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Old 11-03-2011, 12:50 PM   #1
disston OP
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Making A Right Fork Leg For Dual ATEs

I have been rebuilding the front forks on my R90/6 the last few days. Working with all these things I look at the fork lower legs and it's plain the the right leg for a single disc is not easy to convert to a dual disk set up. But If one had two left lowers one of them could be converted for use on the right leg. And it doesn't look hard to do at all.

The axle hole in the left lower is smaller so it can be drilled to fit the right side. There is the same amount of beef to the area of the fork lower of the two legs. In fact they appear to have started life as the same rough casting. The axle hole needs to be larger on the right leg.

The pads for the caliper appear to be cast with a wide seat area. This is machined flat and the outside edge is cut off. When the left fork lower is put on the right side the cut off portion will now be on the inside. Merely cut the pad area on what will be the outside when placed on the right leg and weld this small piece to the other side of the pad. It will have to be machined flat again. Maybe some filling because of lost metal in cutting but not a big deal.

That is it. Drill one hole larger and change the caliper pad, cut ,weld, machine flat.

Is this not as easy to do as I think? I am not a machinist so it is entirely possible that something I don't see here is going to cost too much money or there is some reason why this just won't work?

Charlie
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Old 11-03-2011, 03:29 PM   #2
crazydrummerdude
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If time is money, and money is money, most people will tell you that it'll be cheaper/easier to just buy the right parts from the get-go.

I would like to see your progress if you do decide to go through with this, though.
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Old 11-03-2011, 06:44 PM   #3
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Quote:
Originally Posted by disston View Post
I have been rebuilding the front forks on my R90/6 the last few days. Working with all these things I look at the fork lower legs and it's plain the the right leg for a single disc is not easy to convert to a dual disk set up. But If one had two left lowers one of them could be converted for use on the right leg. And it doesn't look hard to do at all.

The axle hole in the left lower is smaller so it can be drilled to fit the right side. There is the same amount of beef to the area of the fork lower of the two legs. In fact they appear to have started life as the same rough casting. The axle hole needs to be larger on the right leg.

The pads for the caliper appear to be cast with a wide seat area. This is machined flat and the outside edge is cut off. When the left fork lower is put on the right side the cut off portion will now be on the inside. Merely cut the pad area on what will be the outside when placed on the right leg and weld this small piece to the other side of the pad. It will have to be machined flat again. Maybe some filling because of lost metal in cutting but not a big deal.

That is it. Drill one hole larger and change the caliper pad, cut ,weld, machine flat.

Is this not as easy to do as I think? I am not a machinist so it is entirely possible that something I don't see here is going to cost too much money or there is some reason why this just won't work?

Charlie
It's been done, I think it's a great solution to a very expensive dilemma.
Let me just put this "wrinkle" in there....
Don't ask your machinist to "drill" out the axle hole, (he'll cringe and turn funny colors) ask him to "bore or ream" to the correct size.
There once was an old guy in Gaithersburg that had done some custom triple clamp work for me once, not far from the airpark, I can't remember his name, but the work was good and the price was right.
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Old 11-04-2011, 02:52 PM   #4
disston OP
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I appreciate the input. I'm rebuilding the front forks of my R90. It was while I was comparing the two styles of fork lowers that I saw this was possible. It comes up all the time but I never do see this solution suggested. I have the much needed right side fork lower piece but I can't use dual brakes till I fix the hydraulics. So I guess I'll have an empty fork lower on the right side till I do that.

I know that machine practices and operations are not what amateurs like myself think they are. Boring or reaming the hole would be relatively easy I think. But creating the flat pad for the caliper seems a bit harder. Still I'm glad it can be done and some day when the price of usable right lowers is exhausted we may see it happening more often.

Charlie
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Old 11-04-2011, 03:30 PM   #5
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Quote:
Originally Posted by disston View Post
I appreciate the input. I'm rebuilding the front forks of my R90. It was while I was comparing the two styles of fork lowers that I saw this was possible. It comes up all the time but I never do see this solution suggested. I have the much needed right side fork lower piece but I can't use dual brakes till I fix the hydraulics. So I guess I'll have an empty fork lower on the right side till I do that.

I know that machine practices and operations are not what amateurs like myself think they are. Boring or reaming the hole would be relatively easy I think. But creating the flat pad for the caliper seems a bit harder. Still I'm glad it can be done and some day when the price of usable right lowers is exhausted we may see it happening more often.

