Gear Issues with 79 CJ5

[gadawg31]

Fellow Jeepers. I have been researching a lot about axles, transfer cases and transmissions, due to a possible unknown problem with my jeep. Here is a questions to start things off:

1. I have been told that the front and rear diff gears must match in order for the jeep to not tear itself apart? Truth behind this?, and explain if true.

2. Current ongoing troubleshooting; removed shift cover plate so I can see the front driveshaft and I can see when it is turning and when it is not. My Transmission is T-150 (3 speed). I know it is a 3-speed, just not 100% it is the T-150 :

When I start out in 1st, it has plenty of power and I can be in 3rd gear by 20mph. It just seems as if it is going to explode by the sound of the motor and sound of the gears. I have worked the Transfer Case shifter (which I have been told is the Dana 20 ) in all gears to make sure it was not stuck in 4L or 4H and I still can't get past 35mph with out it sounding like it is going to blow up.

Other people have stated they believe the PO may have changed the gear ratio to a very low granny gear and that is why I asked about the matching gears for front and rear.

With that said, I have read on this forum that many of you have the 3-speed and it is nothing for it to drive 60mph with no problems.

I am in the process of cleaning each component off so I can get actual numbers and see what type Transmission , Transfer Case and front/rear ends I have.

Do any of you have any speculations as to what would cause it to do this or have any of you had the same scenario. Thanks in advance.

More to come, once it stops pouring and I can get under and get numbers.

John

 

[sjc115]

...

1. I have been told that the front and rear diff gears must match in order for the jeep to not tear itself apart? Truth behind this?, and explain if true.

...

The gear ratios need to match otherwise the front and rear wheels will turn at different speeds. That would cause all kinds of problems for your Transfer Case and Transmission (unless you were on ice and the wheels were free to spin without traction).

 

[Posi]

1. I have been told that the front and rear diff gears must match in order for the jeep to not tear itself apart? Truth behind this?, and explain if true.

I understand a lot of folks believe you can't run different gearsets, the truth is you can. Later Jeeps came from the factory with different gearsets like the yj, some have 4.10 in the front and 4.11 in the rear. I've run 4.10 and 4.09 without any issues. The factory does this because of the different size housings and how well the ring gears will fit. This doesn't mean you can run 4.10 and 3.73 the results wouldn't be good however, .001 won't make a difference.

2. Current ongoing troubleshooting; removed shift cover plate so I can see the front driveshaft and I can see when it is turning and when it is not. My Transmission is T-150 (3 speed).

You verified the front shaft is not turning? Do you have drive flanges or lockout hubs? If hubs, are they unlocked?

Other people have stated they believe the PO may have changed the gear ratio to a very low granny gear and that is why I asked about the matching gears for front and rear.

I run 5.38s with a 60hp Flathead and get up to 50-55MPH chances are your axle gears are not numerical higher. Also, if you have the hubs unlocked and the driveshaft isn't spinning difference gearsets wouldn't matter.

 

[davey25]

I think he's talking about like running 4:10 and 3:54 type of situation..which would be a big deal but yrs a few off no biggie..why don't you turn your wheels and count the yoke turns and get your ratio...sounds like you may be in 4 low..do you notice a difference shifting the Transfer Case ?

 

[mtnwhlr]

Unlocked the hubs and put the Transfer Case is in 2HI and see what it will do.

 

[johnbilt]

At tachometer will tell you actual rpm's. Your description makes it sound as if the tcase is stuck in low range. Your jeep should make 60mph no problem in Hi range.

You can verify the diff ratio by marking a tire and turning the driveshaft by hand and counting the revolutions.

 

[gadawg31]

Posi:
"You verified the front shaft is not turning? Do you have drive flanges or lockout hubs? If hubs, are they unlocked?"

--Yes, the hubs are unlocked. At least they are in the unlocked position.

mtnwhlr:
"Unlocked the hubs and put the Transfer Case is in 2HI and see what it will do."

--Hubs are unlocked, at least they are showing unlocked and I do have it in 2H and the front drive shaft is not turning at all when in 2H.

Johnbilt mentioned that is sounds like the tcase is stuck in low range, but if the Transfer Case is stuck the front drive shaft would be turning correct?

I guess that is one big question now; if the Transfer Case is in 2h, the front driveshaft should not be turning correct? The way I understand it, is that the front driveshaft will not turn unless you put the Transfer Case in 4h or 4L. This is why I am really concerned about the sound and not being able to get it up to highway speeds.

Could there be a possibility that the hubs are stuck and if they are, wouldn't that make the front drive shaft turn?

From listening to the comments so far, it seems that I can rule out the gears being a mismatch or too low. I seems to be something with either the Transmission , Transfer Case or hubs, maybe all together.

JD

 

[Hedgehog]

I'm going through something similar but no where near as drastic.

Understanding how 4wd works. ..... First in the drive train from the engine is your Transmission . Unlike motorcycle and race car transmissions the gear set you get from the manufacturer is essentially what you will have, no changing ratios in the Transmission . No matter what Transmission you have the fact is you simply have what you get.

Next is the Transfer Case , lets ignore the Twin Stick conversions, IT's job is it to transfer power output from the Transmission in a few configurations. 2 wheel high which is 1:1 .... 4 wheel high which is 1:1 ..... 4 wheel low, this is where it starts to get interesting. With kits like a tera low gear set you can get ultra low low range, but high will always be high. With that being said the D-18 had a provision for an over drive allowing the small engines of the time to crawl with enough power off road and run at highway speeds on the pavement. Also remember, in the older Jeeps it was NOT recommended to run in 4 wheel drive on pavement or other hard surfaces.

