Collinster742002
Collinster742002

Rebuilding the Getrag 232 Four-Speed Transmission

Original Author: Mike Skolones

Rebuilding the Getrag 232 Four-Speed Transmission

Parts Needed:

  • Transmission seals kit
  • Transmission gaskets kit
  • Transmission bearings kit

We are working on getting part numbers for all these parts and kits. There is also a lot of information about pulling and replacing the tranny itself in the Five Speed Conversion article (see Index).

[Editor's Note: This Article was put together from several of Mike's posts on Roadfly, and should not be taken so much as a "how-to" as a "what-to-expect" article. Although there is some very specific info here, you should secure access to a good shop manual and follow its instructions in light of the benefit of Mike's experiences as conveyed below.]

Introduction:

A while back the Getrag 232 4-speed transmission in my ’74 '02 bought the farm, and I decided I wanted to try rebuilding it on my own. Having done so, I am very satisfied with the results. The car was off the road for less than a month (barely), and it only cost me about $400 for new bearings, synchros and gaskets. I hate to estimate how much labor I put into the rebuild, but it's less than 100 hours, including time to design and fabricate tools necessary for disassembly and reassembly. The new transmission is much quieter than the old one, shifts smoothly, and so far doesn't leak!

Before you get started doing this, be aware that you could go through a whole STACK of used boneyard (cheap!) trannies (esp. 4-speeds) before coming close to the cost of doing this. However, just knowing that the thing IS rebuilt is satisfying, and there is hardly a finer pleasure than working with a fresh manual box. Besides, swapping trannies gets boring, I'm sure, after a while. Finally, although I have only done this to a 4-speed G-232, most of the following would also apply to the ever-popular G-245 five-speed conversion tranny (a bit more on this later).

Getting Started: Picking a core

In terms of picking the core for your rebuild, the obvious place to start is with the box you've got! However, there are a few other considerations. First, 1972 or newer units have stronger synchronizer sets. The older ones (up to sometime in '71, I think) had "Porsche" style synchronizers, which are inferior and might be NLA. The later, better, units had Borg-Warner synchros, which have the bonus of being much more common and easy to find. Second, make sure that the mainshaft (the output shaft) is not damaged where the output flange couples to it. Up to '76, the G-232 had coarse coupling splines, while the later, '76-up (inc. 4-speed 320is) unit had fine coupling splines. On the older, coarser, ones, the flange sometimes loosened up slightly and caused the splines to wear. If the tranny you are trying to rebuild has worn splines, you will need a new mainshaft--which is very expensive new, and if you find a used one in another tranny you may as well just rebuild that other tranny instead. To see if the mainshaft is worn, remove the coupling flange and pry out the seal; then inspect the splines where the flange slides onto the shaft. Look for the usual suspects in terms of wear: play, overly polished surfaces, etc.

When I finally got the box out of my '74 apart, I found that the (allegedly "rebuiltâ€) gearbox was actually a '68-vintage box with Porsche-style synchros and what seemed to be a new mainshaft. I think the "rebuild" (P.O.) job it was given was really only a mainshaft replacement, though they may have freshened the synchros (the Porsche-design synchros are marginal even when new). They certainly hadn't replaced the rear layshaft bearing, because it was the original ball-style bearing, not a roller bearing as is found in '71 and newer; any decent rebuilder would have updated the weak ball bearing with the later roller bearing, especially because it's a direct swap. It was this ball-style layshaft bearing that failed and caused the "thunk-thunk" when my car's gave up the ghost: The metal cage that keeps the balls separated in the raceways had come apart. A fellow '02er I had met on Roadfly was kind enough to have given me a spare 232-box as a possible core, and sure enough I decided to use that ('71 Borg-Warner synchro) box with the newish mainshaft from the '68 box that was in my 1974 car… (following me here? ;))

Fabricating Special Puller Tool

In order to actually disassemble the box, you will need to fabricate the special input shaft bearing puller I used, or buy the $400 item from BMW. If you've looked at one of these bearings (they are virtually identical to the rear stub axle bearings) you'll have noted that the balls are held separate by two-piece stamped steel carrier that prevents one from inserting anything through the bearing. I decided that the best approach would be to remove this ball carrier and make up "jaws†or pulling rods that fit into the bearing race.

If you do decide to try this method, be careful not to drill too far through the ball-carrier; first you will hit a shim or two, then the input shaft gear itself, which you don't want to drill.

To make the puller, I used ½†drill rod; 1" steel pipe; 5/8" all-thread; two 5/8" nuts; 1/8" drill rod (for pins); a bench grinder; a drill press, hacksaws and files, a vernier caliper and scales. The half-inch drill rod will make the 'jaws' they're not really jaws, more like keys that will lock in and allow the operator (that's you) to gently and surely pull the bearing off the shaft.

Picture the end of the jaw being a sphere equal in size to a bearing ball, but the sides of the sphere are ground flat so that you can insert the jaw through the bearing race gap. Once inside, you rotate the jaw 90 degrees so that the spherical surface of the jaw-end mates up with the bearing races. I cut two pieces to length and ground parallel flats in one end, width equal to the gap in the bearing race. Then using the grinder and files, shaped the key to fit the bearing. I had an extra bearing hanging around to use for measurements. The one-inch pipe is the "body" of the puller. Square steel tube would probably work better, but I didn't have any lying around. I drilled three holes in the pipe, one each for the puller jaw rods, one in the middle for the all-thread. I drilled 1/8" holes in the back end of each jaw rod for pins, and cut a suitable length of all-thread for the puller screw. A nut is secured to one end of the all-thread by drilling a hole through the nut and rod, then inserting a pin. I decided to continue using the channel-steel brace so as to support the input shaft against sideways forces, so I drilled two more holes in the channel to allow the puller rods to pass through them.

