You get a grinding noise when downshifting in your 1994 Jeep Wrangler Why?

Answer 1

It possible that youre still going too fast to get into that gear. The clutch and pilot bearing could worn out also. Good luck.

for each speed and gear there is a specific speed at which it is safe to downshift to the next gear with a known blip strength. being human you cant be perfect and know exactly what blip strength will do right for just about any speed to any lower gear (demanding the car shift whenever you feel like it), So you have to simplify things a bit and make it known where you can get away with doing the same blip all the way on down the line. the most gentle blip possible. shifting wherever the car feels like it. You gotta jump through some circus hoops. the car is a whole lot more picky than you ever thought and if you arent willing or able to make repeatable very high blips, then your options will be all the more limited and shifting slow and drawn out. which is the norm.

use the gear ratios in conjunction with the final drive ratio to make a graph of the vehicle speed to rpms. find discreet speeds where there are 300 rpm differences. and then use post it notes to mark on the speedometer where those places are. if you cant do that, just secure a copy of a manual displaying a speed to rpm wrt gear graph. i know it sounds riduculous. on the track yo dont worry because you expect damage while full out. but you are on the road, you have to be gentle or incur the wrath of the mechanic touching your wallet.

in rpms and mph that formula is 6.51*k*V/r = Wrpm where k = gear ratio of chosen gear x final drive ratio, and r = radius (IN FEET) of your rear wheel(s).

the final equation to find those exact spots is V= (dW*r)/(k2-k1)6.51 where k2 is the effective gear ratio for the chosen lower gear to shift into. and k1 is the gear you inhabit before the shift. dW is the supposed blip you wish to use in rpm's.

there should be 4 of these spots for a 5 speed, and if you change the dW by 10% and recompute either way, you will get the range, the bands you will see.

the point is, you arent missing out if you arent using the tachometer. things happen too fast in shifting to rely on that. you rely on the speedometer and sure enough there are little 'bands' that if your needle rests inside of that band, it is safe to downshift with a known force of blip, most notably, for me on the streets, the softest one. its really just a soft stroke of the gas. it stands for about 300 rpms on a small tacoma.

the band for 5 to 4 is wide and very forgiving (it lies farthest out). 4 to 3 is a bit smaller and lies towards a lower speed. 3 to 2 is a little hitler mustache of a zone (probably near 20-30). Sooo small and all alone. 2nd to first is like splitting hairs, you do it with such gentleness and even then you get a slow kick in the butt. that sir, is a 2 mph wide zone somewhere inbetween 0 and 10mph.

the math is grueling if you dont make a graph of it, but with the post it note appliques you should be able to do very close to perfect downshifts even in tight and hairy traffic conditions where you kind of need it the most.

on the track its one size fits all and you follow by ear and you know in what gear each turn must be taken because things move too fast even to look at the speedometer.