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Vibration

7K views 33 replies 5 participants last post by  1Sick 32 
#1 ·
Hi to all, and I hope I'm doing this first post correctly.
I've read many posts on here about vibrations, and even though close to my nightmare, they're not quite the same. I just bought a 32 roadster in July, and have noticed a vibration that starts at 45 mph and disappears at 75 mph. It is a pulsing spaced at 1 seconds intervals, and it starts at the firewall, and heads to the back under the seat. I have run the car up to 55 mph and put it in neutral, and the vibration is gone. I have also left the car in second gear and taken it up to 55, and no vibration. The cars sports a Jag rear end, and at 75 mph it only turns 2700 rpm, and at 55 it is 2000 even. The tires have been rebalanced, and the motor and tranny mounts are fine. It has been brought to my attention that the stall converter might not be right ( I know nothing about stall converters), and if the stall is to high, it could be a problem because the car generates little rpm. The car is like new, and only had 5200 miles on it. It just bugs me that this is the only problem it has, and unless you drive at 40, you experience it every day.
I've read some posts on here, and a lot of guys have done a ton of things to find the vibrations. This one, after the above tests, seems to definately be an rpm (engine) related issue. Any, and I mean ANY help you can give will be appreciated. Thanks in advance, GW
 
#2 ·
How about sitting still in neutral; then gradually changing rpms up and down? There should be no vibrations in your mirrors, or place a fluffed up rag on the cowl or hood to watch.

2nd thing, you may be misdiagnosing by using the 2nd gear @55; that changes the load on the driveline compared to normal driving at 55.


To me, the pulsing sounds like driveshaft, ujoint, or maybe enen halfshaft. But you need to prove that the engine, flexplate and convertor are Ok as you sit in neutral. Try that rag deal and really go all over the rpms slowly, trying to get a vibration to show....before chasing elsewhere
 
#3 ·
Thanks for the ideas F&J. I have gone out and did the rpm test as you mentioned, 0 to 3000 rpm, and it gets a clean bill of health. No vibration. The drive shaft sports a sticker on it that reads, Drive Line Service of San Diego / Dyna Balanced, and it looks like it has zero miles on it, let alone 5200.
One thing I forgot to bring up, and it was brought to my attention was, I'm running Billet Specialties wheels and the back tires are BF Goodrich Drag Radials. A mechanic said that the tires don't hold a balance good, but I had them checked and they were fine. Have any other ideas for things to look at?
Thanks, GW
 
#4 ·
This is hard to diagnose without being there.

Not likely, but worth a look: Get under the car and grab both ends of the driveshaft to feel for up & down play, especially at the front where the trans output bushing is. On very rare occasions, the wrong yoke O.D. size could cause a lot of movement there.....or a bad/loose pinion bearing at the differential.

Failing that, maybe borrow a set of rear wheels & tires?
 
#6 ·
Thanks F&J and SSedan64
Checked the drive shaft and maybe at the trans there is a thousandth or two play. Very minimal, and nothing at the back end. SSedan64, your comment is correct about the tires, but with this Jag rear it is impossible to break the tires loose due to the gearing. Maybe in some water, but I even doubt that. The two rear axles show no sign of being balanced, IE., drill marks, weight added, etc., if indeed they would be balanced that way.
I mentioned the stall converter in the first posting, but haven't heard yea or nay about it. Any comment on that, just to get it out of my head. I have a 383 stroker roller motor that I was going to put in this car, but I was told not to waste my time and money as long as the Jag rear was in there. With a 4000 lb. stall, it would eat itself up, and never perform the way it did in the other car I have. Now, like I said before, I know nothing about stall converters, but it kind of makes sense that if the car at 75 mph turns 2700 rpm, maybe the converter in this car is higher and never engages. Yes, NO???
Any other ideas before I TRY to find tires and wheels for this thing? Thanks in advance, GW
 
#8 · (Edited)
1Sick 32 said:
I have a 383 stroker roller motor that I was going to put in this car, but I was told not to waste my time and money as long as the Jag rear was in there. With a 4000 lb. stall, it would eat itself up, and never perform the way it did in the other car I have.
I wouldn't be concerned about a 383 with the Jag rear. The Jag diff is a Salisbury (Dana in the US). I know of a LOT of 454BB converted Jags running these as they are extremely strong.
One guy races in Australia with a twin turbo 454 in an XJ6..

