Love1955oldsmobile

I am going put a 1958 Oldsmobile complete rear end swap into my 1955 98. I am changing the differential to a 1962 2.56 ratio. I want to keep my existing 1958 axles. Can i change the side gears from the 1958 into the 1962 differential? If I can change the aide gears, is there any tolerance issues? Is there any other pittfalls I need to know? Will this change the overall drive shaft length? I know the rear ujoints are different. Is there a way to mount a magnet inside to catch the iron debris if any after cleaning the interior?

Thanks. Ron

Charlie Jones

Check the distance between the springs on the '55 and '58 .
You may or may not need to move the spring perches .

If we are talking about open rears ( not limited slip ) then 58 thru 64 diff cases are the same . In any given series .
This would lead me to believe that '58 differential gears would fit a '62 diff .
The differential gears can be swapped without removing the diff case from the carrier . Check the shop manual .
The drive shaft length may very well be different .

You can get a magnetic drain ( and fill ) plug to catch metallic debris .

Love1955oldsmobile

Thanks for the info.

H.A.M.B. says 1939 thru 1964 side gears interchange.

On the drive shaft, the 1955 is one solid shaft but the 1958 is 2 piece so i am not sure how to measure nor do i have access to either the 58 or 62 for any type of measurement.

I know the 1955 slip yoke on the transmission allows for movement. I just dont know for how much movement. Nor do i know how much extra movement oldsmobile allowed as overkill.

I guess mark existing end of drive shaft then install the 58 rear end and see where things line up?

Ron

Charlie Jones

The H.A.M.B. is wrong on this one .
From the Oldsmobile Chassis Parts Catalog ;

Group 5.527 Gear package , Differential side and pinion
1937 thru 1952 All , part # 509520 (10 spline axle )
1953 thru 1956 All , part # 517249 ( 16 spline axle )
1957 & 1958 exc. Anti-Spin Diff part # 524573 ( 28 spline axle )
1959 thru 1964 exc. Anti-Spin Diff , or F-85 Part # 533509 ( 31 spline axle )

Olds kept increasing the axle size , and the spline count , as the cars got heavier and more powerful .

Charlie Jones

When you get the axle installed, with the weight of the car on the wheels, push the trans yoke all the way in.
Then pull it out 3/4 inch. Measure from the center of the front u-joint to the center of the rear u-joint.
You will need this measurement to get a new driveshaft made . The yokes and u-joints will be different on each end .

Charlie Jones

Quick question ;
Why do you want to go to all this trouble to install a 2.56 ratio in your 1955 98 ?

Love1955oldsmobile

Several reasons.

To increase mpg.

To reduce engine rpm
Reduce engine noise (basically fan noise).

I am using a 1958 371 engine. Original engine long gone before I got this basket case.

I am not interested in speed. The mpg is the driving focus followed by quietness.

Ron

Tedd Thompson

Have you insulated underneath the hood yet, helps some, and do you have a shroud installed, helps divert the noise a little. Fan noise isn't that loud on mine, nothing I would change a rear end over.

On all my toy cars, I just fill it up and close my eyes when paying. The price is worth the pleasure I get for the ride I get...Tedd

Love1955oldsmobile

Thanks for reply.

Hollander says 57/58 fits but does not go into details.

I hope some here can provide guidance and the pitfalls to watch out for.

I have some rear springs from a 56 98 that should fit for heavier duty as it weighed more.

Have front springs out of 55 98 convertible that should be hd as well

The rear ujoint is different between 55 and 58.

This is a parts car that is being returned to daily driver. It has factory air and has the a/c shroud.

I recall that my 60 pontiac with a/c at 70 mph you could hear the shift from 3rd to 4th by the fan but the tranny was so smooth you could not feel the shift. I can't remember the noise on my first 55 no a/c as at 70 mph and windows down you can't hear anything.

The guy I got this 55 from pulled engine and tranny and left in weather. Not a good deal.
He had painted body and upholstery.

A/c cars came with 3.42 so a 2.56 will cut rpms quite a bit.

I have aquired most the parts to start putting it back together.

Starting from the rear and moving forward.

Will use a 55 hydromatic to rear of 58 gmc/olds truck engine.

Thanks. Ron

Charlie Jones

This is going to be a problem .
The 55 trans and flywheel will bolt up to a 58 engine , but the 58 engine was externally balanced.
This means that weights were added to the flywheel and front pulley to balance the engine.
A large weight will have to be added to one side of the flywheel to keep the engine in balance .

Love1955oldsmobile

True that starting in 1957 Oldsmobile switched to external balancing.

The correct year crank shaft pulley has the balancing material cast into the crank shaft pulley.

I have a 1956 Oldsmobile with factory air where I used a 1959 crank shaft pulley by machining out the counterbalance weight.
Using this method would allow 1949 thru 1956 Oldsmobile owners access to crank shaft pulleys with a greater number of belt grooves to add power steering and/or a/c.

There was two or three ounces of cast iron that was removed. I did not record the actual weight of the material removed.

Ron