1988 944 Parking Brake Shoe Replacement
04-24-2007, 10:36 PM
#1
Instructor
Thread Starter
1988 944 Parking Brake Shoe Replacement
ARRGGG!
After discovering that mine had the friction surface delaminating and 'chunking' to various degrees on all four, I opted to replace both sides w/rebuilt units since 1) I feared used ones might go in a few years as well and 2) new ones from Porsche are around $170.00 US.
After much screwing around today I found that two of the four rebuilt shoes paired together will allow the disc/hat to be reinstalled with no problem at all - perfect fit with no drag - on either side or position (Leading/Trailing)!
The remaining two will just not let the disc/hat go back on. As far as I can tell there is no designated 'Leading/Trailing' shoe and all four are identical to the eye.
And yes, the handbrake cable assembly is at full slack and the star adjusters are fully collapsed. The parking brake actuating 'scissors' at the bottom of the assembly even wiggle just a tad on both sides with the shoes installed so they're definitely NOT putting pressure on the shoes and trying to expand them.
Whatever side (or position) I try to place one (or both) of these two 'problem' shoes on it becomes a no-go (especially when they're paired) so to my question: can a brake shop evenly reduce or 'radius' these two shoes to thin them down about .5mm each? I'm sure that's all I need.
The shoes were not free but they're not expensive enough to go about the hassle of returning what with shipping and lost time and the possibility of just getting more of the same. I positively HATE this aspect of lower 'price-point' items... Besides, the rebuilts DO look good/well done - they're just a tad too thick on two of them. What a bitch!
Barry
NEVER underestimate the infinite amount of time a 1 Hour Job takes...
After discovering that mine had the friction surface delaminating and 'chunking' to various degrees on all four, I opted to replace both sides w/rebuilt units since 1) I feared used ones might go in a few years as well and 2) new ones from Porsche are around $170.00 US.
After much screwing around today I found that two of the four rebuilt shoes paired together will allow the disc/hat to be reinstalled with no problem at all - perfect fit with no drag - on either side or position (Leading/Trailing)!
The remaining two will just not let the disc/hat go back on. As far as I can tell there is no designated 'Leading/Trailing' shoe and all four are identical to the eye.
And yes, the handbrake cable assembly is at full slack and the star adjusters are fully collapsed. The parking brake actuating 'scissors' at the bottom of the assembly even wiggle just a tad on both sides with the shoes installed so they're definitely NOT putting pressure on the shoes and trying to expand them.
Whatever side (or position) I try to place one (or both) of these two 'problem' shoes on it becomes a no-go (especially when they're paired) so to my question: can a brake shop evenly reduce or 'radius' these two shoes to thin them down about .5mm each? I'm sure that's all I need.
The shoes were not free but they're not expensive enough to go about the hassle of returning what with shipping and lost time and the possibility of just getting more of the same. I positively HATE this aspect of lower 'price-point' items... Besides, the rebuilts DO look good/well done - they're just a tad too thick on two of them. What a bitch!
Barry
NEVER underestimate the infinite amount of time a 1 Hour Job takes...
04-25-2007, 04:07 AM
#4
Instructor
Thread Starter
AznDrgn,
I thought about hand sanding but my hands & eyes are just not that good at precision sanding! Especially on a curved surface!
Truth be told, if I could get the disc/hat on then one slow lap around the neighborhood with me lightly modulating the handbrake (so I wouldn't cook the shoes and end back up in the 'chunking' boat) would probably 'radius' them fine!?!? 8-0
I just want to get this done in a manner where the PB works AND I can depend on it to help stop the car smoothly & evenly if the primary braking system goes down - I.E. using it in its 'Emergency Brake' role since this is a street car.
While I'm not interested in doing 'Handbrake Turns' I do want 'even braking' from the PB at highway speeds if the driver of the car ever needs it and that requires a few things. In this case, shoes and drum surfaces in good condition, proper shoe adjustment (both left and right) and a properly adjusted/operating handbrake cable & lever assembly.
Accurate and fairly complete PB 'shoe to drum' contact is why I'm hesitant to hand sand (don't even mention asbestos - although the rebuilts look like they're metallic). I'd probably introduce some 'low/uneven' spots and I'd like to know I have all of the friction surface contact area I've paid for available to me if I ever need the PB in a VERY bad way.
Hang on! I'm getting on my Soap Box Now ;-)
It doesn't happen in most folks lives but in another life and time I once DID need the PB in a car at about 80mph. With one rear wheel braking well (and capable of locking) and the other rear wheel 'out to lunch' I almost wet my pants and lost the car (if you ever have to do this NEVER, NEVER take your finger/hand off the release button/grip. If you do you may NOT be able to get OFF the E-Brake in time to recover!)
