Update: Installed: M5 (4-pot) Caliper Rebuild Questions

[MarkD in NJ]

Hey Folks,

I know a few of you have rebuilt 4-pot M5 calipers and most of my questions have been answered through good search results.

If you split the calipers, did you reuse the bolts and caliper seals? I found conflicting posts elsewhere as to whether the bolts were reusable or not.

Thanks in advance
Mark

[cgraff]

Hey Folks,

I know a few of you have rebuilt 4-pot M5 calipers and most of my questions have been answered through good search results.

If you split the calipers, did you reuse the bolts and caliper seals? I found conflicting posts elsewhere as to whether the bolts were reusable or not.

Thanks in advance
Mark

You can reuse the bolts if they are in good condition; they are not torque-to-yield. I'd replace the seals. Last time I checked the seals are available from Walloth and Nesch in germany or BMP Design.

If you want, you can always obtain the correct hardware from a good metric hardware shop.

-Chris

[wkohler]

Ian in Portland bought his seals - and pretty much everything necessary to rebuild the calipers from Germany. Not the cheapest things in the world, but it's the only place you can get them.

[Walt]

My understanding is the bolts are torque to yield and should not be reused. The seals were not available from Germany last I checked and one from Carl Nelson @ LaJolla cost a pretty penny.

I'd leave them together unless there is a compelling reason to split them.

Walt

[cgraff]

My understanding is the bolts are torque to yield and should not be reused. The seals were not available from Germany last I checked and one from Carl Nelson @ LaJolla cost a pretty penny.

I'd leave them together unless there is a compelling reason to split them.

Walt

1. Where did you get the information on TTY?

2. Here's the seals, available from Walloth and Nesch:
http://www.wallothnesch.com/e/brake/bra ... I%20/%20M6

You can also replace your pistons if you wanted to as well.

-Chris

[Walt]

Chris,

They didn't have these parts when I sold you those M5 calipers, I corresponded with them, and Carl is the one who said they were stretch bolts. One time use.

Walt

[cgraff]

Chris,

They didn't have these parts when I sold you those M5 calipers, I corresponded with them, and Carl is the one who said they were stretch bolts. One time use.

Walt

Well, now they have the O-rings. I remember that up to ~1998 or so you could still get them from BMW dealers. Same with the pistons - up until some point in the 90s, the rebuild kit came with the pistons.

As for stretch...Carl is wrong on this one. Sorry.

Although the old shop manuals (E9, E3) *recommend* replacement of those bolts, they are not stretch bolts, aka torque to yield bolts. They are perfectly reuseable if in otherwise good condition. Not only do the factory manuals not specify the torquing procedure for a TTY bolt for them, the bolts themselves are standard metric bolts - they are nothing special. Of course, if you think they've been *overtorqued* for whatever reason, then you're stuck, you need to find replacements. I remember sourcing a suitable replacement at some point years ago...but I don't have that information anymore. You can show the bolts and ask any MechE this, and they'll agree with what I just said.

-Chris

[MShimon]

Alright, a MechE mention! I'm a senior in MechE right now at ISU(Iowa State). Materials sure are interesting, but not really my thing.

[Walt]

Hey, not professing the expertise, just relaying info from a typically knowledgeable source.

I, however, am not one to doubt you, Mr. Graff. And, BTW, it's nice to correspond with you again. It has been a few years. there are precious few of us that date to the UUC digest, M535i and first Roadfly boards.

That said, I'm now running Brembos, solely due to pad replacement simplicity.

Regards,
Walt

[cgraff]

And, BTW, it's nice to correspond with you again. It has been a few years. there are precious few of us that date to the UUC digest, M535i and first Roadfly boards.

Regards,
Walt

Yup, same here! ...even the Welty E-mail Digest...remember that one?

-Chris

[Walt]

And, BTW, it's nice to correspond with you again. It has been a few years. there are precious few of us that date to the UUC digest, M535i and first Roadfly boards.

