"a-queried" 
5-speed A750 trans won't shift in to 5th gear.
- Thread starter MongooseGA
- Start date
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- Thread starter
- #322
You win 20 internets for this. I usually only give them out 5 at a time but this made me snort beer out.This thread has been really interesting to follow. This forum is just a fantastic wealth of knowledge.
In the spirit of the holiday season, I (very) loosely summed things up to a classic tune.
On the twelfth day of Christmas,
my true love gave to me
Twelve hundred Mud members viewing,
Eleven CDLs a-locking,
Ten gear selector a-checking,
Nine harnesses swapped out,
Eight pins a-testing,
Seven ECMs a-frying,
Six FSMs a-queried,
Five Techstream codes,
Four fluid changes,
Three valve bodies,
Two shift solenoids,
And a 4-speed A750!
My air compressor s*** the bed today while doing some plasma table things. So I loaded up my sheet steel and went to a buddy's house to use his table to finish my projects. Interestingly, Gerry shifted in to 5th one time on my 7 minute ride there. Wow, this is great! Didn't happen again on the rest of the drive or trip home. Dash lights were on for both drives.
I can also confirm that cruise control does work when without 5th.
Just waiting on the trans harness, L4 pickup switch (which USPS has definitely lost) and I've also ordered the 2 transmission speed sensors.
It's starting to fix itself.
- Thread starter
- #324
Yeah all I've really had to do was act out the song above.
- Thread starter
- #325
Wiring harness, speed sensors, and L4 switch are all either delivered or en route. Everyone cross your fingers and toes.
2001LC
SILVER Star
New wire harness and parts?
Food for thought:
5th/OD, working in cold weather just after ECT to minium.
One of the very difficult things. Is checking resistance of wires. Small changes in resistance, takes a very good multimeter to measure. It's also affected by temperature. As temp goes up, so does resistance.
With most wires, we don't know what resistance should be when new from factory. Once speaking with airframe mechanic. He commented checking all wire resistance. I ask; "How do you know, what resistance should be? Do you have a book of specs?" _- "We compare, to new wires/harnesses on the shelf". He also talk about how many issues, are from bad grounds. Said, oxidation at ground connection and in ground wires. That if one sees, where wire lug attaches, oxidation (discolor). You can bet, it's traveling up under sheathing. This changes resistance!
As I've mentioned earlier. Some of the most difficult issues I've diagnose. Have been resistance issues. Few examples:
Brake control wire. Easy one:
Clue RH junction back had water entry,
Clue 1) knowing windshield replaced and had water leak in past.
Fuse in RH junction box, stuck and had oxidation
Wire blocks, with signs of less than perfect seal. Resistance.
Food for thought:
5th/OD, working in cold weather just after ECT to minium.
One of the very difficult things. Is checking resistance of wires. Small changes in resistance, takes a very good multimeter to measure. It's also affected by temperature. As temp goes up, so does resistance.
With most wires, we don't know what resistance should be when new from factory. Once speaking with airframe mechanic. He commented checking all wire resistance. I ask; "How do you know, what resistance should be? Do you have a book of specs?" _- "We compare, to new wires/harnesses on the shelf". He also talk about how many issues, are from bad grounds. Said, oxidation at ground connection and in ground wires. That if one sees, where wire lug attaches, oxidation (discolor). You can bet, it's traveling up under sheathing. This changes resistance!
As I've mentioned earlier. Some of the most difficult issues I've diagnose. Have been resistance issues. Few examples:
- Brake booster motor permaturally fail, due to high resistance in brake control wires. This one easy to spot under boot at lead screws connection.
- HVAC issues due to ground fault resistance. Was two part. One resistance at RH junction box ground fault and bad main lug harness connection to RH junction box. This one 1/2 dozen Dealer ships and specialize tired to fix, unsuccessful over 5 year period.
- Watertight AHC wire housing block, with signs of water entry.
Brake control wire. Easy one:
Clue RH junction back had water entry,
Clue 1) knowing windshield replaced and had water leak in past.
Fuse in RH junction box, stuck and had oxidation
Wire blocks, with signs of less than perfect seal. Resistance.
- Thread starter
- #328
I'll take it if I can get some good karma points lol!
- Thread starter
- #329
So my Ms and I set out to replace 2x transmission speed sensors, L4 pick up switch on the case, and the external wiring harness (part number mentioned here earlier. It's the one that connects to the 3 big plugs on top of the bellhousing, visible looking straight down at the back of the engine). Having someone to hand you tools and parts while you're on a creeper is legit, especially if they're a beautiful woman. I learned there is a second external harness on the trans, but I do not have it on hand currently. While under the truck, I also disconnected my Lutz auto speed calibration unit, just to rule out any funny business with him.