Not quite what I needed at the time but I must say the car WOULD stay put on a hill at ZERO mph! YMMV on that observation! ;-)
That's what I love about TRUE race cars - there's so much stuff like this you can dump. Not needed, it's excess weight/additional complexity and just another failure point. What makes this type of 'system deletion' possible (and I'm not talking just PBs here) is that the car is constantly exercised to its fullest and always under pretty expert scrutiny (driver and tech guys) in a VERY controlled environment. Any faults will hopefully be caught quickly (but sadly not always) and addressed before they become an issue.
When you consider a system like a PB in a true racing context, in most scenarios the need for one isn't really there so it's one of the first 'road based' systems to go from a design standpoint. For street cars, however, the PB still plays an important and dual role - from the lowly 'holding me on a hill' role to the mighty brake pedal straight-to-the-floor-with-no-effect 'Holy **** - PLEASE DON'T FAIL ME NOW!!!!' role.
Unlike a racing car, our street cars may go for thousands of miles without ever having a close examination or thorough exercising of a 'Critical System' component, especially if it's a mundane one like a PB. I did the same and that's why my jaw dropped when I saw the condition of the PB shoes. Holy Smokes! - It's such a small part of the whole but what if a big chunk of 'already loose' PB shoe had decided to come off and lock a rear wheel while I was enjoying a fast bend at near full left or right side suspension compression?
I like to think I'm pretty good in the 'car control' arena but I'm definitely no Hans Stuck! It gives me the chills to even think about being blind-sided by a system as simple as the damn PB and its components at the wrong moment!
On street cars many folks normally assume that 'Critical Systems' such as tires, brakes, wheel bearings, steering, suspension components, fuel containment and drivetrain items (those that could fail and unexpectedly lock-up a wheel) will always be there when we need them and NEVER fail. Maybe so, Maybe not... And the latter is especially true as these cars age.
Ok, OK - I'm getting down from the box now... ;-)
Sorry for the less than brief response. I admit it - where cars are concerned (race or street) and as my age progresses, I'm really becoming an 'All Critical Systems Working' ******* (but in a Nice way...) and E-Brakes now fall into my 'Critical Systems' list for those cars equipped with them.
So, with all this 'high & mighty' attitude, how/why did I let the 944's PB shoes get so bad in the first place? Hell man, they're only PBs, right? Never again will I think that. I almost learned it BIG TIME once and let the experience slide (ah, the insulation of youth!) - I don't need another episode like that now that I'm older, smarter, better looking and worth more... ;-)
As for hand sanding, knowing my lack of expertise in evenly sanding things round I'll pass and hope a qualified brake shop can do something for me.
Barry
Paranoid?!?!? Me?!?!? You're just saying that because you're trying to kill me! ;-)
I thought about hand sanding but my hands & eyes are just not that good at precision sanding! Especially on a curved surface!
Truth be told, if I could get the disc/hat on then one slow lap around the neighborhood with me lightly modulating the handbrake (so I wouldn't cook the shoes and end back up in the 'chunking' boat) would probably 'radius' them fine!?!? 8-0
I just want to get this done in a manner where the PB works AND I can depend on it to help stop the car smoothly & evenly if the primary braking system goes down - I.E. using it in its 'Emergency Brake' role since this is a street car.
While I'm not interested in doing 'Handbrake Turns' I do want 'even braking' from the PB at highway speeds if the driver of the car ever needs it and that requires a few things. In this case, shoes and drum surfaces in good condition, proper shoe adjustment (both left and right) and a properly adjusted/operating handbrake cable & lever assembly.
Accurate and fairly complete PB 'shoe to drum' contact is why I'm hesitant to hand sand (don't even mention asbestos - although the rebuilts look like they're metallic). I'd probably introduce some 'low/uneven' spots and I'd like to know I have all of the friction surface contact area I've paid for available to me if I ever need the PB in a VERY bad way.
Hang on! I'm getting on my Soap Box Now ;-)
It doesn't happen in most folks lives but in another life and time I once DID need the PB in a car at about 80mph. With one rear wheel braking well (and capable of locking) and the other rear wheel 'out to lunch' I almost wet my pants and lost the car (if you ever have to do this NEVER, NEVER take your finger/hand off the release button/grip. If you do you may NOT be able to get OFF the E-Brake in time to recover!)
Not quite what I needed at the time but I must say the car WOULD stay put on a hill at ZERO mph! YMMV on that observation! ;-)
That's what I love about TRUE race cars - there's so much stuff like this you can dump. Not needed, it's excess weight/additional complexity and just another failure point. What makes this type of 'system deletion' possible (and I'm not talking just PBs here) is that the car is constantly exercised to its fullest and always under pretty expert scrutiny (driver and tech guys) in a VERY controlled environment. Any faults will hopefully be caught quickly (but sadly not always) and addressed before they become an issue.