Charlie
i should check with my favorite welding AND machining guru in SanJose and see if he wants to do some of these.
He's done it already, (iirc) and is WELL versed in BMW motorcycle modifications.
I should check to see how many i have. It might be "cheaper by the dozen" so to speak.
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Old 11-04-2011, 08:16 PM   #6
Rob Farmer
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Are the correct ones really that hard to come by in the states? I've got two sitting under my bench. nobody wants them over here.

Just have a look on euro ebay

Rob Farmer screwed with this post 11-04-2011 at 08:43 PM
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Old 11-04-2011, 08:54 PM   #7
wirewrkr
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Are the correct ones really that hard to come by in the states? I've got two sitting under my bench. nobody wants them over here.

Just have a look on euro ebay
The price is astronomical when you find one over here.
I am guilty of charging a premium when I sell them, but the market is the market, (I never twist anyones arm and force them to buy)
they don't last long when I advertise a set or just one.
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Old 04-10-2014, 01:06 PM   #8
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Quote:
Originally Posted by wirewrkr View Post
i should check with my favorite welding AND machining guru in SanJose and see if he wants to do some of these.
He's done it already, (iirc) and is WELL versed in BMW motorcycle modifications.
I should check to see how many i have. It might be "cheaper by the dozen" so to speak.
I know this is an old thread but... can you tell me who your buddy in SanJose is? I would like to have him modify a leg.
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Old 11-05-2011, 02:50 AM   #9
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Why bother upgrading a marginal brake by adding another one?

I'd get me a set of Brembo sliders, calipers, disks, or whatever comes along, dump the cable operated MC and fit a bar mounted one.
And if it isn't a straight fit, you can always mix/match/machine to make it fit.

BMW is like Lego for big boys.

Paul.
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Old 05-24-2012, 08:55 AM   #10
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Why bother upgrading a marginal brake by adding another one?

I'd get me a set of Brembo sliders, calipers, disks, or whatever comes along, dump the cable operated MC and fit a bar mounted one.
And if it isn't a straight fit, you can always mix/match/machine to make it fit.

BMW is like Lego for big boys.

Paul.

I know this is an old post. If you are running a spoke wheel it is nothing like Lego's. I am curious to know if you have finished your conversion. I just did one and I'm starting another(spoke wheels and Brembo calipers).
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Old 01-25-2013, 08:23 AM   #11
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Quote:
Originally Posted by PaulRS View Post
Why bother upgrading a marginal brake by adding another one?

I'd get me a set of Brembo sliders, calipers, disks, or whatever comes along, dump the cable operated MC and fit a bar mounted one.
And if it isn't a straight fit, you can always mix/match/machine to make it fit.

BMW is like Lego for big boys.

Paul.
Yah,but putting real brakes that stop pretty hard on forks barely strong enough for what they already have could be an issue with flex. I do agree the ATE's are kinda goofy and weak though.
It also seems like welding on the lower fork area could lead to warpage issues,I guess an machinist/welder would contend with this.
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Old 01-25-2013, 09:38 AM   #12
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I am considering (i.e. in the process) of doing this conversion. My reasons are: cost and availability - $400 for a Brembo front set of lowers is a bit high and left lowers are easy to find; better brakes - I can live with decent (still, not great) ATE dual brakes; it's period correct - not that the bike has any collector value, but it looks right; it is not permanent - the original right lower can be reinstalled. Drilling and reaming a new hole is no problem and cutting off the tang to weld on the other side may just be the excuse I need to get a spool gun. I think the tang has no function - other than looks.

I have another brake line and rotor with pads, so another ATE caliper, a piece of M10x1 steel brake line, and a brass brake line tee are needed. I got a set of /7 lower forks for $80.00 shipped and can live with losing that amount if this doesn't work out. I'll probably swap the ATE caliper to the right side to test the modified fork and rotor operation before finishing the conversion.
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Old 01-25-2013, 10:33 PM   #13
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Originally Posted by Stan_R80/7 View Post
I think the tang has no function - other than looks.
Oh, but they do have a function! They keep the caliper from flopping up or down. The caliper also swings, and has to slide easily on those 'wings'.
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Old 01-25-2013, 09:46 AM   #14
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You need five (5) longer bolts that hold the rotors on.
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Old 01-25-2013, 11:39 AM   #15
Voltaire
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After racing my conversion for a year I'm happy with it, can't ever see myself converting to Brembos.Although ATE's in their original form combined with age are not flash, once you go to 13mm m/c, stainless lines and CAST IRON discs they work a treat.
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