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MG MGB Technical - Rear Knock Update

Initial thread was knock in rear end on accel and decel.

Sounded like thrust washers in diff.
Was also asked to llok at how much play between drive shaft and wheel turning, U-Joint and Hub Splines.

Results after inspection this weekend.

1. U-Joint seemed tight but out of phase with front u-joint according to Les's illustration. When I look at the rear u-joint orientation and the front u-joint orientation, seems to be different by about 45 degrees. About half the distance between bolts.

2. Wheel spline condition and play.
Hub splines are not a perfect pyramid with the top flat. The top seems to be angled towards the rear. The angled top flat of the pryalid seems to have a sharp edge at the rear of the angle. The pryamids are about 1/16" in height.
I put the wheel on the splined hub without the knock-off on. I attempted to rotate the wheel left and right. I get about 1/4" play either way before the drive shaft moves. Once the knock off is tighten, no play but I would expect this.

3. Diff play. With the wheel off and looking at the outer radius of the rear brake drum, I can rotate the drum outer edge about 1" before I get the drive shaft moving.

Questions:
Phasing of U-Joint need to be corrected and how?
Splines worn out of specification? Need new hubs?
too much play in diff? Need new thrust washers?

Thanks for everyone's time and effort.

Best regards,
Doug
DT Toms

Also, wanted to add that I cheked all bolts in the rear end, they were all tight.
Did look like the bushings in each end of the leaf springs were shot.

I also did find 1 source of knocking that seems to occur when I hit a bump. When I had the new exhaust put on, the pipe just in front of the rear wheel was hitting the lower shock link end during full axle travel. Broke the connection infront of hanger and rotated last section of pipe away from shock link.

Still have the knocking on quick accel and decel both.
DT Toms

Doug,

1. Yep, the yokes are misaligned. Remove the locking collar on the slip joint of the yoke (it's a serrated sheet metal tube/collar). You can then seperate the two pieces and reorient the yokes (line up the fixed yokes). Reassemble, tighten the locking collar and grease the slip joint via the grease fitting on the side.

2. You don't say where you're measuring the 1/4" 'free play'. However, from your description it sounds like you have significant wear on the splines. Most likely the wheels will have a similar amount of wear too.

3. This probably should be done too (check the archives), but I would deal with item 1 and 2 first.

Good luck,
Tom
Tom Sotomayor

Tom,

Contact me about the MG octagon shirts you were interested in.

Mark
Mark Saylor

I found my prop shaft was all out of alignment. As Tom says you lineup the fixed yokes. There may also be a couple of small etched arrows, one on the shaft and the other on the yoke to show the alignment. Mine has these but it took a lot of cleaning up of the shaft to find them.
Simon Jansen

Thanks Tom,
I will take a look at the slip joint you are describing and see if I can find it. Is it on the transmission or differential end or both? If both, does it matter which to loosen and correct the phasing?


I will also check the inside spline in the wheels. Forgot to check this.

Does anyone know what the height of a new spline would be?
Best regards,
Doug
DT Toms

To respond to Tom's other question, the 1/4" play in the wheel was measured on the outside radius travel of the tire itself before engaging drive shaft.

Best regards,
Doug
DT Toms

Doug. The tech article and illustration on "Les's" website are by Tom Sotomayer, so he has a rather good idea of what we are discussing. I too, after Tom had been visiting and we discussed this common problem, found an out of alignment yoke, installed by a professional mechanic. The result was badly worn U joints and more looseness in the splined section that was present on my two "spare" drive shafts. The U joints, later, after the yokes had been aligned, wore quickly, but did not seem to make much noise. Noise only appeared, as a nock, at the point where the wear was to a dangerous point. Thus, if you have been driving with the out of proper alignment yoke, I would replace the U joints.

Nocking from the rear can also be caused by the rear shocks being loose (check and tighten them to the body), the drop links from the shock to the underside of the springs being worn (actually found one that had come out and the link needed to be replaced), rear anti sway bar being loose or the rear end. On wire wheel cars, it can be caused by worn hubs and wheels also.

There is always a little "slop" in the rear end because the parts engage with some tolerance--they are not a perfectly machined fit. The 1/4" you mention seems to be similar to what I see on my cars.

I would pull the drive shaft, orient the yokes correctly, install new U joints and bolt it back in. While I had the car up in the air, I would check the shocks, links, sway bars and spring hangers for tightness. At that point, you should be able to limit the variables, if the nock is still present, to the rear end.

