Help with Brake Upgrade, Rear Vented rotors Options

[Racing916]

hello,

I am currently upgrading my 914-6 to vented rotors. My hope was to take a Front "M" caliper and mount it on the rear using the 911 (69-83 Rear) vented rotors. I mock fitted the caliper and rotor and it looks like I need to place a small spacer between the caliper and the mount on the rear trailing arm (not a problem) The issue is the 911 rotors get larger as you get closer to the brake surface and rub on the "M" Calipers. Has anyone else had this issue? I realize they are larger for the parking brake, is there a parking brake delete option? 914-6GT vented rotors, suppliers?

Thanks for any help, back to the drawing board!

Steve

[Jeffs9146]

I think it is easier to put the spacers between the two halfs of the original 914-6 caliper and retain the e-brakes! (IMG:style_emoticons/default/confused24.gif) Someone told me you can mill the rotor diamiter????

[Van914]

Steve,
That is the set up I am running on my car. I bought the rear rotors from Steve at Air Cooled Racing in PA.. I used harden washers for the spacers and longer bolts from NAPA. Works great for me.
Van914

[Eric_Shea]

48mm pistons on the rear?

OK... I give up. (IMG:style_emoticons/default/wacko.gif)

Hey, send me your 914-6 calipers and I'll give you a freshly rebuilt pair of M-Calipers for the backs. (IMG:style_emoticons/default/wink.gif)

[Racing916]

Thanks for the reply Jeff. I would think shrinking this raised area would weaken the integrity of the rotor (see attached picture)? My car is mostly a track car with a cage, so e-brake is not to important. Also I want to use the M Calipers because I can than match the racing brake pad compound of the front calipers wide "A". I am using Hawk Blues, and currently Hawk does not make a pad for the rear 914-4 calipers that I know of.

[Racing916]

Steve,
That is the set up I am running on my car. I bought the rear rotors from Steve at Air Cooled Racing in PA.. I used harden washers for the spacers and longer bolts from NAPA. Works great for me.
Van914

Hi Van,

where id you get the vented rotors for your car?

Thanks
Steve

[Racing916]

48mm pistons on the rear?

OK... I give up. (IMG:style_emoticons/default/wacko.gif)

Hey, send me your 914-6 calipers and I'll give you a freshly rebuilt pair of M-Calipers for the backs. (IMG:style_emoticons/default/wink.gif)

Hi Eric,

I left you a confusing message to your business number. I just rebuilt the M calipers and thought you might have a rotor that would work.

steve

[Eric_Shea]

Use "Rear" M-Calipers with the #31 pad (Hawk makes those for the front and rear of a 71 911 as an example). You will have a bolt on solution that will not "totally" ruin your brake bias (it will be the same bias the car you got the front calipers off had). You'll need a 5mm spacer for under the ears.

This is what ever 914 racing in the HSR 2.0 liter challenge uses. Frank Beck goes faster than anyone I know in a 914. It works well and prevents them from visiting the wall backward.

[Racing916]

Use "Rear" M-Calipers with the #31 pad (Hawk makes those for the front and rear of a 71 911 as an example). You will have a bolt on solution that will not "totally" ruin your brake bias (it will be the same bias the car you got the front calipers off had). You'll need a 5mm spacer for under the ears.

This is what ever 914 racing in the HRS 2.0 liter challenge uses. Frank Beck goes faster than anyone I know in a 914. It works well and prevents them from visiting the wall backward.

Eric,

I have a J-west brake bias valve, so I will not be using the stock proportioning valve. will a 5 mm spacer help my caliper from hitting the raised part of the rotor made for the parking brake?

[davep]

What M calipers are you wanting to use on the rear? 48mm 911 front, 42mm 914/4 front, or 42mm 911SC rear, or 38mm 911 rear?
All take the M pads, but there are big differences in the size of the caliper.
I would not use the 48mm fronts, they are just too large. I don't know of any 911 or 944 variant that uses such a large piston area on the rear of the car; it just unbalances the braking so much.
The 914/6GT rear rotor is a perfect fit for the rear when a 20mm thick rotor is called for.

[Racing916]

What M calipers are you wanting to use on the rear? 48mm 911 front, 42mm 914/4 front, or 42mm 911SC rear, or 38mm 911 rear?
All take the M pads, but there are big differences in the size of the caliper.
I would not use the 48mm fronts, they are just too large. I don't know of any 911 or 944 variant that uses such a large piston area on the rear of the car; it just unbalances the braking so much.
The 914/6GT rear rotor is a perfect fit for the rear when a 20mm thick rotor is called for.

Dave,

The calipers are in my dads garage but they were fronts of a early 911, I am thinking they are a 48mm but I could be wrong. Is the 48 MM to big if I am using Wide "A" calipers up front with a proportiong valve to adjust? I think I might have jumped in the deep end without doing enough research, I will measure the calipers tomorrow and see.

