Brake problem

[Layne]

3- if you are happy with item 1 and 2 then you should check the vacuum first regardless what size or type booster you get . The amount of vacuum you have available is crucial before any booster can use that and translate it to extra braking power. You can have a ...super duper double mega tron ..booster and if you don't have enough vacume it will not do you any good. With your new motorics instaled I am not sure as I am learning more about E9 engine options but where do you get your vacume from and how much vacume is available, and how fast it build up (recovers) is crucial . After you verify proper amount of Vaucme no less than 13-14 pounds preferably more then you should press the pedal and see how much it drops and how soon it recovers after you let go of the pedal....
4- if all checks out fine then you should check or replace your. "Check valve "...

This is probably part of the deal. I measured 12 inches of mercury on the engine at idle, which is much less than a typical engine, but seems to be fairly typical for M30's. Probably the reason why a 7" single diaphragm booster can be sold for american hotrod applications, a chevy V8 would likely have 20"Hg.

 

[Tony.dreamer]

I am not familiar with BMW engine vacume capability. But a professional brake Shopcan verify if lack of Vacume is your issue. They should have test equipment I would try the to see what happens when you press the brake with vacume Guage clamped in between the booster and check valve . See how much it drops and when you let go how soon it recovers. I also assume you feel very confortable with item 1 and 2 i listed earlier . I said those from experience. It has always amazed me how I have neglected the simple parts and worked on solutions on the more complex side of the problem, and after tons of hours knowing the complex side of the systems is working we found out the the issue arose from the simple side.
One other solution, perhaps your last options in my opinion , you can try is getting an electric vacume booster a very nice ones are expensive but you can get a decent one for less than $300. Personally I have not tried them I have other friends that have talked about them.

Best of luck!
Hope you find what the issue is .
Cheers
Tony P.

 

[Ohmess]

And vacuum on the various M30s will vary depending on compression.

 

[Peter Coomaraswamy]

Those who had the misadventure of being around me last year at Legends will remember my shameless touting of the power bleeding systems available and how awesome they are for bleeding brakes and clutches. Just in case you missed that constant verbal digression I will state it again; pumping brakes to bleed out air is truly archaic and a pressure bleeding system, available at around 100.00, will change your life! Everything will work better, helps shortness of breath, E.D. and shrink hemorrhoids.

 

[sfdon]

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[sfdon]

good product

 

[Gary Knox]

I'm in full agreement on the Motive Products Power brake bleeder. Been using one for well over 10 years. If this one got 'lost', I'd immediately buy another before I had to do another brake fluid replacement.

Gary

 

[Layne]

UPDATE:

I was mistaken about the universal boosters I posted above... They use an American bolt pattern (Chevy I assume). 3-1/8" square pattern on the firewall side, and 3-3/8" on the master cylinder side. The E9, and practically every European car I've seen, uses a 72mm square pattern on the firewall side and 60mm on the MC side. As far as I can tell, there's no such thing as a universal booster with European dimensions, they're all application specific for something. So I have no idea what the 7" one I removed is for.

I learned about the Smart Fortwo booster from some 2002 guys looking for a cheaper replacement for the 2002tii booster. It's nearly identical to a tii booster, dual 175mm diaphragms, 72mm and 60mm bolt patterns. The problems are the MC pushrod is very short, the Smart MC goes way up inside the booster. And the MC bolts are rotated 15 degrees relative to the firewall mounting bolts. So the E9 MC would have mounted at a 15 degree tilt. I solved both problems by taking the booster apart in a hydraulic press and putting it back together rotated 15 degrees after extending the pushrod. Also had to extend the pedal pushrod, but that would be the same for any booster.

Anyway, the results: It works PERFECT. Pedal feel and the amount of pressure needed are excellent. Was able to lock up the wheels, but not too easily.

 

[Ohmess]

Great find. Guys changing to the triple weber set up now have an alternative to hunting down a tii booster.

 

[Layne]

Great find. Guys changing to the triple weber set up now have an alternative to hunting down a tii booster.

You could also use the Smart master cylinder.... It solves both difficult problems of the MC pushrod length, and the 15 degree tilt, eliminating the need to dismantle the booster. It's also a 23mm bore, the same as the E9 and tii. The only issue then is the Smart MC has only two 12mm outputs that would have to be adapted to five 10mm outputs. And of course the pedal pushrod still needs to be extended, which is pretty easy since the Smart one is long already (easy to weld without fear of damaging the booster). I made a sleeve to fit over it and used a portion of the original E9 pushrod to extend it, and welded them together.