E21 Brake Master Cylinder Advice

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Jones the shark
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E21 Brake Master Cylinder Advice

Post by Jones the shark »

Hi all, so im sure this question has been asked before, just looking for some good sound advice from the E21 collective.

Im currently restoring a E21 316 which a previous owner has fitted a M20B25 engine from an E30, so a substantial power increase on the M10, but they didn’t do any upgrades to the brakes.

The brakes were ok but the pedal never felt brilliant if im honest so my plan is to make the brakes as good as possible using BMW parts, who doesn’t like good brakes ?

I was looking at doing the Volvo upgrade but not over keen on the grinding out of the calipers, but its an option. Iv since acquired a pair of 323i front struts and brakes so this is my preferred option for the front brakes.

Iv also acquired a pair of 323i trailing arms and calipers so a rear disc upgrade is the plan for the rear end.

My car is a 76/77 production car so it has the twin servo 2002 / E9 style brake setup and i will be having the servos rebuilt as i think its long over due, i want to keep this style of brake setup as i think it suits the car better and keeps an original look to the car.

I also acquired, in with some spares, a 22mm bore master cylinder from a E9 / E12 which will need re sleeving / re sealing.

So the question is, would i be better to stick with the 20mm original master cylinder from the 316 or would the 22mm M/C be a better option ? Not sure if the 22mm would cause issues with the brake pressure regulator ?

Sorry if this is a bit long winded but just wanted to give any interested reader the background and parts involved in my project to save lots feedback questions.

Cheers


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Jeroen
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Re: E21 Brake Master Cylinder Advice

Post by Jeroen »

The stock brakes are not over dimensioned but you still should have a decent pedal feel, and otherwise something is up for an overhaul. Servo's defo are a good starting point, also old brakes hoses tend to get clogged up as the rubber dissolves inside the hose. And take calipers apart completely so they are absolutely clean and have fresh seals. Some proper pads, and it should all feel much better even though the RHD brake linkage will always take some of the brake feel away.

If the 22mm master is a straight fit you could definitely fit that, no issues there, but its not a necessity. I'm now running a setup of Wilwood 4 pot fronts and E30 rears and the stock master cylinder still works fine. Good feel, hard pedal, and stopping power aplenty.
Regards/groeten, Jeroen

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Jones the shark
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Re: E21 Brake Master Cylinder Advice

Post by Jones the shark »

Hi Jeroen

Many thanks for the reply, my plan was to have all the brake hydraulic’s professionally overhauled, this would include sleaving / sealing of the master cylinder and the servos and full strip replate / rebuild of the calipers, and obviously new hoses all round.

I think i will stick with the 20.4mm standard E21 master cylinder as that is what the brake system was designed around, i was just wondering if the 22mm bore master cylinder gave better braking results or any benefits while i was at this stage of planning.

Many thanks Matt
Wilmo
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Re: E21 Brake Master Cylinder Advice

Post by Wilmo »

The bore is bigger, which leads to a larger area. Pressure is given by force per area. When the area is increased, as is done by a larger bore, the force needs to become bigger as well. And thus leads to more pedal pressure.

Summary: bigger bore equals to a bigger leg pressing on the pedal.
Jones the shark
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Re: E21 Brake Master Cylinder Advice

Post by Jones the shark »

Hi Wilmo

Many thanks for the reply, very good explanation. I think i will stick with the stock 20.4mm master cylinder as i dont want to change the characteristics of the feel of the brake pedal.

Il probably look to sell on the E9 master cylinder at some point.

Cheers Matt
Wilmo
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Re: E21 Brake Master Cylinder Advice

Post by Wilmo »

You could take some special care of the linkage. Maybe beef it up here and there a bit and make sure all bearings are nice and tidy. That might give some extra feel to the pedal.

I wouldn’t grind on calipers either. But I believe it is because of the E21 have smaller diameter calipers than the Volvo. So one option could be to try to find larger discs. Jeroen and I both drive with Wilwood conversions. Jeroen with a more stock approach and I went bonkers. It is nice and modern technology so definitely worth to take a look at.

I have as well a four cilinder and at the rear I have Golf III front discs and Golf IV rear calipers which work like a charm, including the fantastic mechanical handbrake, not the silly brake shoes of BMW. And I would take out the brake pressure limiter as well. Replace it with a regulator so you have always the same percentage of braking power at the rear. The limiter limits it to a maximum pressure. So at full braking it is not near the 25 or 20% you think you have.
Jones the shark
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Re: E21 Brake Master Cylinder Advice

Post by Jones the shark »

Hi Wilmo

Yes iv looked at the Volvo conversion but as mentioned not keen to grind out calipers and add washers for the disc to pad alignment, i have a set of 323i calipers so will stick with BMW parts for my brake parts.

My master cylinder bolts pretty much to the brake pedal & has 2 remote servos as it is a 76/77 car, i think the linkage you mentioned came around when E21’s had a face lift ?

Could you recommend a regulator that would work with my setup ? Again due to the age of the car now maybe the original limiter is not as good as it once was ?

Many thanks Matt
Wilmo
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Re: E21 Brake Master Cylinder Advice

Post by Wilmo »

I was thinking you had a right hand drive car... btw, you have an early one, and the proportioning valve is different there. But I would replace it anyhow with a Wilwood 260-12627. That one has M10 fittings.
Jones the shark
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Re: E21 Brake Master Cylinder Advice

Post by Jones the shark »

Yeah it is a RHD and is the old style setup.

Thanks alot for the part number of the Wilwood regulator, much appreciated.

Many thanks Matt
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