1977 R100RS Instrument Cluster mismatch

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kingcowie
Posts: 28
Joined: Wed Oct 28, 2020 1:29 pm
Location: Wollongong

Re: 1977 R100RS Instrument Cluster mismatch

Post by kingcowie »

Chaps, Great posts and agree with comments .
Firstly this is the vin results..so the bike is right on the cusp of change.

All points lead to that it should have the old cluster as the front mc in under the tank, the cluster connector does not match the instrument pod, the instrument has no brake level light. The wiring has been chopped but not changed, very confident original

BUT why is there no provision for mechanical tacho cable in the front of the engine or was there an instrument cluster that had a brake level light and electronic tacho.

Here is some photos for back ground.

I will check the wiring diagrams when go into the workshop, just 6am here.

Thanks Shane
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Shane
Wollongong, Australia
71 R75/5
64 R50/2 Project
77 R100RS Project

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srankin
Posts: 187
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA

Re: 1977 R100RS Instrument Cluster mismatch

Post by srankin »

BUT why is there no provision for mechanical tacho cable in the front of the engine or was there an instrument cluster that had a brake level light and electronic tacho.

Shane, your bike may well have been built in 77 but is not a 77. I don't know about AU but here in the states we get bikes and cars built in one year sold as another year car. For example a car built in 2019 may in fact be sold as a 2020 model. As a 2020 model, it will have the 2020 features but still have been built in 2019.

I am convinced now this is the case with your bike, it is NOT a 77RS, but is a 78RS. As I have said, the 77RS was a one year model. In 78, things such as the drum brake and spoked wheels of the 77RS were changed to disc brake and snowflake wheels. At the same time, the mechanical tachometer found in the 77RS was changed over to an electronic tachometer.

The change over from mechanical to electronic tachometer is the reason why you don't have a port in front of the engine for a tachometer cable. There was no mechanical tach in 78.

The more important issue and the one causing you the biggest problem is the incorrect instrument cluster you have. To answer your question, yes, there was an instrument cluster that had a brake level light and an electronic tachometer. This is a 78RS feature and Kurt and I have supplied pictures of the proper cluster for your bike.

After 81, BMW changed things agin by moving the front master cylinder out from under the gas tank and onto the right handle bar. At that time, they eliminated the brake level warning light and the wiring to go with it. The instrument cluster you have is for one of these bikes.

So bottom line, your bike may have been built in 77 but is in fact a 78RS. You have the wrong instrument cluster for the bike. There will be no port in the front of the engine for a tachometer cable as the tachometer for your bike is supposed to be electronic.
The pictures you recently sent gives me a good idea the original wiring is in place. When you install the proper instrument cluster, you very well may solve all your wiring problems. St.
Owner of a 84, R80RT and 78, R100RS

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kingcowie
Posts: 28
Joined: Wed Oct 28, 2020 1:29 pm
Location: Wollongong

Re: 1977 R100RS Instrument Cluster mismatch

Post by kingcowie »

St

Apologies i missed that point about the instrument cluster can be supplied with electronic tacho and a brake light, i thought the photos were of the cluster with mechanical tacho.

Great work and i will start looking for the correct instrument cluster.

I just clocked something also, in that when i bought the bike i noticed that the PO had installed a new rhs controller for the handlebars. I would bet they were trying to run down why the indicator lights don't illuminate on the cluster.

Many Thanks again for your detective work.

Regards
Shane

PS i have now available a redundant instrument cluster with no brake light and electronic tacho
Attachments
IMG_5612.jpeg
Shane
Wollongong, Australia
71 R75/5
64 R50/2 Project
77 R100RS Project

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srankin
Posts: 187
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA

Re: 1977 R100RS Instrument Cluster mismatch

Post by srankin »

Shane, the right hand switch looks to be the proper one for the bike.

I have done business with this company in the UK,https://www.motorworks.co.uk/vlive/Home/index.php

Not sure who you have in AU for used parts, but they may have the cluster you need.

Once you get the correct cluster, I think you will find things may just start working the way they should.

If not, I would go into the head light shell and check the position of the wires for the right hand control switch.

Did you find wire and plugs for the front master cylinder and front brake switch? They should be there unless the PO cut them out with wire cutters.