After swapping the parts, I reconnected the battery and hooked up TechStream. I found the 2 persistent codes (L4 pick up and ABS system malfunction) and was able to clear them. After this, I performed a zero point calibration through TechStream while the truck was level in my garage.
Results? Well, I have 5th gear again. Not a fluke one time thing, we've been driving it today and have gone through several key cycles at this point. Downshifts occur with a jab of the throttle above 40MPH again, which seemed to be the threshold where that wouldn't occur while the 5th gear issue was present.
However, the VSC lights (and only the VSC lights, no BRAKE or CEL) are still present after stepping on the brake pedal to put the truck in gear. Additionally, the VGRS light has come on at each key cycle, even though it's cleared itself during each drive. Is it possible this is a vestige of the ZPC that will take some more mileage to work its way out completely? FWIW, although I've been driving my W126 for a few weeks, the steering does feel a bit 'off' running down the road at 60MPH. Not bad, just a little more responsive/jerky than I'm used to it being. Again, could be me being used to the old Benz.
I'm going to go ahead an order the ABS wiring harnesses for each corner as I've seen those to be culprits for the VSC lights here before. I will also leave the Lutz calibrator (calibrater?) disconnected for a while until I'm confident the 5th gear fix sticks this time.
I really hope this puts the transmission issue to bed. It's been a s*** year, I'm ready for a win. Happy New Year!
After swapping the parts, I reconnected the battery and hooked up TechStream. I found the 2 persistent codes (L4 pick up and ABS system malfunction) and was able to clear them. After this, I performed a zero point calibration through TechStream while the truck was level in my garage.
Results? Well, I have 5th gear again. Not a fluke one time thing, we've been driving it today and have gone through several key cycles at this point. Downshifts occur with a jab of the throttle above 40MPH again, which seemed to be the threshold where that wouldn't occur while the 5th gear issue was present.
However, the VSC lights (and only the VSC lights, no BRAKE or CEL) are still present after stepping on the brake pedal to put the truck in gear. Additionally, the VGRS light has come on at each key cycle, even though it's cleared itself during each drive. Is it possible this is a vestige of the ZPC that will take some more mileage to work its way out completely? FWIW, although I've been driving my W126 for a few weeks, the steering does feel a bit 'off' running down the road at 60MPH. Not bad, just a little more responsive/jerky than I'm used to it being. Again, could be me being used to the old Benz.
I'm going to go ahead an order the ABS wiring harnesses for each corner as I've seen those to be culprits for the VSC lights here before. I will also leave the Lutz calibrator (calibrater?) disconnected for a while until I'm confident the 5th gear fix sticks this time.
I really hope this puts the transmission issue to bed. It's been a s*** year, I'm ready for a win. Happy New Year!
Happy New Year! Not gonna say anything to jinx anything, otherwise.
- Thread starter
- #331
I've been searching but haven't found the thread/post I'm looking for. Someone on here replaced their ABS sensor harnesses with aftermarket from Rock Auto, but the parts they pulled from the box were Denso. I *think* it was Holstein brand on RA, but haven't been able to confirm. Anyone happen to know? Less than $40/side is better than $200/side!
2001LC
SILVER Star
Make sure to clear (REC) from VGRS. There is also a very long calibration of VGRS. States only needed when VGRS CPU replaced, but hey worth a shot.
- Thread starter
- #333
Thanks, I will try this. My laptop was near dead at the end of the ZPC so it's been on charge since. I'll hook it back up and see what we can find.
- Thread starter
- #335
Man I bet she's got some great milk in there
Besides the Holstein cows, are you saying you've had luck with Holstein brand car parts?
Sadly, no. I only have experience with the cattle.Man I bet she's got some great milk in there
Besides the Holstein cows, are you saying you've had luck with Holstein brand car parts?
But, here is the thread.
- Thread starter
- #337
I'm a big fan of cattle. I'm having some for dinner tomorrow.
I just found the post. It's here: How To: Wheel Speed Sensor Replacement - https://forum.ih8mud.com/threads/how-to-wheel-speed-sensor-replacement.881128/post-11576016
But unfortunately RA doesn't have these parts in the brand mentioned. So, I'll figure it out.
***Edit, correction. RA does carry Wells brand as mentioned in the linked post. It's called WVE, W being Wells.
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- Thread starter
- #339
I'd be lying if I said I didn't just shop the s*** out of 200s this last weekend.
I think we'll add some cooling seats to Gerry and at that point, what's the difference besides an extra 150 HP?
Eyedaho
SILVER Star
If the issue stays fixed, will you reinstall the speed calibration unit to see if it comes back?
