HIGHWAYMAN: Bringing the Devore 928 back from the dead
12-05-2016, 07:48 PM
#197
Banned
Thread Starter
A good CV gone bad....
So today I was planning on refurbishing the CVs. In preparation, I bought 32 cases of paper towels, and 14 gallons of carb cleaner. For those of you that have done this job, you get the joke - it is among the messiest jobs you can do on a car.
I have been surprised by some people's lack of knowledge when it comes to all things constant velocity. For example, I have seen people strip down both ends of the axle and put all the bearings, cages, and housings in a bucket of grease remover.
Only problem with that is that the bearings are matched to the CV housing and cage, kind of like a group of piston rods. They bearings need to stay with the cages and housings they came out of. You can switch the CV from end to end on an axle, as long as it stays with its bearings.
So I strip down the first axle. Shaft looks good, cleans up nice. Then I spot the problem inside the CV housing....grooves made by the bearing over time. You can see where I have my razor blade pointed at them. Deep enough to feel with your fingers.
The problem with this increased play is that it allows the bearings to move around more, providing a looser fit, which can increase heat and friction. Considering this is a race car, these CVs are absolutely a NO GO.
For a great read on CV technology, read Roland Kussmaul's new book. Roland was a 36 year engineer at Porsche, responsible for the 959 rally car and the 956/962 development. Needless to say they had tons of trouble with CVs on the rally cars....great read.
Yes, all the CV housings look like this.
As to their replacement, I have opted to go with 930 CVs. For starters, a 930 CV is dimensionally similar to the 928 CV where it counts - spline count, bolt circle, etc. There are some minor differences, but I am not concerned with them.
As a contrast, 928 CVs (if you can find them) are $200+ dollars each. 930 CVs are $50 each.
And boosted 930s have made more power than most 928s....so we're good there. This way, If I have CV issues, I am only $200 away from a whole new set. They should be here this week.
I have been surprised by some people's lack of knowledge when it comes to all things constant velocity. For example, I have seen people strip down both ends of the axle and put all the bearings, cages, and housings in a bucket of grease remover.
Only problem with that is that the bearings are matched to the CV housing and cage, kind of like a group of piston rods. They bearings need to stay with the cages and housings they came out of. You can switch the CV from end to end on an axle, as long as it stays with its bearings.
So I strip down the first axle. Shaft looks good, cleans up nice. Then I spot the problem inside the CV housing....grooves made by the bearing over time. You can see where I have my razor blade pointed at them. Deep enough to feel with your fingers.
The problem with this increased play is that it allows the bearings to move around more, providing a looser fit, which can increase heat and friction. Considering this is a race car, these CVs are absolutely a NO GO.
For a great read on CV technology, read Roland Kussmaul's new book. Roland was a 36 year engineer at Porsche, responsible for the 959 rally car and the 956/962 development. Needless to say they had tons of trouble with CVs on the rally cars....great read.
Yes, all the CV housings look like this.
As to their replacement, I have opted to go with 930 CVs. For starters, a 930 CV is dimensionally similar to the 928 CV where it counts - spline count, bolt circle, etc. There are some minor differences, but I am not concerned with them.
As a contrast, 928 CVs (if you can find them) are $200+ dollars each. 930 CVs are $50 each.
And boosted 930s have made more power than most 928s....so we're good there. This way, If I have CV issues, I am only $200 away from a whole new set. They should be here this week.
12-11-2016, 04:44 PM
#198
Banned
Thread Starter
Hubs and Wheel bearings
Sorry for not posting, been away this week dealing with the Evil Turbo Targa, which is getting painted one of my favorite colors, Mexico Blue.
So this weekend I thought I'd tackle the hubs and wheel bearings. Pretty straightforward job, but has some pitfalls for sure.
The first thing you might miss is that when you press the stub axles out of the hubs, it will usually destroy the old bearing, splitting it in half and leaving half of the old bearing race stuck on the stub axle.
If you don't know what you're doing, the old bearing race on the stub axle looks like it belongs there. It's usually covered in road crap, and the same color as the stub axle. I have seen many people try to press the stub axle into the new hub with the old race on, which causes the stub axle not to seat properly.
The old bearing race is a bitch to get off, but there is an easy trick to doing this. For starters, there is no way to press it off or use a gear puller to move it - there are no bearing surfaces with which to grab onto.
The race itself is made of hardened steel and impervious to most tools. However, hardened steel has one primary weakness - it is brittle.
Score it with an air cutting wheel, then hit it with a drift or metal chisel and a BFH. The steel cracks easily, and the old race comes right off.
So this weekend I thought I'd tackle the hubs and wheel bearings. Pretty straightforward job, but has some pitfalls for sure.