Thanks
Steve

[Eric_Shea]

I have a J-west brake bias valve, so I will not be using the stock proportioning valve. will a 5 mm spacer help my caliper from hitting the raised part of the rotor made for the parking brake?

No. It's not made for that application.

As Dave says..., all of those calipers take the same pad. The early 914 front is the same casting as the 911 rear.

So... the caliper you want to use that won't fit, has the same pad size as the one you should use and will fit. The one you should use has a proper 38mm piston and will get you closer to perfect brake bias.

You can still use the fancy biasing valve if you'd like. You'll just have the proper caliper for the job. All good, no downside.

I've led the horse to the water. (IMG:style_emoticons/default/biggrin.gif)

[Racing916]

Eric,

Sorry I read your reply fast and did not see that you called for rear "m" calipers. ahhh... what to do??

Eric do you want to trade a set of rear M calipers for my rebuilt front M calipers (IMG:style_emoticons/default/smile.gif) (IMG:style_emoticons/default/tongue.gif)

Thanks for all the replys

[Eric_Shea]

what to do??

Install rear M-Calipers and fret no more, especially if you want not for a parking brake. Best possible caliper for the job, it fits, pads are plentiful, they're a dime a dozen and you can now rest peacefully. (IMG:style_emoticons/default/lol3.gif)

[Eric_Shea]

Eric do you want to trade a set of rear M calipers for my rebuilt front M calipers

Like "other" 911 items, we use them as donors to supply 914-6 calipers with GT spacers. None in stock. (IMG:style_emoticons/default/wink.gif)

[brant]

I've had vented rear rotors on a 914....
absolute waste of time
but the way to do it is to take a set of SC rotors, turn them down, and then vent the caliper...


when I built my 2nd 914 race car I left them off!
solid rear rotors are more than adequate!

have you ever overheated your rear brakes?
neither has anyone else...
absolutely unnecessary..

but hey if you want to waste 20lbs or rotational mass fine with me
makes it easier for me to pass you!

I'm at 1837lbs wet with an all metal -6 racer now...
not something you can achieve with vented rear rotors!
(I'll be taking another 20lbs off this winter, by changing out to a mag engine case)

b

[J P Stein]

I ran SC rears with S fronts. The stock 4 pooper rears were just along for the ride with the S fronts....with the adjustable porp valve wide open.....after 5=6 months of use, the machinihg marks were still on the the -6 rotors.
These actually do some work. Bour a 1/8" (washers) spacers between the caliper & trailing arm mounting area.

Out brake me if ya can in that heavyweight, Brant. (IMG:style_emoticons/default/biggrin.gif)

[brant]

I think I'm a bit outgunned JP!

at one of the races this summer
they had an evening event...
after many beers.... they had all of the drivers stand on a scale and fill sand bags until each hit 250#

then 4 equal go karts were lined up on the 2.5ish mile track
each heat of equal weight'd drivers went out side by side
the winner of the heat progressed to the semi-finals and beyond...

I didn't win anything
but it sure was fun being dead equal to all of your competitors in weight and power...

I'm thinking that I'd need to shed more than a few pounds to run with JP!

hope your doing well
brant

[Racing916]

I've had vented rear rotors on a 914....
absolute waste of time
but the way to do it is to take a set of SC rotors, turn them down, and then vent the caliper...


when I built my 2nd 914 race car I left them off!
solid rear rotors are more than adequate!

have you ever overheated your rear brakes?
neither has anyone else...
absolutely unnecessary..

but hey if you want to waste 20lbs or rotational mass fine with me
makes it easier for me to pass you!

I'm at 1837lbs wet with an all metal -6 racer now...
not something you can achieve with vented rear rotors!
(I'll be taking another 20lbs off this winter, by changing out to a mag engine case)

b

Brant,

My car is pretty well gutted. The car probably weighs a little under 2000 lbs. I have a 2.7 six that has been heavily modified and at Watkins Glen on the high speed sections the car seems to not have enough brake to stop the car without braking earlier than some of the later cars without running into them. I have had somewhat of a mushy pedal, we have added cooling, bled the brakes a bunch, new master cylinder (19mm), changed the proportioning valve that we thought was the problem. We also have tried several different brake fluids (racing) and the problem seems to come back year after year. I pump the pedal on the straights to make sure something is there because in the past it wasn't. Also, i have put a temperature gauge on the front and rear rotors and the rears are much. much hotter than the front. I get that this could be because they were not vented like the front, but thought the upgrade to vented in the back and a bigger master cylinder, and rear piston might help the problem.

steve

[Eric_Shea]

absolute waste of time

Agree... that said, there's only about 4.2lbs. difference.

Vented = 13.6lbs each
Solid = 11.5lbs each