When you consider a system like a PB in a true racing context, in most scenarios the need for one isn't really there so it's one of the first 'road based' systems to go from a design standpoint. For street cars, however, the PB still plays an important and dual role - from the lowly 'holding me on a hill' role to the mighty brake pedal straight-to-the-floor-with-no-effect 'Holy **** - PLEASE DON'T FAIL ME NOW!!!!' role.
Unlike a racing car, our street cars may go for thousands of miles without ever having a close examination or thorough exercising of a 'Critical System' component, especially if it's a mundane one like a PB. I did the same and that's why my jaw dropped when I saw the condition of the PB shoes. Holy Smokes! - It's such a small part of the whole but what if a big chunk of 'already loose' PB shoe had decided to come off and lock a rear wheel while I was enjoying a fast bend at near full left or right side suspension compression?
I like to think I'm pretty good in the 'car control' arena but I'm definitely no Hans Stuck! It gives me the chills to even think about being blind-sided by a system as simple as the damn PB and its components at the wrong moment!
On street cars many folks normally assume that 'Critical Systems' such as tires, brakes, wheel bearings, steering, suspension components, fuel containment and drivetrain items (those that could fail and unexpectedly lock-up a wheel) will always be there when we need them and NEVER fail. Maybe so, Maybe not... And the latter is especially true as these cars age.
Ok, OK - I'm getting down from the box now... ;-)
Sorry for the less than brief response. I admit it - where cars are concerned (race or street) and as my age progresses, I'm really becoming an 'All Critical Systems Working' ******* (but in a Nice way...) and E-Brakes now fall into my 'Critical Systems' list for those cars equipped with them.
So, with all this 'high & mighty' attitude, how/why did I let the 944's PB shoes get so bad in the first place? Hell man, they're only PBs, right? Never again will I think that. I almost learned it BIG TIME once and let the experience slide (ah, the insulation of youth!) - I don't need another episode like that now that I'm older, smarter, better looking and worth more... ;-)
As for hand sanding, knowing my lack of expertise in evenly sanding things round I'll pass and hope a qualified brake shop can do something for me.
Barry
Paranoid?!?!? Me?!?!? You're just saying that because you're trying to kill me! ;-)
04-25-2007, 08:28 AM
#5
Three Wheelin'
Clamp the shoe in a vice and then use a long strip of sanpaper like the stuff the use on plumbing or buy a belt sander belt and as long as you keep below the edges of the shoe it should sand itself pretty evenly.
04-26-2007, 09:20 PM
#6
Instructor
Thread Starter
Folks,
Thanks to OSHA (and for good reason I'm sure) it looks like AznDrgn has the only way out save a real machine shop & more $ than it's worth (plus the aspect of guys in black OSHA logoed jump suits dropping from the sky yelling 'Freeze - hands (shoes?) where we can see'em!).
In the old days it was termed 'Brake Shoe Arcing' and a nifty little ANCO machine did the job. OSHA canned it due to the dust hazard and only really old brake shops may still have the machine. I did find one but after the owner sized me up and agreed to give it a shot the shoes turn out to be to small to fit the machine. Oh Well...
So out to ACE I'll go for an 80 and 120 grit belt sander belt and a dust mask. I'll clamp the shoes in a hefty vise and hum 'Zippity Do Dah' while I work! I KNEW all that shoe shine work in the Army would pay off some day ;-)
Barry
"Uh, permit? I, uh, didn't know I needed a permit.... sir..."
Thanks to OSHA (and for good reason I'm sure) it looks like AznDrgn has the only way out save a real machine shop & more $ than it's worth (plus the aspect of guys in black OSHA logoed jump suits dropping from the sky yelling 'Freeze - hands (shoes?) where we can see'em!).
In the old days it was termed 'Brake Shoe Arcing' and a nifty little ANCO machine did the job. OSHA canned it due to the dust hazard and only really old brake shops may still have the machine. I did find one but after the owner sized me up and agreed to give it a shot the shoes turn out to be to small to fit the machine. Oh Well...
So out to ACE I'll go for an 80 and 120 grit belt sander belt and a dust mask. I'll clamp the shoes in a hefty vise and hum 'Zippity Do Dah' while I work! I KNEW all that shoe shine work in the Army would pay off some day ;-)
Barry
"Uh, permit? I, uh, didn't know I needed a permit.... sir..."
04-29-2007, 12:51 AM
#7
Instructor
Thread Starter
Folks,
OK, the PB shoes are on, bedded, properly adjusted (left/right) and will haul the car down smoothly (but slowly of course!) from 60 MPH - but what a chore!
As I estimated, only .5mm needed to be removed from each of the two 'problem' shoes but doing it evenly was the issue. Using 80 grit paper strips for a 'body work file' in a longitudinal direction and 'shoe shine' like fashion DID work but it 'crowned' the surface both longwise (length) and crosswise (width). Using a measuring caliper frequently helped detect this so out came the good old metal file to knock down the high spots.
