Rebuilding LD-19 calipers. How to do it?

[swiftdrivr]

Anyone got a schematic or instruction set / how-to article on rebuilding LD-19 calipers? After 20 years, i think it's time.

[Brian C in Az]

Here are some you tube videos showing you how to rebuild calipers.

https://www.youtube.com/watch?v=cRUOChic7bc

[Brian C in Az]

Here's a previous thread with the how to's

http://www.apexspeed.com/forums/showthread.php?t=23175

[Jerry B.]

Jim......
After viewing the video from BMW man I have to comment. Yes the block of wood.....BUT NO on the pliers on the pistons.....and a VERY no using oil
on the piston seal or any internal caliper parts. Use only brake fluid or paste for lubing.... (Availiable in small tubes, AP or Tilton).

Using air to remove pistons, use safety glasses and would limit air to about max 50 psi.or less. Watch your fingers!

After 20 years you might split the caliper halves. You will need the small o-ring between
the halves as well as the two piston seals each side, also making it a lot easier.

Do clean with VERY fine Scotchbrite the pistons and the bore. If there is any notable corrosion/nicks/grooves there you might get more parts. Check the caliper to pad backing abutments for rust or grooves.

Plan B might be to send them to Porter .....comes back nicely plated.

[Brian]

I rarely reuse the pistons when I rebuild calipers, so I get them out any old way. If they are really too stuck to get out with hands I use pliers (yes, I would use pliers) if I have a car with working brakes handy I put the caliper on, bleed it out, and push the pistons out with the brake pedal. If I don't have a handy car with a working brake system I use a grease gun. Develops up to 10K psi of pressure and zero expansion factor so no risk of popping something across the room. I usually split the caliper to replace the seal and to make sure the bores and drillings are all perfectly clean. I install the pistons while the caliper is apart, I use either fluid or the assembly grease if I have some, I torque the bolts to 35 ft lbs.

JMW

Brian

[Swift17]

After 20 years you might split the caliper halves. You will need the small o-ring between the halves as well as the two piston seals each side, also making it a lot easier.

WARNING, WARNING .... WILL ROBINSON ... WARNING

Do NOT mix up the calipers half's if you take them apart - they are machined as set - before removing them from the car/upright, stamp the tops something like "LFO/LFI" "RFI/RFO", etc. Failing to do so will require you to upgrade to new calipers ........ (I agree it is time to rebuild)

Also if Tom a/k/a "BrownsLane" will pipe in, he can recommend the paint to use from a rattle can to re-paint -- he uses it in his restoration and I used it - works great -- Also I left all the original seals/plugged the holes in-tack and with duct tape over the original seals +area I cleaned them by glass beading - and used liberal air to blowoff thereafter

[kea]

Call me if you have any questions/problems. I've done quite a few over the last 30+ years. I also have genuine AP Racing seals (1.625") that you would need.
As an option, if you don't feel up to it, you could send them to me.

[Don Denomme]

After 20 years I'm almost sure that the pistons will be pitted. Check with Keith regarding new pistons. Stainless would be nice.

[racerdad2]

I'm sending Keith all my calipers & master cylinders to be rebuilt. He fabbed all new hydraulic lines for me when I replaced my clutch & pressure plate. Very nicely done. I'm looking forward to totally trusting my brakes next year. I never hit them really hard this season.

[rickb99]

Best way to rebuild LD-19 or LD-20 calipers is to put them in a Box and ship to Averill Racing Stuff. Guaranteed excellent work when done.

[swiftdrivr]

Thanks, Guys. I will watch the videos, mark my sides, and decide if I want to tackle or ship. many thanks.

[chuck cecil]

Jim
You can bring them over and I will help you.

[swiftdrivr]

Thanks Chuck,
How have you been? Haven't seen you in a while.

[chuck cecil]

Had to have surgery , now recovering.

[swiftdrivr]

Glad to hear you are on the mend. I trust you will be ready for the spring races then?

