Lola T91/50 rear brake pad challenges

[mikey]

So I'm down to sorting the brakes on my F3000. I've noticed some issues with the setup that was on the car when I bought it.

In the rear, the brake pads seem to be about 0.050" too wide (i'm calling across the face of the pad the width, as in from the outer circumference of the rotor to the circumference of the rotor hat). Is this an issue? the pad material overhangs the outer edge of the rotor. and on the RR side, it also is slightly touching the rotor hat and has self clearance.
I also received two additional sets of pads with the car. One set is used and exhibits the same symptoms as the ones that are installed on the car. the other set is new and has been machined to an acceptable "width", however its installation height is still too far outboard and overhangs the rotor outer edge the same, while the inner edge has a lot of clearance to the rotor hat. there is a small tab in the caliper that is bolted on which the brake bad rests upon. I suppose if I shim that pad stop it could let it sit further in to center on the usable rotor surface.
either way, seems like more than one should have to go through for brake pads. I'm either adding shims in an area that never had shims before or I'm having to machine custom brake pads?
It leaves me wondering if the car has something else off - like mismatched calipers or rotors, or if I'm worrying about nothing?

Sorry for all my confusion, my last car was a pro formula mazda and everything was easy to order through star race cars!
Here's some photos:
These show pad overhang on outer edge of rotor and interference with the rotor hat on the inside. See how the inner radius of the brake pad backing plate is scraping the rotor hat above the bolt.



Here are some photos to show the difference between the pads on the car and another set that were in a box that have been machined differently. This first three is one that was on the car, you can see how if I rest it on the rotor hat it is wider (top to bottom) that the rotor braking surface area.



These next thwo show a smaller set of machined pads and backing plates that would be good if they could be centered on the usable rotor braking surface area. The last photo is the two types of pads against each other so you can see what has been machined off the one set.



open to all thoughts / opinions / advice.

thanks!
mikey

[tlracer]

As with your other question about disc clearance (or lack of...) I wouldn't be happy with this. What pads are fitted an are these the correct model specified by AP for the calipers?

I can't see that the correct ones would need the backplates machining to fit, if I'm understanding your pictures correctly. Also the correct pad shouldn't be contacting the disc bell (although this goes back to the question of whether the correct discs are fitted).

[Garey Guzman]

Yeah, I can't imagine the current front and rear brake interferences leaving the factory like that. I'd guess that the rotors, front and rear, were changed rather than the calipers. One would presume the pads are for those specific calipers but that should definately be double checked!!

[J Leonard]

Looks to need the caliper spaced away from the upright to get pad to hat clearance. Then the rotor will be to small in diameter. New rotors with out drilling? The caliper mount studs look to be already at their minimum. When the caliper is moved out you need to check wheel clearance. Are the rotors and hats the same front and rear?

[mikey]

updated the front brakes thread also.. but here's some more info as I've dug further into this. the front and rear rotors are identical, but different center hats. the rotors are 10-13/16 (275mm) dia x 1" (25mm) thick. front and rear rotors dimensionally the same, however the fronts are slotted while the rears are cross drilled. I believe the rear hat is original, I do not believe the front hat is the original nor does it seem to match what would have been original. the tell-tale is the current front hat is bolted to the hub with 4 bolts. the hub flange has been drilled and tapped for it. the hub flange also has a 5 hole pattern that appears to have been the original rotor hat mounting holes.
I cannot find brake discs in this size. These are the closest, however they are 1/8" or 6mm larger diameter.
https://www.pegasusautoracing.com/pr...sp?RecID=10697
The description for them says Lola F3000 (unspecified year) but also mentions they bolt to the original Brembo hats. My hats have no manufacturer markings or part numbers that I can find. Maybe this car originally came with Brembo calipers? found a spec sheet for a T96/70 that has Brembo calipers.

the car has different pads in the front and rear. The front pads look like they were originally these:
https://www.pegasusautoracing.com/pr...?Product=PF740
however they have been machined down on the inner radius to fit. Approx 0.15" was removed I believe.
the rear pads kind of look like these:
https://www.pegasusautoracing.com/pr...?Product=PF745
however as previously noted, have also been machined down on the inner radius to fit.

