[DeTomaso] Steering Rack Bearings - 1622 ZZ are not the right ones!!

Tue Aug 31 08:30:12 EDT 2010

Richard

The inner race was destroyed and the balls had fallen out.  Even in that 
condition, there seemed to be adequate engagement of the pinion and rack. 
The outer case through which the pinion passes has very little side to side 
clearance and until that is elongated, would keep the pinion centered.

Lars, the bearing guy, seems to know his craft. He has helped out the 
Pantera guys with other needs as well.  He stated that the bearings we were 
replacing the stock set with were vastly superior.

JT

----- Original Message ----- 
From: "Richard Barkley" <rlbpantera at earthlink.net>
To: "John Taphorn" <jtaphorn at kingwoodcable.com>
Cc: <rgg at gregorycook.com>; "Detomaso List" <DeTomaso at realbig.com>
Sent: Tuesday, August 31, 2010 1:51 AM
Subject: Re: [DeTomaso] Steering Rack Bearings - 1622 ZZ are not the right 
ones!!

>  John,
> Good to hear from you.
>
> First the good news: Turns out that the 1622 ZZ bearings are of the 
> "deep-groove radial" type as listed here:
> http://www.intechbearing.com/1600Series-DeepGrooveBallBearings2Shields.html
> The (maybe) bad news follows.
>
> From wikipedia we get http://en.wikipedia.org/wiki/Ball_bearing
>> For single-row deep-groove ball bearings, SKF's documentation says that 
>> maximum axial load is circa 50 % of maximum radial load, but it also says 
>> that "light" and/or "small" bearings can take axial loads that are 25 % 
>> of maximum radial load.[3]
> http://tinyurl.com/284clmh list a 1622 ZZ that has a static radial load of 
> 747 lbs. so the axial load rating would be about 375 lbs. But not all 
> bearings are created equal. Here is one that is rated at only 354 static 
> radial.
> http://www.dynaroll.com/1600seriesZZ.asp
>  Anyway, all of the axial load would go to just one of the two bearings, 
> depending on which way the steering wheel is turning.
>
> So the question is, what are the likely loads? The load will be 
> proportional to the torque (force) turning the steering wheel. For normal 
> driving the max would be at low speed, say parking the car and turning the 
> wheel while not moving. If the pinion has a 45 deg pitch on its "threads" 
> then, ignoring friction, the axial force will be equal to the force on the 
> rack. If you have a 1 ft dia steering wheel and turn with, say, 12 lbs 
> with each hand you generate 24 ftlb of torque. If the contact point on the 
> pinion with the rack is at a 1/2" radius, there will be a factor of 24 
> multiplying effect. So the net axial force on the bearing will be 24 x 24 
> = 576 lbs. Yikes!
>
> When you exceed the static load rating of a bearing, the elastic limit of 
> the balls (and maybe the race) is exceeded and one or more of them will be 
> deformed. Over time I guess you would end up with a bunch of lumpy balls 
> that wouldn't roll too smoothly. But I don't think there is much chance of 
> the bearings blowing apart, but maybe not. If the cage that locates the 
> bearings around the race gets eaten up or rusts away, the balls fall out 
> and... no more bearing.
>
> The thing the worries me is Rob wrote: " When we took the rack apart we 
> found that top bearings that sit in an open race where in many pieces." 
> What kind of bearing was in there? Were they the original "Angular 
> Contact" type or had they been replaced with radial BBs? Had all the balls 
> fallen out or were the races broken? The thing that worries me is that if 
> both bearings let loose (one first the second later) like the top one did 
> it seems possible that the pinion could no longer contact the rack and you 
> would LOOSE STEERING! If this happened at high speed, it could be 
> catastrophic...... It may be that the rack has a fail safe design, so even 
> it both bearings fail you can still steer, but I wouldn't count on it.
>
> Richard
>
> On 8/29/10 5:25 PM, John Taphorn wrote:
>> Hi Richard
>>
>> Good info.  The rack is in place and ready for testing when the car gets 
>> under power in a couple months.
>>
>> Since the pinion's shaft clearance, in and out, is contained by spacers 
>> in the rack's housing, I would think the axial loading minimal. 
>> Although, perhaps I misunderstand the application of "axial" in this 
>> application.
>>
