Dr Bob - do you have sufficient cable left over for one more? I'd be interested in building a replacement too, have to see when I can swing by and get it - but no great hurry if you are willing to put it aside for me.

I did look at some nice SGX 1/0 Cable at waytek but minimum quantities are 100 feet - expensive & super heavy to ship...

Alan

 

If I were local, I would do this immediately.

 

Update-

Got a couple of the ground straps from Dr. Bob late last week, Waytek # 36282 (http://order.waytekwire.com/productd...016%22%20LONG/). Dimensionally these are slightly greater in cross section than the factory cables, and are the same length as the current replacement factory cables (which is to say, a little too long in my '90 GT with a group 48 battery in it. But with the terminal rotated a bit on the (-) post, it all fits fine). Not bad for an $11 strap and $1.50 of heatshrink..

Poking through old threads on ground straps, there was a discussion about the possibility of corrosion over time between the brass(?) ground strap mounting point on the body, and the strap terminal itself. The Waytek strap end ain't brass. Issue?


Here is a 'naked' Waytek strap, the old strap off the GT, and a Waytek strap with 1" 3M heat shrink wrap installed.

 

Rob is there any measurable resistance difference?

 

I have a new factory replacement strap as well, and can tell no differences in resistance between the waytek strap, the new factory strap, and the 20 year old used factory strap, using my multimeter. But the engine cranks much better with the new straps, no question.

I honestly have no idea why a new strap makes a difference- there doesn't seem to be anything visually wrong with the old strap (except that the insulation is partially melted at one end.....). I'll cut the insulation off it and shoot a pic tonight.

Landseer's got a good shot of an old strap that more clearly illustrates how they can go bad:

https://rennlist.com/forums/7283996-post9.html

 

My money is on this

 

My money is on this:

(lets peel back that insulation to show the full horror...)

Alan

 

Alan--

I have the terminals but didn't pop for more cable than I needed. There wasn't enough initial local interest to justify getting 50' to do four more cars. The cable is available locally (here) from marine stores, and can be had for less from internet suppliers. I have the crimpers (clamp and hydraulic, you choose...) so the cables can be made up in 30 mins or less. I fly through PHX too regularly, so we could arrange a hand-off of a cable at security sometime if it comes to that.

The 1ga crimp battery ends from waytekwire have enough room in them for an extra bit of wire, maybe 8-6ga., if you want to crimp in the pigtail that way to your power distro block in the battery well. The Ancor branded starter-end lugs have zero extra room.

FWIW, the protective sleeve on the battery cable turned out to be a simple PVC flex sleeve disuised as a 1/2" PVC sprinkler pipe flex repair section from Home Depot in black. A spritz of spray silicone and it is a snug fit on the Ancor cable. Under $2 with sales tax.

 

For those playing along at home, the 2ga replacement strap is noticeably heavier-duty than the original. Rob can weigh them and give an absolute value, but I'd guess 50%+ heavier in the braided section.

My original strap shows no external signs of deterioration, and has no extra-flexi sections that I can discern. The car started OK with the original, with just one instance of almost-stranding as noted in the original post. The resistance in the cable did not show appreciably with an Ohm meter. But the symptoms...

Car would show 14 Volts charging with engine cold, reading on the dash gauge and at the jumpstart terminal. Also at the battery positive to ground. Hot soaked idle in stop-and-go with all the fans running full, AC on and headlights on, the dash gauge would dip to 12 volts or a bit less. Starter would spin noticeably faster for the first couple starts after return from a work trip, during which the battery sat disconnected. I'd put the maintainer on the battery overnight, still disconnected from the car, when I got back to make sure it was fully charged before I drove it any.

With the ground strap replaced, the battery seems to be charging better, certainly to a higher voltage than with the original strap. The starter is a lot peppier. Biggest improvement is hot idling with AC on. Yes, we've had a few 80º+ afternoons here when the AC got some use. Voltage readings at the battery are better than before, telling me that the battery is able to see full charging current compared with before.

----

I replaced the alternator with a new Bosch unit a couple years ago now, chasing the low-voltage problem. It didn't change the situation appreciably. I had the original alternator out on the bench over the weekend, and pulled the regulator/brush holder to inspect it again. Honestly, I'd have no trouble putting the original ~95k miles alternator back on again and not worry about it a bit.

----

Shipping on the new ground cables and other bits was enough to justify grabbing three extra grounds for Rob's two cars plus his adopted step-car. Thy are cheap enough that they could easily be PM items on any 928 that still has the original. We added the 1" heat-shrink sleeve so that lifting the frame end truly isolates the battery from ground, and IIRC the length to do a few straps was around $5 at the local Fry's Electronics.

I'm sure that our suppliers have new Porsche ground cables, and some of the more intrepid may choose to find some similar to what we used, and add the sleeve for you. Either way, this was a very simple and worthwhile fix to what was an elusive problem. Took me a few years of casual meter sleuthing, and even then it was the reminders from 'listers that finally stimulated the ground strap change.

 

Oh the Huge Manatee....

The GT's ground strap (22 years old, 115K miles, never out of the L.A. basin) was bad. So I opened the GTS's ground strap as well (19 years, 105K miles, lived all over the country), it's even worse:



So Alan, why the corrosion at the battery end? Proximity to acid vapor in an (admittedly) non-vented battery application? Somehow I doubt either car's battery has had the vent tube setup since the original batteries went dead in 1995 and 2001, respectively.... Or some other 'physics' reason?

Honestly, the GTS has always been a slow cranker as well, worse when warm. I just always assumed it was the extra compression in the stroker motor, but a new Waytek strap has cured the GTS as well.

Obligatory weight comparison:

Stock, sans insulation: 216 grams.



Waytek strap, sans insulation: 280 grams. (I'll leave the density of steel vs. copper calculations to the resident materials scientists....)

 

Rob - I think you will find the new one is Tin plated copper (including the ground end). I would still say the Waytek strap is about 50% heavier duty than the stock one.

Why the heavy oxidation - don't know for sure but H2SO4 is nasty stuff even in light vapor form... mine had no venting either - and this was a major reason I added it back in right away...

Besides - more empirically - thats pretty much exactly how mine looked too...

Alan

 

I think the tin is a marine requirement?

Measuring resistance might not show anything with a conventional meter, but measuring voltage drop across the strap while cranking might give some interesting numbers.

I think there is some type of travel over the surface of the battery, which is the idea behind the felt rings dipped in ATF (or maybe something else) that go on the terminals.

 

The group 48 battery has provision for an external vent hose. There was none in my car when I bought it though (22k miles, second battery replacement installed) I added a section of 1/4" plastic hose scavenged from the garden cabinet, the stuff you use for drip irrigation. Passed it through the gaiter where the positive cable exits, and routed it down behind the battery box heat shield to end a couple inches below the bottom of the battery box.

The felt rings with ATF offer a supply of oil that will wick up inside the gaps in the lead terminals and the clamp by capillary action. That wicked oil reduces the possible exposure to any corrosive vapors that would otherwise damage the terminals and spoil the electrical connection. FWIW, they "shouldn't" be needed with a properly vented battery, but they are cheap insurance just in case. Unfortunately, they don't do anything for the braid in the ground strap.

 

I guess I'll need to get a new "strap-on"

 

Seems like you can replace both the engine ground to chassis and the battery ground strap for $30 or $40. Probably worth doing every few years.