It seems the front pads fit the rear calipers just fine, other than the install height being off. if the pad stop could be changed it could fix the positioning.

the whole thing is quite puzzling.. I definitely can't move the rear rotors, only have 0.12" clearance inside the wheel. the front is slightly better, about 0.19" clearance. the AP calipers and pads seem like they are really for the larger 11-15/16 rotor which I don't think I can fit to my car due to wheel clearance.

the AP calipers I have are super nice of course, so maybe the answer is just the correct shims and pad stops and continue to modify brake pads to fit.. although I still haven't found a source for the rotors either..

[mikey]

found in an info pack that AP calipers were original to the car, although it was 6 piston front and 4 rear, not the same 4 piston all the way around that I have. The rotors were possibly Lola specific hats and discs? need to find a good source for the right parts info..

[tlracer]

Might be worth contacting Pit Lane Spares ( www.pitlanespares.com) who have a large Lola parts inventory from 1990 onwards.

[Charles Warner]

Hedre is the spec sheet for LOLA F3000 Brembo brakes. The dimensions shown should help you determine if your pads atre correct.

I have the entire manual so drop me a PM if you need more info.

[dereklola]

Mike asked me to help throw some light on this subject.

Please remember that this car was built in 1991, an update of their 1990 T9050 model.
They were not 'spec' cars - those came later - the better teams stripped, rebuilt and
improved them before racing them - not just to go faster but also to suit their suppliers and sponsors.
So talk of "how the car left the factory" is not pertinent - the team probably changed it anyhow
- both before racing and while racing.

This particular car was raced in Japan. The team had been racing the 1990 model and did not
get the 1991 until midway through the season. So who knows what if anything was ex-factory and
what if anything they used from their 1990 car, I'm thinking wheels and brakes in particular. And
speaking of brakes I understand many Japanese teams used 4-pot front brakes unlike in Europe
where they preferred the 6-pot. That info came to me from an AP engineer who spent time in Japan
with the F3000 teams.

The car was raced in Japan in 1991 and 1992. It then stayed as a show car in the main sponsor's
head office - less engine, less brakes but with rotors. It then came to the US and then me in 2002.
Finding brakes was a problem - Lola had no information - AP were confused - they thought they
knew but then contradicted themselves. I finally I talked to a team with three of these cars running
the Euro-Boss series (combined F1/F3000). They used Euro cars with 4-pot fronts. Sold me the rear
calipers (CP3567) and I bought new fronts from AP (CP4125).

I started racing the car in 2009. By 2012 I investigated new rotors. Then met the above mentioned
AP engineer who had retired to the US. He confirmed all I have mentioned above. Decided rear rotors
were OK and and found a local machine shop to machine new AP castings to dimensions measured
on my front axle (some very minor differences). The 'different' pad location bits were part of that.
Everything went together fine and worked fine.

Pads. AP could not supply pads to suit those calipers. Nor could the UK supplier they recommended
(forget their name). So I went with my old favorite KFP Carbon-Kevlar pads. They did need some
minor machining to fit and so I made a simple jig to ease that. I rapidly realized that 'exact' fit was
not necessary hence some of the variations shown in the pics. Specifically the pad overhanging
the OD of the rotor is no problem - it is not "show car" perfect but has no effect on braking.

The two interference problems shown are minor. The front hat interference solved itself (!). The rear
pad retaining bolt was probably due to changing the caliper mounting 'shims' - I initially used hardened
washers then changed to full size and half size AN washers. The gouged casting can be used as is or
re-machined or can be replaced by two steel tubes - same as they do on the more modern AP calipers.

Rotor hats - I do not know the source - they came with the car - possibly because the car used Japanese
Work wheels. But no problems that I know of. Yes - 3 front and 6 rear wheel drive studs.

