40mm brake upgrade

[ACR steve]

I just had the 40mm calipers put on the rear of my acr.The rears now lock up much faster then I thought they would.I know this means they are now working but I am just wondering what others have thought after they had this done.My rears now lock up first ,I tried trail braking and nothing weird but I had thought they should be more even front to rear(I also did steal braided lines and Motul 4)

[AG98RT10]

Have you checked to see if your proportioning valve is in place? My experience with the 40's is that with stock valve in place, you should still be able to modulate braking fairly well so that rears don't lock first.

Not sure why your rears are locking first, unless you or someone else removed that valve.

[ACR steve]

I didnt change anything but the rear calipers.So if the valve was there it still is.I can modulate the brakes but under thresh hold braking they want to lock first.

[Tom, F&L GoR]

Other vehicle things:
More weight in front/less in rear than usual? (is rear light?)
Same tire compounds front and rear? (are fronts stickier?)
Same brake pads (new?) front and rear? (non OEM pads that heat up more slowly?)
Same shock settings front and rear? (loading the tires at different rates?)
Is there a chance the proportioning valve is disabled? (It's a few minutes to look and bleeding one rear brake)

You've got a well tuned car if you haven't commented that the right front behaves different from the left front. The only other report to date close to rear lockup was someone with race rubber, lots of front weight shift, open runway at an airport, spent all day threshhold braking, and saw it on video.

[ACR steve]

Tom we didnt change anything but the brake lines and your rears and the dot 4 fluid.....I will call you tomorrow

[beckertb]

I just installed the 40 mm rears as well. My findings are the same, though I have upgraded to the Brembo BBK on the front. Prior to the rear caliper swap, the fronts locked very prematurely, not it is just the opposite........my rears lock prematurely. I have the stock proportioning valve in place. When I figure it out, I'll let you know.

Best regards,

Ben

[PhoenixGTS]

I have had my 40mm calipers from Tom on for quite awhile now. With my taller 19" rear tires, even with my proportioning valve seal removed the front locks first (passenger front before the driver's). Best mod I have done to my car so far. I thought it was plain dangerous without it. Next step is to make a spring spacer for the drooping driver's rear and see if I can get that passenger front tire hooked up a bit better.

[Jack B]

Tom:

what did you mean ab out bleeding one rear brake?

[PhoenixGTS]

Tom:

what did you mean ab out bleeding one rear brake?

To inspect the proportioning valve you have to open the rear half the system which then must be bled through at least one rear brake to make sure no air entered when you had the prop valve apart.

[Jack B]

Phoenix:

If you had air in the rear, wouldn't the rears be less likely to lock up first? It sounded as though Tom was testing the prop valve.

[ACR steve]

Beck,I will be talking to Tom this afternoon to go over how the installation was done and I will let you know if he has any theory on why we are having this problem.

[PhoenixGTS]

Phoenix:

If you had air in the rear, wouldn't the rears be less likely to lock up first? It sounded as though Tom was testing the prop valve.

I believe Tom is asking that he check and see if a previous owner removed either the spring or seal from the prop valve. In order to make this inspection, the rear of the system has to be opened and therefore bled afterward. I don't believe he is saying needing to bleed the rears would contribute to the complaint.

[ACR steve]

Ron,sorry I erased your PM before I could respond (to fast on the trigger) but I spoke to Tom today and he is a great guy and we are setting up a time to meet and try to figure out why mine is locking up.PM me and I will keep you posted. I will say however that Tom really stands behind his product.Its a nice thing to see.

[Ron]

No problem Steve. Was just wondering what brake pads and tires you had on your car.

Thanks

p.s. I know Tom well and there is no better.

[ACR steve]

Ron,all stock,3700 miles