drill an 8mm hole for the shank of the booster bolt to pass into the interior. Using a metric step drill bit works great
- open up the big hole 1/2 inch to the right (I used a Dremel and a cut-off wheel. Remember to stuff a damp rag in the from the inside to keep sparks from going into the interior; ask me how I know!)
- bend the brake hard lines as needed, (go easy if by hand), and you are done.
Use smaller boosterEdit
Boosters are ordered from largest to smallest amount of assistance (ie increasing pedal stiffness).
Apparently same level of assistance as stock E30. However, a remote reservoir and different master cylinder (such as E34) are needed.
You will need:
- Remote reservoir from E32 740i
- new expansion tank (34-3-21-160-576)
- 2 plugs (34-3-11-163-464)
The Porsche 924 and 944 boosters have a 10 mm shaft, so they merely need to be shortened and threaded around an additional 1/2". Feels worse than standard mushy E30 brakes, so E32 25mm master cylinder upgrade is recommended. Other boosters below are possibly even worse for pedal feel.
Info from r3vlimited The rods must be shortened, and either
- weld on the E30 rod, or
- Thread the E21 rod: It has a 12mm shaft, so it must be ground down in order to be threaded properly. I threaded my 320i booster with a 12x1.5 die first, then filed off the threads evenly. I then threaded it further with an M10x1.5 die.
From Jason89i r3vlimited.com
- Whack off the threaded end, shorten rod, reweld. Stuff damp rags down against the rod to keep heat from transferring down to the [rubber] diaphragm.
- Grind down the rod (unthreaded portion is thicker) evenly and die the threads. I had a difficult time getting the booster rod out of the diaphragm, so throwing it on a lathe was not an option.
From 86325e r3vlimited.com
- Go ahead and make measurements of your E30 brake booster. Write down the length of the rod and the position of where the clevis fork is screwed on it. Then I used tape to mark the corresponding places on the E21 brake booster. I then securely braced the E21 booster without damaging it while I cut the rod down to where it needed to be.
- Now you've probably already noticed that the rod diameter is a lot thicker than what the diameter of the threads were on the end of the rod. What you need to use is a tap and die set. Choose a diameter that will still safely fit in your clevis fork. This part you want to take it slow and do it right. You want the threads to be straight. Be sure to use some cutting oil. You also are going to have to go buy a nut for the back side of the clevis fork to hold it into place. You might want to write down the sizes of the taps and dies you have and then go find and buy the nut. I cut everything first and then had a hard time for some reason finding that size nut, ended up having to drive over to Arlington for it, but anyway. Boring out the clevis fork to your desired size is easy, just put that in a bench vise, take it slow, and make it straight and even. On the brake booster, I didn't have a vise that would work, so a friend came buy and we used vise gribs to hold the rod as straight as possible and to keep it from spinning as I cut the threads onto the rod.
- Then clean everything up and all the shavings off. Screw you nut on to your clevis fork rod and then screw on your clevis fork. Look at the E30 brake booster measurements you wrote down and set the modified E21 booster to the same measurements. Once you put the booster in the car you might have to rotate the fork a half turn or so either way to get it perfect. You'll put the booster in after you get the engine in. The way my engine sits in the car its very close to the rear of the intake manifold but it clears. I didn't have to file any of the fins off. Doing this wasn't all that difficult at all, the hardest part making sure that the threads were done as straight as possible
From Brew r3vlimited.com
- I wouldn't attempt to remove the rod. Just modify it with it on the booster. Are you rethreading it? I just had my buddy cut the rod off the e30 booster and weld it to the e21 rod, after measuring of course. Works great.
The Porsche 924 and 944 boosters have a 10 mm shaft, so they merely need to be shortened and threaded around an additional 1/2".
BMW 2002 Edit
The rods must be shortened, and the E30 rod must be either welded on, or you must thread the rod. The thread size is M10x1.5.
The brake booster can be removed completely, however the lack of power assistance will result in a firmer pedal. Opinions vary regarding whether this is an acceptable solution. The booster delete could be DIY or Massive Brakes offer a booster delete kit.