Getting rid of 40mm Rear Calipers

[Tom, F&L GoR]

I have a few 40mm calipers available and looking forward to getting rid of them!

What I mean is that I now "own" a baker's dozen of the rear calipers which should make the turn-around effort more efficient. My goal is to have 5-6 pair at the machine shop while I have 5-6 pair "on the shelf" and for sale. The shop does these as fill-in work, so their turn-around time can be 2 days or two weeks, which sometimes is a little hangup. Once I sell these two pair, I can put this pattern in place.

When it happens (6 in, 6 out), Mr. Herbert, I'll put up a banner ad, be a real site advertiser, and hopefully avoid ever getting hammered for selling something in the discussion forums! Or I can resort to other tactics like posting Jack B happy with his 40mm calipers! (which he is, and is put here with his permission.)

In the meantime, it's still word of mouth. A pair is $630 plus your cores; I send them, you swap them ("seamless exchange") and send me your old ones back.

If you have questions about what these larger rear brakes are and what they do, I can send you a one page summary. I have rebuild instructions (if you want to know how the parking brake works inside the hydraulic piston) I'd be happy to send you, too. If you've seen board comments and want to discuss them, let me know.

Question: since Dodge doesn't sell small parts for these brakes, you're forced to buy a whole caliper just to repair a torn dust boot. Any interest out there in an "OEM" refresh service that maintains the 36mm piston but replaces the consumable items? Please email or PM me if so.

[PhoenixGTS]

For any noobs out there that are not familiar with Tom's 40mm rear caliper upgrade, it is a must have item on pre-ABS cars. I personally think the pre-ABS cars are dangerous without it.

[Chuck 98 RT/10]

I wouldn't be too worried about the banner stuff just yet. As far as I know, the rear brake caliper upgrade is your only product and I'm betting it is relatively low volume.

However, if you ever show up with a Comp Coupe I will start getting suspicious.

[slaughterj]

Tom, what kind of turn-around do you want/expect for the swap? I don't want to order too far in advance of getting around to doing it, and having you left hanging...

[Chuck 98 RT/10]

Knowing you Slaughter, better wait until the Gen IV comes out.

[Tom, F&L GoR]

Chuck, you're a pisser. There are ~15,000 Vipers out there and when this started, I would have bet these brakes would only be of interest to the 1% that actually track their car. And you, of course. But I've sold more to guys that had a deer jump in front of them, slid into the back of a Camry on a wet road, found the median when someone cut them off, etc, etc, so the market is a little bigger than I thought. Done OK with just word of mouth, satisfied my need to break even for the first few sets long ago, and could do better if I could manage my inventory (meaning: have some inventory!) If the 6+6 schedule works, I don't mind a little advertising; right now I won't because I wouldn't be able to guarantee that I always had one ready to go.

Geek of the Realm Solutions has the 40mm caliper resize, a 38mm resize undergoing secret testing for a special application in a Viper market that already enjoys enhanced braking, and we can rebuild OEM calipers if you don't want to spend $450 for a new one. (One, not pair!) In fact, if someone's old calipers do need some repair, you're hosed, since the service manual doesn't show how. It's actually less expense to buy the resized, rebuilt calipers than buy OEM calipers.

We also have the nifty "Quick Clutch" kit that quickens the clutch pedal action in Gen 1 cars, like Sean's part for Gen 2 cars. ruckdr likes it!

There's a third and fourth product coming soon and more ideas that are worth while. All are the "gee I wish the car had come that way" kind of stuff.

Jon, I owe you a favor anyway, so give me an expected date you would want to do the swap and I'll make sure you have them. Since I know where all the calipers are, I can arrange that easily rather than have you sit on a pair.

[jcaspar1]

Tom,
Tell me that the special application for the 38mm calipers if for use with front StopTech owners who want a bit more rear bias!

[Tom, F&L GoR]

Jeff, you got it. Interested?

Someone on the board, who described himself as an honest man, will tell us all how it works out, hopefully having a report by the end of the month.

See, Chuck, another product demand explosion! PM me if you need a company prospectus.

[Chuck 98 RT/10]

No track time until end of April now Tom. Viper Days Sebring.

[Tom, F&L GoR]

There go your stock options.

[carguy07]

Tom, what is the advantage of going to the 40mm caliper over just using an adjustable proportioning valve with the stock ones?

[Tom, F&L GoR]

carguy07, that would be going the wrong way! "IF" the rear calipers were large capacity, you could tune the rear braking using an adjustable proportioning valve to reduce the rear brake line pressure. This assumes the rear brake is a little too large to start with, for instance, having a four-piston caliper on the rear.

