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No Reverse anymore in A904
https://slantsix.org/forum/viewtopic.php?t=57425		 Page 1 of 3
Author:  SageRad [ Fri Apr 03, 2015 8:11 am ]
Post subject:  No Reverse anymore in A904
I'm starting a new thread because unfortunately i kind of hijacked another thread about reverse clunk -- i'm sorry to post same thing here, but this is a different problem with a different subject, and now it's urgent for me. I'm poor and this is my work truck, i need to be making money, i'm a carpenter.

The reverse gear stopped working yesterday. But it didn't just go away all at once. It took longer to shift into, and i had to rev the engine and it would clunk loudly, and then it would be engaged in reverse. I drove around yesterday and at first, it would go in reverse after revving and a CLUNK! but finally i had to push the truck backward a few times before i got home, and that's not cool when a cop sees you pushing your truck on the street.

Now the truck is in the driveway and i can't back it out.

Early this morning i followed Dan's advice, and checked for fluid flow to the oil cooler. It's good flow, about 1 quart per 20 seconds.

I dropped the tran pan, and the fluid is decent, not red like new, but not burnt. The filter is good. There's nothing bad in the pan or on the magnet. I had changed the fluid a couple hundred miles ago and adjusted the throttle valve linkage and the bands then. I thought i had fixed the slippage with these actions, because it ran well for a couple hundred miles -- and i actually got some work done and made some money!

But now, the reverse gear isn't there, and i opened the transmission and looked at the low-reverse band. The band looks and feels good. It's not broken. There's no sign of shrapnel or burning. The servo looks good, as far as i can tell from underneath it. Nothing else seems out of place to me. I'm a beginner, so there's a lot i don't know, but nothing jumped out to me. I've been studying pictures and all the books and how-to's that i can for the A904.

I had adjusted the rear band to 4 turns back from "snug with a short wrench". It worked for a week and then this failure started to happen.

Any more ideas, i would be grateful.

Is there more i can check without dropping the transmission? Would it help to make the band adjustment a little tighter, like 3 1/2 turns back from 72 in-lbs?

I want to figure out if this is busted and i need to replace the tran, or if there is more i can do right now.

Grateful for any help.

Sage
Author:  SageRad [ Fri Apr 03, 2015 9:25 am ]
Post subject: 
I adjusted the rear band to about 3 1/2 turns back from snug with a short wrench. Still no reverse at all.

I also put in nearly a quart of Lucas transmission fix.
Author:  SageRad [ Fri Apr 03, 2015 9:59 am ]
Post subject: 
I found this post from 2002 that has a similar pattern as my problem.

A transmission that got bands adjusted, works fine for a week, then the reverse disappears.

And then the solution that Reed did was to re-adjust the low-reverse band. Then his reverse worked again.

Now my guess is that my "snug with a short wrench" is too loose because i'm not a super-experienced mechanic so i should either find my torque wrench (i used to have one) or buy a new one and do it right, with the actual spec of 72-in-lbs and then back off 4 turns. That is correct, right, on a 1987 A904? At least i think it's an '87 although now i've been finding out that this truck was modified before i owned it, for example, it's got a rebuilt Holley carb from an earlier era.

Here is the part number on the driver side right above the pan:
Image

If that helps anyone determine what kind of A904 this is. It reads PK4431566.
Author:  Reed [ Fri Apr 03, 2015 10:10 am ]
Post subject: 
12 inch pounds is about as tight as you can get it using your fingers. Since that last adventure with rebuilding 904s, I have actually bought an inch-pound torque wrench. However, I rebuilt three 904s and adjusted the bands to finger tight and then the specified number of turns out and they worked fine.

If adjusting your band does not solve your problem then you might have worn clutches. Sorry, time to tear it all down.
Author:  SageRad [ Fri Apr 03, 2015 10:19 am ]
Post subject: 
Reed, you are the star of the other thread. Good to have your advice, 13 years later!

Interesting theory, that the band "seated" itself and that was you Ping. I wish i had a ping. Mine is not engaging the band, i think. Or could it be the front clutch. I haven't been at high speeds so i don't know if i have direct drive gear, and that and reverse seem to be the only two that use the front clutch according to Tom Hand's guide.

Do you mean 72 in-lbs or the 12 in-lbs?

I certainly did it much tighter than finger-tight -- i used a 6-inch wrench and estimated what i thought was 12 lbs at the end of the 6-inch wrench. And then i backed it off 4 whole turns. Here is a video that i got the phrase "snug with a short wrench".

If i should be going to finger-tight then backing out 4 turns, then i must have it too tight right now.

I'll give it a shot as you say. What do i have to lose except another hour, and my mind? But if i have the band too tight, would that make it not work? I thought that should work, but would give a friction feeling in other gears due to the band rubbing the drum.
Author:  Reed [ Fri Apr 03, 2015 11:12 am ]
Post subject: 
You know, it has been so long since I adjusted the bands on a 904 I can't give you an accurate answer. What I recall off the top of my head is you loosen the lock nut until the adjuster turns freely, tighten the adjuster until finger tight and then back it off the specified number of turns. Then tighten the lock nut.