The first thing you might miss is that when you press the stub axles out of the hubs, it will usually destroy the old bearing, splitting it in half and leaving half of the old bearing race stuck on the stub axle.
If you don't know what you're doing, the old bearing race on the stub axle looks like it belongs there. It's usually covered in road crap, and the same color as the stub axle. I have seen many people try to press the stub axle into the new hub with the old race on, which causes the stub axle not to seat properly.
The old bearing race is a bitch to get off, but there is an easy trick to doing this. For starters, there is no way to press it off or use a gear puller to move it - there are no bearing surfaces with which to grab onto.
The race itself is made of hardened steel and impervious to most tools. However, hardened steel has one primary weakness - it is brittle.
Score it with an air cutting wheel, then hit it with a drift or metal chisel and a BFH. The steel cracks easily, and the old race comes right off.
12-11-2016, 04:56 PM
#199
Banned
Thread Starter
Next, I cleaned up the hubs real nice. I also removed the parking brake shoes and assorted crap, for two reasons:
1. Less complexity.
2. Not a good idea to set the parking brake after racing with super heated brakes. The thing can weld itself in place and cause trouble.
I suppose weight savings is a benefit, but the parking brake gear probably weighs only a pound per side, and then with the cables and handbrake lever maybe 5-6 pounds more, so not a huge amount.
With the hub cleaned really well, especially paying attention to the seating area for the bearing, it's time to put the new bearings in.
I threw the new bearings in the freezer overnight, and this morning, I gently heated up the hubs with a propane torch. The goal here is to get it warmish, not glowing red.
With the hub heated, you put the frozen bearing in it slot, and it will slide most of the way in by itself, using only light hammer taps to seat it in.
You can really only tap it far enough to make it flush, and from there it's off to the press for the final little bit.
I use the OLD bearing as a surface to press on.
Remember, you are only pressing it in that final quarter inch so that it can clear the groove for the (totally redundant) massive circlip.
Tap the old bearing out with a hammer. It's only barely in there and it will just fall off.
Put the circlip back on.
Next, press in the stub axle, and **very important** make sure you use a socket that matches the OD of the bearing on the top side, or else you will separate the bearing halves as the stub axle gets pressed in.
Now the hub is complete with new bearing. Keep in mind two things:
1. The bearing will have a lot of drag, and be hard to turn. This is because the grease is still frozen!
2. You might feel an eccentric wobble as you turn the stub axle by hand. THE BEARING WILL NOT ACHIEVE IT'S FINAL TOLERANCE UNTIL THE AXLE NUT IS PROPERLY TORQUED DOWN! So nothing to worry about. It's pretty loose until the axle nut is on to cinch the two bearing halves together!
1. Less complexity.
2. Not a good idea to set the parking brake after racing with super heated brakes. The thing can weld itself in place and cause trouble.
I suppose weight savings is a benefit, but the parking brake gear probably weighs only a pound per side, and then with the cables and handbrake lever maybe 5-6 pounds more, so not a huge amount.
With the hub cleaned really well, especially paying attention to the seating area for the bearing, it's time to put the new bearings in.
I threw the new bearings in the freezer overnight, and this morning, I gently heated up the hubs with a propane torch. The goal here is to get it warmish, not glowing red.
With the hub heated, you put the frozen bearing in it slot, and it will slide most of the way in by itself, using only light hammer taps to seat it in.
You can really only tap it far enough to make it flush, and from there it's off to the press for the final little bit.
I use the OLD bearing as a surface to press on.
Remember, you are only pressing it in that final quarter inch so that it can clear the groove for the (totally redundant) massive circlip.
Tap the old bearing out with a hammer. It's only barely in there and it will just fall off.
Put the circlip back on.
Next, press in the stub axle, and **very important** make sure you use a socket that matches the OD of the bearing on the top side, or else you will separate the bearing halves as the stub axle gets pressed in.
Now the hub is complete with new bearing. Keep in mind two things:
1. The bearing will have a lot of drag, and be hard to turn. This is because the grease is still frozen!
2. You might feel an eccentric wobble as you turn the stub axle by hand. THE BEARING WILL NOT ACHIEVE IT'S FINAL TOLERANCE UNTIL THE AXLE NUT IS PROPERLY TORQUED DOWN! So nothing to worry about. It's pretty loose until the axle nut is on to cinch the two bearing halves together!
12-11-2016, 05:43 PM
#200
Team Owner
the lower control arm mods are pretty cool
Last edited by Mrmerlin; 12-13-2016 at 10:09 AM.
12-11-2016, 08:14 PM
#202
Banned
Thread Starter
I actually used to do the oven thing back in the day until the wife put a stop to that:-)
As for the heating thing, I am only getting it warm-ish. There are reasons why I do it this way:
1. I don't like to handle 300 degree parts. It changes the nature of the operation to something that adds a whole 'nother layer of hassle.
