More about rear brakes!

[bobl]

I posted this on the other forum but wanted to post it here also. To me, it was an eye opening discovery and I've never seen it discussed in this context before.

I have a bit of a different slant on the braking story. As many on here do, I have the Cobra 11.65 rear brakes and single piston front brakes with Whitby power brakes, HPS pad on front and HP+ on the rear. After getting the car running I went through the pad bedding procedures and thought the car stopped very well. So, last week I start reading these brake performance threads and it got me to thinking. I went out and showered down on the brakes and sure enough the front wheels locked easily. No way could I lock the rears. This is where it gets interesting. After a few hard stops I put a temp gauge on the rotors. The rears were 100 degrees, front 350 or so. Obviously the rear brakes were doing nothing. I put the car on jack stands. Idling in first gear I slammed on the brakes as hard as possible. It barely lugged the engine down, much less kill it! The rear brakes were doing absolutely nothing! I have a proportioning valve on the rear brakes, turned all the way down. I thought this may have been causing a problem so I took it off. Nope, same thing. Next I put it on the front brakes and turned it all the way up. Same thing. It was at this point the light bulb went off. It appears when bedding in the brakes the fronts grabbed so quickly the rears never even actuated. They were not bedded in at all! So, with the proportioning valve (on the front) turned all the way up I went for a drive. At first it would barely stop. I then went through some high speed stops and it started getting a lot better. I read the temps again and the rears were up to 250 and the fronts at 350. I put it back on the jack stands. This time it took very little pedal pressure to kill the engine while idling in first gear. What an amazing improvement. I then turned the proportioning valve back down and it stops great. I’m betting a lot of folks have had this same problem when thinking the rear brakes were really bad. Hope this information helps others.

Bob

[srobinsonx2]

Thanks Bob. It is on my list to perform my brake tuning. I have the big brake set up from Gordon Levy. The fronts rotors are 13" and the backs are 12" (I think). Maybe Gordon can verify. I have the standard wilwood pads that came with my set up. I will use your temp gun idea to make sure I go through the bedding process. It may also help with tuning. That temp idea is genius. Thanks.

[CraigS]

Although I haven't taken temps I have noticed the same thing. Basically new pads take a while to start to work. On occasion I have driven maybe 1/2 mile at a time w/ my right foot on the gas to maintain speed and my left foot lightly applying the brakes. I follow that by at least a mile of no braking to get temps back to normal.

[initiator]

Although I haven't taken temps I have noticed the same thing. Basically new pads take a while to start to work. On occasion I have driven maybe 1/2 mile at a time w/ my right foot on the gas to maintain speed and my left foot lightly applying the brakes. I follow that by at least a mile of no braking to get temps back to normal.

CraigS - you do this after a normal bedding process or instead of?

[CraigS]

CraigS - you do this after a normal bedding process or instead of?

I did it as a mix w/ the normal bed in. There have been times when there is too much traffic to be doing 50-10mph stops so I substitute. The brake lights may have a few people wondering but at least I can get my new brakes working.

[PeteH]

Bob,
thanks for sharing this, the temp reading is a great idea. I only go carted mine but noticed the pads were barely making marks on the rotors, and wondered about the balance. Now I have a method to use as a barometer of sorts when I do go to bed the pads in.