88 Bonneville, Tyre question + Tranny problem

[Richard_uk]

Hi,
I have just joined, my name is Richard and I live on the south coast of the UK. I have a 88 Bonneville 3.8 V6 (vin code C).
The door sticker has worn away so could anyone tell me the factory tyre size for the 14" rims shown in the below pic?
it currently has 205/70/r14 rear and 195/75/r14 front, thse tyres arn't shown in the pic(old).

ALso I know my transmission (440-T4) needs a rebuild as it slips. Sometimes if i accelerate very gently it slips and there is no drive at all for a few seconds. Everytime i put my foot down the kickdown works ok, but it always then slips causing the tach to bury itself way past the redline. although in this situation it accelerates quite fast, but if i don't lift off the engine will probably die.
I figure that as it has 180,000 miles and previous owners didn't service it. a rebuild will cure this.
But my question is that it dosen't shift into 4th untill 55mph, but it should at about 40mph. will the rebuild fix this or is something else wrong?
oh, i changed the fluid (original fluid was very dirty but not burn't) and the tv cable and vac modulator are ok too.
thank you.

[maxwedge]

Welcome to AF. I believe it was 205/75/14. Go to tirerack.com, enter the car and the proper size will come up. At moderate throttle a 55 mph o/d shift not too far off. You could also check for good vacuum to the trans modulator. BTW, I have relatives in Devonshire.

[Richard_uk]

Excellent. Thank you.

[Jrs3800]

55mph is normal.... The earliest that it will shift into OD on that Trans is 50 Mph...

In third gear at about 35-38 you will hit the TCC lockup and in 4th gear you will hit it almost the same time as the shift... If you get to 55 and slow down a bit say to 46, the trans will stay in 4th gear and with light throttle you will hit the TCC lock in 4th gear at roughly 46-47 Mph and the engine will run at about 1300-1350 Rpms at that point...

You should have the 2.84 Gear ratio Code F17 on the RPO label on the spare tire cover...

One of the problems these 440-T4's had was how quickly it would heat up and then start to burn the fluid.. Usually a good trans cooler will keep them happy for a long time...