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  #1  
Old 10-04-2003, 02:30 PM
ww111
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Tps

Ok all (and Trevor) here it is:

OK, Its' Done. It's a Carbon track. (well, it's black) deposited on a white plastic wafer about 0.001" (0.02mm) thick . The white plastic piec is 0.063" Thick there are 2 wipers and 2 tracks. it's a unique setup to be sure.
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  #2  
Old 10-04-2003, 02:31 PM
ww111
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more

Just the good bits

Collins
92 pearlie
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  #3  
Old 10-04-2003, 08:01 PM
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TPS

The wiping contact bridges the two black tracks and turns in an anti clockwise direction as the throttle opens in respect of the element, as viewed in the photo. Therefore as the throttle is opened an increasing length of the wide part of the track is inserted in the negative leg of the voltage divider circuit and a lesser length to positive.

The resistance portion of the track will consist of a conductive plastic element on a polymide laminate. The non resistant portion will have a copper laminate base so as to eliminate resistance over this part of the circuit. Conductive plastic elements are not prone to wear as are carbon elements.

The week link in the design will be the extremely short sprung length incorporated in the wiping contacts and the lack of resilience will result in loss of spring pressure over time. It may be possible to reset these if the unit can be stripped and reassembled successfully. This will have to be looked into. It is rather interesting that only one contact is bifurcated.
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Last edited by Trevor; 10-04-2003 at 08:43 PM.
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  #4  
Old 10-04-2003, 08:51 PM
ww111
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Both contacts consist of "brushes" with "bristles". I think I probably damaged the one side whan I removed it. The conductive plastic track is a very reliable setup as it's in all of the MAF sensors that Bosch used in their "L" jetronic fuel injection. Including most '80s British Leyland / Lucas products. I think the exact number was a bazillion and six.
The wipers on these units is a copper half-round at the end of a piece of stainless steel.

Other than that, what you said!

(you did misspell weak)

Collins
Rear wheel bearings next weakend!
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  #5  
Old 10-04-2003, 08:58 PM
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Originally posted by ww111
Including most '80s British Leyland / Lucas products.
SWEET JESUS, NO!!!!

the prince of darkness!
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1987 928 S4 (Black) SOLD!
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  #6  
Old 10-04-2003, 09:02 PM
ww111
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Yes, it's true... BUT!!! when you pulled the Lucas sticker off the FI components there was always that effecient BOSCH logo there to reassure you...

Whew!

Collins
Why warm beer? Lucas refrigerators!
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  #7  
Old 10-04-2003, 09:11 PM
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Collins thanks for getting inside the thing.

Ok ! It was a weak week !

Was the contact pressure adequate do you reckon, or had the SS backing lost some tension ?

Now that you are aware of exactly what is involved, do you think the back cover portion could be cut off say with a fine hack saw blade to be replaced using epoxy or other suitable adhesive. The saw would remove some material and so reduce internal clearance but if this a factor possibly reinforced gap filling glue or a gasket may get over the problem.

However if the contact pressure proved still reliable it would appear the anticipated cause of faults can be put down to contamination of the contact area and cleaning with fluid without dismantling could provide a reliable fix in most cases as has been reported in several posts.

P. S. Is it possble that the damage you presume you caused in respect of one bifurcated contact was in fact not something you did, but rather an existing fault in the unit and which gave you the cause for its replacement ?

Regards and thanks again, Trevor.
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Last edited by Trevor; 10-04-2003 at 09:54 PM.
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  #8  
Old 10-05-2003, 10:59 AM
ww111
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I would not suggest trying a rebuild of the unit.

I scored the long side of the top with a razor blade until I could get the fine blade of a screwdriver in and chipped away at the side until the cover would pull away from the base. altho' it's not a "sealed" unit, mine had NO contamination. And cleaning would be the only thing you could do besides increasing the tension on the brushes. If the unit is worn, my advice would be throw it away and buy new.

Now about that Hub Tamer...

Collins
I'm amassing WAY to many old Suby parts...
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  #9  
Old 10-05-2003, 09:08 PM
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Thanks Collins but could you please be more specific in regard to the questions I raised in my post which I repeat as follows with additions, as this would be of great help and much appreciated : -

Was the contact pressure adequate do you reckon, or had the SS backing lost some tension ???????????

Now that you are aware of exactly what is involved, do you think the back cover portion could be cut off say with a fine hack saw blade to be replaced using epoxy or other suitable adhesive. P.S. and if possible exactly where should the cut be made ????????????

The saw would remove some material and so reduce internal clearance but if this a factor possibly reinforced gap filling glue or a gasket may get over the problem. P.S. Is it possible to achieve restoration of the cover granted some dexterity and basic skills ???????