Yep, you have a redundant cluster for a newer bike. St.
Owner of a 84, R80RT and 78, R100RS

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kingcowie
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Joined: Wed Oct 28, 2020 1:29 pm
Location: Wollongong

Re: 1977 R100RS Instrument Cluster mismatch

Post by kingcowie »

St
Yes i still have the wires for the front and rear mc level switches.

Also i have chased down rhs control wires and they work fine.

Thanks for your hep and i will post my results, once i find one.

Regards S
Shane
Wollongong, Australia
71 R75/5
64 R50/2 Project
77 R100RS Project

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kingcowie
Posts: 28
Joined: Wed Oct 28, 2020 1:29 pm
Location: Wollongong

Re: 1977 R100RS Instrument Cluster mismatch

Post by kingcowie »

Shane
Wollongong, Australia
71 R75/5
64 R50/2 Project
77 R100RS Project

User avatar
srankin
Posts: 187
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA

Re: 1977 R100RS Instrument Cluster mismatch

Post by srankin »

BMW, equals Bite My Wallet, LOL. this looks like the correct part, and it is in darn good shape. From what my Mate in Melbourne tells me, the cost of things in AU is a lot higher than here in the US. Looking at the price being asked, and knowing the cost of stuff in AU. I think the price is reasonable.

One thing you might want to make sure of is that it is from an R100RS. The reason I say this is because of what I mentioned in a previous posting about the speedometer having to match the final drive ratio. The letter and number combination at the bottom of the speedometer (W=691) gives a reference number for the gearing in the speedometer in conjunction with the numbers stamped on the final drive for gear ratio.

I am afraid I don't have a cross reference for metric speedometers, so I can't say for sure the speedometer matches with your final drive. IF the R80 bike AND the 78RS both have the same final drive gear ratio, it would be safe to say this is the correct speedometer.

OKAY, I wrote a lot about the speedometer, despite the speedometer, the cluster itself is correct for your bike. This will I hope, solve the electrical problems. I think it is safe to say the speedometer matches and there will not be a problem there.
If there is, that can be dealt with later and is not a show stopper. St.
Owner of a 84, R80RT and 78, R100RS

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schrader7032
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Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX

Re: 1977 R100RS Instrument Cluster mismatch

Post by schrader7032 »

Snowbum writes about pinions and gear ratios here:

https://bmwmotorcycletech.info/ringgears.htm

The speedo value of 0.691 is the metric equivalent of 1.112 and should be coupled with a final drive of 33/11 so that the speedometer readings are somewhat close to reality.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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kingcowie
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Location: Wollongong

Re: 1977 R100RS Instrument Cluster mismatch

Post by kingcowie »

Alright Warning ahead this may disturb some people.

I have a barn bike that has the wrong instrument cluster as identified earlier. To get a new 2nd hand one from ebay over $1000 AUD ie a 1978 R100RS with brake light and electrical tacho. But i had an idea of how to rewire the unit so as to match the incoming wires. It took quite a bit but i cracked it. I still have an issue of no light lamps for low brake fluid but i have another idea on that.

I have included two drawings the first with how it should be wired up with the plug and instrument cluster matching. The second is what i have the non original newer and easier to get instrument cluster of high beam lamp at bottom and electronic tacho. In summary this combination has two problems no light lamp for brake fluid and secondly the ground from the turn indicator lamp runs to nothing. So simply i got a spade connector and bridged Pin 12 and Pin 11 and this allowed ground for the indicator lamps. All other functions work.

This bike is a stripped down r100rs and my intention for this is to keep it stripped down, improve the brakes, put on a single police seat and ensure it runs well. I am on way.

To address no brake fluid level lamp i may look at handle bar mounted front brakes or a indicator lamp else where.

Thank you for your input it certainly helped.

Happy man.

I will test it further and if no faults i will solder the spade on
Attachments
Layout plug vs cluster newer cluster spade connector.jpg
IMG_5855.JPEG
IMG_5854.JPEG
Layout plug vs cluster original.jpg
Shane
Wollongong, Australia
71 R75/5
64 R50/2 Project
77 R100RS Project

User avatar
srankin
Posts: 187
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA

Re: 1977 R100RS Instrument Cluster mismatch

Post by srankin »

Or, you can just not worry about the brake level light at all.

You may find the cost to switch to a handle bar mounted brake cylinder to be less than the instrument cluster but close.

Happy you got the rest of the lights sorted out. Have a good ride. St.
Owner of a 84, R80RT and 78, R100RS

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