I just built a 1986 4runner – 4 cylinder – 35 inch tires, 5 inch lift, Marlin crawl box (stock gears), axles have 5.29s. I just finished the build, ran the Rubicon with it – everything worked as designed. My E-brake is not hooked up yet. This weekend I parked on a hill (shut down engine, put it in gear and took my foot off the brake). It was stopped and then I felt the rig shift and it slowly crept like 2 inches, then stopped then crept like 2 more. I had someone look under the hood as this was happening and the fan was turning, so that leads me to believe that it isn’t the clutch. It didn’t seem to happen as much in first as in 2nd or 3rd. I was in 2 wheel High. I engaged the crawl box (still in 2 wheel high) and I would have thought it wouldn’t have crept backwards because the gearing in 2nd with the crawl box would be near 1st without the crawl box. This didn’t seem to be the case. It did the same thing.

Seems to drive fine. I am thinking there is an issue with compression?? I will verify that the sparkplugs are tight (try the easy things first). Then I am going to try a compression check.

Any ideas, thoughts, etc?? Am I going down the correct path – thinking low compression – leaking somewhere?

I, mean, I have always been under the impression that with a manual transmission any gear 1-5th would hold the vehicle up on a hill, no matter what the gearing and no matter what the size of the engine – is this incorrect???

Tim (S.F. Area, CA)

 

it isnt the engines job to stop the car from rolling.... fix the parking brake... that what it is for.....

 

thanks (I think). I plan on fixing the parking brake. But in the mean time I am interested if my understanding that the engine should keep the vehicle from rolling back is correct or not. Also, if anyone else has found this same thing to be true and I shouldn't worry about it, or if I have a major engine issue that is starting to become apparent. Last thing I want is to be in the middle of a trail and have my engine fail.

 

Like he said, get teh brake fixed. BUT: The engine only keeps the vehicle from rolling by the compression it develops. The weight of the truck plus the gear ratio must overcome the compression the cylinders develop as the pistons move. If you have a compression leak, say a bad rings, leaky HG, etc. , the truck will roll more easily against the engine than a vehicle whose compression is up to par. Do a compression test and see how it turns out. Can't hurt anyway.
Hope that helps a little...

 

Yep, 2ToyGuy pretty much covered it. Engine compression braking is not infinite, afterall a couple of horsepower starter motor has enough oomph to turn the engine over. 4000 lbs. of truckon a hill can easily do that. And pistons don't seal really well al slow speed, compress one over several seconds and most of the air pressure will leak around the piston rings.

 

For what it's worth my 22RE did and the 3.0 will also do that on a hill. Park it on a Chevy, that helps.

 

My old 85 with a 22r did the same thing with big ass tires, and it burned a little oil, thus having slightly low compression. My e-brake was also broken, so parkign on any hill required a curb.... although that doesn't help much if the weight of your truck will just push you over the curb with the nice size tires

 

Yeap they are all right and you saying that the truck did stop for a bit then started the roll again tells me that your compression is more than likely okay. The piston seal is not heald over time and the compression will "leak" off slowly....the rate that you have above does not seem alarming or indicate any problem other than the parking brake is not working.

 

Great idea! I'll remember to do that!

 

thanks guys!!!!!!

I just wanted to see if my experience was the same as others - and it is. I swear when I got back from the rubicon and parked it on my sloped drive way, now 3 weeks later it slowly rolls down the driveway... maybe the transfer case, or new crawl box has loosened up. I just compression tested my cylinders - cold (I know you are suppose to do it warm) and I got 180 -185 on all 4 cylinders (5 rotations) so everything there is good.

 

Anothier thing, drop it in low gear before parking. Helps a little.