Poor Braking In Reverse?

[1550vt]

I don't make this stuff up folks. I am weary of hearing about things like trunk leaks and door hinges..........so lets open another discussion. I noticed that when I rolled backwards down a hill and applied the brakes, the feel was entirely different and the pedal had to be depressed much harder to stop. This was when I still had drum brakes and I am aware that the leading -trailing shoe issue in drums may come into play here. I have since converted to disc and noticed the same thing. One would think that when the caliper pistons clamp down on the disc, it would not matter which direction the rotor was turning, but obvioulsy it does. These are 4-pot calipers and the brakes will slide the wheels on any pavement at any forward speed. These are the rears I am talking about. The fronts are single pots and they work about as well going in either direction. I am not a "brakespert" and there may be a scientific explanation for this. Could it be some difference in the load shift? When you brake going forward you shift all the load to the front and away from the rear. Going backwards, you shift all the weight to the rear and into the brakes.

Somebody go outside, coast down a hill backwards, jam on your rear brakes and tell me if they work as well going in the wrong direction.

 

[lzski326]

Heck mine don't work very good going forward. hope their not worse in reverse. I don't think I can push the brake peddle hard enough to slide the wheels. My DFT with single rear caliper was better than this Triglide with dual calipers. If it ever quits raining I will try them in reverse.

 

[1550vt]

We may have opened another bag of TG worms. I think I had read some post somewhere concerning some TG brake issues, maybe premature pad wear or something. I built these I have myself and they are simply fantastic......going forward anyway.

 

[WildBillH]

Most likely air in you brakes lines
Calipers with multiple pistons can trap air if the bleeder hole is shifted from the 12:00 position producing a pocket of air at the top of the caliper bore which can not be dislodged.

This can cause a difference in braking performance to be better going forward than reverse.

Bill

 

[Ironhorsepilot]

Izskie, you may not want to put the brakes on while reversing the TG. I heard that it can trip the fuse.

 

[1550vt]

Wild Bill....My bleeders are not precisely TDC, but more like 11:00 AM, so you may have something there. I need to pull the wheels off here in a few days and check pad-wear and stuff. I will go through another good bleeding process then. These are Tokico radial 4-piston calipers as used on current crotch rockets and are almost the same thing as the AP racing caliper, so I know I have good lockers and they are well balanced to the stock FLH rear brake MC. That's one reason I chose them.

Hey Ironhorse...this is not a TG, but an older FLH Lehman conversion. I am proud to say that I have never blown a fuse while slamming on brakes and I can wash mine all I want to without fear of a trunk leak. I am a lucky man indeed!

(You know I am kidding and I really feel for all the folks with TG issues.)

 

[Tonyd]

it also depends on the caliper placement on the axle....rearward or forward of the axel.....and pads do wear in a direction

Tony

 

[1550vt]

I have converted a few old cars in my day and usually, there is a "choice" as to how you want to mount the caliper, but they all had 4-wheels. I did consider this and spent some time paying attention to what the caliper orentiation was on vehicles in all the parking lots I went through for a while. However, I have to admit that I did not see many trikes out in those lots, so the science on that study was flawed. I have these on mine oriented toward the front and not top-dead-center. I had a wheel space issue and could not easily get the tires on-and-off if I had placed the calipers on the very top of the rotor. I also chose this position to get the bleed screw right on top of the caliper. I understand your point. I think as long as I can find a technical and understandable reason for it, I will be okay with that. I rarely back up at speed anyway and they hold just fine uphill at a traffic signal or stop sign.

Does anyone know the orentiation of the calipers on factory trike disc brake systems. I am willing to bet they are on top and I think all the ones I can remember are.

Izski...if the TG has ABS brakes, that could explain why yours don't "feel" good. You should not be able to lock-up all the wheels with ABS, but I don't know if the TG's have ABS.

 

[Gorilla]

VT I'm having a problem finding a hill here in the keys. I will keep you advised. Ted

 

[WildBillH]

This is what I found…and my opinion.

There is no real one accepted standard, as to what the best location for mounting disk brakes. Opinion dictates what is better or worse, I think a lot depends on the application, sometimes in the cost is everything.

The location of the caliber is to move the weight distribution around while braking, or in some applications to lower the center of gravity, this being most of the case, with cars, to cause the front to drop shifting breaking power to the front of the car where weight will help in the breaking process and traction. Even with the weight of a car actual stopping distances will vary more with the type of brake pad then the location of the caliper.

The other point is to do with air flow, in both the aerodynamics and brake cooling. This would be a very low priority on a trike.

As for caliper placement on a custom trike make it look good.

I still think it is air in the line somewhere and most likely not much. Try sucking brake fluid through the bleeder valve. Sucking the brake fluid prevents air in the brake fluid from breaking up under pressure. I normally do this after the vehicle sets a half hour or so to allow and air to accumulate in high areas.

This has works for me in the past. The following link is an example of what the bleeding tool is.

Amazon.com: Mityvac 7000 Automotive Tune-Up and Brake Bleeding Kit: Automotive

 

[1550vt]

I know the turf where you live there Ted. Actually, I can't imagine why a person ought to be too concerned about stopping power in reverse at speed anyhow. I just noticed it while backing down my long driveway one day testing my new brakes. I was leaving two good black marks going up the drive and could not leave any backing back down. It will stop, just not as "solid". The pedal is not soft, it just feels like somebody squirted a little oil on the pads in reverse braking. This was the very same condition I had with the drums and I just assume there is some dynamic reason for it. I have had some pretty good responses here from you folks and gathered some good food-for-thought.<br />
<br />
I suppose I could change the orentiation to the rear of the rotors just for fun to see what happens and I will bleed them good again like Bill suggested. I probably need to let well enough alone. The heat index is up close to 110 this week around here and I have set-up a bunker in my basement to battle the heat-wave.

AC set to 72 and the fridge full of Budweiser! I don't need to be out fooling with brakes this week for sure.