Lotus Elan

Replacing master cylinder on Plus 2

PostPost by: stugilmour » Sun Feb 08, 2009 5:41 pm

I want to remove both brake boosters on my Federal dual brake system Plus 2. I wish to replace the master cylinder with a smaller bore unit to retain reasonable brake feel and pedal effort without the boosters. I have read over info in the archives, but remain confused on a few points. Most of the posts are several years old, so I expect folks have better experience with their set-ups and parts availability options may have changed? Sorry for the length of the post, but trying to clarify this part clearly in my own mind. Grateful for any corrections, omissions, etc.

1. What bore tandem master cylinder would be appropriate for this application? I read that 5/8" (0.625") is the setup on the two seater Elan, but I think this is for the single master setup, not the tandem? Perhaps this is more appropriate for the smaller two seater stock rotor size than for conversions to Plus 2 brakes?

2. Alternatively, appears some have used 7/10" (0.700") bore. The Dave Bean catalog calls up this size as p/n 036J_0628 for use in the S3/S4 & Sprint, Europa S2. Not sure if this is just a matter of availability, or a preferable size to the 0.625"? Perhaps the 0.700" is designed for use with boosters and the 0.625 is preferable for no booster setup? The above p/n appears to have the same casting number, bore size, rebuilt kit, flange, etc. as the call-up for Cortina GT 10/66 to 9/67 (non-servo) p/n 028J_0681. Is there a Girling p/n call-up that would more accurately nail down this apparently common part?

3. Are direct replacement Girling tandem master cylinders available? I have a few leads on some suppliers from the archive remarks, but without the part number or original application details for the above sizes, I am not sure what to ask for. As I will have to order from a supplier outside of Canada, it is very helpful if I can be completely specific on the part number required, as it is probably not practical to return it if incorrect.

4. I checked out the Tilton site as this manufacturer was mentioned in the archives. Not sure if folks that have used the Tilton installed single master as per British/Euro setup, or if they offer a tandem setup. Is the Model 74 Tilton an appropriate tandem cylinder that would offer direct bolt in? I think it is a tandem cylinder from the detail drawing (dual outlet ports), but I am not sure.

5. The Tilton 74 cylinder appears to have dual AN3 output ports. Is this the correct size for the Lotus application? Does one use a bubble flare for connection?

6. Re-sleeving of the existing M/C component was mentioned as an alternative, primarily at White Post Restorations. Any follow-up info from folks that have used this alternative? I am not adverse to the re-sleeving. However, I would prefer to just get a new replacement part (if available) in case things don't work out with the modified setup; this would allow me to re-install the stock system with the existing parts.

7. Would I retain the pressure differential valve (Lotus p/n 50_J_6053) in the revised setup?
Pedal box 1.jpg and
Pedal Box 2.jpg and
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PostPost by: denicholls2 » Mon Feb 09, 2009 5:33 pm

M/C bore size differs primarily for the boosted/unboosted variants. The larger bore will give you less pedal travel and require higher effort, and was intended for boosted applications (some claim it's OK for unboosted too).

The smaller bore will give you more pedal travel and require lower effort, and was to my knowledge the original size for all unboosted M/C's.

To add to the muddle, there are also near-fit alternatives from both Nissan and SAAB applications, not sure the bore size, at least for the Europa.

Some folks use two Tilton singles with a balance bar to achieve a dual setup that offers adjustable bias. Some engineering required.

I believe that the pressure valve is of a particular bore size and cannot be swapped between two sizes.

My Europa's MC is a White Post restoration and works quite nicely, but does have a very stiff pedal (making me suspect it's a larger than original bore, but I could just be spoiled on modern booster systems.) It does the job in the end. The PO had the work done and I understand it took more than one try to get right. I've also seen other posts regarding this vendor that suggest mixed results. You might want to do your own research on the Europa Knowledgebase by searching White Post for postings.

The SAAB and Nissan alternatives have the advantage of being more modern, hence easier to find seals, etc. I understand both to be bolt-in, with the possible exception of what side the brake lines enter the cylinder (requiring minor re-plumbing). Again, this relates to Europa applications and some research to confirm my memory is advised.

I also believe that a Girling unit is still available (or was recently, at any rate) with the swapped-side issue. Vendors wanted gold-like prices for them, however.
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PostPost by: CBUEB1771 » Mon Feb 09, 2009 8:38 pm

The dual circuit master cylinder used on the Federal +2 has 0.87" bore and the servos have maximum force multiplication of just under 3:1. Going to a 0.63" bore master cylinder give only a 1.95:1 line pressure increase compared to the 0.87" bore master. Hence your pedal effort will increase by a good 50% by removing the servo and going to the smaller master, all other things equal. I did this a long time ago and was very unhappy with the result. I went back to the servo. AP Racing now has master cylinders down to 14 mm bore and higher coefficient pads have come a long way. I suppose it is worth trying again but I would not make the change without reinforcing the pedal mount mouning area. I have attached my spreadsheet for checking line pressure ratio when swapping for one master cylinder bore to another. Keep in mind that pedal excursion also changes and that would be a real concern with the smallest master cylinders.
AP Racing Master Cylinder Comparison.xls
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