2. The bearing is left in the freezer overnight.
3. With the tiniest amount of warmth from the torch, the bearing more or less slides in there. The press is using VERY little force. So if there is, say 10 tons of pressure required to press the old bearing out, there is a tiny fraction of that to help it back in, doing it my way.
4. Even across other Porsche models, heating the hubs is not necessarily required.
These hubs are totally overbuilt, never had a problem.
As for the heating thing, I am only getting it warm-ish. There are reasons why I do it this way:
1. I don't like to handle 300 degree parts. It changes the nature of the operation to something that adds a whole 'nother layer of hassle.
2. The bearing is left in the freezer overnight.
3. With the tiniest amount of warmth from the torch, the bearing more or less slides in there. The press is using VERY little force. So if there is, say 10 tons of pressure required to press the old bearing out, there is a tiny fraction of that to help it back in, doing it my way.
4. Even across other Porsche models, heating the hubs is not necessarily required.
These hubs are totally overbuilt, never had a problem.
12-12-2016, 12:45 AM
#203
Intermediate
This is a very cool thread! I recall seeing this car on Craigslist for a looooong time and always hoped somebody scooped it up. Happy to see it in CA! As for the lack of rear swaybar, that's familiar to me. I tracked a Nissan 370Z and a popular track car "mod" is taking off the rear swaybar or keeping the stock one on while buying the stiffest front you can find. The combination gets rid of a ton of oversteer that those cars are well known for. The rear suspension is allowed to flex and sort of do its mechanical job. Anyways, have a blast with the car man. I hope to see it in person someday at the track.
12-12-2016, 01:12 PM
#205
Banned
Thread Starter
This is a very cool thread! I recall seeing this car on Craigslist for a looooong time and always hoped somebody scooped it up. Happy to see it in CA! As for the lack of rear swaybar, that's familiar to me. I tracked a Nissan 370Z and a popular track car "mod" is taking off the rear swaybar or keeping the stock one on while buying the stiffest front you can find. The combination gets rid of a ton of oversteer that those cars are well known for. The rear suspension is allowed to flex and sort of do its mechanical job. Anyways, have a blast with the car man. I hope to see it in person someday at the track.
Thanks! Really interesting to see the Z behaved in the same way.
I was telling Carl that when I did the suspension setup on the Camaro I worked with a GM engineer to fine tune the setup. The Camaro wants a MASSIVE rear sway and almost no front sway - opposite of the 928 and Z.
He told me it was this way because for safety reasons, there is a significant amount of understeer built into GM's Zeta platform.
I guess I wonder why the 928 is designed with so much oversteer built in.....
12-12-2016, 02:38 PM
#206
Rennlist Member
Oversteer built in?? I'm not an expert on this stuff, but my impression was that the stock 928 had understeer. In fact, the adjustable drop-links I installed in the rear were supposed to take the understeer out I thought?
I'm not a track guy so I could be all wrong...
I'm not a track guy so I could be all wrong...
12-12-2016, 03:02 PM
#207
Banned
Thread Starter
Bureau...
Not a track guy either (yet), but full stiff on the front sway and full soft on the rear sway fights oversteer. So I presume that is what we are trying to cure.
Maybe some track guys can chime in?
Not a track guy either (yet), but full stiff on the front sway and full soft on the rear sway fights oversteer. So I presume that is what we are trying to cure.
Maybe some track guys can chime in?
12-12-2016, 04:51 PM
#208
Rennlist
Basic Site Sponsor
Basic Site Sponsor
Next, I cleaned up the hubs real nice. I also removed the parking brake shoes and assorted crap, for two reasons:
1. Less complexity.
2. Not a good idea to set the parking brake after racing with super heated brakes. The thing can weld itself in place and cause trouble.
I suppose weight savings is a benefit, but the parking brake gear probably weighs only a pound per side, and then with the cables and handbrake lever maybe 5-6 pounds more, so not a huge amount.
With the hub cleaned really well, especially paying attention to the seating area for the bearing, it's time to put the new bearings in.
I threw the new bearings in the freezer overnight, and this morning, I gently heated up the hubs with a propane torch. The goal here is to get it warmish, not glowing red.
With the hub heated, you put the frozen bearing in it slot, and it will slide most of the way in by itself, using only light hammer taps to seat it in.
You can really only tap it far enough to make it flush, and from there it's off to the press for the final little bit.
I use the OLD bearing as a surface to press on.
Remember, you are only pressing it in that final quarter inch so that it can clear the groove for the (totally redundant) massive circlip.
Tap the old bearing out with a hammer. It's only barely in there and it will just fall off.