The number of turns to back the adjuster out varies by year. I did a quick web search for the trans ID number you posted and came up with this form another forum:

4431566 B,D A904, w/LONG EXTENSION, B1,2-D1,2 w/225 Eng., H-STALL, After 8-5-1986 PILLETTE Built, After 8-11-1986 WARREN Built


So you must have a late 86 or 87 truck, one of the last slant powered vehicles built.

If I were you, I would drain everything out of your transmission and start over with fresh fluid. Additives to the transmission fluid are just plain unnecessary and not a good way to spend money. Use Dexron VI trans fluid. With the pan off, adjust the low/reverse band and the kick down band.

I am away from home right now and don't have access to my shop manuals, but here are the adjusting specs I found via a web search:

Kickdown band- torque adjuster to 72 inch pounds (finger tight) and back the adjuster off 2 1/2 turns.

Low/Reverse band- 72 inch pounds and four turn backed out.

I have found this diagram to be invaluable in diagnosing 904 transmission problems:

Image

It looks like if your reverse band is fine and adjusted properly then your front clutches might be worn out. Does your truck go into 3rd gear with no problems?
Author:  SpaceFrank [ Fri Apr 03, 2015 11:26 am ]
Post subject: 
I love that diagram.

So in Reverse, the only elements in use are the front clutches and the L/R band. The only other time the front clutches are in use is in 3rd gear in Drive, which he said he's not sure he's driven fast enough to reach.

The only other time the L/R band is in use is when the gear selector is in 1st. If you have any room for the truck to move forward, maybe you should put it in 1st (not Drive) and see if it moves forward. If not, then the problem lies in the L/R band. In which case you should get your hands on an inch-pound torque wrench and make sure you're doing the adjustment perfectly.

If it does move forward with the gear selector in 1st, then you're wasting time messing with the L/R band. That would mean your front clutches are bad and you're looking at a transmission rebuild.
Author:  SageRad [ Fri Apr 03, 2015 8:14 pm ]
Post subject: 
I think my front clutch is bad, because i do have Manual 1st gear.

I re-opened it, and re-adjusted the rear band a bit looser, but that didn't give me reverse. And now, i can sometimes hear a weird rattling when i try reverse. Gives me the shivers because i think it's the front clutch.

Anyway, there might be a salvage tran with 90,000 miles on it, for $350. Maybe that's my next step.
Author:  Charrlie_S [ Sat Apr 04, 2015 5:11 am ]
Post subject: 
The only way to check the front clutch is to see if you have 3rd gear. Even if you have manual 1st, the f/r band still may not be working, as he rear sprag will take over automaticly.
Author:  Reed [ Sat Apr 04, 2015 7:17 am ]
Post subject: 
If you have the tools and skills to remove and install a 904, you have the tools and skills to rebuild one. The 904 is a very simple transmission that is easy to rebuild. I taught myself how to rebuild them over a weekend by using a factory service manual and slowly disassembling one.

Don't be afraid to dive in and rebuild your transmission. All parts are readily available.
Author:  SageRad [ Sat Apr 04, 2015 9:07 am ]
Post subject: 
Reed thanks for posting that encouragement, i pretty much decided to do exactly that. I can't see buying an unknown 90k miles A904 for $350 and paying someone $300 to install it, when i could try it myself and got nothing to lose but time, and lots to gain in knowledge and confidence.

I getting ready now to do it, lifted up the truck and learning more about it. I'm figuring out how to drop the tran.

Can't wait to get into it. But i have to make it speedy because i'm running out of money and need to get back to work.
Author:  Reed [ Sat Apr 04, 2015 10:14 am ]
Post subject: 
If you were closer to me, I would trade you your transmission for a "fresh" 904 I rebuilt a few years ago. It is a 1979 model that I completely rebuilt to stock specifications. Never been run, but everything is new inside. Ready to go.

I get most of my transmission parts from http://www.makcotransmissionparts.com They ship fast and have reasonable prices. If your transmission was working mostly fine then you likely just need clutches and maybe bands. You would probably be fine with "master kit" part no. 12006C. This includes, paper gaskets, O rings, lip seals, metal clad seals and sealing rings, friction clutch plates & standard steel plates. This would be a stock/daily driver rebuild with no fancy parts or upgrades. $70.46 plus shipping.

I also recommend the transmission assembly lube and the ATSG service manual.
Author:  SageRad [ Sat Apr 04, 2015 1:32 pm ]
Post subject: 
Reed, thank you very much. I just ordered the kit and the book, $102 and free shipping. I'm looking forward to this new adventure.

Got my starter out, and now i'll get the crankshaft out.
Author:  bigslant6fan [ Wed Apr 08, 2015 2:27 pm ]
Post subject: 
Before you take the Trans out,do the pressure tests shown in the service manual.you will need two pressure gauges that go to at least 300 psi.It might just be a bad seal in the low-reverse servo. I would also check the seven digit part # on the Trans to find out what model year it is before ordering parts. You might be adjusting the servo to the wrong specs.
Author:  SpaceFrank [ Thu Apr 09, 2015 8:10 am ]
Post subject: 
Quote:
The only way to check the front clutch is to see if you have 3rd gear. Even if you have manual 1st, the f/r band still may not be working, as he rear sprag will take over automaticly.
I didn't realize that. :shock: So much for my test, then.
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