I retro kit is availbale to use Dana 44 gears set..if it you use a turbo..or
blower..
My Jag has the older Salibury with a built 350..very strong. These were used at LeMans and the 6 had about 350+hp. Diff problems are quite rare..

However..
If the IRS is not exactly trued in the install you might get vibration from shaft angles
 
#9 ·
SSedan64
I have a 350, mild cam, and running a TH350 trans.
Docc
Thanks for the input. The car, visually, is perfect. It looks as good on the bottom as the top, and was the one reason I bought it. But, as we now know, it has a problem. Would it pay, since I am going to get the rear axles rechromed, to have them checked for balance, and would a drive shaft balancer do them? I have read that the Jags came in all different widths. Would it be possible that someone cut to fit, and maybe didn't re-balance? Thanks again for all the help, GW
 
#11 ·
1Sick 32 said:
SSedan64
I have a 350, mild cam, and running a TH350 trans.
Docc
Thanks for the input. The car, visually, is perfect. It looks as good on the bottom as the top, and was the one reason I bought it. But, as we now know, it has a problem. Would it pay, since I am going to get the rear axles rechromed, to have them checked for balance, and would a drive shaft balancer do them? I have read that the Jags came in all different widths. Would it be possible that someone cut to fit, and maybe didn't re-balance? Thanks again for all the help, GW
It's possible they may be out of balance. But like F&J said, they would have to be very unbalanced being so short. Worth a check anyway.
The reason I asked about the trans is when using a Overdrive such as 2004R or 700R4 with a lockup torque converter clutch and numerically low ratio gears. When the engine is turning very low rpms it can transmit the engine firing pulses through the drive train and cause vibrations that can be almost impossible to correct without changing the rear gears.
It really doesn't sound like your torque converter has a high stall speed since it's not turning but 2700rpm @75mph. Do you know what the rear ratio is?
 
#12 ·
Thanks again for the replies. I have no idea what the ratio is. I was hoping with the speed and rpm's I noted, maybe you guys could figure out that one...haha! It's possible I could call the guy I bought it from in hopes he would know. I know there's a logical answer that if it was in the rear, why the vibration starts from the front of the car and works it's way to the back. Is there a mathmatical way to come up with a ratio, or is it wrench time? GW
 
#13 · (Edited)
1Sick 32 said:
SSedan64
I have a 350, mild cam, and running a TH350 trans.
Docc
Thanks for the input. The car, visually, is perfect. It looks as good on the bottom as the top, and was the one reason I bought it. But, as we now know, it has a problem. Would it pay, since I am going to get the rear axles rechromed, to have them checked for balance, and would a drive shaft balancer do them? I have read that the Jags came in all different widths. Would it be possible that someone cut to fit, and maybe didn't re-balance? Thanks again for all the help, GW
The axles are chromed..the differential was installed by someone who may or may not have aligned the unit true to the rest of the drivetrain. The axles may have been cut to size..so it is difficult to know without some measurements what maybe going on.

Sometimes rods are built as show more than cruisers..a little misadjustment doesn't reveal itself around town..but open road may not have been concidered.
I have always thought that this mod was for the look as certainly no hotrod is going to need or be able to handle like an XK-E..nor be driven like one. The complexity of the IRS is not needed.
The cage obivously holds the unit together..but shims..and the relation of the fulcrum shafts through the horseshoe shims..even worn bushings could cause a vibration at speed. The diff is held by 4 bolts top..14 on bottom plate..if anything is loose..it will be noticable.

