LERN ME: Classic GM Convertibles Edition

Yup, time for another "LERN ME" thread...

Tony Sr. (aka My Dad) is getting up there in age, and he's looking to ditch his Harley for something older with four wheels. Back in the day, he had a few GM cars he was really fond of, including a 1966 Olds Cutlass, 1969 Pontiac Lemans, and a 1970 Olds 98 Convertible. He's looking to pick up something along those lines in drop-top form to serve for cruising duty. 

We've narrowed it down to the 1964-72 GM A-Bodies, specifically the Oldsmobile and Pontiac lines, or maybe an Olds B-Body for good measure. I've found a few examples that look interesting:

1965 Olds Cutlass

This one looks decent. It's not entirely original, but it comes with a bunch of spares and the original engine.

1970 Pontiac Lemans

Again, not original, but it looks solid.

1970 Olds 98

My parents had a green 1970 Olds 98 Convertible back in the day, although it was a darker green that looked better than this one.

I was born and raised on GM A-Body stuff, but never really looked at convertibles. I figure they are pretty much the same deal as their fixed roof counterparts, but with additional body bracing underneath. What should I be looking for when checking these out with him?

I have no idea but I would buy that Olds 98 and never look back:  

In reply to ¯\_(ツ)_/¯ :

It's pimptastic! It might be a little much for my dad, though.

This is my '69 Olds Delta 88:

Mostly the same care underneath as that 1970 98. Here's what I can share.

Suspension bits are not the same as an Impala, but close. Tie rods ends, bushings, springs, stuff like that can be had. I gave up trying to find a new center link, so I'll have it rebuilt someday.

Some interior bits swap to the Cutlass, but not much. You won't find any repro interior fabric or panels, period. The convertible top itself should be available. The mechanism for the top (not the frame itself) should be available.

Big disc brakes up front, big drums in the back. It will stop better than you expect. Brake parts are no problem.

There are no repro wiring harnesses, you are on your own for any of those repairs.

Exterior trim bits are nonexistent outside of NOS or used parts.

If I were to buy one, it would be the one you posted. It is damn near perfect and complete, anything mechanically wrong can be fixed. The engine is a 455 with hopefully dual exhaust. If it doesn't have dual exhaust, finding the proper exhaust manifolds is a bear because of the steering rack location. Transmission is a TH400, dead nuts simple and reliable.

It won't be fast, but the 455 will make it move comfortably. It will drive like your living room couch, and handle just about as well. I love mine, 19 years of ownership so far and counting.

The Oldsmobile 98 is actually on the c body not the b body.

The c body was used for the higher end full size cars

https://en.m.wikipedia.org/wiki/GM_C_platform_(1936)

MotorsportsGordon said:

The Oldsmobile 98 is actually on the c body not the b body.

The c body was used for the higher end full size cars

https://en.m.wikipedia.org/wiki/GM_C_platform_(1936)

I'll be dipped, I learned something new today. I just assumed it was a stretched B-body. I farmed some parts off 98s over the years that bolted right on my 88.

MotorsportsGordon said:

The Oldsmobile 98 is actually on the c body not the b body.

The c body was used for the higher end full size cars

https://en.m.wikipedia.org/wiki/GM_C_platform_(1936)

I was today years old when I learned that GM made a full-size C Body.

In reply to Tony Sestito :

For the A-bodies, they are pretty much the same as their sedan counterparts, but there are a few large gussets at key points in the frame.

Do NOT buy one without getting under it.  Look at the point where the rear axle arches come down and turn into the main sill rails.  This corresponds to the place just below the rear quarter windows, and the nook where the top frame folds into on either side of the back seat.

Water collects there, both in the body pan and the frame rails below, thanks to one of those gussets.  The main rails will rust right through from side to side there.  You can patch / reinforce them, but they will probably need attention NOW if they haven't already been taken care of.  By this point somebody probably makes a fix-it kit, but I don't know that for a fact.

In general, convertibles will be more susceptible to rust because of leaky tops.  Otherwise, except for reinforced frames they will be essentially the same as the equivalent hardtops and sedans.

GM A body cars have an advantage when it comes to finding parts, in that they shared the same chassis and suspension across all GM makes.  Full size cars up until 1970 were mostly different underneath for Chevy, Pontiac, Buick and Oldsmobile so finding parts for non-Chevy cars can be more difficult and expensive; after 1970 there was some commonality and then after 1976 they were pretty much the same (although convertibles were dropped after 1976 so that takes them out of the running for your situation.)

If you want disk brakes, they were mostly optional prior to about 1970 but there are kits for adding them.  Also, a lot of A body GM cars had two speed transmissions in the 1960s, newer ones will have TH350 or TH400 three speed automatics.

Having said all that, buy what you like as long as you get one in the best condition you can.  Parts are available for all of them and anything can be fixed, but of course it's always better off to start with one that's in good condition.

I'm a Pontiac guy so I'd go for the Lemans.  The big Olds looks pretty cool, too, but I wonder why they didn't include any pictures of the interior.

That 65 Olds is awesome 

Tony Sestito said:

MotorsportsGordon said:

The Oldsmobile 98 is actually on the c body not the b body.

The c body was used for the higher end full size cars

https://en.m.wikipedia.org/wiki/GM_C_platform_(1936)

I was today years old when I learned that GM made a full-size C Body.

And full-size Cadillacs were D Bodies. 

I'm more of a Pontiac guy myself, but my dad was always an Olds guy first, then Pontiac. If he was going to get a Pontiac, he pretty much wants a 1969 Lemans, which he thinks is the best looking of all the A-Body cars. I tend to agree with him, although, I'd rather a GTO myself. He also really likes the 1966, 1969, and 1970 Cutlasses.

I personally know more about the Pontiacs, especially the drivetrain bits. One thing that concerns me is the same thing that concerns me about my own Trans Am: the starter circuit. Mine has headers, and between those and the higher compression than stock, the thing has serious hot start problems. Olds engines that I've had don't do this, so maybe one of those would be a better choice. I don't want him to end up stranded anywhere!

On these big GM convertibles, I was always drawn to the final years of '74-76.  The biggest of the big ones!  

I like them all but for these I might be most drawn to the Pontiac Grandville. 

In that same vein and slightly newer, I could dig a Buick Riviera ('82-'85 fwd) as a good cruiser.  

http://www.buickrivieraconvertible.com/index.php

In reply to Tony Sestito :

There’s things that can be done to help reduce the chance of that happening.

Heat shielding the starter and a switch to cut power to the ignition should help avoid that issue. 

If it has a tough time cranking when hot, switch the ignition power to off, get it spinning  and then turn on the ignition power. 

Hiding the switch and leaving it off when parked can also work as a theft deterrent. 

If you want to get fancy you could use a relay and a delay circuit to eliminate the need for user interaction.  

To make it fail in a way that wouldn’t strand anyone you could use a normally closed relay. If my memory is correct, supply the relay from the starter to open it (cut ignition) power when cranking) and the right size resistor and capacitor on the  ground side of relay would close the relay once the cap is charged. You’d also want a way to drain the cap, maybe a second relay and resistor to the ground side of the cap to bleed off the charge once done cranking?

In reply to John Welsh :

My father had a 1972 Grandeville convertible, brown on brown with a tan top, garage kept and babied its whole life.  My sister / nephew have it now.  It was a creampuff, and should still be.  With the 455 / 4bbl it would move out in that classic big American car way.

Neither my 326 / 2bbl 1967 LeMans, nor our 1969 428 / 4 bbl Bonneville wagon, nor the 1972 Grandeville had consistent hot-start issues.  Maybe occasional, but not particularly frequent or chronic.