Highway rpm gh sigma (convertor slip??)

[4g54gemi]

Hi, I have a 1981 gh sigma auto. At 100kph it sits on 3100rpm in top gear. It has a 3.23 diff in it (confirmed by diff tag and physically checking revolutions), 77 inch rollout tyres (24.5 inch diameter). At 100ks it should be on 2750rpm. Ive got an autometer tacho in it so im assuming its pretty accurate. So assuming it is accurate it has approx 12% convertor slip which doesnt seem right to me. Tell me what your thoughts are or experiences with gh auto sigma's .

Just a pic of the tacho.

thanks

[DanTurboLancer]

Hey mate,

Well first question, have you done the build up?
Might it have a 3000rpm stall?

Could third gear Band be slipping?
So it is a gearbox problem rather than convertor?

Where did you get your calculations to figure what your RPM should be?
is it from an online chart that you can show us the link?

[4g54gemi]

The motor and gearbox I assume are factory 100000ks, although it feels like it has a stall (you can stall it up to 2500rpm on the brake easily) but I cant imagine the granny who owned it before me putting a stally in it . It even feels like it slips when cruising in 2nd, 1000rpm flair. the formula I use is: MPH (62.15), divide by 10, times gear ratio (32.3 not 3.23), divide by wheel circumference in inches (77), times "1056" = 2753rpm.
Also another one for HP is 0.00426 times mph (1/4 mile mph) times equals, equals (on standard calculator) times car weight in pounds (include driver and fuel) = HP at flywheel.
Thanks

[DanTurboLancer]

haha well Who says Granny wasnt a Street drag hoon on her way to church and shopping ;)

I thought going off you pic of the gauges, you may have done some work to it.

From what you describe, it is very likely you need to get your Auto inspected,
serviced, and possibly likely to need a rebuild.

If these are the same as the Falcon Borgwarner auto, you can adjust the Band tension.
But they Very commonly snap, which will mean rebuild.
New oil and change the Pan filter Could help.
But i dont know if you know autos.
I would get it inspected buy an auto specialist shop.

It would be very cheap to rebuild, but im not sure of your budget.

[4g54gemi]

Yeah adjusted the bands the other day and shimmed the relief valve up changed oil etc and put a cooler on it. im thinking it may have a 1600 sigma convertor in it or something like what happens with holden 6's and gemini convertors. The oil has stayed clean enough so I think the clutches may be ok, I guess all I can do is wait and see. Heres the car anyways http://www.sigma-galant.com/viewtopic.php?f=48&t=5484 . To give you an idea .

[amgis_obrut]

12% converter slip is no good starts creating a lot of heat and other problems

what size tyres are you running like aspect ratio width etc

also did the 1c shift kit work for you

[4g54gemi]

Yeah the 1c shift kit (or a small washer) made them slightly more positive, before that and the cooler and oil change it would slip ridicously into top under power when hot. Now it goes in nice actually more positive than the 1-2 upshift. 185/75r14 tyres. Thanks

[amgis_obrut]

have you checked the speedo against a GPS ??

3100 rpm should be closer to 120 kph