If you think it's the IRS..I'll point you to places that can answer more of this. First, get codes off diff so to identify the exact year/model Jag donor. Most likely a XJ sedan..as these are cheapest at plentiful in yards. I would guess yours has the earlier center mounted disk/calipers (next to diff housing). The 94 XJS on..moved the brakes outboard.


I at one time long ago..wanted to put the E Type IRS under my XK120 (V8)..but having thought about the complexity..and benefits..decided to just keep the live axle. I much easier..simpler..system. So long as I'm not racing at Laguana..I'll only know cause I don't have to deal with the inboard calipers heating up by differtial and exhaust.. :p
 
#14 ·
Here is just one post from the Jag board..similar to your situation..there are many..however these are in cars with factory installed units

I posted some time ago about the “road vibration” my 69 2+2 was
experiencing and its finally taken care of.
The symptoms seemed much like tires/wheels, a vibration at 55mph
and above, but smooth running in the city. I replaced the wheels
and got new tires... that did nothing My second thought was
universal joints, but there was no clunking when coming to a stop
and I couldn’t feel any appreciable slop in the joints. I could
feel a nibbling in the steering wheel at road speeds, so the rack
mounts were the next item. It didn’t make any difference in the
vibration. Next, the right front wheel had some play when yanking
on it top and bottom, so I put new wheel bearings in. Not the
problem. A friend said the lower ball joints were showing some
wear, so we replaced them. Not the problem. Finally, very annoyed
and in a foul moods, we dropped the IRS and drive shaft. With new
universals, the 2+2 runs smooth as can be. This was the first time
I’ve seen bad universals that didn’t click or clunk when coming to
a stop. I originally bought this 69 2+2 for my wife to tool around
in until we get her 120 on the road, but it runs so smooth now
 
#16 ·
I think Docc is on the right track with questioning the Jag setup.

The original description of "that type" of vibration on a "normal" rear wheel drive car, with much more miles on it, would be just like a U-joint that has those wear "ridges" caused by lack of grease or caused by "not enough or NO driveshaft-to-trans angle" If a U-joint is running too straight, the needle rollers don't move at all and then the rollers can't keep wiping grease back and forth....then ridges form on the U-joint stubs.

So, if you find that your joints don't have ridges from improper angles, then maybe the Jag is not set up properly??? I have no experience with those, or how fussy they are ...or aren't.
 
#17 ·
Thanks to all 3 of you. I will take the day to examine the diff., and get the needed numbers off to Docc. I'll also see about figuring out the ratio on that site SSedan64. Is there an easy way of posting pictures? Seems if you guys could see what I have, it might possibly help. Thanks again, and I'll keep you posted, GW
 
#18 ·
1Sick 32 said:
Thanks to all 3 of you. I will take the day to examine the diff., and get the needed numbers off to Docc. I'll also see about figuring out the ratio on that site SSedan64. Is there an easy way of posting pictures? Seems if you guys could see what I have, it might possibly help. Thanks again, and I'll keep you posted, GW

You can start your own pic gallery here...see the top of the page and look for 'photo gallery"...or you can put up pics on photobucket.com or tinypic.com and then copy the url of the pic you just added to those, and then click on "insert image" right above your new post, and paste that url..it is the yellow square that looks like a scenic picture.



Checking ratio with a jack.. If it's posi (both rear tires locked together) you need to jack up both rears off the ground. Then a chalk mark on the main driveshaft, and a mark on one tire near a mark on the floor. Then turn the rear tire one exact turn while counting the turns on the main driveshaft. A 3.23 rear would turn about 3-1/4 turns of the shaft OR a 3.70 ratio would be about 3-3/4 turns.

