1937-1957 Buick Oldsmobile Pontiac suspension upgrade
A suspension and disc brake upgrade on a 1937-'57 Buick, Olds, or Pontiac (BOP) is complicated by many variables and side issues. In addition, there is little information on the topic, and few aftermarket parts are available.
With minor variation between models and years, Buicks, Oldsmobiles, and Pontiacs share a common frame and front suspension. Chevrolet did not have this setup.
 Original suspension details
- The front suspension is made up of unequal length upper and lower control arms and coil springs.
- The coils sit in a spring pocket on the lower control arm, and a spring perch built into the frame on the upper end.
- Steering is thru a kingpin steering knuckle. Alignment is accomplished with an inner and outer concentric screw adjustment in the upper steering knuckle mount (accessible by removing the grease fitting and inserting an allen wrench into the hole).
- There are two types of shock arrangements. Roughly, '37–'49 (not all 3 changed the same year) have a lever action shock that is built into the upper control arm and serves as the upper control arm mount. 1950s models went to a separate tube type shock. Some were internal to the spring, some external. The upper control arm is still a fixed frame mount, with caster/camber adjustment in the concentric sleeves.
 Key shortcomings of the original suspension
These cars actually drive reasonably well, and this basic suspension technology was a mainstay for 50 years. However, it does have certain shortcomings:
- These cars came with zero to 1/2 degree of negative caster. When they were originally engineered, this was a reasonable setup. Negative caster makes the car easier to turn, and gives greater control in muddy ruts and other bad road conditions that were prevalent in the 1940s and 1950s. However, modern roads and increased speed limits favor positive caster, as it allows the car to stay centered and stable at today's highway speeds. High positive caster became more common as power steering became common. Conversely, manual steering is fine at higher speeds, but requires greater effort in low speed situations, especially parking lots. Manual steering works best at about 1-½ to 2 degrees of caster, which is a compromise between high speed stability and slow speed turning effort.
- Due to the up and down-only rotation of the control arms, and cross-rotation of the king pins, any attempt to add more caster is fraught with problems. Anti-dive geometry is impossible in this setup.
- On the pre-1950s models, the lever action shocks also present problems. They're hard to find, expensive (about $200 each plus $100 core charge if yours aren't rebuildable), and even in perfect working order, they have their shortcomings. The shocks are basically only good for a stock-only application. Raising or lowering the vehicle puts them out of their designed operating range. Increasing or decreasing weight with engine and transmission swaps alters their effectiveness.
- The hubs/drums run on ball bearings. While reasonably durable if properly maintained, tapered roller bearings are generally thought to be stronger, more stable, and better able to withstand continuous high-speed driving. Ball bearings are now hard to find and cost about $200 for the full set. By comparison, a full set of tapered bearings will run about $25.
- The brakes are, obviously, inadequate: non-power assisted 4 wheel drums with a single reservoir hydraulic system.
Most attempts to gather advice will result in one of two stock answers: Mustang II or some type of GM subframe.
In this application, the standard Mustang II recommendation may be misguided. It can work well on Chevys, however, their straight frame rail makes installation straightforward, and the weight is within specifications. For BOPs the frame rails are neither flat nor straight. There is also a built-in spring pocket, which requires modification of the frame rails. And, there may be a weight issue.
The GM subframe approach is definitely viable, and some would say the best possible solution. If you have the tools, welding and fabrication skills, and your car is stripped to the frame, it might indeed be your best option.
But if your car is assembled with the engine in and fenders on, or your fabrication skills are minimal, or you just don't like the idea of hacking your frame, the information in this article may be useful to you.
The brakes on these cars definitely need improvement.
The brakes should be handled first, because the decision you make on the brakes determines the spindles you'll need, and you must have your spindles before you can design your suspension. The information listed here is general in nature and varies from model to model and year to year. Earliest models had 1-3/8 inch by 11 inch brakes with 1 inch ID wheel cylinders.
Postwar, they were 2-1/4" by 12”, with 1-1/8” wheel cylinders. The most basic upgrade would be to the later, larger, components. Control arms and spindles are unchanged for 20 years, so this is a basic bolt on. Even the shop manuals refer to this upgrade.
