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Thursday, February 29, 2024

Doug's Domain

Doug Vetter, ATP/CFI

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Tuesday, August 22, 2017

Overhauled Transmission Arrives

I got a call this morning from my transmission shop indicating the unit was ready for pickup so I ran over and got it. The shop owner's overall opinion of the unit seemed positive and he said it was in generally very good shape, especially for the mileage since the last overhaul (140K miles). The hard parts (with unknown total mileage) were also found to be in good shape. He took this time to point out that the 4L30Es installed in the Isuzu tend to eat planetaries but mine were like new. I asked why the Isuzu application has issues and he said it's likely just a load issue (too small of a transmission for the weight of the vehicle).

As he indicated previously only a few of the steels on the overrun clutch were burnt. He wasn't really sure why this clutch took the abuse since usually it's the 2nd clutch that burns. But since he found all of the other steels in such good shape and determined that the factory steels were of generally better quality than the aftermarket units he replaced only the burnt steels on the overrun clutch. That served to keep my cost in check.

He replaced all the bushings as requested, including the center support bushing which is not typically included in the bushing kits. I actually requested the center support bushing replacement up front but he said he normally replaces that anyway because it's critical to delivering oil to various parts of the transmission and if the clearance opens up too much it can result in oil starvation. He also found the sprags slightly worn but he makes it a practice to replace the units anyway in all transmissions he overhauls as they generally take a lot of abuse.

When we spoke about the band, he confirmed that the most likely cause of the wear was a lack of band adjustments over the service life of the unit, but he also pointed out something I learned earlier -- band wear can also be caused by a flaky band-apply solenoid. Since I replaced all of the solenoids it's likely the wear won't progress as rapidly if I conduct the band adjustment procedure periodically from now on.

To wrap up the conversation I asked him what he would recommend to average owners as far as an overhaul interval for this transmission. He replied that there are no hard and fast rules here -- transmissions all seem to wear at different rates based on how the vehicle is driven. Given that I put 140K on the soft parts and the hard parts have even more time on them, I suppose the thing to take home here is that contrary to the opinion of some, the 4L30E is a pretty stout transmission, and even if you follow BMW's brain-damaged "no maintenance" policy as I did, the transmission should last at least 140K miles. If you replace the fluid and filter as well as adjust the band every 30-50K miles (depending mostly on the quality of the fluid) you might get a lot more mileage out of the unit.

The shop owner and I discussed converters early on in this process and I told him that based on my research the Precision unit was the least likely to have issues, so I requested and received a Precision unit with my overhaul. He used this opportunity to point out that he installed the Sonnax pump bushing, which is intentionally undersized so that it must be honed to fit. As a result I'm confident that the clearance is neither too close (which would cause the bushing to spin and destroy the converter pump shaft) nor too wide (which would cause an oil leak). This is not necessarily guaranteed to be the case if you use the bushing provided in the overhaul kits.

Back at the garage I took a close look at the frictions and the few burnt steels. Frankly, they all looked pretty good to me. There were indeed few black spots on the overrun steels but nothing like the severe burning across the entire face of the steels I've seen elsewhere. I could see wear on the low sprag but the overrun sprag looked to be in like-new shape. The band also looked to be in relatively good shape but the center friction did appear to be riddled with cracks and slightly thinner than the outboard frictions. Given how the band operates I imagine this is a typical wear pattern.

The total invoice was a reasonable $1275 and I must admit I am very happy with the shop owner's ability and willingness to discuss all aspects of my build. I'm expecting no issues but naturally I must reserve final judgment until the unit is installed in the car and my tech and I have given it a clean bill of health. As they say, the proof is in the pudding. Stay tuned until the end of the project.

Second Batch of Powdercoating Delivered

Once the transmission was back at the garage perched on a furniture mover I grabbed the second batch of parts I needed to have blasted and refinished and took those to the powdercoater. They were willing to blast the rusty areas of the oil dipstick guide tube and clean up the tensioners while I waited so I put those back in the car and left five brackets, the horizontal truss support, the AC compressor support and the fuel filter cover with them. The parts should be ready by the end of the week.

Speaking of the fuel filter cover -- while walking around the back of my garage today I found the original cover in a crate along with some of the front brake components I neglected to throw away in 2012. The filter cover is rusty as hell but it's still in one piece so I'm considering having it blasted and refinished just so I have a spare because it is no longer available.

More Painting

Returning to the garage I managed to spend a few hours prepping the blasted components for a couple coats of VHT primer, as well as putting a couple finish coats of VHT Cast Aluminum on the heat shields I started yesterday. The most obvious thing I've noted about the cast aluminum color is the vibrant flake in the paint. It's a bit too flashy for me but I did want something as reflective as possible for the heat shields and I suppose this is it. I did not originally plan on painting the tensioners but after they were blasted it seemed like the most logical thing to do. I'll see how the finish holds up.

Next Up

I'll put two thin finish coats of VHT Cast Aluminum on the tensioners and related parts, and then get to work on the hood release cable.