Rear End Noises in the TR6

Date: Mon, 03 Apr 1995 16:42:30 -0500 (EST)
From: Bob Lang
Subject: Re: Strange Rear End Noises

Bob McLaughlin, The TR6 differential is very prone to failure. There are a number of potential failure points. As for rebuilding the unit, there are some special tools required for the job. A diff rebuild requires that you have measuring devices to set end float and bearing preload etc. These tools are not usually found in the average back-yard mechanics' tool set, but an amateur rebuild is possible. Len Renkenberger outlines the procedure in his "Six Tech" diatribe. The most common method to fix actual differential problems on the TR6 is to replace the whole differential unit. This is not too difficult, and a reasonable diff. will cost you roughly $200. Rebuilding will undoubtably cost you more, but should last longer than just replacing with a used diff., especially considering that the pedigree (history) of a used diff. is usually an unknown factor.

However, if you are hearing grinding noises coming from the back of the car, I might suggest that you investigate other potential causes prior to replacing the diff. One such reason is that the diff is rather bulky, and the job should be done with two people. Also note: It is possible to remove the diff. without taking out the exhaust system. I know, I have done this... twice. Note: I have replaced my differential within the last 12 months.

Probably the most common rear end area problem is U-joints. There should be no play in those. Also note that the little rubber boots that cover the axle shafts should be intact. If those boots are cracked or slit or gone, you could get squeeking sounds as the axle splines grind themselves to bits. To check the u-joints, jack up the car and (with the transmission in nuetral) try to rotate the wheels. There should be _no_ squeeks. Note: there are six u-joints on the TR6, two for each axle, and two for the "propellor shaft". Replacement is messy but relatively straight forward.

The next most common area of failure is the rear hubs. Jack the car up and try to move the wheels in any direction (like when you check for front end play). There should be _no_ play (actually there can be up to .002" of bearing play at the hub itself, and this measurement is referred to as HUB END-FLOAT. If you rock the wheel and there is play, you need your hubs fixed. IMPORTANT COMMENT: rebuilding the hubs requires special tools. PLEASE have a professional rebuild these so as not to wreck what you have. Most mechanics (good/bad/or otherwise) that have not worked on these hubs will ruin them. I know, I have several ruined hubs in my garage.

The differential has two failure modes: bearing related and gear related. Both failure modes can produce noises, but typically they exhibit noise such as whining or humming. Exception, the pinion bearing can produce clunking sounds if the bearing preload (I think) is set wrong. The clunk comes from the pinion trying to move around in order to mesh properly. The bearing failures will first produce whining sounds, and will later produce grinding sounds (if left too long to repair.) To check this: jack the rear end. With the transmission in neutral, slowly rotate the wheels. if you feel some resistance followed by immediate release of resistance with an accompanying "clunk", you may have identified an incorrect pinion setup or worse. If you suffer catastrophic gear failure, you will experience some amount of vibration followed by one or more sharp "clang"ing sounds followed by either the wheel locking up (very bad at highway speeds) or complete unloading of the drive train (motor revs, wheels do not propel the car forward (or backward.)) I have had this happen to my TR6. I happened to be driving up a hill when the diff. broke. Major bummer.

Then again, you could just be hearing a variant of the broken diff mount syndrome. Check for cracks in the frame where the differential mounts to the frame. This problem usually manifests itself as the a sound in the "clunk" variety. I suppose complete failure in this area might make more than a simple "clunk", but undoubtably a "clunk" is a possible predecessor to a failure. Bottom line: you need to jack up the car (or put it on a lift) to help diagnose this noise. Repairs can be expensive back there, but waiting too long _will_ be expensive. Good luck, and let us know how you make out, rml -

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