post from racing forum

[Gblake2613]

thought maybe some of you could answer the steering question/maybe brake too...

"I am starting to think about my brake system on my TR3. I want to use a dual circuit and I have been looking at the overhung pedal assemblies offered by Tilton in the Pegasus and Speedway catalogs. Has anyone used one? Which ratio are you using 5.5 or 6.2? Has anyone tried making their own dual m/c bake setup using the original TR pedal box? How difficult was it?

When using a dual circuit, how do you select the size for the m/c bores?

I assume that when you switch to a dual circuit the 5 way with the restrictor on the lower front frame rail is no longer required, is this correct?

On more question for today. What is the correct size splinned coupler for the input to the steering rack? When I miked it, it looked like it would need to be a 36 spline 5/8" diameter. I can not find this size coupler anywhere. Should it be a 9/16"-36 spline? I don't have the original TR couplers (that are no longer available) since this is a TR3 going on a TR4 frame and I did not get a complete steering assembly from my donor frame.

Thanks,

Greg"

 

[Alan_Myers]

Hi,

I think a dual circuit brake system is a very good idea. It's useful for a number of reasons, two being safety and redundancy, which are why dual circuit brakes are found on most (all?) modern cars.

On the race track, however, there is the added benefit that it can be set up to allow some adjustment while driving. It's very handy to be able to tune the brake balance front to rear for changing track conditions, or even to fine tune braking for different parts of the course.

There are two ways to do the adjustment. If using dual MCs, it can be adjusted with a mechanical balance bar. The alternative is to install a proportioning valve in the rear circuit, which reduces the amount of hydraulic pressure going there.

www.revingtontr.com offers a couple different dual MC brake setups for TR2/3 (and TR4). They have pretty much worked out all the details of bore sizes to make for a reasonably balanced system, but don't provide info about what bore sizes they are using. There are two types of setups offered for TR3 and TR4. One is the same way the factory set it up: It uses the early TR3 MC that has both MCs in a single cast unit, splitting the reservoir and using one side for front braking, the other side for rear. This just means adding a MC for the clutch. This arrangement was used on Triumph's factory rally cars, including the TR4s.

The other setup uses three completely separate MCs with remote reservoirs: Two are for the brake system, one for the clutch. It will take some experimentation to arrive at the right size bore, unless someone can provide an answer here. I've not been able to get really good any info on this.

There will be some differences, car to car, depending upon how the rest of the brake system is set up. Things that will effect MC bore requirements include whether using 4-piston calipers or the original 2-piston Girlings, if using race grade brake pads and shoes, what size slave cylinders are used in the rear drums (smaller 5/8" Morgan SCs are often used to increase pressure going to the rear shoes).

Another alternative I'm seriously condidering is simply converting to a TR6 MC on my TR4. This means changing the pedal box to a TR6 version, too, but looks like it might be the easiest approach of all for me. I'm not sure if the same could be done on TR3, though.

The TR6 pedal box mounts quite differently than TR3 or TR4, but since the inner body panels of TR4 through 6 are so similar, I won't need to do very much modification.

The TR6 MC is a single bore, dual circuit unit. So, the only way to make this adjustable is with the proportioning valve.

Neil Revington says the dual circuit setups he offers will increase pedal effort, and sometimes people who install them also opt for a brake servo assist. (A problem I have with that is I'm running Weber sidedraft carbs and a hotter cam, which mean there is no place to pick up vacuum for the servo, and cam timing will likely mean little vacuum available, anyway... The only solutioin I see is to have vacuum provided with an electric pump and stored in a reservoir, as is done on some modern cars, trucks and RVs.)

Sounds like great fun putting that TR3 on a TR4 frame! I plan to build a "Beta", too, some day. I already have the frame and much of the suspension squirreled away for it.

With regard to the steering, why not just track down a TR4 flex fitting? I'm sure you can find one. There always seems to be someone parting out a TR4 or 4A on eBay, for example.

The rubber part of the "knuckle" is widely available and easily replaced. (Actually, TR4 use *two* identical steering flex joints, one down by the R&P, the other up by the firewall where the upper steering shaft attaches.)

I think it *is* 9/16 x 36 spline, but have not actually measured it. I know some folks replace the TR4 steering joints with more solid u-joints of various types, and 9/16 x 36 seems pretty common. however, if your TR4 frame is the earlier type with the solid aluminum steering rack mounts, or if you are retro-fitting solid aluminum steering rack mounts to the later type, you might want those two rubber "knuckles" in the steering column to help reduce harshness a little.

Hope this helps!

/ubbthreads/images/graemlins/cheers.gif
Merry Christmas!

 

[YankeeTR]

In addition to Tilton, I'd talk to ECI brakes in Vernon, CT and Master Power Brakes in North Carolina. All three of these outfits are experts at brakes for hot rods, race cars, etc. They will give you the straight answer you are looking for.

I used to use Neal brand pedals in my circle track cars. They are similar to the Tilton set-up and have a balance bar set-up, too.

Remember, you will have to use a residual pressure valve in both circuits...a 2 lb for discs and a 10lb for drums.

you can finds many parts suppliers at www.roadsters.com