Keep the ACR or buy a ACR X

[MBPERF]

This conversation came to mind this past Saturday evening...

I was testing my new ACRX at Road Atlanta this weekend. Brad Daugherty, former Tar Heel and Cleveland Cavalier was there. He's a seven foot tall racing enthusiast. Loves Richard Petty, that's why he wore #43 when he played ball.

So I asked him if he could fit in an ACRX. He said, "No wa. My wife has a Viper and I can't get in it." My idea was to buy another ACRX and plug him into it as my "celebrity" driver. After he said that I thought of your comment.

(I am 5' 10" and 180, so I can fit fairly well.)

So David how did your initial testing go with the X ?

 

[MBPERF]

Mine is exactly the same way dont feel like anti lock but its from a the hardest braking zone. Very hard pedel then if you kinda repress it goes to normal. Maybe a new thread on this as we are hi jacking mp's thread.

No worries guys ..... I have been reading the brake issues here as I too had this ( or something similar) happen when at VIR . About three times over the entire weekend where I would be coming down the front straight heading into T1 I would hit the brakes hard and everything was great then the pedal would go down about another 1" or so part way through the braking process. Still had brakes but very unnerving when that pedal moves downward more than expected. Once I was scanning the outfield past turn 1 thinking I was going to do a little off roading in the X .

 

[David Pintaric]

So David how did your initial testing go with the X ?

Car ran fine, driver needs work.

Road Atlanta is a track I've never felt comfortable at in the past, and this past weekend was no different. I've reviewed my in-car and compared to a few other drivers and I THINK I know what I need to do to improve...maybe.

 

[bluesrt]

No worries guys ..... I have been reading the brake issues here as I too had this ( or something similar) happen when at VIR . About three times over the entire weekend where I would be coming down the front straight heading into T1 I would hit the brakes hard and everything was great then the pedal would go down about another 1" or so part way through the braking process. Still had brakes but very unnerving when that pedal moves downward more than expected. Once I was scanning the outfield past turn 1 thinking I was going to do a little off roading in the X .

maybe dum question but i guess you have a good new fluid in there? brake fade can happen quicker with old fluid,even if it has a few hours on the fluid..

 

[ViperGeorge]

I did a vacuum check on the brake booster, and the check valve, both are fine i went ahead and ordered a new vacuum line, and check valve, they was under 30 dollars shipped. Tom sessions also says if the anti locks brakes dont finish there cycle or you let off once you kick them in it takes a second for the antilock to figure out what is going on resulting in a stiff pedal, Seems very likely. One reason i ordered a vacuum hose also is that it lays across the valve cover and gets quite hot, Could be getting hot and collapsing or kinking?

The back straight at VIR is, as you know, very long. Sustained wide open throttle may be the culprit for the brake issue. Under wide open throttle the engine is producing very little if any vacuum. Even the smallest bleed down of vacuum in the booster during the long run down the straight could mean that by the time you go to the brakes at the end of the straight there is too little vacuum reserve left in the booster to give you full power braking. The booster will operate again shortly because once you lift off the throttle the engine vacuum returns and then supplies the booster with vacuum giving you back your power brakes.

 

[ViperGeorge]

One more thing, the problem with vacuum boost is more acute on boosted cars and some people will put an electric vacuum motor on the car to supply continuous vacuum to the booster regardless of engine vacuum. Did this on my 65 supercharged Mustang. I realize the ACR-X is not supercharged but a vacuum motor would still apply.

 

[lmcgrew79]

Seems like a good point gbatejan. I guess everything is fine, just no power braking for a short time. MB if your pedal was dropping, that is more scary, maybe boiled fluid, over heated, small amount of air? What type of fluid you running? I use castrol srf and have never got a soft pedal yet. I also replaced all my bleeders with speed bleeders as i noticed a lil bit of dirt mixed with fluid on a 2 calipers last season, only did it while on track. The torque specs for bleeders are only 10 ft lbs or 120 in lbs, i think most of these are over tighened and mess up the seat. Just something to keep an eye on.

 

[ViperGeorge]

Seems like a good point gbatejan. I guess everything is fine, just no power braking for a short time. MB if your pedal was dropping, that is more scary, maybe boiled fluid, over heated, small amount of air? What type of fluid you running? I use castrol srf and have never got a soft pedal yet. I also replaced all my bleeders with speed bleeders as i noticed a lil bit of dirt mixed with fluid on a 2 calipers last season, only did it while on track. The torque specs for bleeders are only 10 ft lbs or 120 in lbs, i think most of these are over tighened and mess up the seat. Just something to keep an eye on.

I believe the reason his pedal was dropping was that the booster came back on-line when the vacuum returned. The first push on the brakes would be like pushing on the brakes of a car with non-power brakes. Actually it would be harder since the brake pedal of a car with manual brakes has more mechanical leverage than the same car with power brakes. On vintage cars where there were options for manual or power brakes the pedal was different in that the pivot point is different for manual braked cars so as to increase the mechanical leverage. If you've ever gotten in your Viper after it has sat for a couple of months and press on the brake pedal before starting the engine you'll see how much harder it is to push the pedal in. Once there is vacuum in the booster the pedal behaves normally and the pedal goes down because there is now a power assist.

 

[MBPERF]

Car ran fine, driver needs work.

Road Atlanta is a track I've never felt comfortable at in the past, and this past weekend was no different. I've reviewed my in-car and compared to a few other drivers and I THINK I know what I need to do to improve...maybe.

Well all the best...... the in car camera and data is really cool. I just used mine for the first time at VIR. After looking this over it helps you see where there is still lots of opportunity to improve ( for me at least) . MB

 

[MBPERF]

The back straight at VIR is, as you know, very long. Sustained wide open throttle may be the culprit for the brake issue. Under wide open throttle the engine is producing very little if any vacuum. Even the smallest bleed down of vacuum in the booster during the long run down the straight could mean that by the time you go to the brakes at the end of the straight there is too little vacuum reserve left in the booster to give you full power braking. The booster will operate again shortly because once you lift off the throttle the engine vacuum returns and then supplies the booster with vacuum giving you back your power brakes.

I would say this is exactly what is happening. The brakes are right back to working well likely as soon as there is enough vacuum to operate. Thanks for the heads up.
MB