berny

Hello,
I have a problem with my beloved 1989 Toyota pickup. It has a 22re engine and w56 transmission with RFIA transfer case. It has manual locking Aisin hubs. I replaced the clutch and accessories 5 or so years ago with a marlin crawler medium duty clutch. The truck is basically stock. The truck has 214k miles on it and runs great in 2wd. When I put the truck in 4wd and drive it, it intermittently surges. The problem is difficult to explain. As the truck is driving down the road in 4-hi at 35-40 miles an hour it feels like one is tapping on the gas. Like the truck jumps forward then slows down then jumps forward and repeats. It isn't perfectly even and varies with speed and varies randomly at the same speed. It is barely noticeable when going under 10 miles per hour. I haven't noticed it in 4 low but that doesn't mean it isn't there. After searching, I thought maybe there was a problem with the propeller shaft bearings. I got under the truck and grabbed it and tried to shake it. It felt solid as a rock. Could it still be bearings? How do I check them? What else do I check? How do I troubleshoot this problem? I searched a bunch but all the four-wheel-drive related problems seem to be about engaging and mine engauges fine. The other threads talk about ADD problems. My truck has manual hubs so I don't think that applies. Any and all help, hints, or references would be greatly appreciated.
My father owned the truck from 90 till 2009 when he sold it to me. I would like to give it to my son when the time comes. Help me keep this family heirloom in top condition.

berny

No replies yet? You all always to seem to be able to help. Maybe I made my post too long and people understandably don't want to read it all. I'll try a summary.


TL;DR
My truck runs great except in 4-wheel drive. Four wheel drive engage is fine but while driving in 4-wheel drive the truck sort of surges faster and slower. What could this be?

Co_94_PU

iTrader: (-1)

Lurching is possibly due to "axel wrap", the axel housing rotates on the springs then unloads that tension causing the vehicle to lurch forward when it drives the shaft at a higher speed.

Look at your transfer case and count the bolts on the cover. This will tell you if it is chain or gear drive. Lurching is bad for both but it could snap or stretch a chain drive. (Read: stop driving around in 4wd at " high" speeds).

The spring wrap could be from mismatched tire sizes, doesn't take much, traction difference or spring fatigue.

scope103

Sounds like a tiny tire size mis-match. My understanding is that is the main reason you don't "drive down the road" in 4wd. In 2wd, a mismatch between tires just causes the differential to slowly rotate; no big deal. But we don't have a "center differential" (or viscous coupling used in some vehicles, like the Grand Cherokee). So if the effective drive shaft speed is slightly different from front to rear, at least one of the four tires has to slip. A little. Unnoticeable in snow or mud, but on pavement the tires will build up the offset and, it would guess, "surge."

berny

Great replies, thank you so much!
It is entirely possible i have slightly differnt sized tires. I had a blow out a few years ago and only replaced the one tire. Later i replaced two others with used tires because I couldn't afford a new full set. I will be sure to get new tires before using 4wd again.
I will count my bolts tomorrow and maybe after i could get advice on checking for damage I have caused.
As far as driving down the road in 4wd I am not sure what to do. I know it isn't a great idea but sometimes there isn't much of a choice. 4 years ago i was driving from Wyoming to Washington in my truck. While driving over the blue mountains in 2wd on pavement the road abruptly was covered in solid ice. I was planning on pulling off at the next exit to put it into 4wd. Before i got the chance the truck started slipping left then right then left. I let off the gas and tried to regain control. There was nothing i could do and i ended up spinning in about 3 circles before crashing head on into the center divider. I wasn't hurt but the truck got dented. After that i resolved to leave it in hi 4 of there is snow and ice out. Now it seems like that is a bad idea. What do you all do when driving over mountain passes in winter? Pull off every five minutes when the road conditions change? This Christmas I'm driving back to Wyoming to visit my grandparents. I'll be going over that same pass, what should i do? I am genuinely curious. It seems wierd asking for driving advice here but i do need it.
I really appreciate the answers about my tires. It makes total sense and i would never have thought off it. Thanks again!

berny

Lurching is the perfect way to describe it. searching for surging brought up engine problems. This happened a couple times last winter. I haven't had it in 4wd since, but winter is coming which is why I'm trying to solve this problem. Good advice, thank you.

