New to us Volvo A35C

The company owner bought a 1996 A35C last week that turns out to have some glaring issues.
1) The gauge cluster says that it has 13978 hours but the computer in the overhead area says that it has 21180 hours. I'm leaning towards that the computer has the right hours but I wanted to check that with you guys before he goes after RB for misrepresentation.
2) The drop box seems to have the proper air actuation to engage 6x6 but it absolutely will not engage the rear wheels. When you press the foot switch, only the front and rear most axle light comes on. The 6x6 and front bogie axle lock lights do not come on. Is there a way I can inspect the engagement ring? What part of the drop box is responsible for the engagement of that? I pushed the front up on a snow bank and it lost traction allowing the front axle to just spin. With it in gear and the front spinning, I got out and looked at the rear driveshaft and gave it a touch. I felt like it was trying to engage or possibly that all the teeth on it were gone.
3) The top bushing/bearing of the articulation point seems to be wrecked and easily has a 1/2" of radial play. I understand that this will require separating it. How much of a chore is this job and are there any special tools required?
4) The trans light and the STOP light come on when it has a load in it. I noticed that one the data display it says that it is a slip detection code. The trans doesn't feel like it is slipping and the tach doesn't indicate this either. The fluid seems old and discolored but is full and doesn't smell burned. I was planning on a fluid drop and filter change and then do it again at the next 100 hours. Any other suggestions on how to verify this without having a scan tool would be great.

1) On a machine of that age either component that registers the hrs could have been replaced by a second hand unit from another machine so either could be right or wrong there is no way of telling without a comprehensive service history.
2) So have you engaged all the drives one at a time to see what engages and what doesn't? have you checked the bulbs in the display to make sure they work first? and the wiring to the which rear drive shaft did you touch to see if was engaging? and can I say just from a safety point (please don't do that again) if the shaft is not spinning from the back of the dropbox to the hitch then you have an obvious problem in the dropbox, is the diaphragm ok, in the top of the dropbox for the six wheel drive engagement? if its torn or worn through it won't be able to engage, there is some adjustment possible on the dropbox but i don't think its as much as engaged to not engaged.
3) You will need stands and a forklift/hoist/crane to balance the front of the machine as you separate it other than normal tools, how big a job it is depends on your skill level. If you've got a lot of play in the hitch you could be looking at a line bore job or new hitch.
4) There are two sensors on the transmission that between them will decide if slip is occurring one on the input is on the oil pump on the inside of the trans, the other on the dropbox clockwise round and down on the casing from the solenoids on the top. if it was just a sensor issue it would do it all the time and the likely suspect would be the output speed sensor, BUT yours is only doing it under load so i suspect it could be correct and there is some slip occurring. drop the oil send a sample and get it checked (cheap enough to do for a definitive answer) i'd also send a sample of the new oil after another 50 hrs just to see what they say

Khyren said:

The company owner bought a 1996 A35C

Click to expand...

If he doesnt have any equipment experience, THIS is your biggest problem.

Is there any error/fault codes registering on the monitor during any of this?

1) I figured that might have been the case with the hours but to know which one is right is anyone's guess. It's an auction truck.
2) Do you have a diagram of the drop box and an adjustment procedure for that? Yes I know it was potentially a huge safety risk, but the snow pile was 12 feet tall so even if it did magically engage, it wasn't going anywhere. Yes it was the shaft coming out of the drop box. I will be checking bulbs today. Someone else asked for a gauge layout so I know what most of the switches and lights are. The ones in the shifter area are mostly unknown. One is for high and low range.
3) This is about what I figured it would be like. The bad part is I don't think I will get it done as the truck needs to be operational last week.
4) I'll try monitoring the input and output speed sensors as the light wasn't constant all the time. I will also do a fluid dump, filter, and sample.

I have been doing operation for just over a yesr now but I don't get much time to operate since they figured out I can fix just about anything. Thankfully, I'm compensated well for it too.

hi a serial number will help as there are two different systems that operate the diff locks
one is straight air the other is electric over air

It's a BM model which I recently discovered which makes a lot of the parts entirely different from the regular production models. SerIal number is: A35CV4211. New development is that the trans will physically be in reverse but the shifter is in neutral. Drive just acts like a trans brake with reverse and drive locked together.

