Sportster Build Hampshire
 

hi

Just introducing myself as I am about to start on an E39 Based Sportster build. It is an idea that has been on the back burner for a while but has suddenly kicked off. Sort of now or never, time to put my money where my mouth is. So I now have a donor car on my drive and an order form in with Marlin.

Sure I will have plenty of questions and thank you in advance for your answers.

My first one might seem a bit of a leap but what are current recommendations on brake servos. I know there were concerns on Metro unit supplied by Marlin and there is a thread from a couple of years ago on a U.S. unit. What are people currently doing?

I'd highly recommend one of the US sourced dual diaphragm servos. I don't know if Mike is still doing his kits - a bunch of us did a group buy after we found them online... Mike kindly handled all the shipping and distribution, as well as getting adaptors laser cut.

Hi Chris, welcome!

The dual diaphragm brake servo is vastly better than the metro servo. Pedal feel and power gives you much more confidence.

The Metro servo is pretty useless. The boost ratio is nothing like the original BMW one and as a consequence you will find it difficult to stop as quickly as most modern cars - unless you are built like the hulk. I would consider the upgrade to the dual diaphram servo almost essential.

I have a couple of new old stock Metro servos as testiment!

Cheers Robin

Hi Chris

I would say using a Metro servo is bordering on dangerous - particularly if you fit disc brakes at the rear: they require more pressure to make them work effectively, which the Metro servo set up is incapable of generating.

A quip by Patrick about driving his Sportster with a Metro servo has stayed with me throughout - "Trying to brake hard behind a modern tin-top with a servo bigger than its engine can be scary!" - summed it up perfectly!

I do not have any dual servos left, but they are easy enough to order from US - but be aware you will have to pay import duty (5%) and VAT (20%) on the total purchase price.

I have some surplus adaptor plates if you go down this route - and can give you the part numbers of the Dual Servo and appropriate Sierra Brake Master Cylinder - if you are interested, ping me a PM.

Mike

Another e39 builder!! There are a few things you might run into issues with! I am currently the furthest ahead with the e39 build to date! ( last time I checked in I was beating marlin!!) give me a pm and maybe we could have a chat and I can point out potential problems/ some build advice!