Co_94_PU

iTrader: (-1)

Drive in 2wd and carry a folding shovel to dig out your wheels only after you have gone into the bank to lock the hub's for 4wd to get you out then put it back in 2wd, or crawl (~10-15mph max) along in 4wd. Carry snow chains for additional piece of mind and to get you unstuck.

You need to be really easy on throttle changes when on a slippery surface at speed. No "letting off" just a gentle deceleration, do not try to appruptly accelerate in fact don't even try to accelerate you risk loosing grip. Once the rear drive wheels loose traction you are in for a ride, you need to exercise restraint and make minor correction trying to avoid a roll over (IE turn toward to slide, but not violently). Clench your buttocks and ride it out.

4wd doesn't really prevent a spin out, it is for getting out of or over and obstacle.

It's a little different than a front wheel drive where if you have traction accelerating will pull the vehicle straight in an over breaking scenario.


In short.. Slow down well before conditions mandate it. Drive slow, its all about enertia, stay safe in snow and ice! The faster you are going the farther off the road you wind up, this might put you out of reach of a passer by with a tow strap or worse OVER a cliff.


... That said regarding damage you're probably OK or out of your league(mechanic wise). As long as it(4wd) works and doesn't make any obnoxious noise, don't sweat it.

Fwiw..
Dropping the tcase is a bit of work. That would give you access to the gears or chain. A chain has a limit of stretch after which it should be replaced. A gear drive has a lash tolerance which would require high quality tools to measure the "lash" and require varies sized shims or gear replacement..

Co_94_PU

iTrader: (-1)

PS. Get a matching set of tires. But you already knew that. And scope explained why. Something has to give and you don't want it to be the transfer case.

berny

I counted 7 bolts on my transfer case. I think that means it is gear driven. I drove less than ten miles with the problem so i think you are right and it is ok. If it does break i won't be stranded right? Just without 4wd. I did my clutch a couple years ago, and the truck isn't my daily driver, so maybe i could repair or replace the t case if needed.

I got matching tires on it today, put it in 4 hi and drove around. I know, i know, but i wanted to test it. The lurching problem is solved! Thank you all so much!
I am having a bit of a revelation about 4wd, how it works and when to use it. Until yesterday i thought if the road was patchy snow and ice it was perfectly appropriate to put it in 4 hi and go, as long as i kept it under 45. Apparently that is not the case. I'll have to do more research.
I'm sure this is impossible, but it can't hurt to ask. Is there some part or mechanism i can buy and install to solve this problem? I'm sure i can't install a center diff on a vehicle not designed for one, but anything at all to help a tiny bit would be cool.

thanks a million for all the help

wyoming9

iTrader: (1)

No if your transfer case breaks depending just where your calling for the Roll back to get home.

If you were driving on hard dry roads in 4wd with your mismatched tires the torque bind will be much worse because nothing can slip

berny

thanks for the info. I have correctly sized tires now, and tested it. The problem is solved now. I am worried about lasting damage. I drove about ten miles while doing this. The truck runs fine now and i hope that as long as i only use 4wd on roads that allow the tires to slip i will be fine. My only worry is that in a month i will be diving from Washington to Wyoming, and don't want to get stranded. I know nobody can know for sure the state of my transfer case, but based on the info, should i be worried? Can i test it in some way? Has anyone here actually broke their t case by doing this? What do i look out for?
thanks all again for the help

wyoming9

iTrader: (1)

If your case doesn`t fail in the month before you are taking the trip you should be ok

Might not hurt to change the gear oil see if any metal chips or shavings come out when they fail it is most often catastrophic with sound effects

Then in that part of the world I am sure you know to have enough gear for when things happen to be comfortable till rescued

Mechanical things break

With all my Toyota`s I never had a Transfer case fail