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Testing A 4-Speed Outside The Car?


gregmharrison
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Hey All,

 

My current 4-speed has a worn 2nd gear synchro and the PO gave me two replacement 4-speeds when I bought the car, but he was unsure of the condition.  Is it possible to "test" whether the synchros are good or bad in a tranny that is out of the car?  I guess I could call a local transmission specialist and ask them, but I figured I'd check with the forum first in case anyone has a good idea.  Also, if anyone knows a good tranny shop in the San Francisco Bay Area that they trust, I would love a recommendation.  Thanks as always!  Greg 

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Just rebuilt a few of these.  They're kind of a PITA compared to some of the other transmissions I've worked on.  I would say that the odds are good on running the used transmission.  If it were me, I would put it in and run it.  If you need any parts, let me know.  I've got a complete 4 speed in pieces that I don't plan on putting back together.

 

Oh, and to the point: No, there is no way to confidently test it outside the car.

Edited by Original_Customs
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I respectfully disagree with reply earlier.  If one has a 1/2 " drive drill/impact gun, short length of garden hose, clamped to 1/2 rod chucked in drill, and other end shoved over the trans input shaft and similarly clamped one can spin trans, shift gears, listen for bearing noise, test synchros, etc. I learned this from Walter M., proprietor of "Walter's Foreign Car Service" in Maple Wood, Mo. where I worked part time as a grease monkey while in high school -circa 1960 to 1963.  I believe Walter's son Ray continues to operate the shop.     

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If you have a 1/2" drill it can fit right on the pilot on the input shaft, spin it (clockwise while looking at the input shaft) and with it turning just run it through the gears, Like Carl said you can listen for bearing noise and see if the syncros work (make sure it has oil in it or you will get a false reading) 

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Thanks for the tip on using the 1/2" drill--very helpful! A year ago I put in a 5-spd "known good" transmission and the 2nd gear synchro was shot. Now I know why I saw a bit of brass debris when I changed the input seal before I put that trans in. I will put this tip to use in the near future--with oil in the trans :) --Fred

Edited by FB73tii
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 Hmmm, I find myself agreeing with Original_Customs, I'm of the opinion you can't properly test a transmission out of the car.

 

 A 1/2" drill motor simply cannot "input" the same horsepower loads that would cause a bad bearing to sound off.  Maybe if the bearings are thoroughly trashed, yeh, maybe/perhaps.  But a bearing on the edge of "bad" might not sound off until loaded up with 100 ft-lbs of input torque.

 

When you stomp on the accelerator, the torque load path through the transmission is quite different than when all the internal goodies are just spinning around with no real load applied at the input shaft, nor any resistive load at the output shaft.  It is the bearings which keep all the internal goodies in proper position during operation, and if you don't load 'em up to a place where they are actually getting close to capacity, you will probably never know they are failed, or failing.  I'm thinking that to properly test a transmission you gotta load it way up on the input shaft, and have a "proper" resistive load on the output shaft. 

 

Anyway, just a few engineering thoughts.

 

Cheers,

 

Carl

Edited by OriginalOwner
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Hmmm--agree it would be nice to test at full load, but any test before putting it in the car (including pulling the seals and checking the oil for debris) is better than nothing. I have two "known bad" 5-speeds that have already been in my car and one "supposed to be good" that is going into the car next. I'll run the test on the bad transmissions first and if the issues show up I'll feel I can learn something by testing the unknown one. I won't get to this for some months, but when I do I'll report back. --Fred

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If you're at home and have a bench to strap everything to, yes, the 1/2" Milwaukee Hole Hog drill CAN find a bad 2nd gear synchro.

 

You have to lock the output shaft, but you'll find that you can't grind 1, 3 and 4 without stalling the drill.  If you can grind #2,

and #2 only, then try the other transmission.

 

It probably won't duplicate the whine of a bad countershaft bearing.  (as Carl points out, above)

 

If you have a reasonably sensitive feel (or a flashlight to look into the filler hole) you can tell immediately if it's the

B-W style synchros or the Porsche synchros.  If Porsche, 2nd gear will (98% chance) be soft, if not outright synchro- free.

 

And reading the fluid, if it's still in there, is always good.

 

But no, there are no positive guarantees on the internet.  You CAN try to stack the odds of not doing it twice in your favor.

 

t

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I tested a 5 speed from an E30 318i before installing it.  Well, actually I tested 3 before getting enough confidence to install one of them.  To do this I made a wooden fixture to hold the transmission and the back end of the shift platform.  I spun it with a big variable speed Milwaulee Hole Hawg, wrapping the input shaft with masking tape first, and always supporting the drill to avoid any side forces on the input bearing. 

 

One of mine made noises that were inappropriate in several gears.  One shifted eratically.  The third one  sounded fine and shifted fine.  The third transmission was externally uglier than the others, if I hadn't tested them it would have not been my choice.

 

I do agree that externally bench testing is not a proper way to test all of a transmission's characteristics, but it saved me from multiple installs in this case.

 

The fixture was pretty simple- The bottom was a sheet of scrap 1/2" OSB "plywood".  The front fo the transmission mounted to a square vertical piece of the same material that was attached to one end of the bottom and had holes cut out for the input shft and 3 of the front mounting bolts.  I used scrap 2x4 to build two rear mounts for the transmission and the rear of the shift plaform. My first attempt didn't include the rear platform mount and I happened to first test the erratically shifting transmission.  After adding the platform mount it did shift better but still not properly, so  I do think it's wise to include that mouning point.  It let me have full confidence in my rebuilt shift mechanism before installing also (DON'T bother to install a transmission without fully checking the shift mechanism and rebuilding as needed if there's any doubt unless you like crawling on your back under the car a lot...)

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