Rear End Ratio, 1965 Pontiac Bonneville Superior

[Lonny Waddle]

Good morning all! The 1965 Pontiac Bonneville will finally be coming together (again) in the next week. The engine issues have been addressed and the TH400 transmission rebuild is nearly finished. I'm having some regret not insisting my friend replace the TH400 with an overdrive unit, but maybe we can eventually get the rear end gears replaced with something taller to make 65 mph cruising a bit easier on the engine? Generally speaking, what rear end ratios were used in these? I'm guessing something around 3:08, or were they geared lower? Going to a 2:56 might take away some of the low end fun around town, but would make road trips a possibility. Thoughts?

[Bill Marcy]

I own a 70 Superior Pontiac and I used to own a 68 Superior Pontiac. Both of these cars are fantastic cruisers. They both have smooth power and a good ride. Going 65 MPH is no problem for either car. Although these have 6.6 liter, or 400 cu in motors and transmission and you have a 389, I think your car should cruise just fine. I do not know what the rear end gear ratio is on either car, sorry about that.

Post some pictures of your 65, when you get a chance. We all like to look at pictures.

[Lonny Waddle]

I’ll need to review the procedure for uploading pictures, especially now that we might actually make some progress! Thanks for the information, we’ll see how it does at speed. Hopefully, you are right and highway speeds won’t be a problem.

[Paul Steinberg]

Do you know for certain that it is a Pontiac Differential? GM was known to use differentials from other divisions when the car was being converted for commercial use... i.e. ambulance, hearse, flower car, etc.. Mr. Marcy learned this with an Oldsmobile that the once owned, and it had a Buick differential installed by the factory when they built the chassis, knowing that it was going to be converted into an ambulance. When it comes to a commercial chassis car, there is nothing universally standard on them.

[John ED Renstrom]

4:10 gears and a 30 inch diameter tire will be turning 4000 at 70 mph. I did that in a 59 chevy with a 283 2 barrel. From SD to La in 1969. The car only had about 170 grand on the clock the problem is you think it can't do it, your wrong. In the 70 one would have jumped into it and run cost to cost at speed never thinking a thing of it. Because ever car turned 3 grand at speed and got 15 mph on the road. Only a few standard cars has OD they were 3 speed sticks with 4:10 gears the turned 3 grand at speed in OD. Don't worry about the RPM it was engineered to do it. You just use to the double od of today turning 1800 at 70. So it seems it is running to fast. Red line on the stock engine is 5500.

[Bill Marcy]

Originally Posted by Paul Steinberg

Do you know for certain that it is a Pontiac Differential? GM was known to use differentials from other divisions when the car was being converted for commercial use... i.e. ambulance, hearse, flower car, etc.. Mr. Marcy learned this with an Oldsmobile that the once owned, and it had a Buick differential installed by the factory when they built the chassis, knowing that it was going to be converted into an ambulance. When it comes to a commercial chassis car, there is nothing universally standard on them.

We are speaking about an ACC Amblewagon that may have been delivered as a standard 1964 Vista Cruiser, subsequently sent to ACC for conversion to become an Amblewagon. They put a Buick Gran Sport rear in it, for quick acceleration. I would not confuse this with any other GM professional car. But, I am not saying that it didn't happen.

[Lonny Waddle]

Originally Posted by Bill Marcy

Post some pictures of your 65, when you get a chance. We all like to look at pictures.

I just uploaded some to an album I created for the car - many more to follow as I didn't do a very good job of documenting the work as it happened. Here are some pictures from when we first got started cleaning it up three years ago, and a picture of the engine at the machine shop from last week. The engine and the transmission are both rebuilt and laying next to the car in the shop. I'm hoping to be able to get them installed this weekend!