P. S. Is it possble that the damage you presume you caused in respect of one bifurcated contact was in fact not something you did, but rather an existing fault in the unit and which gave you the cause for its replacement P.S. Was there evidence of severe contact wear. ????????

The object of the exercise was to find out the actual cause of malfunctions. If contact pressure is the common problem it should be possible to fix this. The mechanism is very simple and on the basis of my experience I see no reason why a good handy man should not be able to restore contact pressure. This could save members money and who knows replacements may become scarce.

Sorry to trouble you with more queries, but it would be a pity not to take full advantage of the trouble you have already gone to and the opportunity you have provided.

Thanks again, Trevor.
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  #10  
Old 10-05-2003, 10:14 PM
ww111
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Jeeze you're pushy!

<< Was the contact pressure adequate do you reckon, or had the SS backing lost some tension ???????????>>

I really have no way of knowing. There is so little current here I would think that even marginal pressure would be acceptable. My guess is that the contact pressure was adequate

<<Now that you are aware of exactly what is involved, do you think the back cover portion could be cut off say with a fine hack saw blade to be replaced using epoxy or other suitable adhesive. P.S. and if possible exactly where should the cut be made ????????????>>

If I had to do it again, I'd do it the same way. That way no material is lost in critical diminsions, and a little rtv or epoxy and everything is back to normal. Photos of the cut to follow

<<The saw would remove some material and so reduce internal clearance but if this a factor possibly reinforced gap filling glue or a gasket may get over the problem. P.S. Is it possible to achieve restoration of the cover granted some dexterity and basic skills ???????>>

Yes, I think you could remove the TPS, take it apart, clean it, put it back together and replace it. BUT, from inspection, I think the failure mode is a wearing of the conductive track. and there is no repair for that.

<<P. S. Is it possble that the damage you presume you caused in respect of one bifurcated contact was in fact not something you did, but rather an existing fault in the unit and which gave you the cause for its replacement P.S. Was there evidence of severe contact wear. ????????>>

I think it was, in fact, my heavy handed approach to the disection. There was some wear on the "outside" track visible on the "good bits" picture in the lower right

<<"The object of the exercise was to find out the actual cause of malfunctions. If contact pressure is the common problem it should be possible to fix this. The mechanism is very simple and on the basis of my experience I see no reason why a good handy man should not be able to restore contact pressure. This could save members money and who knows replacements may become scarce.>>

Like I said, this isn't a current dependent device. More than likely in the MA range. I think contact pressure has a minimal effect. This was a mechcanical sensor operating in a rough environment from 0 deg F to 200 deg F for 100K miles or around 3000 hours. I'd suspect it was at the end of it's designed life

<<Sorry to trouble you with more queries, but it would be a pity not to take full advantage of the trouble you have already gone to and the opportunity you have provided.>>

No problem.
Collins
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  #11  
Old 10-06-2003, 02:24 AM
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Collins,

Possibly I have been pushy in my effort to assist other members and I make no apology for that.

Regardless of the current passed by the device constant contact pressure and smooth output is vital. Marks on the conductive plastic element are unlikely to indicate a fault. Typical similar quality devices have a life expectancy of 10 million plus operations. However the contact arrangement seen in what you have pulled to bits leaves a lot to be desired.

Although I am confident that repair is possible I will take the matter no further.

Thanks in any event, Trevor.
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  #12  
Old 10-06-2003, 08:08 AM
ww111
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1st of all, I neglected to put a smiley after the pushy comment. It was purely in jest.

Now, on to better things.
This unit was replaced and the problem persisted. So more than likely this unit was good. It was a bad ground that was repaired to fix the problem.

Secondly. If the TPS has a MTBF of 10,000,000 hours or Cycles it would not be unusual to have a failure in one of ten cars at the 100,000 mile mark.

I still stand by my thinking that contact pressure in this application is not critical. The unit is a simple voltage divider for a Milli-amp signal. Only if contact pressure were non-existent would there be an indication of a error.

Also from a manufacturing and maintenance standpoint it would be unwise to have contact pressure a critical issue. Engine vibration, heat and others all have an influence on pressure. Going over a bump, or taking a hard corner varies contact pressure. I think the engineers took this into account in their design.

Lastly you're talking about a lot of work to fix a $100 part that's required to be stocked till 2007. I'm a lot more concerned about the tranny, as it's expensive, complex, breaks with regularity, and is beyond the scope of the average mechanic. My $0.02

Cheers
Collins
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  #13  
Old 10-06-2003, 09:11 AM
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Quote:
Originally posted by ww111
Lastly you're talking about a lot of work to fix a $100 part that's required to be stocked till 2007. I'm a lot more concerned about the tranny, as it's expensive, complex, breaks with regularity, and is beyond the scope of the average mechanic. My $0.02

Cheers
Collins
yeah, i think if you are trying to save a few bucks by rebuilding the TPS, then the SVX may be the wrong car for you.
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1987 928 S4 (Black) SOLD!
1997 SVX LSi (Ebony) SOLD!
2005 Legacy GT (Silver) [Cobb Stg 2+] SOLD!
1987 928 S4 (Black) SOLD!
2005 Forester XT Premium (Crystal Gray Metallic) SOLD!
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  #14  
Old 10-06-2003, 07:30 PM
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Quote:
Originally posted by ww111
1st of all, I neglected to put a smiley after the pushy comment. It was purely in jest.