Gee, with all these issues where do you start. Maybe part it out to recover your costs. If the transmission is bad, exchange units are available on ebay for $17000 plus a core charge of $6000
then you have to consider the cost of the hitch parts and possible line bore
Plus you don't know what condition the drop box and associated diff locks and longitudinal locks are like.
you can disconnect the ECU from the transmission for testing but it will only allow you gears 2&3& reverse
remove connectors EA and EB and connect to plug on fire wall
it may help you isolate the transmission issues
Note the last A35C truck I worked on dragging in neutral was caused by warped clutch plates in the transmission

After putting the connectors on there like you suggested, neutral is actually neutral again. Reverse still has some go but forward is still lacking. It is kind of stuck in a hole it backed itself into. I'd be willing to bet that if I can get 6x6 engaged fully and have those two forward gears, my boss will just say send it. I bought a manual today and printed off a good portion of it. I discovered that I need a Contronic box to properly see things and also program the ECU. The ECU has definitely been replaced recently. This is likely why the ECU says that it has 21k hours. The other thing that point to an ECU replacement is that it doesn't have either of the exhaust or transmission retarders programmed into it. That seems to be why they don't engage or display that they even exist. I'm fighting a bolt on the floor so that I can get to the shifting box to see what's going on in there. The code that it was showing was 493. Slipping under lockup. I've got a long way to go just to get it going. After the job it was purchased for, I think it is going to go back to RB to be sold if it isn't parted out first.

Hi here is the diff lock air circuit for your serial number
Normal operation no diff locks engaged. Drive is through the drop box differential to the front and rear drive shafts.
Only the front axle and the front bogie axle are connected.
Air toggle valve #15 controls the front axle transverse diff lock
when that is engaged, both front wheels should turn together.
Air toggle valve #19 when applied controls air to the front and rear bogie drive shaft lock, at a minimum one wheel on each axle should spin.
it also supply's air to the relay valve in valve block #16 this valve shifts and blocks park brake release air flowing to the drop box longitudinal diff lock. The diff lock is spring applied and now locks the front axle group to the rear axle group
This allows a minimum of one wheel per axle to drive with differential action.
Floor push button valve #23 supply's air directly to the front and rear bogie axle transverse diff locks. It also supply's air directly to the front axle transverse diff lock and also supply's air to the relay valve in valve block #16 this blocks park brake air from the drop box diff lock allowing the spring to engage the longitudinal diff lock
All six wheels are locked. This is true 6 wheel drive

I think my next plan is going to pull it out of the hole with the dozer tomorrow and air it up with a compressor so I can fix all the freaking leaks without it running. It leaks so much air it won't get over 6 bar anymore. Then hopefully get the trans to work right. Thanks for the heads up on the air lines!

Air leaks in the cab are fixed. But there are plenty more to go. The front diff locker diaphragm is shot and just pressurizes the front diff. I should have someone with me Monday to help me check the rest of the lockers and maybe get the dog clutch checked and adjusted. The trans still flips out when I have the ECU connected and reverse is still neutral. I'll be checking the trans harness for shorted/stripped/rubbed wires as well. Shouldn't be too bad with the floor completely out of it. My boss already said that even if I have to make it manually shift the solenoids for 1st and 4th, do it.

Update time... After ohming and continuity testing all of the pins on the ecu and cleaning all of the connections in the harnesses, the transmission works as a transmission in the forward gears. It still says there is slip when the converter is locked up. However, reverse is super soft but will eventually give full engagement. Then after a little while, you have no forward or reverse gears. If you turn it off and wait about 10 seconds, you have gears again. I put the ecu connectors back on the testing ports. Reverse is solid and 1, 2, 3 is solid as well. What are the rotary switches on the ecu and does the battery inside it being dead as a hammer effect anything? I also was able to the the 6x6, diff, and longitudinal locks adjusted so all of those work again. And of course, fix one thing and another shall appear... The calipers on 2 wheels are leaking now.

Further update... Turns out after talking to an industrial transmission reman guy, it was a K1 and K2 clutch pack failure and we did indeed have to put in a transmission. The truck has steadily been hauling material for the past 2 weeks now.