The file was used only in a crosswise (width) motion combined with slowly moving it along the length of the shoe to knock off the central 'crown'. I also had to use more pressure on the middle portion of the shoes (longitudinally speaking) to restore a proper 'radius'.
Work progress was slow. Man, this lining material is HARD! It took about 45 minutes for each shoe considering all the measuring that was goin on. Back and forth (sand/measure/file/measure/repeat) was the order of the day until I'd reduce the shoes .5mm each. The only upside was that I found I'm better at this sanding/filing stuff than I thought!
After bedding the shoes in with a few EASY stops from 10, 20 and 30 MPH it all settled out fine. One more adjustment at the wheels (to account for the stuff I ground off bedding) got me an acceptable stop from 60 MPH and solid hill holding at 3 clicks on the handbrake. Works for me!
What a TON of work to get this right :-( and I'm not happy at all on having to go through this. Watch those rebuilt shoes is all I can say. I pulled and measured the 'good' ones against the 'problem' ones before I started the 'sand/file' stuff and the difference was obvious with the measuring caliper - .5mm to a full 1mm variance in some areas. I guess you get what you pay for but $170 for OEM shoes seemed outrageous so I went the rebuilt route.
Oh well, I learned a new skill so all's not lost. If you ever have to do this just make sure you work SLOWLY, measure often (both longitudinally and horizontally), wear a mask and do it outside with PLENTY of ventilation. I used a box-fan to keep air flowing from behind me to keep the filing dust AWAY from me.
Also make sure you're cautious during the 'bedding' process. At first my 'good' side would lock-up before the 'sanded/filed' side (at 10 MPH in the driveway no less!) and I'm sure that was due to my 'less than perfect' surface profile! Just take your time and give the shoes/drums sufficient time (say 15 minutes at speed to promote cooling airflow) to cool off between applications.
I truly hope this info helps SOMEONE SOMEDAY. Such a STUPID problem AND thread... as I started this post with, I say again - ARRGGG!
Barry
Replace your PB Shoes? Sure, NO problem... ARRGGG!!!!!
OK, the PB shoes are on, bedded, properly adjusted (left/right) and will haul the car down smoothly (but slowly of course!) from 60 MPH - but what a chore!
As I estimated, only .5mm needed to be removed from each of the two 'problem' shoes but doing it evenly was the issue. Using 80 grit paper strips for a 'body work file' in a longitudinal direction and 'shoe shine' like fashion DID work but it 'crowned' the surface both longwise (length) and crosswise (width). Using a measuring caliper frequently helped detect this so out came the good old metal file to knock down the high spots.
The file was used only in a crosswise (width) motion combined with slowly moving it along the length of the shoe to knock off the central 'crown'. I also had to use more pressure on the middle portion of the shoes (longitudinally speaking) to restore a proper 'radius'.
Work progress was slow. Man, this lining material is HARD! It took about 45 minutes for each shoe considering all the measuring that was goin on. Back and forth (sand/measure/file/measure/repeat) was the order of the day until I'd reduce the shoes .5mm each. The only upside was that I found I'm better at this sanding/filing stuff than I thought!
After bedding the shoes in with a few EASY stops from 10, 20 and 30 MPH it all settled out fine. One more adjustment at the wheels (to account for the stuff I ground off bedding) got me an acceptable stop from 60 MPH and solid hill holding at 3 clicks on the handbrake. Works for me!
What a TON of work to get this right :-( and I'm not happy at all on having to go through this. Watch those rebuilt shoes is all I can say. I pulled and measured the 'good' ones against the 'problem' ones before I started the 'sand/file' stuff and the difference was obvious with the measuring caliper - .5mm to a full 1mm variance in some areas. I guess you get what you pay for but $170 for OEM shoes seemed outrageous so I went the rebuilt route.
Oh well, I learned a new skill so all's not lost. If you ever have to do this just make sure you work SLOWLY, measure often (both longitudinally and horizontally), wear a mask and do it outside with PLENTY of ventilation. I used a box-fan to keep air flowing from behind me to keep the filing dust AWAY from me.
Also make sure you're cautious during the 'bedding' process. At first my 'good' side would lock-up before the 'sanded/filed' side (at 10 MPH in the driveway no less!) and I'm sure that was due to my 'less than perfect' surface profile! Just take your time and give the shoes/drums sufficient time (say 15 minutes at speed to promote cooling airflow) to cool off between applications.
I truly hope this info helps SOMEONE SOMEDAY. Such a STUPID problem AND thread... as I started this post with, I say again - ARRGGG!
Barry
Replace your PB Shoes? Sure, NO problem... ARRGGG!!!!!