If it is NOT a posi; jack up only one wheel. do the same marks but this time turn the tire TWO full turns. Use the same formula as above. You have to turn the tire twice to allow for the spider gears in a non posi
 
#19 ·
Docc
I have some numbers for you, and a couple questions. On the bottom of the diff...4HU-004-25
LEYS 8
030 ? this last one is really hard to make out, since I'm upside down looking backwards with a mirror and flashlight. Looks like 030, then the longer I look , it turns into letters. If you absolutly need to know, I will figure out a way to get them. I measured the lenght of the axles, and from center of universal to center of universal is 16" +- 1/8". Now you mentioned that the diff is held by 4 bolts on the top, and 14 on the bottom plate. Well, I found the 4, but unless I'm blind, I see no bottom plate with 14 bolts. The back cover has 12, and that's about as close as I get to 14. There is a flat bar that goes from one fulcrum bolt to the other, on the engine side, and from that bolt goes an adjustable rod on a 45 degree angle to the chassis, on both sides. Other then the 2 rods, 4 bolts, and 4 shocks, I see no other connection to the chassis. The brakes, as you noted, are inboard next to the diff.
In regards to the drive shaft angle, I had the car into a mechanic here in town for another issue which was a caliper sticking, and I mentioned to him about the vibration. He said it could be the the drive shaft or related parts of it. He checked it out, and said it was fine. He really didn't know much about the Jag rear. The guy is a rod mechanic, and every club around goes to him. He knows his stuff. Southern Arizona?? Half tempted to drive the car to you for a look!! That's one boring drive through that dessert though!
F&J
I never have luck posting pictures, for some reason, but I will attempt it. They'll be up later today, I HOPE! I will try to get on the ratio today, or maybe tomorrow. Thanks, GW
 
#22 ·
The cage not only offers quite a bit of strenght but positions the IRS and limits flex.


Note where the shocks are mounted..compared to your mounts. Yours relies on the upper mount which seems to allow some twisting..by the shocks on the upper mounts. Also it seems there is a second mount postion hole ?



This is a Jag diff only in the most basic term. Highly modified..with just the "guts". This is what I meant about these conversions..usually more for looks than actual operation. The vibration IF in the diff could be from any twisiting and therefore binding on bearings..usually located by the strong box section housing.
 
#24 · (Edited)
Also..the front trailing link mounts on yours..

Compared to this


When these units are put in hotrods..quite a bit of structure is removed. The locating mounts now are small diameter rods. The coil overs are mounted to the body attachment bracket..instead ot the box section housing.

There is not much Jag left in the diff..so hard to diagnose with so many variables.

Sorry..

This assembly is why I didn't attempt the conversion on my XK120. I have seen these done but A LOT of welding..cutting..and precise measurement is required to put the ENTIRE cage in place.
 
#25 · (Edited)
F&J

There just so much going on dynamically that is changed..it's hard for me to guess where a vibration could be coming from IF in the diff area.

The link mounts could flex or the front triling link mounts..either could transmit a frequency due to the round rods..like a thick guitar spring. I would guess that would be a rythymic "drubbing" vibration.
Under load the torque of the diff turning..is controlled by the box housing and large section trailing links mounted with donut bushing.
All of that is gone.

The diff itself looks like a dana as these are similar..but the rear housing is more "styled" than the Salisbury.

The gear ratio on Jags are on metal tabs bolted to the diff..but these are obviously not on this modified case.
Gears were mostly open..2.88 to 3.55 with BW or GM trans.

Dana gears are not uncommon mods..with LSD and practically any ratio that fits.

On full bodied cars..like SuperPerformance Cobras..or say a 36 full fendered Ford..the unit is more complete when installed.

On the Cobra rep..handling accuracy IS EXTREMELY important..as some of these are qualified for vintage racing..or just hammered because of the performance intentions of such a historied car.

Also..as to the rigid mount to that top bracket..I guess the rotational mass of the gears could also give a little "feel" right into the frame..
As this looks like a glass car..and seats mounted somewhat back..mighht even be located quite near the differential mount.

A lot going on back there. They look great hangin' back there..but much of the good looks is the removal of the structure that makes this IRS so good..

I probably would always prefer a live axle in a rod like this...IF I wanted to cruise and drive..which is why I have my cars..to use..
 
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