BUMP into first...?

Relatively new owner of a '74... Relatively new to the Bronco... Have always been a CJ owner - ooh, I think that is blasphemous around here. However, this site is tremendously more informative and entertaining than anything in the Jeep web world. It really is great.

Question. I'm running a 351w, 3-speed floor conv. (original, rebuilt trans as far as I know), Dana 20, 5.5 susp, 3 body lift, on 36's. When I shift to first and begin to release the clutch there is a considerable bump where if feels like it is dropping into gear. The truck drives and shifts fine. I'm just concerned that my lack of knowledge of a potential problem could lead to big problems down the road.

Also, everything I've read suggests upgrading transmissions with the lift/tires. Any thoughts on either of these two concerns?

Thanks in advance for any help. You Bronco guys aren't AS bad as the Jeep crowd has made you out to be all these years...Ha!

My rough guess is slip joint on the rear driveshaft. It may be too short for the lift and binding up. Also rear spring perches on the rear axle have been kown to round over and allow the axle to rock in the U-bolts.

Not being there in person and trying to decipher someone elses description of a problem is a little hard. Others will have ideas as well.

Welcome to the Bronco world, I think the majority of us have or still own Jeeps :-X :-X :-X

Not sure on the tranny issue, wonder if there is some slop in the linkage.

As far as aftermarket transmissions, its nice to bring these into the modern age as more transmissions come onto the junkyard market. It depends on what you do with your Bronco too. If it is a majority wheeler and you tend to trailer it to the trails and just drive around town (minimal freeway) then the np435 is a very good swap, it has an awesome ~ 7:1 granny gear that is a blast out on the trails (I have that in mine). It has been a popular swap since the Broncos came out and can be done pretty inexpensively. If you drive yours a lot on the street/hiway the NV3550 is a fun swap as it gives you a 5 speed out of the modern Jeeps. I have one sitting in my garage screaming to be used!!! This swap is pretty easy and there are very good kits out there but will run at least 1200-1800 for the swap. If you want to stick with ford then the ZF is a great swap, more of a truck feel to it but a good granny and overdrive.
Then there is the realm of autos AOD, AODE 700r4, 4r70w, etc. The AOD seems to be the most straight forward swap for an auto but the kits for the explorer 4r70w are good but require an aftermarket controller for the electric shift. Anyways, this is a little info, if you go to the tech area you can see some articles on swaps, etc.
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I forgot to add that the rear drive shaft has been lengthened to accommodate the lift...if that helps.

With regards to the trans. swap. I do some off-road mostly trails, but the majority of my driving is around town. I look to do some highway driving for extended trips, etc. so a trans swap in the future is appealing. Ideally I would try to keep costs to a minimum - but I'm not naive to the $ that goes into trans work (I had an '87 wrangler for years- nightmare). Thanks for info. I appreciate it a ton!

Any other ideas about the first gear issue would be great!

what broncobowsher said is probably correct I have a similar sensation with my rig, I am going to ditch my small bearing 9 inch and go for a GM 14 bolt with a 4 link, but until I do that I have a nasty nasty nasty 5 inch block back there for my lift, "I bought it that way I would never do that" so my axle has some pretty wicked wrap at times that makes for some funny feelings, my guess is that with those big 36 inch meats and that 351 you are having a like wise problem, it's not that serious but you may need a 4 link arb lockers fuel injection on board air thats if you're lucky, I think my problem is far more serious.

PhorD said:

I forgot to add that the rear drive shaft has been lengthened to accommodate the lift...if that helps.

With regards to the trans. swap. I do some off-road mostly trails, but the majority of my driving is around town. I look to do some highway driving for extended trips, etc. so a trans swap in the future is appealing. Ideally I would try to keep costs to a minimum - but I'm not naive to the $ that goes into trans work (I had an '87 wrangler for years- nightmare). Thanks for info. I appreciate it a ton!

Any other ideas about the first gear issue would be great!

Click to expand...

I agree just because your driveshaft was lenghtened, doesn't mean the slip joint on the rear driveshaft or a U join't can't be bad.

Could also be a bad motor mount, Loose body mounts, a bad transmision mount, loose transmision cross member, or something funky in the rear differential. Without looking at it, I am just guessing, so it's hard to say

My guess is still the rear driveshaft, mine did the exact safe thing before I got a new rear driveshaft. So crawl under the truck, grab the driveshaft, and yank on it at different angles. Maybee remove the clips to the rear yoke, and see if there is play in the slip joint. After all a 1/2 inch wrench and 5 minutes later they are off.

You may also be able to just lube the driveshaft, and U Joints, sometimes that will get riid of the clunk, or make it just a little quiter, if so thats the problem.

As far as a trans swap
If the 351 is pretty stock, a NV3550 would be a nice swap

Since you have a 3 inch body lift, a NV4500 or maybee a Ford ZF would be a great swap if you have a high HP 351

br0nc0xrapt0r said:

my guess is that with those big 36 inch meats and that 351 you are having a like wise problem, it's not that serious but you may need a 4 link arb lockers fuel injection on board air thats if you're lucky.

Click to expand...

I doubt he needs any of that, I bet it is in the driveshaft, at the worst in the rear differential. A 4 link ARB and onboard air are cool, but to fix his problem, I bet it will be a lot easier fix.

does it shift sticky or stiff? i'm wondering if your clutch isn't out of adjustment a bit. how far off the floor does the clutch engage?

Thanks for the ideas guys...pretty cool. So, the clutch engages appropriately when lifting from the floor - maybe 2-3 in's.

The shifter shifts smoothly (knock on wood) haven't had it really snag up b/t gears or anything. I've actually been impressed with the performance of the trans, but still thinking about upgrading. Yeah, so there are no when hangups with the way the truck shifts and the "bump" problem only occurs when shifting from neutral to first. It doesn't do it, say, if I am in reverse backing up, and then put it intto to gear and release the clutch.

You guys are great. More help than I thought I would ever get!

-Patrick

Sounds like it is some good axle wrap going on. Do you have blocks in the rear? What gear ratio? If blocks that will add a lot to it. Super soft springs will as well, especially combined with big tires and a 351W. I'd start off by checking to be sure everything is super snug back there, U-bolts, springs, shackles, driveshaft, crossmember mounts, etc.

One more thing to check is the tranny/transfer case crossmember bolts and bushings. If they're loose, it will give you some movement in the drivetrain. Have someone watch your drive train for movement when you take off in 1st.

Welcome to the Bronco obsession. CJs are cool, I almost bought a CJ8 b4 i found my '73. As far as an answer to your question, there is a lot of good info already here that I would have suggested and places I would look if I had your concerns particularly the driveline slip spline and spring wrap-up. Oh and Welcome to the message board too.

Congrats on your convert... enjoy the ride, it's likely to last a looooooong time! *~*~*WELCOME*~*~*


don't forget to vote...

Have to agree with the others, probably axle wrap. Easy for someone to spot though.

If you have "blocks" I can almost guarantee it. Worn springs and adding blocks are a sure recipe for axle wrap.

When you take off (or apply power at low speeds) the pinion gear tries to "climb" the ring gear, of course it can't... so the springs bend into an "S" shape as the axle rotates. The axle "over rotates" because the larger tires/mass are harder to move.

This can bind up u-joints and forces the drive shaft to shorten and lengthen (via the slip joint splines) very quickly. Any of this could be the noise you are hearing.

There are other possibilities, but that is where I'd look first.

And Welcome to the forum. Lots of nice folks here.