C4 Atlas 4 speed issue

[68rockcrawler]

Hey guys, I put a C4 and 4 speed Atlas in my Bronco a couple of years ago and only wheeled it a couple of times since doing so. It hasn't spent any time on the street with this setup. I had a T18 and stock Dana 20 before that. The Atlas is the 10.34 only because I bought it used, not necessarily because that's the ratio I was going for. Ever since I installed this setup it has struggled to do maybe 20 mph (no speedometer) with all highest gears selected. I just verified today that I am getting all gears in the C4 and moving between gears in the Atlas changes the possible speed, but not by much. I do have one ton axles and 40" tires, but that was no problem when I had the T18 and Dana 20. Also, 5.38 gears in the axles. I know, stupid low, but even with all that, gearing calculators say I should at 2,500 rpm at 55 mph with this setup, which is laughable knowing how much it is struggling to do around 20 which has me in the 3,000 to 4,000 rpm range.

Is there anything I could have done wrong installing the transmission that would allow it to shift, but not really allow it to go much faster? When I shift the Atlas, the speed difference is pretty small, not double or triple like it should be and not like I used to get between high and low in the Dana 20.

Any thoughts on what my problem might be?

 

[Broncobowsher]

I would carefully check the Atlas shifters again. Actually driving it. Don't do anything else and check both high and low range of the doubler box. Absolutly sure that one is in the higher range. After that go and do the same with the Atlas. You might have routed a shift cable differently so the knob indicates backwards or something weird like that.

You did hook up the vacuum line to the C4 modulator? You have tried both automatic and running the shifter through manual 1 and 2nd gears as well?

I bet it is something really simple, but it is hard to tell what is going on without actually being there. Don't know how custom the install is or anything else. And you are not exactly close by either.

 

[68rockcrawler]

Every shift of the doubler and Atlas did result in higher or lower while driving it. I do actually have knobs on it that are backwards from what they should be, but I have that figured out.

I thought I heard that the C4 won't go into 3rd without vacuum and I'm definitely getting 3 gears manually, but not if I put it in drive. I have a winter's shifter and the guy I bought the transmission from said it's a standard pattern valve body, so gear next to neutral should start me in 1st and go through the gears right? That doesn't happen. It only shifts manually and gets the gears with 3rd next to neutral and 1st clear at the bottom of the shifter. I know I need to check the vacuum.

 

[Broncobowsher]

Without vacuum the transmission sees 100% load, so it won't shift into 3rd at light load. Full throttle it will shift normal as full throttle is no vacuum. Your 3rd gear that you are feeling, might actually be a downshift into 1st (without engine braking).

 

[68rockcrawler]

I don't have a vacuum gauge. If I pull the vacuum line off would it be possible to tell if it's getting vacuum by putting my finger over the end of the hose or do I need to check for exact amount of vacuum?

 

[Broncobowsher]

Just that it is there. IF it sticks to your finger you have good vacuum.

 

[68rockcrawler]

I have vacuum. It doesn't quite stick to my finger, but it's definitely sucking.

 

[BUCKWILD]

standard pattern on that trans is P,R,N,D,2,1. you are thinking reverse pattern that in P,R,N,1,2,3

 

[68rockcrawler]

So, like a modern vehicle when I put it in drive (3 on the shifter) it should start out in 1st then go up through the gears, right? 3 or drive position only gives me 3rd. The previous owner didn't think that he put a manual valve body in it, but couldn't remember for sure.

 

[jmhend]

Drew can you feel it shifting through all three gears? Have you tried to shift it manually?

 

[JeffG]

Do you have a cover that will allow you to view the planetary housing while shifting? Since the lever comes out of the top to select the desired range, perhaps something is interfering with it fully shifting in the 1:1 high range?

 

[68rockcrawler]

Drew can you feel it shifting through all three gears? Have you tried to shift it manually?

It won't shift automatically, only manually. When I put it in drive, that's 3rd, not drive like a normal car.

 

[68rockcrawler]

Do you have a cover that will allow you to view the planetary housing while shifting? Since the lever comes out of the top to select the desired range, perhaps something is interfering with it fully shifting in the 1:1 high range?

Shifting the planetary definitely doubles whatever gear I'm in so I think the planetary is shifting correctly.

 

[jmhend]

Hmm seems weird. Maybe the modulator. I think there are two different colored bands ( green and orange).

Sent from my SM-N960U using Tapatalk

 

[garberz]

Is the intermediate housing the short 3” adapter? If it is, then you definitely have a reverse manual valve body.

Mark

 

[Apogee]

You should be able to pick an RPM and and measure your speed (GPS app on your phone if your speedo is in question), and then back solve for the gear ratio which should tell you what gear you're in. Is the torque converter locking properly? Do you have a transmission temperature gauge and if so, what's it doing?

 

[68rockcrawler]

Is the intermediate housing the short 3” adapter? If it is, then you definitely have a reverse manual valve body.

Mark

Looks longer than that

 

[garberz]

Looks longer than that

Yes, that’s the standard length adapter. Your trans still has the governor, so there would be no mandatory reason for a manual valve body.

Mark

 

[68rockcrawler]

I ran it up and down the street today, in drive and it went through all 3 gears. It went from 1st to 2nd about 2 seconds after getting it going. That seems weird.

Running it down the street reminded me that my steering is pretty wandery so I'm going to need to do some work on that before I try any real speed runs to get mph/rpm combination figured out.

I could never feel the torque converter lock up like I can on my modern vehicles.