GT40s.com - View Single Post - GTD Spindle / upright impact on braking performance

Malcolm · 08-31-04, 05:41 AM

What I think you talking about is Spindle Flex leading to pad knock back. The standard GTD front spindles sometimes did and sometimes did not suffer from this problem. GTA917 races his 40 on these spindles and during my conversations with him I do not recollect him saying he had this problem. Also Julian KS doesn't suffer from it either. and he also does competitive events on slicks. However I did suffer from it and I know of others too who had this problem. Therefore to me it is a lottery whether you get it or not!

I never noticed it causing uneven pad wear and don't see the connection. As you are cornering the spindle flexes and pushes the pistons back into the caliper. Unless you are hard on the brakes in a corner (not recommended!) the force required to do this is really quite small. It shouldn't show up in uneven pad wear especially when considered against wear from 160 mph stops such as you have done.

The classic sympton of spindle flex is that when you go for the brakes, in a straight line after some cornering, you have a long pedal that pumps up on one push. I remember having to left foot the pedal stiff on straights before corners during competition to save my braking distances getting too long!

From this problem replacement front uprights have been used by those that lean their cars into corners. I understand that Roy Smart can make these for you from the GTD (Poole) factory designs plus subsequent improvements that have been incorporated. Paul Thompson can say more on this as he is more aware on what is on offer.

If you are gettind wedge shaped pad wear then check your brake calliper mounts are mounted equally around the disc ie they are not at an angle before you even start to use the brakes. I made my own bracketry and found that I had to be really carefull in the alignment of the calliper to the disc.

Another solution to knock back is to use anti knock back springs. These little springs sit inside and behind the brake caliper piston and exert a small level of force permanently on the piston pushing the pad back onto the disc. I use these on my Alcon calipers with satisfactory results. I have not noticed shortened life expectancy of the brake pads either!

I still use the single pot caliper at the rear on a vented disc. Are your rear brakes vented? They need to be! I have found that with Alcon 4 pot fronts and the single rear pot, I get a good balance on braking and can brake as much as I ever need to in competition.

How big are the pads in your Wilwood calipers? If small in surface area then they could overheat quicker than a larger pad of equal material, wear faster and be less effective. Multiple piston calipers may sound great but they have to be of the correct size to be better than a lessor pistoned but correctly sized caliper. Maybe the fronts are working too hard? Do you get brake fade?

Silly thought? Could the smell actually be the clutch?

Anyway I hope this helps.

08-31-04, 05:41 AM	#2 (permalink)
Malcolm Malcolm Gold Supporter Join Date: Jun 2003 Location: Surrey, UK GT40: GTD Posts: 1,568 Rep Power: 30	Re: GTD Spindle / upright impact on braking performance What I think you talking about is Spindle Flex leading to pad knock back. The standard GTD front spindles sometimes did and sometimes did not suffer from this problem. GTA917 races his 40 on these spindles and during my conversations with him I do not recollect him saying he had this problem. Also Julian KS doesn't suffer from it either. and he also does competitive events on slicks. However I did suffer from it and I know of others too who had this problem. Therefore to me it is a lottery whether you get it or not! I never noticed it causing uneven pad wear and don't see the connection. As you are cornering the spindle flexes and pushes the pistons back into the caliper. Unless you are hard on the brakes in a corner (not recommended!) the force required to do this is really quite small. It shouldn't show up in uneven pad wear especially when considered against wear from 160 mph stops such as you have done. The classic sympton of spindle flex is that when you go for the brakes, in a straight line after some cornering, you have a long pedal that pumps up on one push. I remember having to left foot the pedal stiff on straights before corners during competition to save my braking distances getting too long! From this problem replacement front uprights have been used by those that lean their cars into corners. I understand that Roy Smart can make these for you from the GTD (Poole) factory designs plus subsequent improvements that have been incorporated. Paul Thompson can say more on this as he is more aware on what is on offer. If you are gettind wedge shaped pad wear then check your brake calliper mounts are mounted equally around the disc ie they are not at an angle before you even start to use the brakes. I made my own bracketry and found that I had to be really carefull in the alignment of the calliper to the disc. Another solution to knock back is to use anti knock back springs. These little springs sit inside and behind the brake caliper piston and exert a small level of force permanently on the piston pushing the pad back onto the disc. I use these on my Alcon calipers with satisfactory results. I have not noticed shortened life expectancy of the brake pads either! I still use the single pot caliper at the rear on a vented disc. Are your rear brakes vented? They need to be! I have found that with Alcon 4 pot fronts and the single rear pot, I get a good balance on braking and can brake as much as I ever need to in competition. How big are the pads in your Wilwood calipers? If small in surface area then they could overheat quicker than a larger pad of equal material, wear faster and be less effective. Multiple piston calipers may sound great but they have to be of the correct size to be better than a lessor pistoned but correctly sized caliper. Maybe the fronts are working too hard? Do you get brake fade? Silly thought? Could the smell actually be the clutch? Anyway I hope this helps.