>> Regardless, we will report back any problems.  Initially, there is no 
>> binding when turning the pinion shaft in either direction.  It appears to 
>> be a very happy camper.
>>
>> I suppose if the exercise requires another $8 in bearings after 10 years, 
>> that will not be so bad.  I'll add that if I faced the same issue today, 
>> I would go with those bearings happily with naive confidence.
>>
>> JT
>> ----- Original Message ----- From: "Richard Barkley" 
>> <rlbpantera at earthlink.net>
>> To: <rgg at gregorycook.com>; "Detomaso List" <DeTomaso at realbig.com>
>> Sent: Sunday, August 29, 2010 6:59 PM
>> Subject: [DeTomaso] Steering Rack Bearings - 1622 ZZ are not the right 
>> ones!!
>>
>>
>>>  Rob,
>>>
>>> I'm afraid to say but you don't have the right kind of bearing for this
>>> application. I went through this about 10 years ago. The problem is that
>>> the rack and pinion gears are cut at about a 45 deg angle which means
>>> there will be an axial load on the bearings about equal to the load on
>>> the rack. Regular ball bearings are meant for primarily radial loads and
>>> can fail quickly with axial loads although, due to the low rotation
>>> rates that may not be the case here. The original bearings have the
>>> balls contacted at a 45 deg angle. Here's a link to pictures and
>>> diagrams on my website.
>>>
>>> http://home.earthlink.net/~rlbpantera/rack/index.html
>>>
>>> Here's the discussion that went on in 2000:
>>> http://realbig.com/detomaso/2000-03/814.html
>>> hit the < or > arrows to move through the discussion. Fortunately nobody
>>> at that time suggested that I use a regular BB as a replacement.
>>>
>>> At the time Larry Stock had some of the bearings and I bought a pair
>>> from him. The bearings you have now may work for a while (maybe quite a
>>> while?) but should eventually fail. A better alternative, if the correct
>>> ones can't be found, would be a deep grove bearing (the 1622 ZZ don't
>>> appear to be that) which are better at handling axial loads.
>>>
>>> Richard
>>>
>>> robert stewart Wrote:
>>> A few weeks back John Taphorn and I removed the steering rack from my
>>> car hoping
>>> for a relatively quick exercise of cleaning to up, painting adding the
>>> zerk and
>>> lube. When we took the rack apart we found that top bearings that sit in
>>> an open
>>> race where in many pieces.
>>>
>>> After a quick consultation with Mike Drew there didn't appear to be a
>>> well know
>>> replacement for the bearing.
>>>
>>> John suggested I visit a good friend of Gray Gregory - Lars Nielsen at
>>> Motion
>>> Industries in Houston. To say Lars was helpful would have been a huge
>>> understatement. He took the rack measured the bits and pieces of the
>>> bearing and
>>> race and identified a replacement suggesting a fully enclosed bearing
>>> instead of
>>> the open one. In addition he took the rack into the backroom and worked
>>> with one
>>> of his shop guys to remove the other bearing and race.  It was quite a
>>> pain to
>>> get out. Heck he even used a parts washer to clean up the rack. Can you 
>>> say
>>> "above and beyond".
>>>
>>> The two bearings which are part number 1622 ZZ cost me about $4 each and
>>> are
>>> fantastic. The rack turns very easily  and even though the bearings are
>>> sealed
>>> the lubricate that we put in through the zerk is still able to move
>>> throughout
>>> the rack as intended.
>>>
>>> Thanks to Gray, Lars and John.
>>>
>>> Rob
>>>
>>> -- 
>>> -----
>>> Sincerely, Richard Barkley
>>>
>>> To Ski or not to Ski, that is the question!
>>>
>>> Richard Barkley (310) 373-6695 (home)
>>> E-mail:  rlbpantera<atsign>  earthlink.net
>>> ZONKEY'S home page: http://home.earthlink.net/~rlbpantera
>>> Mammoth Lakes Vacation Condo: 2BR+loft/3Bath - Horizons 4 #186 (760) 
>>> 934-6758
>>> Condo web address: http://home.earthlink.net/~rbarkley
>>>
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>>
>>
>
> -- 
> -----
> Sincerely, Richard Barkley
>
> To Ski or not to Ski, that is the question!
>
> Richard Barkley (310) 373-6695 (home)
> E-mail:  rlbpantera<atsign>  earthlink.net
> ZONKEY'S home page: http://home.earthlink.net/~rlbpantera
> Mammoth Lakes Vacation Condo: 2BR+loft/3Bath - Horizons 4 #186 (760) 
> 934-6758
> Condo web address: http://home.earthlink.net/~rbarkley
> 