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Tuesday, June 16, 2009

Pete Bahr Rebuilds the JH 5 Speed Shift Linkage

The JH 5 spd Getrag Transmission and Shifter assembly is similar to that used in some BMW models. I found it hard to believe that the BMW designers came up with such a poor design, but they did ! ! Their choice of materials and structure is such that the assembly will wear out in time. I have no idea how long it takes, but the sand

, dirt, and heat will certainly take their toll on the various components. The Linkage-Gearshift flexible joints are such that wear will take place even without the elements, because of high compressive stress loads on the materials. There are 18 joints or bearing surfaces that are subject to failure – WOW.
Bad Shifters can be made to perform better than new, with a longer service lifetime, by replacing wear points with materials less subject to wear. i.e., replace Nylon with Bronze.


Well, since the Shifter is behind a British engine, it’s always full of grease, oil and other road crap. De-greasing with GUNK, brush, detergent and water wash generally gets the crap off the parts. Wife generally not happy about final clean-up in her kitchen sink though.
Time = 1 hour + 1 beer.

With it all cleaned up, it’s time to get out the files, emery cloth and deburr tools.
Time = 1 ½ hour + 1 beer.

Well, now comes the hard part. Some of these Shifters have parts that are so mashed up that it is impossible to measure – I know what the dimensions should be, but……………. The key here is to document all the dimensions on sketches or drawings so the next phase (design) will yield drawings that reflect the capabilities of the existing parts. The new parts to be developed and the modified parts must all fit together.
Time = 2 hours + 1 beer (after measurements completed).

First time I did this, drawings took a couple of days to do. It is a bit easier for subsequent Shifters since I have that reference drawing set to start with. Funny, there is always an issue. Sometimes the factory parts are different from the last Shifter set. Don’t know how some of this can happen, but that’s the Jensen factory (or, perhaps BMW) for you. In total there are about 12 drawings required, being a mix of new, modified and assembly drawings. Machine shops must have proper drawings and will follow them exactly. If the drawing is not correct, neither will the part. The cost is the same for parts that fit and parts that don’t fit. Tolerances on the multitude of bearing fits are closer than 0.001 inch, and some of the bronze bushings must be press-fit into mating parts. Be certain to specify the raw material and surface finish as required. This part of the process is not for the faint of heart.
Time = 2 hours + 3 beers after I’ve finished.

Well, now that the drawings are complete, we will have to write up an order sheet – part numbers, quantity etc. Make copy for the shop and one for me. Get in the car and make the trip to the shop. Review the order and ask for a completion date / lead time. Always double the quoted time. Ask for a cost estimate and join in the laughter. This is a time and material job, not fixed price. For Pete’s Kits items, I always hope the final cost will be less than the price I’ve quoted to Jensen Healey owners.
Time = 1 ½ hours. No beer, as the New Jersey laws do not allow you to drink and drive.


After a reasonable period of time, phone the shop and confirm that the lead time is, indeed, twice what was quoted. Finally, drive to the shop (avoid the commuter rush hour). Check the box of completed parts and see if they are all done and the parts that should fit together really do. Well, you forgot to make PN 99267 – “OK, OK, I’ll make it today and drop off at your house on my way home”. Yeah, really.
I can’t stand the pressure, how much is this going to cost me? Wow, THAT MUCH! “Well, I should really charge you more, but I’m a nice guy”. Thanks, here’s a check. Drive home and hope the rest of the parts arrive tonight.
Reviewing the parts at home, I find three parts that I didn’t order. I was able to buy 5 of these parts from Delta at $10 each – the three made at the shop cost me $22.68 each. What a bargain. In any case, I now have an inventory of this part enough for 7 more Shifters. That’s enough to last me till the year 2025.

ASSEMBLE SHIFTERS AND SHIP....... the exciting conclusion to come!