[swiftdrivr]

Hello,
Just looking for opinions and ideas. The pistons look like they are unusable, but before I turn them into model car wheels or feet for a plater, I thought I'd post and get advice. The Grooves in the callipers are another issue. I cleaned with CRC brake clean, a product whose reputation took a hit from this effort. Brake cleaner, Cue-tips and tooth brushes seem to have failed to clean enough, but left some concerning marks [unsure if they are just lines inscribed in the old brake residue or not, but it seems unlikely plastic cue-tips damaged the wall.
Anyone got any thoughts or advice?
Thanks in advance.

[racerdad2]

Just my thoughts, certainly not an expert opinion. When I'm flat out and dynamite the brakes, I want complete confidence in my braking system.

That's minor corrosion for a street car and may be of no concern on a Formula car. That said, I'd buy new parts if it's in the budget.

I left a lot of time on the track this year with older calipers.

Installing all new brake components this winter so I can have complete confidence in my brakes.

[old 59]

I would give the pistons the floatation test.

[Jon Jeffords]

I would give the pistons the floatation test.

Drop them in a bucket of water? If they sink, scrap 'em?

[Charlie Schmidt]

I believe Carroll Smith said to use the nearest lake.....

[old 59]

Drop them in a bucket of water? If they sink, scrap 'em?

Nailed it!

[john f]

Pistons are junk, pitch them. Surface finish on bores does not matter. Pistons seal on seals only, not the bore. Bore just holds pistons concentric to seal surface. Scotch-brite or 400-600 grit wet dry sandpaper with oil on the bores to clean up is fine. Install seals and pistons with some brake fluid on them and you are set to go. Just my $0.02.

john f

[swiftdrivr]

I wasn't too concerned with the actual bore, although maybe I should be. I don't seem to be able to clean the slot where the seals sit, especially the near side, without using more force than would seem advisable, given that I was told a scratch to the surface can ruin the caliper. I used brake-clean, a toothbrush, Q-tips and the end of a cable tie, but either they scratched the lines into bare metal, or there is still enough debris in the channel to show a line scratched into the debris. Any ideas?

[DaveW]

I wasn't too concerned with the actual bore, although maybe I should be. I don't seem to be able to clean the slot where the seals sit, especially the near side, without using more force than would seem advisable, given that I was told a scratch to the surface can ruin the caliper. I used brake-clean, a toothbrush, Q-tips and the end of a cable tie, but either they scratched the lines into bare metal, or there is still enough debris in the channel to show a line scratched into the debris. Any ideas?

You probably need something like a Scotchbrite pad, or very fine steel wool to get the old hardened crud out of the groove. I'd stay with a fine abrasive pad to avoid leaving any steel strands lying around or embedded in the groove.

If, after using something like this, you can still see and feel scratches, you may be out of luck and need to replace the caliper(s).

And I agree that it is not a good idea to re-use those pistons when you can get new ones for a fairly reasonable cost.

[swiftdrivr]

Thanks guys,

[rickb99]

..... especially the near side, without using more force than would seem advisable, given that I was told a scratch to the surface can ruin the caliper. I used brake-clean, a toothbrush....

Any thoughts on carefully using a dentil pick??

[DaveW]

Any thoughts on carefully using a dentil pick??

I'd worry that a dental pick would leave scratches. In that regard, I use a wooden electrical pick ("spudger") to remove seals and o-rings from their grooves.

[Jon Jeffords]

You probably need something like a Scotchbrite pad, or very fine steel wool to get the old hardened crud out of the groove.

If you are tempted to use steel wool (0000), I highly recommend you vigorously use hot soapy water and a new toothbrush to remove the "third body" particles. BRAKE CLEANER IS NOT A SUITABLE SUBSTITUTE TO REMOVE STEEL WOOL PARTICLES.

[swiftdrivr]

I'm going to try the scotchbrite, then rinse well with ?brake clean then brake fluid? Wish I'd thought about the wooden pics for seal remover. Good idea.