Put the circlip back on.
Next, press in the stub axle, and **very important** make sure you use a socket that matches the OD of the bearing on the top side, or else you will separate the bearing halves as the stub axle gets pressed in.
Now the hub is complete with new bearing. Keep in mind two things:
1. The bearing will have a lot of drag, and be hard to turn. This is because the grease is still frozen!
2. You might feel an eccentric wobble as you turn the stub axle by hand. THE BEARING WILL NOT ACHIEVE IT'S FINAL TOLERANCE UNTIL THE AXLE NUT IS PROPERLY TORQUED DOWN! So nothing to worry about. It's pretty loose until the axle nut is on to cinch the two bearing halves together!
1. Less complexity.
2. Not a good idea to set the parking brake after racing with super heated brakes. The thing can weld itself in place and cause trouble.
I suppose weight savings is a benefit, but the parking brake gear probably weighs only a pound per side, and then with the cables and handbrake lever maybe 5-6 pounds more, so not a huge amount.
With the hub cleaned really well, especially paying attention to the seating area for the bearing, it's time to put the new bearings in.
I threw the new bearings in the freezer overnight, and this morning, I gently heated up the hubs with a propane torch. The goal here is to get it warmish, not glowing red.
With the hub heated, you put the frozen bearing in it slot, and it will slide most of the way in by itself, using only light hammer taps to seat it in.
You can really only tap it far enough to make it flush, and from there it's off to the press for the final little bit.
I use the OLD bearing as a surface to press on.
Remember, you are only pressing it in that final quarter inch so that it can clear the groove for the (totally redundant) massive circlip.
Tap the old bearing out with a hammer. It's only barely in there and it will just fall off.
Put the circlip back on.
Next, press in the stub axle, and **very important** make sure you use a socket that matches the OD of the bearing on the top side, or else you will separate the bearing halves as the stub axle gets pressed in.
Now the hub is complete with new bearing. Keep in mind two things:
1. The bearing will have a lot of drag, and be hard to turn. This is because the grease is still frozen!
2. You might feel an eccentric wobble as you turn the stub axle by hand. THE BEARING WILL NOT ACHIEVE IT'S FINAL TOLERANCE UNTIL THE AXLE NUT IS PROPERLY TORQUED DOWN! So nothing to worry about. It's pretty loose until the axle nut is on to cinch the two bearing halves together!
That circlip in your second to last picture is not seated in the machined groove for the circlip in the hub (you can easily see the "witness" marks on the circlip where it originally/should sit), because the wheel bearing isn't fully seated into that hub (which is quite visible in the last picture of your "completed" assembly....there's a "gap" between the bearing and the upright.)
Quite simply, you did not get the aluminum hot enough for the bearing to drop all the way to the "seat".
These bearings never need be pressed in. Properly done, they will drop right into the uprights, with no force other than one's fingertips.
You use your upright on the track (or the street) and the wheel bearing will "walk" right out of the upright...the circlip (not in the retention groove) will pop right out of the hub and the bearing will follow it.
As we all know, with heat, the upright expands more than the wheel bearing....because it is made out of aluminum, while the bearing is made out of steel. This is a huge problem with what seems to be "bearing play", when uprights are hot, on all of the 911 series cars. Cup Cars, with their big brakes and high heat transfer are famous for this "play" between the bearings and the uprights, when hot. Put one of these cars up in the air, fresh off the track, and give the top and the bottom of the tire a wiggle....the play will astonish you!
The bearings, in these "track" cars, will quickly pound the uprights out of round and the uprights need to be changed on a routine basis to maintain a "tight bearing fit". Uprights are completely trash from this bearing pounding after any 24 hour event....and it is very difficult to get the wheel bearings out of a vehicle that has been run at the 12 hours of Sebring (very rough course), they are so badly pounded. On track cars run on smoother courses and more intermittently, uprights can last as long as 40 hours.
Because you are a "911 guy", you know all of this, of course....this information is for all of those following along, at home.
The point is, when the uprights get hot...the wheel bearings will be loose....and the only thing keeping the bearing in is that circlip in the groove. No circlip or circlip not in the groove....the wheel bearing walks right out....resulting in "rather interesting" vehicle dynamics.
__________________
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
greg brown
714 879 9072
GregBBRD@aol.com
Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
Last edited by GregBBRD; 12-12-2016 at 05:50 PM.
12-12-2016, 06:04 PM
#210
Rennlist
Basic Site Sponsor
Basic Site Sponsor
That totally explains why the bearing is still not seated in the picture with the hub already pressed in....at which point it is impossible to properly seat the bearing without putting all the pressing pressure on the ***** in the bearing....ruining the bearing.
Totally sure....