The single reservoir master cylinder is located under the floor and bolted to the frame. A new split system master cylinder and power booster will be an amazing transformation of your stopping ability. Several aftermarket master cylinders and 7” boosters (with universal pedal mounts) are available. With a V8 engine swap, a 7” booster seems to be the most you can squeeze under the hood.
The Geo Metro hanging pedal and 7 inch booster is one option, but the MC (master cylinder) is small. Didn't chase down a match, but the center hole and bolt pattern appear to be typical GM. Be sure to get one designed for a booster application, and pay attention to the pushrod length.
Pulling the old pedals out was twice the work of putting the new one in. In this case, the unit was located just outboard of the steering column in order to clear the engine. Under the dash, the hanging pedal was slightly bent to the center, to get a good pedal position. And a new, larger pedal pad (more appropriate to a large car and automatic transmission) was welded on.
 Drum brake upgrade
If you elect to do a power-only upgrade, and keep 4-wheel drums, be aware most master cylinders are designed for a disc/drum setup, and you will have to add 10 psi residual valves to the front lines.
- The front drums and hubs come together, at about $130 each
- Wheel cylinders are $32 each
- Shoes are $25 plus cores
- Hardware is $15, flex hoses are $25 each
- The above mentioned wheel bearings are $200
So, a complete brake job will run around $600 just for the two front wheels, without the master cylinder or booster.
 Disc brake upgrade
Aftermarket parts options:
- Scarebird Classic Brakes makes a setup for many General Motors makes and models. They supply the brackets for the calipers and the correct spacers for the spindles/rotors, and a tech list of parts to finish the job, for $100-$150, depending on application. For example, for a '58 Pontiac, they supply the brackets and spacers. From any source, new or used, you need a pair of '77 Bonneville 12-inch hubs/rotors, a pair of '88-'91 GM truck calipers, and 2 choices of flex hoses, depending on whether you want them 12 or 15 inches long.
- Classic Performance Parts sells a tapered bearing conversion kit.
If you are using all new parts, you can have disc brakes cheaper than rebuilding the original drum setup.
- Your original drum setup used 1/4" brake lines. 3/16" is recommended for disc brakes.
- Many aftermarket master cylinders have metric fittings. You may find yourself putting different fittings on each end of your new lines to convert from metric to inch. There is a direct metric match to the 3/16" line size, so that is not a problem.
- Master cylinder size is important, but slightly flexible. One option is the Corvette-style master cylinder, with ports located on either side. This makes installation easier, and they're fairly cheap.
- The 1" bore will do the job, but expect the pedal travel to be a bit long. On the other hand, a 1-1/4" or larger master cylinder will move the fluid faster (shorter stroke), but the small 7-inch booster might not be up to the job, the result being a too-hard pedal effort. Your original master cylinder may push the discs fine as far as volume goes, but pressure could be another matter.
- Virtually all cars will need an adjustable proportioning valve. Any change from the original setup – front or rear weight change, tire sizes, line sizes, rake or tail drag, disc conversion, etc., has the potential to throw your brake system out of balance.
- Most disc conversions will require at least 15 inch wheels; check it out before you order.
- The project in this tutorial used a Corvette 1" ID master cylinder, and a 7" single stage booster. This combination turned out to be "close enough". The brakes are a vast improvement over manual drums, but not perfect. Stopping power is great, until about the last 20% of pedal travel, as several test panic stops revealed. At the very bottom, you just can’t push hard enough to lock them up. The system probably needs a 9 or 10 inch booster to be perfect. There simply isn't enough power in a 7 inch booster to lock up a set of 215/75x15 tires on a 3500 pound car, on dry pavement.
 Improvements two years later
Never really happy with the 7 inch booster. Moved some things under the hood to get more room and installed a 9 inch dual diaphragm booster from a mid 1990s Camaro. Now it stops like a new car. I'll never use a 7 inch booster again.
 Front suspension
The original idea came from an article in Rodder's Digest magazine that showed a suspension upgrade for a '55 Pontiac. Reading this article, which has some decent pictures, will get you thinking in the right direction: Project Strat-O-Streak.
The upgrade discussed in the article will work on all 1937-'57 BOPs, because they all have the same basic setup. The '58 Pontiac lower control arms are the key. They are a direct bolt in, exactly the same as the originals, but with ball joints instead of king pins. '59 and later BOPs went to a completely different control arm mount. '58 Buick lower control arms are not symmetrical, so they won’t work.