[DaveW]

If you are tempted to use steel wool (0000), I highly recommend you vigorously use hot soapy water and a new toothbrush to remove the "third body" particles. BRAKE CLEANER IS NOT A SUITABLE SUBSTITUTE TO REMOVE STEEL WOOL PARTICLES.

Agreed. That's why I said the abrasive pad is preferred to not chance leaving bits of steel wool in the groove.

[john f]

You're making too much of a deal about a slight scratch. You can see the machining marks or ridges in the groove from the original manufacture of the caliper, yes? Those grooves have not caused a problem and a few more will not make any difference. As long as you do not put a 20 or 30 thousands groove going crosswise in the seal groove, it will seal. I'd say " don't worry about it". Just my $0.02.

john f

[DaveW]

Maybe I'm just being over-cautious due to working with air suspensions for years at work, but I think any non-circumferential grooving/scratching over a few 0.0001's deep is a potential leak path. If you can feel it by running a probe over it, it is a possible problem. It is not as important in a totally static seal, since the seal will conform to the scratch, but in this situation where the seal can move slightly due to piston motion, it is more likely to cause a problem.

Circumferential grooves are often used as an aid to sealing, so unless those are just awful, they will not cause a problem.

[swiftdrivr]

Thanks again. I am off to the shop, scotchbrite in hand. As I don't much care for surprises when I hit the brakes, if in doubt, I'll use this as an excuse to go to aluminum calipers. If it's a safety issue, I can sell it to the woman who keeps me from going bankrupt from my addictions.

[swiftdrivr]

Okay, so the new seals went in without too much drama, and the pistons all required lots of force, but seem to slide in and out appropriately when I push the brake pedal, suggesting to me that they are in correctly and working, but my pedal seems way long. I used to have a quarter inch of travel, got concerned at a half inch and did all this, and now I have an inch and a half of travel. I have heard that the seals need to "set", and the brakes would feel bad the first session, but I wasn't expecting this. Any thoughts?

[formulasuper]

Gotta be some air in there somewhere. Are the bleeders at the very top of the calipers? If not you might have to tilt them while bleeding.

[swiftdrivr]

After bleeding about a liter of fluid, we realized I had the bleeders at the bottom of the calipers. We fixed that, [and I'll be hearing about it for years] but still, the pedal travel is enormous.

[Jon Jeffords]

With the bleeders all closed, watch the relative motion of your master cylinder pushrods when repeatedly stroking the brake pedal from zero to full effort. Do they both move about the same distance? If one moves a lot more than the other, that is the end with the air in the system.

I have seen brake and clutch hose routing that had a 'hump' in the system that was harboring an air pocket that could not be burped out by manual pedal actuation. It took the use of a vacuum system to put a long enough 'pull' on the fluid (say ten seconds) to finally drive the air bubble out of the hump and into the horizontal lines where it would then be bled out successfully.

[swiftdrivr]

Jon,
I have a hump, which never caused trouble before, but I'll stick the Mighty Vac on it in the morning, and see if that helps. Thanks

[Brian]

Do the pads have much movement after the pedal is released? With new seals it's real common for the pistons to retract a lot, enough for the pads to rattle back and forth in the calipers. A couple of real brake applications in the paddock fixes that.

Edit: I did some math for you. Assuming LD-19's with 1.625" pistons, and a .700" master cylinder and a 3:1 pedal ratio, 1" of pedal travel equates to around .3" of pushrod travel (after slop). MC piston area is .38sq in so you are moving around .115 cu in of fluid. Two LD-19's have four pistons, each piston has 2sq " of area, so 8 sq " total piston area. .115 cu in would need .014" per piston. Normal piston movement is maybe .002", so you have around 12 thou per pad of excess pull-back, which I often see on newly rebuilt calipers with just seals, no dust seals and such. So don't despair...

Brian

[swiftdrivr]

That's some impressive calculating! as the MightyVac wasn't so mighty, and quit sealing the first weekend I got it (NAPA will be seeing this again) I will bleed by hand in the AM, and if things work out, I will fill you in after practice / testing Fri or Sat. Thanks again