The BMW tool that accomplishes this same task but saves you from destroying the bearing you are trying to pull in the process of pulling it costs $400. The one bearing and a whole set of gaskets costs around $100, so if you're not in the business, the hand-fabbed tool is probably the best bet!

Some Reflections:

(0). The inner workings of BMW's gearbox (and many others, most likely) is easily the most beautiful and satisfying mechanical assembly on an ‘02. I've had my whole car apart over the years, and there is no comparison. A gearbox is one of the neatest things ever created. The machining and materials are stunning, and the rebuilding process is quite satisfying.

(1). Rebuilding the 232 is actually quite straightforward; it's simpler and easier than building a motor, IMHO. If you have decent mechanical skills, good patience, and you are organized, then refreshing a BMW transmission is feasible. Pay attention to how things come apart, and invest in one of the friendly shop manuals to help keep things straight.

(1.5) If major parts (shaft or gears) need to be replaced, try to find used ones. The gears are very hard and normal wear will not kill them, so used ones should be fine if you replace them in pairs. Otherwise the cost will outweigh the benefit.

(2). Shimming is the most interesting part. You shouldn't rely strictly on measuring tools for this; you should feel the effect of the shims as you go through the assembly, and decide for yourself whether the fit seems OK. (Professionals will probably laugh at this notion, but if you've never assembled a gearbox before you should pay close attention to how the assembly feels and behaves both before and after the rebuild. If it doesn't feel right to the hand, it probably won't work well when it's hooked up to a motor).

The manuals give you a method using a depth gauge, where you determine the necessary thickness of shims to capture the input shaft bearing, layshaft bearings, and mainshaft bearing. I did it with my homemade depth gauge and the vernier caliper, plus lots of trial-and-error assemblies to get a feel for the effect of different shimming techniques. With the gearbox in neutral there should be no real drag between the input shaft and the mainshaft. If there is drag, it's because the 4th-gear synchro clearance is incorrect, which will cause rapid synchro wear whenever you're not in 4th gear. I assembled and disassembled the tranny numerous times before I declared it finished; on several of these trials I installed only one component or another (e.g., input & mainshafts, no layshaft) to determine the fit of that component. In the end, you want the reassembled transmission to feel right to your hand. Things should spin freely, with minimal drag and noise, and absolutely no fore-aft slop in any shaft.

(3). Although special "factory" tools might make the job easier, as I described above, you can tool up for a 232 rebuild using only a decent gear-puller set (mine was $39 at Harbor Freight), some hardware-store drill rod, channel steel, and large C-clamps. The "factory" bearing extractor costs $400 and allows you to remove the bearing without destroying it. My homemade bearing puller requires one to destroy an old-style input shaft bearing (one with a metal ball carrier) in order to dismantle the transmission. If you rebuild with new-style bearings (they have a delrin or nylon ball carrier), you can remove/replace these numerous times without damaging the bearing. Unless you plan on building your own boxes for racing, and so will be tearing them down constantly, odds are you won't be trying to reuse the old bearings anyway. In my buildup I used the old scrap bearings for all of my trial shimming and assembling, then installed the fresh bearings only during final assembly.

(4). If you replace the rear seal in your 232 because the old one leaks, beware that there are two diameters of seal: the 38mm seal fits the old-style (coarse-splined) mainshaft, and the later mainshaft takes a slightly larger one (39mm? I'm not sure). If you just call and order a seal, odds are you will get the later one, which will never seal appropriately if applied to the earlier mainshaft.

I have to say, that the worst part of the whole effort (the part that caused me to swear the most) was putting the new tranny back in the car. I don't have a tranny jack, and the light weight of the 232 tempts one to bench-press it into place. It works, but it's not pleasant. Every other time I've had the tranny out on this car I've removed the motor as well; putting in the tranny from underneath easily qualifies as my least favorite operation. [A tranny jack is VERY easy to make¦ see the "Five Speed Conversion" article in this same section of the FAQ for more details. Ed.]

Finally, just some notes on the differences I have discovered between the 232 4-speed and 245 5-speed in terms of rebuilding them. I am not SURE about this, but they may be even easier to rebuild than the 4-speed. This is because you MAY not need to pull the input shaft bearing to split the case and take the tranny apart. The Close Ratio 5-speed (rare factory option) described in the Haynes manual does not require initial bearing pull to separate the cases, so I can only wonder about the Overdrive version).

GOOD LUCK with your own rebuild, and if you have any questions, please feel free to post them on the Message Board!



User Feedback


Mike -

Thank you for the article, I enjoyed it. 

I'm about to undertake a 4sp rebuild for my 75 02 and was wondering if you have any pictures of the tools you fabricated?  If so, could you post them ?

 

Thanks,

Eric

Share this comment


Link to comment
Share on other sites

Hi  - I enjoyed the writing above and it certainly opens my mood up about the prospects of doing this myself....but....can someone comment on a parts house out there or tranny shop out there that has these rebuilt already and all I do is send in my core?  Seems like $800 would do the trick? For my VW I can get a "factory rebuilt' from several cos mail order... 

Share this comment


Link to comment
Share on other sites


Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now