The final part of the drive train ....... The differentials take the power from the Transfer Case (drive shaft) and puts the power to the ground. This is where mocst versitility in gearing is found. You've seen various numbers like 5.38 gears. These are high torque low speed gears. It was common in the '80's to have factory installed 2.73 gears in your Jeep. These are high speed, in theory higher mileage gears.

So, for your Jeep to be acting as you are describing two variables, possibly three exist. 1 - your Transfer Case is in low range and can't get out for some reason. 2 - You have VERY low crawling gears in your differential. 3 - There's a very slim chance your PO put in a D-18, installed very low gears in the Differentials and relied on the over drive to make life liveable on the street.

Why have the same differential gears in front and rear. Try this tie your hands to the bumper of a car going 40 mph and your feet to a car doing 35 mph. I believe that fairly quickly you will understand why its bad to have one set of wheels turning faster than the other.

 

[gadawg31]

Hedgehog, quick question. You stated the one possibility could be the Transfer Case in in low range. With that said, shouldn't I see the front drive shaft turn if it is stuck in low gear?, or could it be in low gear and not engaging the front drive shaft? If the later is a possibility, that would make sense why it feels like it is in low gear and I am not seeing the shaft turn.

JD

 

[mtnwhlr]

If the hubs are unlocked and the Transfer Case is in 2WD you should be able to crawl under it and turn the front drive shaft by hand.

 

[Old Dog]

Can you shift the Transfer Case to low range? If so does it make any difference?
Some Dana 20 's can have a 2wd low if the are wore enough. I'm thinking that some how it is stuck in 2wd low.

 

[Hedgehog]

A Jeep Transfer Case is a rather stupid brute. It is either in gear turning the drive shaft or it isn't with the drive shaft not turning. In my quick write up I totally missed mentioning the front hubs. If the Transfer Case is in 4 wd without the hubs turned in or on I suppose the Transfer Case will turn the drive shaft but the front wheels won't be engaged. Also, just for the sake of arguement. Even with the Transfer Case in 2wh and the hubs disengaged the front drive shaft can turn. This is more from all the grease or fluid moving around the disengaged drive gears than actually being driven.

As Old Dog wrote above. Yes it is possible to have a warn tranfer case shifter find a gear set that isn't supposed to exist. So, 2 low is possible.

Do you have one long shifter and one short one? or do you have a long one and two short ones? I ask this because the gears have to be shifted in a stock Transfer Case in a certain pattern. THis would be for a twin stick Transfer Case . To go into 4 low first the rear drive needs to be in low before the front gears can go into low. Going into 4 high first the rear needs to go into high, then the front will be free to go into high. With the single stick a proper gear shifting pattern is automaticlly followed. That is inless the thing is warn...... Now isn't that clear as mud.

You need to put your Jeep in 4wd low, then find 4wd high and 2wd. Find all those gears, drive a little in all of them and you will know more of the story.

 

[IOPort51]

What happens in 4 hi?

 

[HackFabrication]

...Some Dana 20 's can have a 2wd low if the are wore enough. I'm thinking that some how it is stuck in 2wd low.

Exactly what I was thinking.

 

[gadawg31]

Thanks everyone for all the great info. I have learned more in the past write-ups, than I have in the past few weeks on the internet. You guys are really amazing with all the knowledge and freindly advise. I had a little time this weekend to play around with it and I am not completely sure yet, but I think it was stuck in some type of low gear. I am presuming 4L, but after hearing everyting you all have had to say, it is some type of low gear. Now, why the front shaft was not turning, I am still out on the limb with that one. I was able to get the single shifter all the way forward and started working my way down. The most important piece of info I received is that the Transfer Case is definately worn or something is wrong inside. When I push the shifter all the way forward (towards the engine), the jeep appears to go into 4H, then down one, 2H, next is neutral and then 4L. When I get down to the bottom, it seems as if there are two 4L gears or this is where my Tcase is very worn. Either way, I was able to pursaude it in and out of gear several times and the RPMs definately dropped drastically, compared to earlier when I drove it around. If I can find some numbers I will post and let you experts decipher what type of Transfer Case I actually have. However; from picture identification it looks like the Dana 20 , with a single shifter. More to come and thanks again for all the expertise.

/r
John

 

[Hedgehog]

The wear we've been speaking about isn't usually inside the Transfer Case , it's in the linkage going to the case. There are bushings (maybe only one) that wear and there is a stud that is supposed to be welded in place, but is prone to breaking the weld. All this makes for a sloppy linkage where a little movement turns into a LOT of movement. If this is the case with your Jeep you can weld the bolt and have a machinist make a new bushing ...... ....... or you can go the same way many of us have gone and order up a Twin Stick conversion. Twin sticks are far easier to manipulate with only a few inches of movement per stick as compared to well over a foot with the stock set-up. THere are some real advantages to the Twin Stick set-up as well .... but I'm not going into those right now. There are a few manufacturers for this and if your handy you can make one your self, but lets be real here, you would be the order one up type. Now that I've worked on one I could make another, but for the first one I ordered one. J.B. Fabrication is a very popular manufacturer with good prices and a large following here on this site.

 

[Posi]

The wear in this "case" is with the shift rails.

I shaved mine down so I could get independent front and rear.