Date: Thu, 26 Jun 2003 22:55:29 -0700
Reply-To: Steve Young <sja_young@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Steve Young <sja_young@YAHOO.COM>
Subject: DIY standard transmission rebuild (long)
In-Reply-To: <4a.1d0ec10b.2bfcbe63@aol.com>
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Hi list,
I've just completed a DIY transmission rebuild of my 84 standard westie. The van's done about 200km since then so its still a bit early to tell if I did a decent job. Here's a bit of info on my experience while its fresh. I didn't find much in the archives about rebuilding trannys so I hope this proves useful. First and foremost I don't intend this to be an endorsement that anyone should tackle rebuilding a transmission. I haven't done anything like it before, but I have been fixing my old vehicles for about 20yrs. That said there were some moments that made me wince.
My transmission was diagnosed as needing a rebuild due to a worn pinion and/or main bearing. There was a nice tree of iron filings on the magnet and has been noisy since I bought the vehicle 4,000km ago.
Tools were a big issue. There's lots of specialized tools used in the Bentley manual rebuild procedure. I worked around most of them.
I constructed a press. The rectangular frame was made out of 2"x10" and 2"x 5" lumber. I sandwiched two lengths together and then bolted the whole structure using 4" long 3/8" diameter bolts and pre drilled 3/8" flat iron. This turned out to be a bit of overkill. My jack could exert two tonnes of lift and it seemed appropriate that build a frame that could stand that amount of force pushing it apart. The original plan was to bolt a bottle jack upside down to the top of the structure. This didn't happen for two reasons. 1/ Bottle jacks don't work upside down, (at least none of my three did) 2/ My local salvage yard didn't have any jacks with holes suitable for bolting to the frame. ( At least so he thought at the time. He showed up two minutes after I reconnected the battery and started the van to say he found a screw jack with holes drilled in the base)
In the end I used the bottle jack sitting in the bottom of the frame and various bits of scrap lumber for braces, (some bagged to prevent sawdust getting in the wrong places) and pressed upwards. Makeshift doesn't really do that arrangement justice.
For gears that could be pulled rather than pressed I had a 6" puller. That too got the Tooltime touch with 6 sections of 3/8' drilled plate I found I could extend the pulling to the full length of the pinion and main shafts. It should be clear by now that I had no intention of making a habit of rebuilding so not investing a lot in tools was as important a goal as rebuilding the tranny.
When I dismantled the differential I mis-read the Bentley manual. It writes about the R and r values (pinion depth measurements), essential for ensuring the correct backlash. I noted that an R value was hand scribed onto my ring gear and thought that was all I needed to carry on dismantling my tranny. Wrong!
I next thing I ran into was removing the pinion ring nut. Not necessarily a hard job but its torqued to c 160 ft/lbs. This made a pinon nut socket an essential tool. I hired one from Long Enterprises. Torque aside its also locked in two places. In my case it was crushed against the pinion bearing. In releasing it I damaged the nut threads. That took 5min to work around by drilling off the nut, but cost me $70 cdn for a replacement.
Once in the transmission I photographed, labelled and carefully bagged everything as I dismantled. There was plenty to confuse. The Bentley manual is pretty clear and has good illustrations to follow but I needed the reassurance of labels matching the manual.
Cleaning took a very long time. It was a good opportunity to look a wear of different parts. the first bit of wear I found was on the main shaft extension where it runs against the pilot bearing. A distinct waist was present. Most obvious wear was on the syncros. The teeth were substantially smaller than the ones in my rebuild kit. Perhaps 2/3 the size. There was also a bit of tooth wear on the 1/2 gear slider assembly. This was notable compared to the 3/4 slider assembly which showed almost no wear. It was also a lot cleaner. Much less black gunk between the teeth. I'm still not sure if this is because the slider has been replaced or because there's naturally less wear/deposition in this area. I decided to take it as a sign that it was replaced during the last rebuild and pass on replacing it this time round. The 3/4 slider is a design weak spot in the pre 87 vehicles so I was gambling the last rebuild included the improved 3/4 slider.
Another area of wear was on the main shaft teeth. Definite chipping around the bottom of the teeth. This was all small and dull metal. Lacking experience I went with assumptions. I assumed this was an old resolved problem. Looking at the main bearing I noticed the outer bearing was turned in the gear carrier. There's an indent taken from the bearing and the reverse gear shaft has a small protuberance that's supposed to lock the bearing in position. The reverse shaft was held tightly in the carrier so I was left wondering if it hadn't been correctly reseated by the previous rebuilder. It would be easy to miss. At least for me. I'd have missed driving the shaft fully home if a qualified rebuilder hadn't pointed it out to me.
I stripped the whole main shaft and most of the pinion shaft. Removing the first gear inner race is essential to remove the pinion bearing. This is at a high torque and requires a special tool. I took a new pinion bearing and the old shaft, bearing, race combo to a local rebuilder. He removed the race, pressed on the new bearing and reinstalled the race. Less than an hours work for him and well worth the money. The downside of that visit to the rebuilder was that my plans to bring the transmission back to him to reset the correct pinion depth were dashed. He explained what I should have already understood from the Bentley manual. As bearings wear the values change. The R value I had was for all new bearings. Since I had no plans to replace the differential bearings the R value was no use to me. To have done the job right I needed to measure the current pinion depth before taking the transmission apart. The advice I got and followed was just to stick it all back together with the
current shims (used for adjusting pinion depth) and cross my fingers.
It was a good project. I plan to drain the oil and see how things are doing at about 750-1000km. I got plenty of challenge and insight into transmissions and that was a key goal. I have saved some money, at least for the moment. If I was to do it again I'd obviously be clear on the r values. That said its a pretty big if that I would make the time to do it again, but if it needed done I wouldn't begrudge a rebuilder the money. All the rebuilders I spoke with were helpful and supportive. At least one would've been willing to take the appropriate measurements and then have me do the rebuild and bring it back to him to set the pinion depth, backlash, etc.
One last step that I should've included on this rebuild, but didn't, was checking the backlash with some gear marker something I could easily have done. http://www.differentials.com/install.html.
Steve
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