Regards,
Walt

Yup, same here! ...even the Welty E-mail Digest...remember that one?

-Chris

Ha, I'd forgotten that one. I do remember now as I believe it spawned the UUC. Funny how one site flames out and creates another.

BTW, who are all these kids that think they practically invented the E28? Bet darn few know what UUC stands for and that the digest preceded Rob's company by a few years.

What ever happened to the fellow with the 335i Bambi Slayer and Rob's partner that started Rogue? I saw Brett @ Techfest in Tacoma last year. And your friend Rob, how's he?

Hope all's well with you.

Regards,
Walt

[cgraff]

Ha, I'd forgotten that one. I do remember now as I believe it spawned the UUC. Funny how one site flames out and creates another.

BTW, who are all these kids that think they practically invented the E28? Bet darn few know what UUC stands for an that the digest preceded Rob's company by a few years.

What ever happened to the fellow with the 335i Bambi Slayer and Rob's partner that started Rogue? I saw Brett @ Techfest in Tacoma last year. And your friend Rob, how's he?

Hope all's well with you.

Regards,
Walt

There's been quite a few Bambi slayers that I knew of...I dunno which one you're talking about in particular, however.

Rogue is still around - but Levinson prefers not to discuss that company for good reason. Rob's doing well and still got the M5 3.8 Touring and a E38 750iL he converted to a manual.

Rob Anderson is now working at BMW in Greenville (after a stint at Robert Bosch in Anderson, SC). He just started in January, and he's liking it a lot so far. He's got a S38 B38 waiting for a reseal and to be installed into his E28...long term project that is.

-Chris

[MarkD in NJ]

Thanks to all who replied.

I had to split the calipers to get a single stuck piston out of each caliper. I had to drill & tap the stuck pistons and thread in some bolts to pull them out.

The caliper half bolts are metric Grade 10.9 or 11.9 (I have to check) and are not torque to yeild but I will replace them with new ones anyway along with cleaning the threads in the calipers. The caliper half seals and pistons are indeed available (and on their way) from http://www.wallothnesch.com/. Shipping was about $40 up to 1kg. (ouch!) Still, the seals (2 sets) & pistons (3) coming from Germany were cheaper than the 'mounting parts" (pad spring and retainer pins) which I can't find for less than $45 per side. (double-ouch!!)

Mark

[cgraff]

Thanks to all who replied.

I had to split the calipers to get a single stuck piston out of each caliper. I had to drill & tap the stuck pistons and thread in some bolts to pull them out.

The caliper half bolts are metric Grade 10.9 or 11.9 (I have to check) and are not torque to yeild but I will replace them with new ones anyway along with cleaning the threads in the calipers. The caliper half seals and pistons are indeed available (and on their way) from http://www.wallothnesch.com/. Shipping was about $40 up to 1kg. (ouch!) Still, the seals (2 sets) & pistons (3) coming from Germany were cheaper than the 'mounting parts" (pad spring and retainer pins) which I can't find for less than $45 per side. (double-ouch!!)

Mark

The pricing sounds painful. Probably a function of the exchange rate as I've seen pricing for parts go through the roof in the last 4-5 years.

Let us know where you source the hardware from. McMaster may be able to help, but I don't know if you'll be able to get the right coating and bolt grade from them.

-Chris

[MarkD in NJ]

Let us know where you source the hardware from. McMaster may be able to help, but I don't know if you'll be able to get the right coating and bolt grade from them.

It looks like Grainger has the right stuff, but I have to confirm length and thread when I get home.

Mark

[MarkD in NJ]

As far as I can tell the bolts are 11.9 M9.0 x 1.25, 85mm length. So far, no sources for the bolts - might be the only part other than the caliper halfs that I have to reuse.

Mark

[cgraff]

As far as I can tell the bolts are 11.9 M9.0 x 1.25, 85mm length. So far, no sources for the bolts - might be the only part other than the caliper halfs that I have to reuse.

Mark

Wow...M9 huh?

Odd.