New info indicates the '41 Buick lower control arm is 20 inches long, rather than 18 inches like the Pont/Olds. Other measurements are the same, so upgrade should still work, with redrilled mounting holes.
Also, we do not have a '58 Olds available to check/measure the lower control arms. What we DO know is '57 is king pin, and '59 is all-new. So '58 is it. We used the '58 Pontiac upper control arms simply because we got the whole front end. Several uppers will work, as it looks like '58 to '60 BOPs all had the same basic dimensions on their upper control arms. In fact, the '58 Buick uppers we used on one conversion had some built-in twist that allowed us to add more anti-dive than we could get with the Pontiac uppers.
As you can see in the photos, the '58 control arms are more substantial than the '41. However, all the dimensions are the same.
The upper control arm mount is a fairly simple fabrication. If you have a post '50s car, the upper mount will differ from this article. The pre-'50s had the lever action shock, therefore no upper shock mount. On both of our tested conversions ('41 Pontiac and '49 Olds) we fabricated the mounts out of angle iron. We used 1/4" 3x3 inch angle iron on the Pontiac, and added two gussets. On the Olds, we had some 3/8" 4x6 inch angle iron, so only added one gusset.
Note in the pictures below how the front mount is higher than the rear mount. This sets up the anti-dive angle. Up to 10 degrees is fine, as long as the upper ball joint is not in a bind. Be sure the frame is level side-to-side, and has the correct front-to-rear angle that you want. With 15 inch wheels, the spindle center was 12.5 inches off the ground. The frame was blocked, so that when the lower A-arm was level, the spindle was 12.5 inches up.
Even a small error here will be costly. It takes 1/2" of shims to adjust just 1 degree of camber. If you need to put additional shims on the rear of the bracket to increase caster, and can't take enough out of the front to keep the camber static, you will have to cut it loose and start over. Unfortunately, you can't do a full alignment until it is totally basically finished and drivable. So, get this part right. If you have any doubts, shade towards the positive camber side, as you can add more shims later to move it towards negative. Likewise, move the upper mount to a position about 3/4" behind the plumb line for the spindle, to set up at least 5 degrees of caster in the neutral position (neutral being the static position as mocked up, before final alignment).
If you intend to add power steering, shoot for 6 degrees in the neutral position, but don't get the uppers so far behind the lowers that you put the ball joints in a bind. In this situation, holes were drilled in the bottom plate of the angle iron, and, when it was mocked up, the frame was drilled and bolted up with 3/8 inch bolts. This was strong enough to allow for assembly of the entire front end, with springs, putting the wheels and tires on it, and setting it on the ground. Everything was double-checked, then torn down and welded in place.
For spindles, the '63 Pontiac spindles advised in the article were used. Unfortunately, when it was set it on the ground, the front ride height was too high. This led to a search for dropped spindles. For BOP, dropped spindles couldn't be found. Chevy drop spindles are readily available, but they come with a problem. Note the side by side comparisons in the picture. The '63 Pontiac spindle has a deep 90 degree bend at the bottom, to clear the wide corners on the lower control arm. The '60s stock Chevy spindle has a 45 degree angle at that location, so won’t work.
The third spindle shown below is the '65-'70 Chevy drop spindle from Classic Performance Products. It's their own in-house design and is very close to the design of a Pontiac spindle. The ears had to be trimmed off the front side of the lower A-frame, but that was a minor modification.
Here is where the bolt-in mock up really paid for itself in time and labor saved. The dropped spindle from Classic Performance Products (CPP) was almost 2 inches longer than the stock spindle. Not a problem, and in fact, they say that the longer spindle gives more stability. However, the longer spindle changed the geometry, and the location of the upper control arm mounts had to be replaced. Fortunately, it wasn't welded in at this point.
CPP's dropped spindle is available alone, or in a disc brake kit. Be sure you get the p/n CP30101 spindle. It has no steering arms built in.
Stock spindles are front steer, and won’t work. With the CP30101, you can just add a pair of '65-'70 stock arms. Flipped over, they fit your rear steer perfectly-even the taper is the right direction. Unlike the '63 Pontiac arm in the article, the Chevy arms are pretty straight.
