M-36 options

Be sure the 258 is a 71 and the starter is on the correct side, otherwise you will have to use a later transmission.

If it is slipping I would say there are trans issues beyond bushings. When it is out is the best time to have it worked on!

You're pretty much stuch with the Borg Warner trannies unless you get a 72 or newer engine. When they are properly maintained and in good condition, there's nothing really wrong with them. On the other hand, if the tranny is air cooled, it may be better to find a 4x series tranny which will be water cooled.

can I use an M44 ?

You have to use a six cylinder transmission. My parts books says 1971 258's got an M43.

I'm pretty sure the M-3x and M-4x bells are interchangeable. The torque converters should interchange as well. In theory you should be able to use your M-37 torque converter and bell with an M-4x transmission. I don't recall anyone who's actually done it and don't have two trannys side by side to compare, but I'm pretty sure it will work. Unfortunately the only way to find out is to try it, or find someone with both lying around willing to check.

The M-4x was used behind 66-71 290/304 V-8s with 2V carb -- any with an aluminum main case (4V 290 used an iron cased M-11, no factory 4V 304s), and all 70-71 sixes (69 was last year for M-3x).

The M-37 was used behind 232s even in Ambassadors. If yours has liquid cooling (lines to the radiator) I'd get it serviced (bands adjusted, fluid changed, and filter changed/screen cleaned) and try it. And replace that bushing. When the bands wear it will slip a little, and if adjusted before they are too badly glazed the trans should last a good deal longer unless you're hot-footing around. Cruising/regular driving you should be fine even with the 258, especially if it's mostly stock. I really wouldn't worry even if it's air cooled only for a regular driver. Tom Jennings has been using an lighter duty M-35 behind a 232 for many years and nearly 200K miles (been rebuilt twice over a 20+ year period) in a Classic wagon hauling camping gear through the southern California desert on many occasions. As long as you don't get too abusive on it the M-37 (slightly uprated from the M-35) should be fine.

If it's air cooled look for plugs on the right side, one in the side of the trans near the bell and another in top of the pan flange near the back. If it has those you can attach an external cooler. If not the trans case isn't drilled for it and it lacks an internal tube for the cooler. From what Matt and I have been able to research, there were two different cases for air and liquid cooled trannys. Can't determine what models got which, but assume that heavy use (taxi and other fleet vehicles) and hot climates would get the liquid cooled, but may have just been the heavy duty option for the six. AC equipped cars might have the liquid cooled trans also. Not enough samples out there to say for sure!

It's not a hard trans to rebuild, if you ever considered rebuilding your own auto trans this would be a good one! You need a TSM and a clean place to work. Pull and tear-down in a 8-10 hour day, reassemble in 8-12 hours, then reinstall. Just be real careful with the valve body! Your's is a perfect self-build situation -- the trans works perfectly, just slips. That usually means no hard parts broken or worn too bad, just bands and clutches worn. Take it apart, replace all seals and wear parts (bands and clutches), a few bearings, and reassemble!


Edited by farna - Jun/19/2009 at 8:35am