Now, on to better things.
This unit was replaced and the problem persisted. So more than likely this unit was good. It was a bad ground that was repaired to fix the problem.

Secondly. If the TPS has a MTBF of 10,000,000 hours or Cycles it would not be unusual to have a failure in one of ten cars at the 100,000 mile mark.

I still stand by my thinking that contact pressure in this application is not critical. The unit is a simple voltage divider for a Milli-amp signal. Only if contact pressure were non-existent would there be an indication of a error.

Also from a manufacturing and maintenance standpoint it would be unwise to have contact pressure a critical issue. Engine vibration, heat and others all have an influence on pressure. Going over a bump, or taking a hard corner varies contact pressure. I think the engineers took this into account in their design.

Lastly you're talking about a lot of work to fix a $100 part that's required to be stocked till 2007. I'm a lot more concerned about the tranny, as it's expensive, complex, breaks with regularity, and is beyond the scope of the average mechanic. My $0.02

Cheers
Collins
Hi again Collins and no problem re the the pushy comment. I am inclined to dig more deeply than others because of my interest and background in things technical.

The ground fault interests me. Surely this was not related to the actual TPS unit, but if so which ground of two was it ?

Cycles not hours is the measure of the specifications I quoted and a cycle is represented by a complete sweep of the element. You are suggesting on average of 100 movements per mile which surely would mean a tired right foot.

Contact pressure IS a critical issue and its absence will result in a faulty unit. The signal transmitted from the TPS is an analogue voltage which is directly derived from the moving contact on the potentiometer. Any variation in contact resistance and more particularly intermittent contact will have an absolute effect on the signal. It is interesting that an important part of published potentiometer specifications includes resistance to vibration for this very reason.

Both voltage and current is low in the application we are debating so that any resistance of a mechanical nature will not be broken down. Contact pressure is the most important factor and the first consideration in any mechanical moving contact assembly. I know because I have designed and my own Company has produced many such devices with success.

I agree that fixing the TPS can be considered out of line with cost but there are many posting who show a willingness to spend time in what can be considered interesting hobby activity to achieve the added value of personal satisfaction. What is often more important is the ability to effect a repair without incurring the delay in obtaining a spare part.

I am sure there will be some out there gaining from our interesting chit chat.

Regards, cheers and thanks, Trevor.
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  #15  
Old 10-06-2003, 08:28 PM
ww111
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<<The ground fault interests me. Surely this was not related to the actual TPS unit, but if so which ground of two was it ?>>
--------------------------------------

I was told it was the signal ground off of the TPS. It's a voltage divider so if the ground isn't there all the voltage goes though the to the output. regardless of position (Day two, DC Circuits) It may also explain the tendancy to flare in corners as opposed to straight line.
-------------------------------------

<<Cycles not hours is the measure of the specifications I quoted and a cycle is represented by a complete sweep of the element. You are suggesting on average of 100 movements per mile which surely would mean a tired right foot.>>
-----------------------------------------

On a part such as this, without a definite cycle I (and the FAA, the USAF, and the entire aircraft and boat industry) use hours. My TPS is moving all the time. Small amounts, but always moving. Occasionally I will use the full range, but using this as a method of measuring use would not be a very accurate indicator. Starting next month I may go all the way to April without taking the unit "Full Cycle" (snow and ice, ya know)

-----------------------------------------
<<Contact pressure IS a critical issue and its absence will result in a faulty unit. The signal transmitted from the TPS is an analogue voltage which is directly derived from the moving contact on the potentiometer. Any variation in contact resistance and more particularly intermittent contact will have an absolute effect on the signal. It is interesting that an important part of published potentiometer specifications includes resistance to vibration for this very reason.

Both voltage and current is low in the application we are debating so that any resistance of a mechanical nature will not be broken down. Contact pressure is the most important factor and the first consideration in any mechanical moving contact assembly. I know because I have designed and my own Company has produced many such devices with success. >>

-----------------------------------------------
You've thrown down the gauntlet, so I'll pick it up! I'll measure the voltage & current through the range of motion with varying pressures on the contacts. I should be able to do this with the signal generator and the scope. (and several pieces of #6 lead shot)

Don't expect the data too soon




Enough Smilies?

Collins
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