Alan Billingham

Just had my 700R4 rebuilt in my 86 IROC, complete with new Torque Convertor. The rear axle is fitted with drum brakes and I believe it has a ratio of; 2HG 2.23 std. One revolution of the wheel to one and a half turns of the prop shaft.
Question is, when lock up happens in 4th gear at roughly 45 mph, what should the drop in RPM be ??? It appears to be about 200 rpm, is this normal ??
At 70mph it is at 2,500rpm, which seems a little high. Lock up is definetly working as I have checked with fitting a seperate switch and I have changed computers and proms with my friends car and that made no difference either. His car, same year only his is a 305 where mines is a 350. His at 70mph is at 1,750 rpm !!!
Both cars are TPI. Any help or advice, gratefully received.

Joshua Leslie

200 rpm seems about right for 45, thats what mine does.

However, the faster I go the more the RPM is dropped when I engage the lock-up(via manual switch)

are you sure of the gear ratio on your car.

with a 2.73 gear and lock up with 245/60/15 tires on my car, at 70mph I turn about 1700rpm. going 100(only did this once) I was barely above 2000.

I have never heard of a gear ratio of 2.23 in any thirdgen, I belive the lowest they ever had were 2.73.

Also, if you have smaller tires, the RPM will be higher at all rpm.

Alan Billingham

[QUOTE]Originally posted by Joshua Leslie
[B]200 rpm seems about right for 45, thats what mine does.

However, the faster I go the more the RPM is dropped when I engage the lock-up(via manual switch)

are you sure of the gear ratio on your car.

with a 2.73 gear and lock up with 245/60/15 tires on my car, at 70mph I turn about 1700rpm. going 100(only did this once) I was barely above 2000.

I have never heard of a gear ratio of 2.23 in any thirdgen, I belive the lowest they ever had were 2.73.

Also, if you have smaller tires, the RPM will be higher at all rpm. [/

My tyre size is 245/50/16 and there is no axle code stamped on the casing anywhere !! Believe me I have scraped and cleaned it like brand new and tried wetting it but still no code to be seen.
I am going with the RPO codes in the centre consol in the car.

Alan Billingham

When I had the manual switch hooked up, even at 70 or 80mph, it still only dropped about 200rpm

Joshua Leslie

86 IROC-Z A4 +L98 V8 9.5:1 5.7 (350) 220@4200 320@3200 TPI ---- ---- 3.27* ----


I got that info off this website.

so, you should have a 3:27 9 bolt Borg Warner rear, so count the bolts on your rear axle, and if its 9, then this is what you have.

those RPM seems reasonable with the axle