For this project, the tie rods only needed to be shortened less than an inch, rather than the 3 inches in the article. This was done by trimming a little off both the inner and outer tie rod threads and the sleeve. No cutting and welding.
Incidentally, It looks like the tie rod ends in this project are closer to the Ackerman line than the '55 conversion in the article. The taper in the Chevy arms was a bit small for the Pontiac tie rods, so they had to be reamed a touch.
The CPP drop spindle/disc brake kit uses Chevelle 11 inch rotors and Chevy S-10 calipers. In this case, it was cheaper to order the entire kit, than getting the individual pieces. And with the kit, you get a matched set: spindles, rotors/hubs, bearings, brackets, calipers, pads, flex hoses, nuts, washers, and even cotter pins, all for about $500.
That's the most straightforward approach: '58 Pontiac upper and lower control arms, and either '63 Pontiac spindles and Scarebird brackets for disc brakes and stock height, or Classic Performance Products dropped spindles and their set-up.
Note: Later a power rack and pinion was added, and the steering arms were changed out. However, the Pontiac arms will work fine on a Saginaw 605 power box upgrade. great stuff but this will only work on 37 to39 cars after you drill new mounting holes for the lower a arms .the 58 arms are 2ins.shorter then the early cars just make sure you line up the spring pocket in the arm with the one in the frame every thing else works.the better set up is to use there ccp spindles and brake kit worth the money
The stock springs should work fine. As the Rodder's Digest article suggested, you will need to spread the bottom of the spring a bit, because the '58 Pontiac spring pocket is about 1/4" larger than previous years. This car required a spring rate of approximately 300 pounds per inch, with a ride height of 9.5 inches, and a free height of 15 inches. '69 Mercury Cougar springs were used. They were listed at 295 pounds per inch, 10.5" ride height and 17 inches free height. Once a full coil was cut off, everything fell into place. They were also 3.88 inches in diameter, or halfway between the original upper pocket and the '58 lower pocket.
Shocks will be a problem on the pre-'50s, without a shock tower. Note in the picture of the frame spring pocket area below: 3 holes in a row. The outer 2 are the original mounting holes for the lever action shock. The one in the middle is drilled at the dead center of the spring pocket, later enlarged to fit the shock bushing.
This project used a pair of shocks from a '79 Dodge Diplomat, with the stem mount on both ends. These are easy to mount through that frame hole. The lower mount had to be fabricated. (Even though the lower Control arms had shock mounts, there were no shocks short enough that fit that mount). With level control arms the ride height on the car was 9.5 inches. That meant a shock collapsed height of about 7 1/2 inches. The Dodge shocks were not only the right ride height, they were designed for a similar weight car. Note: The '58 Buick has an external shock mount, riveted to the frame. You could get a set of those, or fabricate some, and have many more shock options than you would with the shocks mounted inside the spring.
 Additional suspension option
For the more adventuresome, and fabrication minded, there is another approach.
The only real issue with the stock lower control arms is the king pin mounts. My buddy with the '49 Olds has a junkyard, but no '58 Pontiacs. He didn't want to wait for one to come in, so we cut the outer end from his lower control arms and welded on a 3/8" plate for a ball joint mount. He did have a '58 Buick, so those were the uppers we used. He had already pulled a complete spindle/disc brake setup off an early 70s Chevy, so we knew going in that the 45 degree angle on the spindle was going to be a problem. As it turns out, the narrower end on the original lower control arms is a blessing. A Chevy spindle can be made to work, but the Ford Courier had a ball joint with a 3-point “crowsfoot” design -- it is very narrow at the outer end, and the Chevy spindle cleared with no problems. There must be several ball joint mounts that could be adapted to the original arms. Just remember, the ball joints point down.
We used his original springs, but don’t have it finished yet, so we may do some adjusting to the ride height when all is said and done. If you use a disc brake kit with the caliper to the front, you will probably have an issue with the sway bar.
 Sway bar
The '40s cars had very small sway bars- 5/8 inch. In this project, a 3/4 inch 1956 Buick sway bar could be bolted in without modification.
A 1958-1964 Chevrolet Impala sway bar is almost a direct bolt on. Several sizes of sway bars are available.
 Steering Linkage
Go to Swapping to rack and pinion steering for the completion of this project.