Closest things McMaster has is 11.9 M8x1.25, 80mm and 90mm, partial thread, DIN.

-Chris

[MarkD in NJ]

Wow...M9 huh?

Odd.

Closest things McMaster has is 11.9 M8x1.25, 80mm and 90mm, partial thread, DIN.

-Chris

Yeah...well, M9 is an estimate on my part because it is larger than M8 and smaller than M10 - compared them at the hardware store today. It seems that some Italian and German cars use M9 for head studs and other engine assembly bolts. I've found a few cases of M7 (on 2 piston) and M9 (on 4 piston) being used on ATE calipers, so that also supports my estimate.

Grainger has something similar to what you quoted from McMaster. 80mm would be too short and 90mm would come out the other side of the caliper, but either way, you would have less threads engaged in the caliper (probably bad).

I haven't found anything close to the rest of the specs in an 85mm length yet.

Mark

[ahab]

Anyone ever try these rebuilt calipers? The price certainly seems right.

Cheaper than my single pot floaters too. Strange...

Aaron

[MarkD in NJ]

Anyone ever try these rebuilt calipers? The price certainly seems right.

Cheaper than my single pot floaters too. Strange...

Aaron

Hey Aaron,

There have been a few threads regarding these calipers and similar ones from other sources. At least two board members purchased them to find that they are E23 7-series calipers and the bolt spacing, amongst other dimensions, is incorrect for the E28. The generic supplier parts catalogs don't differentiate between E23 and E28 M5 calipers, assuming that BMW used the same 4-piston units on all cars. The brake pads are the same size, however. The E23 4-pot calipers are probably cheaper than single pot calipers because there is so little demand for the stock that exists.

Most places I spoke to could not find E28/E24 M5/6 calipers in stock, but could rebuild my cores for an unknown price – they would have to start the job to get an idea of how much work was involved.

Even though it probably cost me more in the end, I rebuilt my cores. After test fitting and grinding the outside casting marks off the calipers as they interfered with my 15x7 E39 Style 29 wheels:
1. I removed the old brake pads, pins, clips, etc. Used wire brushes on my bench grinder, die grinder and electric drill to clean off as much crud as possible.
2. Soaked everything in PB Blaster overnight, un-bolted the caliper halves, removed bleeder screws, dust seals and pistons. 2 of the pistons were rusted in place had to be drilled and tapped so I could thread in bolts to pull them out – this was UGLY!
3. Soaked everything in paint thinner overnight, cleaned with brake cleaner and dried using compressed air to blow out all fluid passages.
4. Honed cylinder bores to remove all corrosion, mostly above the piston o-ring seal. Re-tapped caliper half and bolt threads. Polished 6 good pistons and 2 new pistons (from http://www.wallothnesch.com) with green Scotch-Brite pad. Cleaned everything again with brake cleaner and dried.
5. Masked cylinder bores, bleeder tops, hose connection holes, machined surfaces that mate to the steering knuckle and piston bodies with blue masking tape.
6. Bolted caliper halves back together using new o-rings (also from http://www.wallothnesch.com) and using ~45 ft.lbs. torque on the bolts.
7. Painted calipers, piston tops and rotor hats / fins with silver Duplicolor Brake Caliper paint. I would have used VHT, but it seems to be out of stock everywhere locally. I let everything cure for a few days.
8. I unmasked everything and soaked the new piston seals in brake fluid. I coated the cylinder bores and pistons with brake fluid and reinstalled the seals and pistons in their bores. I made sure the pistons were not jammed and used small channel-locks with rubber jaws to squeeze the pistons in past the seals. I installed new dust boots and clamp rings on the calipers. Remember that brake fluid is possibly the worlds best paint remover, so make sure you clean any spills or drips off the calipers immediately. I had to touch up a few finger prints and drip marks after reassembly.