Unfortunately non-ABS Viper single piston rear calipers were derived from a Renault Alliance / Eagle Premier (pictures here) and this same generic caliper is now also used on the new Lotus Elise. All of these obviously weigh a little less than a Viper, and the result is that for the Viper, they are too small. You need to increase the brake capacity in the rear to get all four tires to contribute their maximum. Therefore, resizing the OEM 36mm piston to 40mm, although numerically slight, significantly increases the brake clamping force of the rears and produces a very nice balance of front to rear braking.

It's an alternative to paying a lot more for four-piston calipers on the rear (and needing to install an adjustable proportioning valve and cut off the OEM mounting arms to do it) and since it's truly the OEM part, you don't need different brake pads, keep same brake lines, looks completely stock, no clearance problem under 17" or 18", uses OEM rotors, and is a swap in & out job.

[slaughterj]

Jon, I owe you a favor anyway, so give me an expected date you would want to do the swap and I'll make sure you have them. Since I know where all the calipers are, I can arrange that easily rather than have you sit on a pair.

I'm probably about 3 months out, so I'll be in touch.

BTW, what's the ramifications of using your calipers with a removed proportioning valve?

[slaughterj]

Knowing you Slaughter, better wait until the Gen IV comes out.

Wouldn't need them on a Gen IV.

[Viper Fever]

Tom e-mailed you the other day would like to do the exchange I have a 97 gts let me know how to get the ball
rolling.Thanks Carl

[Chuck 98 RT/10]

I'm probably about 3 months out, so I'll be in touch.

Three months? Aren't you going to be a little busy around then?

[carguy07]

Thanks, Tom. I was never really sure why you guys were upgrading the calipers.
Do you need to remove the stock proportioning valve spring on a bone stock car or just swap out the calipers?

[Tom, F&L GoR]

Jon, Keith-
Proportioning valve: OEM installed mechanical pressure regulator required to meet federal regulations. Intention is to limit rear braking capacity under high brake line pressure (i.e. heavy braking) so the rears don't lock up as the weight pitches forward and off the rear wheels. In a Viper, it's useless, as the the rears are too small to lock up. Many owners have already disabled the proportioning valve and (with OEM rear calipers) still can't lock the rears first.

Notice it's "disabled" and not "removed." You still need the piece of plumbing there to connect the master cylinder to the brakes. There was a little debate when this "mod" first showed up, but looking at the proportioning valve cutaway drawing in the service manual will show that removing the cup seal does not connect the front and rear systems, so the safety feature of the dual braking system is left intact.

A 40mm caliper in the rear increases the braking capability of the rears and therefore puts the point of all four tires locking up closer together (i.e. flat spotting the fronts becomes hard or impossible to do instead of easy to do.) Now the system is much closer to each wheel doing the appropriate amount of braking.

When the rear wheels actually do some braking, the "feel" while braking in turns that you've gotten used to will change a little. The rear tires have to now do both cornering and braking work, so the net effect is that the car will feel like it's rotating a little more than before. If you autocross or road race you'll appreciate this. But I like to point it out and explain it, then say to you to start with just the caliper swap, see how you like it, and if you want a little more rear braking, remove the cup seal of the proportioning valve to disable it. It's something you can easily put back if you don't like it; changing to 40mm rear calipers is like changing the channel, and the proportioning valve change is more of a fine tuning to driver preference.

From comments I've gotten, many with the 40mm rears do disable the proportioning valve, myself included, and they range from frequent track attendees to all street use. Obviously that leaves the other half that didn't disable it also doing track and street use... If I had to put a percentage on it, of the hundreds of calipers I've sold ( <-- notice, Chuck? I'll be by in the CC soon.) about 60% probably remove it.

Carl, sent you email. Thanks.

[ViperRay]

I removed my prop valve with Tom's 40 mm rears and like it. I use the car almost exclusively for the track now.
No premature rear wheel lockup for me.

Whether you lock rears first or not can depend in part on other mods (tires, suspension, aero etc.).

You might want to check it out first with prop valve intact.

[slaughterj]

I removed my prop valve with Tom's 40 mm rears and like it. I use the car almost exclusively for the track now.
No premature rear wheel lockup for me.

Whether you lock rears first or not can depend in part on other mods (tires, suspension, aero etc.).

You might want to check it out first with prop valve intact.

Already disabled, so...

If I stick with stock tires, I should be fine?

[99 R/T 10]

Already disabled, so...

If I stick with stock tires, I should be fine?

No, now go to JonA's house and get your brakes done in time for the race....................

[ViperRay]

You'll want to test drive the setup in a safe environment if possible (track?).

Do you have the piece that was removed from the prop valve in case you need to reduce the pressure to the rear calipers?

Since it's already out, I'd try it first that way and reassemble the valve if needed.

[slaughterj]

Thanks!

And Mike, why should I got to JonAzzhole's house? LOL