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Help

K

Kevin Reichert

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Name is Kevin, have never owned a diesel but currently looking at one. This is where i need help, its a bering/hyundai with a 3.8 detroit deisel with 113000 miles. Everything i have read states this is a good motor, problem is the allison automatic transmission. The overdrive does not work, it goes along fine, shifts good, but in current condition can only hit 45mph. The fluid is clean, not burnt or anything. Is this a common problem, and can it be fixed at a reasonable price. Any help is gratefully appresiated.
 
Welcome, I can't help you with the mechanical issues, but we have some here that can guide you. Enjoy the site.
 
Do you know which transmission is in it? Or at least what year it is? I'm not familiar with that vehicle or engine combo, so I don't have a clue which allison would be in it. If it's an allison world 1000(they didn't come out until 99), then it could be one of many things, and would require connecting a scan tool to it loaded with the allison doc software to see what it is seeing. Otherwise I would suspect it would have the old at545 in it which was the old mechanical trans used in MANY applications up to around 02 or so I believe. Common shift problems with them from my experience has been worn or misadjusted throttle kickdown linkage as that trans shifts entirely off of throttle input and governor pressure. I ran into one before that had stumped a few shops where it would max out at 50, ended up being the linkage had worn to the point it was no longer pushing the linkage at the trans side. I adjusted the rod out about 3/8" to make up for wear, and it dropped right into high gear when we drove it.
 
Did a little digging and found some info. It is called a 3.8l detroit, but the engine is actually by VM MOTORI, and I believe is called the VM638. The transmission is an at-542 which is supposed to be very similiar to the at-545, just setup to be shallower. It has no overdrive gear in it, high gear is 1:1. It is very sensitive to the throttle kickdown adjustment, and they only want to shift at high RPM's, even with properly adjusted linkage from what I could find. It also regarded as a light duty trans by allison standards with a 230hp and 485 lb ft torque input rating.
 
Thanks for the info, but does that mean the top speed is 45mph? Some (not from here) tried telling me they made a 542 and a 542e, the first was machanical and second one was electical. He sail if trans fluid was clean and not gritty and still shifted without any issues it was most likely the 542e and it was the celinoid for the overdrive that was bad. This is why i have come to you gentleman, because i have no idea what is going on and wheather or not it would be worth buying in current condition. Thanks again
 
For starters, there is no overdrive in this transmission. They are geared for a 1:1 in high gear(4th) so that they could run highway speeds in direct(most with these 4 speeds seem to run 65-70 at wot in 4th). I just looked and some of these late model units have an electric modulator in them. I couldn't find much info on it. Some say the modulator effects line pressure at 65% throttle and greater while others say it was added to make the transmission downshift under load which is a known issue that transmissions did not like to downshift. I hadn't ever encountered one of these with any electrical input, so thats a new one on me. From the little info I could find, it sounds like you need to get a pressure gauge on the trans, and go from there. You're messing with something I just have no experience with. But from what I could find, if it has low line pressure, the 3-4 clutch pack can burn out(they say it's the 1st one to go), but it could be linkage adjustment, governor issues, who knows without diaging it.
 
Thank you, i tried looking things up myself found some thing but still not what i was asking. Then everyone else started giving input and i got lost. When i found this site i knew from what i read this was were i was meant to go. Now not sure if i want to chance buying it or not, as i am sure from what i have found parts and repairs are not cheap.
Thank you again
 
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