I’ve had the calipers with PBR Metal Master pads and E32 750il front rotors installed on my 533i for a few days and I do like the pedal feel over stock. It might be pad choice or the fact that I have more forward brake bias now, but even when warmed up, the brakes do not seem to have the same grab or initial bite as the stock brakes did (BMW rotors & pads). The brakes are easier to modulate, especially when braking over bumpy surfaces where I used start to lock the front wheels under heavy braking. I do still have my mostly used up stock rear brakes intact and a set of E34 M5 rear calipers, MM pads and vented rotors in boxes so maybe I’ll install that setup.

Thanks to everyone here who helped answer questions and give good direction! I hope there is some useful info in this post for folks to use in the future. Thanks for the space.

Mark

[cgraff]

Anyone ever try these rebuilt calipers? The price certainly seems right.

Cheaper than my single pot floaters too. Strange...

Aaron

I’ve had the calipers with PBR Metal Master pads and E32 750il front rotors installed on my 533i for a few days and I do like the pedal feel over stock. It might be pad choice or the fact that I have more forward brake bias now, but even when warmed up, the brakes do not seem to have the same grab or initial bite as the stock brakes did (BMW rotors & pads). The brakes are easier to modulate, especially when braking over bumpy surfaces where I used start to lock the front wheels under heavy braking. I do still have my mostly used up stock rear brakes intact and a set of E34 M5 rear calipers, MM pads and vented rotors in boxes so maybe I’ll install that setup.

Mark

Nice work Mark.

Just an aside, I've found that the Metal Masters vs PBR's deluxe do have a difference in 'initial bite' between them, and the stock BMW pads (e.g. Textar or Jurid or whatever they use).

The stock BMW pads have the most initial bite, but they will fade in very hot weather with prolonged use much faster. The PBR deluxe are low dust pads, but give up a tad bit of the stock BMW pads in terms of initial bite. The MM give up a bit more on top of that.

-Chris

[MarkD in NJ]

Nice work Mark.

Just an aside, I've found that the Metal Masters vs PBR's deluxe do have a difference in 'initial bite' between them, and the stock BMW pads (e.g. Textar or Jurid or whatever they use).

The stock BMW pads have the most initial bite, but they will fade in very hot weather with prolonged use much faster. The PBR deluxe are low dust pads, but give up a tad bit of the stock BMW pads in terms of initial bite. The MM give up a bit more on top of that.

-Chris

Yeah Chris, Thanks. Another great thing about the M5 front calipers (and E12, E23, Volvo 240 & Toyota 4Runner) is that it takes 30 seconds to change the brake pads. I see myself trying a bunch until I find my favorite, although if I was going for selection or economy, I would have just installed my 750il front calipers in the first place.

I tend to compare everything to my E30 track car with Hawk HT10 pads. The car is light and the brakes are throw-a-chain-around-a-tree, make-your-eyes-pop-out good.

Mark

[ahab]

At least two board members purchased them to find that they are E23 7-series calipers and the bolt spacing, amongst other dimensions, is incorrect for the E28. The generic supplier parts catalogs don't differentiate between E23 and E28 M5 calipers, assuming that BMW used the same 4-piston units on all cars. The brake pads are the same size, however. The E23 4-pot calipers are probably cheaper than single pot calipers because there is so little demand for the stock that exists.

Mark,

That would make sense. I have a set of E23s on the bench and am familiar with the differences, no way are they gonna fit. I have the 750s on my E28 but I much prefer 4 piston fixed calipers, my other car has a set of Brembos and changing the pads requires a pair of pliers and as you said, 30 seconds. Removing the wheel is a bigger pain.

Sounds like you did a beautiful resto on those. Did you take any pics?

Aaron

[MarkD in NJ]

Sounds like you did a beautiful resto on those. Did you take any pics?

Aaron

They did come out quite nice especially considering the starting point (neglected calipers from a yard in Canada). The brake fluid messed with my paint job a bit - if I ever rebuild them again, I will powder coat them. I was going to take some pics as I went along, but got carried away and before I knew it I was putting everything back together!

I will post a pic or two next time I pull a wheel.

Mark