SM420 Grinding noise when I jam on the brakes?

I have a new SM420 installed in my Jeep and it works great but when I jam on the brakes really hard I can hear some grinding noise in the trans... has anyone else had this problem.

 

I've been building manual transmissions for over 20 years and that's new to me. I think I'd start by looking at u-joint/driveline angles and see if there is binding there under deceleration or if the trans is shifting around hitting something. When hitting the brakes the rear axle pinion wi move downward changing u-joint and driveline angle. This could cause noise/binding issues if the angles are excessive.
Do you have a suspension lift? If so, how much? What are your driveline and U-joint angles? How long is your rear driveshaft? How much clearance between the transmission and body? Is it possible you are bearing trans to body contact noise? What about the condition of the transfer case? Is it rebuilt? Used? Good or unknown condition? Lots of variables.


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Everything is new, just put it all together over the past 5 years and now just starting to drive it and finding very few issues. I've paid attention to the drive shaft angle so they are in line with each other... 3.5" lift, rear drive shaft is very short, have the correct angle on the rear pinion, have Tom Woods D/S (CV Style). The body has an 1" body lift besides the 3.5" lift, the trans is close to the body but it has clearance. Transfer and trans are rebuilt.

When I stop normal no noise but when I jam on the brakes as it comes to a stop it sounds louder and louder until I stop and it goes away... like something is swinging into the gears and when I stop it swings back.... if that makes sense. I know there so MANY variables but just thought it might have been something in the trans that was over looked.

May have to check the front axle angle again. The rear was very vital but the front was a very long D/S, compared to the rear, and it seemed fine. The noise is from the front, it may be amplified through the transfer case/trans.

 

Just a wild shot, but I'm wondering if the rear differential could be the source, given the noise is worse when it is 'reverse' loaded under braking.

 

I'll have to check it out this weekend and see where the noise is actually coming from. I was testing the brakes when I noticed it.
If any thing the rear differential might be a degree too high so when it brakes it should go downward to zero so don't think that would be an issue... paid more attention to the rear d/s since it was so short, it's a cv style.

 

I was thinking maybe the ring and pinion gear, due to the characteristics of the noise... but only a guess.

 

Disconnect rear D/S and drive in front wheel and see if you still get the noise.

 

Check that the axle U bolts are tight too.

 

PeteL I have little knowledge with the axles, took the cover off and check them out and they seemed ok and just put the cover back on and filled with oil. Bought them from different people but have the same gear ratio, 5:38, Dana 44 front and rear, full float.

Walt I'll do that with the front and rear shafts, that's some great advice!! I'll have time on Sat. and let you know.

Mike the D/S are new and just installed so I know that's all tight but will recheck it while I'm removing them for this test.

 

Wouldn't be the fan getting into the shroud would it, when the engine mounts flex??

 

More of a grinding noise than a fan clanking noise... just looked and the radiator, fan and shroud and it's still black with no scratch marks...

 

It was the front drive shaft. Need to put in taller shim to correct it. Thanks for the advice... I took the front D/S out, jammed on the brakes and and the noise went away!!

 

So was the shaft too long?

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Glad it was a rather simple fix. Good for you.

 

Tymbom, no, I need more shim. Have to break out the protractor and figure it out but it will resolve my issue, guessing 6 degree.
It has maybe a 2 degree now.....

 

You do realize if you shim the front pinion up caster will go towards negative and cause handling issues right? Possibly death wobble at the worst and severe wandering at the least?


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It doesn't sound like an angle problem though. I could see if the slip yoke was jamming on the shaft because the angle was off, but it doesn't make sense. It seems to me like if you're jamming on the brakes and you get a grinding sound, when you take the front shaft off and it goes away, its not a problem with the angle of the pinion... Maybe the shaft is binding and causing the sound to travel into the transmission and transfercase? I would check the slip yoke and U-joints to make sure everything was moving freely.

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I can see the possibility of the front shaft binding but not unless your in four wheel drive. Now if the front shaft was made too long (sm420 changes D/S length) and jamming on the brakes which shifts the drive train forward, it might put too much binding on the transfer case causing the grinding. (just a thought).

 

yup you have to make sure the castor is correct in the front and do something else with the driveshaft. perhaps upgrade it like you did the rear. Or just put on locking hubs so the front shaft isnt spinning .

 

Caster, not castor. Completely different.

Search for castor and you'll find information about castor oil, a Roman god and poisonous beans.