Huskyfox

Last year I had my U-joints replaced due to what seemed like a lot of play (car bucked a lot if decelerating gradually while in gear and under 2k RPM) At the same time my clutch had started having issues fully engaging, to the point where I couldn't shift sometimes, and so also while I was there asked them to check that out.

Once my mechanic notified me that the U-joints had been replaced I was appointed to take my car to a good transmission specialist he knew to have my clutch replaced. Shifting was so bad that I took it there immediately and wasn't paying attention to if the vibration was there or not (but I think that I would have noticed it)

After having my clutch replaced and driving it home I noticed a very deep, bass-like vibration from about 37-43Mph or so, seeming to be at its worst at 40Mph. The vibration certainly seems to be coming from the rear, it cannot so much be felt as it can heard, and it's especially bad if the windows are up. At any speed above 45Mph it goes away, and I’ve driven up to over 100Mph without hearing it. Hearing that it seemed to be from the drive-shaft I took it back to my main mechanic and he replaced the sagging transmission mounts, and said that the drive shaft could have become unbalanced.
Seeing as I was purchasing a lot of parts around that time anyway from Mazdatrix I bought their new aftermarket replacement drive shaft, that came with its own set of larger U-joints.

After that was installed it seemed that it had been improved, it was still there but to a lesser degree it seemed, and within a narrower rage of speed. However now I feel like it may have just been me looking (begging for) an improvement because it's certainly not any better now.. for about a year I’ve had to put up with it, it's bad enough to give you a headache within 20min. I also have had new tires put on and balanced just to be sure.
The vibration is completely based on speed, not which gear or the engines RPM. (it will still be there if I coast down from above 45mph with the transmission in neutral and the clutch either engaged or disengaged)

If anyone has other ideas where to check or what to try PLEASE let me know, thank you.

Kentetsu

Have you had the alignment checked?

Huskyfox

Yeah it has been aligned since.

lovintha7

Check your wheel bearings.......Early FB's had notorious front outer wheel bearings going bad. Also, If you can, pull out the axles and look at the rear wheel bearings. When my front ones went bad, I coulda swore that it was in the middle, or back of the car. Have the driveshaft balanced for ***** and giggles, you never know, a weight *could* have fallen off in transport. I doubt it could be anything in the tailshaft. Possibly the rear end gears, but that usually doesn't disappear at higher speed. Just a few thoughts and my $0.02

Rx7carl

A bad front wheel bearing will druve you nuts, as it never sounds like its comming from the front of the car. From what your describing, Id definately pull both front hubs and clean/inspect all 4 of the front bearings.

rxtasy3

iTrader: (2)

checking the rear axle bearings wouldn't hurt either.

Huskyfox

Thank you all, i'll give those a go. Is it difficult to change wheel bearings or axel bearings?

CHEF_EG_1

on the fronts? no. the rears take some finesse and wrestling, though.

Huskyfox

Incase it matters I have a GSL, so my rear brakes are also disk, donno if that effects difficulty for replacing wheel bearings.

PS: My car still does that bucking thing when decelerating in gear from 2k RPM and under, even with those U-joints changed twice and the new drive shaft... what else develops lots of play? There is 126k mi on my car and I think the previous owner put a junk yard transmission in it from an 83. (has typical orange writing on it, part number and year)

rotariesrule

definitely rear wheel bearing rumble. it sounds like a deep rumble. you will need a new bearing and a new bearing collar for each side. the worst part is getting the old bearing and collar off. you either have to have a long bearing puller or cut them off with a dremmel tool. then you have to press the new bearing and collar on. or you can bring the shafts to a machine shop and let them do it. the bucking can be fixed by adjusting the carb.

Huskyfox

Well that certainly sounds promising, I will give that a go ASAP, I’ll likely need to have a mechanic do it though, unless someone can appoint me to where there are more details on the procedure. Note that I have minimal auto mechanical experience and just standard tools (I do have a dremel of course, everyone should have one!) I also have the factory workshop manual for this car. I'll do what I can and let the board know the results. Thank you again. Please feel free to continue suggestions if anyone has more.

Also I agree about the bucking being related to carb. adjustments. I have tried basic adjustments such as the idle-mixture and throttle adjustment. I find without either raising it far too high or low it doesn't seem to help, what else can I do? Thanks.

JDGJr85GSLSE

Damn! I have this exact same problem, but I haven't started to diagnose.

thanks for asking. And many thanks for all the great responses. this forum is invaluable!

JDGJr85GSLSE

Would you recommend buying the bearings from an Rx specialty store, the dealer or a local parts shop? thanks