If I've missed anything please let me know.

Derek

[mikey]

Derek,
Many thanks for weighing in, a lot of this info will save me from chasing ghosts.. Always impressed by your memory, I hope I'm as sharp as you are in my later years! I will call you tomorrow to see how you are doing.

Cheers,
Mike

[mikey]

All,
Just providing an update, after reviewing some Brembo engineering drawings for required clearances and tolerances related to the braking system rotors, calipers and pads, as well as their relationships to each other (positionally), I am hopeful that I have figured out how to make everything work. The basis of my path forward is that I don't believe there is a known set of components that fit this car without some amount of customization. Therefore I am picking which parts going forward will be customized. Currently the pads, rotors and caliper pad rests/stops are all custom. No big deal for the caliper pad rests/stops to be custom, likely will never have to change them once I have a set machined to my specs. Custom rotors are also not that big of a deal, as others have pointed out. My goal is to eliminate custom pads. Sharing some more photos and notes here:

These are the 3 pad types I got with the car. The top one is a front pad, the middle and bottom are rear pads. The backing plates are all the same width. The top one was on the front and the bottom one was on the rear of the car as received. The bottom one is the rear pad that overhangs the outer circumference of the rotor and interferes with the rotor hat on the inside radius of the pad (issue pictured above in this thread).

The front pads and the middle style rear pad have been machined along the inner radius to make them narrower across the face.
The middle pad is physically narrow enough across the 1.60" dimension to fit on the swept area of the rotor, which is 1.71" across. The bottom pad cannot fit as-is, hence the interference issues with the hat and the overhang previously mentioned. Brembo engineering drawings call for a maximum overhang of 0.3mm and a 2mm clearance between the pad and the rotor hat. I currently have as much as 1.3mm overhang and as little as 0.0mm clearance to the rotor hat. When the machined version of the rear pad, pictured in the middle, is used, it then becomes a matter of getting it to center on the rotor swept area. We'll discuss that in a minute.
The fronts are properly positioned relative to the rotor for the front setup.


So now we look at the other important dimension of the pad backing plate. The "ear" height upon which the pad rests in the caliper.
Notice the front pad has a narrower ear, allowing it to sit further into the caliper.

Now 0.06" difference may not seem like a lot, but it is 1.5mm and recall the Brembo spec that says 0.3mm max overhang. So what I have determined is that if I use the front style pad in the rears, along with removing the 0.062 washer shim on the caliper radial mounting bolts, then the caliper moves inboard and the pad moves inboard and then everything is happily positioned. And I am hopeful that I have found new pads that actually match the dimensions of the custom machined front pads. I think these pads from PFC will be the ticket for all 4 corners of the car, provided that indeed prove out to be dimensionally close to the machined front pads I have now. The top and middle pad pictured above have nearly the same surface area, with the top pad having wider pad surface whereas the middle pad is narrower on the outer radius and wider on the inner radius than the top pad (no "scalloped" corners). This is a drawing of the 740 size pad that I will buy and try:


And here is what the rear setup looks like with the front style pad inserted and the shim removed from the radial mounting bolt:
The pads do not overhang the edge of the rotor.



There is sufficient clearances between the pad and the rotor hat




As an aside, I found it curious that the larger bottom piston overhangs the pad backing plate. The piston is nearly centered on the pad, the other side is past the pad as well. Since a larger rotor is impossible with this caliper, I can only surmise that it is normal for the piston to be wider than the pad, unless there is another style pad with a larger backing plate on the same size pad as shown here.



I will consider my rear brake challenges solved, provided that the PFC 740 size fits without machining. I will update once the pads are in.

I hope somebody in the future can benefit from this little excursion I have been on for the past few days. My realization is that vintage cars require a bit of engineering know-how in order to make the current supply chain work. And in many cases for some parts there simply never was a supply chain! Any original drawings you can get your hands on helps a lot!

Cheers,
Mike