Les
Les Bengtson

Les,
Thanks for your comments.
I did check the rear shock links, I couldn't tighten them any more. I am not sure how you tell if there worn, but I couldn't tighten them nor could I move them that would indicate play in the link connection?

I also made sure all leaf spring mounts and U-Bolts were tight. Everything was tight, but the bushings in the leaf spring shackles and the U-Bolts rubber pad sets looked like they could use being replaced.

On the U-Joints. How do you detect they are worn? I can't move the flanges relative to one another?
Looking at the parts catalog, looks like u-joints pair, one on each end?

Funny that the Moss illustration on page 32 shows yoke flanges (fixed parts) at 90 degrees relative to each other? They should be same phasing correct?
Thanks for your patience, still learning.

Best regards,
Doug
DT Toms

Looking at the link on the Moss site, http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29023 , the drive shaft itself, without u-joints, is shown in phase (as an exploded view).

Wayne
Wayne Pearson

Doug,

The slip joint is at the transmission end. Although I have seen driveshafts installed backwards so that it was closer to the rear axle!


Mark,

You have mail.

Tom
Tom Sotomayor

Wayne,
Your correct.
I was looking at PDF file frol Little British Car Company page 32. A different illustration.

I will make sure they are phased according to the illustrationyou reference and Les' reco.

Still haven't seen a good archive or response saying what tells you u-joints are bad?

Also seem a lot of threads reco taking it to a drive tran resource and having u-joints installed.

Best regards,
Doug
DT Toms

Since you have to remove the driveshaft to put it in phase, just replace the u-joints. They're not that expensive, and you should be able to get them from a local parts house. That way, you know they are good. Try to get them with a grease fitting.

However, with the driveshaft out of the car, you can flex each joint in your hands and feel roughness or looseness.

Wayne
Wayne Pearson

Good point Wayne,
Thanks for your input.

Best regards,
Doug
DT Toms

The UJ's are in phase when a line drawn through the center line of the cups on each flange on the end is parallel with a line drawn the same way on the other flange. I just replaced my drive shaft in toto with a brand new one because the yokes were worn so badly where the bearing cups fit that the cupps were rocking back and forth. The spline was also shot.

I did check for phasing before installation and the new one came out of the box phased.
Richard Smith

I checked hub splines, they look ok but I am trying to get a digital caliper today to measure versus Les' specs.
What I hadn't checked, was inside wheel splines. I haven't pulled the wheels off the car to re-check, but looked at the spare last night.
Someone said there is part of the spline that doesn't wear, so you can compare outer spline area to inner spline area. Boy oh boy, if the wheels on the car are similar to spare, my slines are badly worn.. Must have been 1/16" - 1/8" difference in wear height versus non-wear height. New wheels will be another $400 ($200.00 ea x 2) looking at Dayton Wire Wheel. Hopefully the hu splines will not measure too worn or those are another $300.00 ($139.00 x 2). Ugh, wife will not be happy :-)

I appreciate everyone's help and patience with us newbies working through our little jewels.

Best regards,
Doug
DT Toms

Folks,

Interesting thread.

There are a few references to "Les's website" and an article by Tom Sotomayer. Could anyone point me either please.

Jim
j w mcglynn

Somewhere in http://www.custompistols.com/cars/articles/
Steve Postins

For information on checking hub splines see:
http://www.gomog.com/allmorgan/wirewheelbalancing.html

Clifton
Clifton Gordon

The best way to check for play in the diff is to put on the handbrake & rotate the driveshaaft by hand. Put a small mark on the diff pinion flange & the casing to check clearance. 1/6" to 1/8" play is good. 1/4" to 3/8" play means the diff gear thrusts & or gears need replacing. If the bronze thrusts are gone check for wear in the diff carrier. I have seen it so bad 2 washers could be fitted. Best to check for spline wear on the hub using a magnifying glass. Check wheel spline wear by looking in from the inside of the hub. Wear is apparent by a ridge in the spline about 5/16" in.
Garth
Garth Bagnall

The best way to check for play in the diff is to put on the handbrake & rotate the driveshaaft by hand. Put a small mark on the diff pinion flange & the casing to check clearance. 1/6" to 1/8" play is good. 1/4" to 3/8" play means the diff gear thrusts & or gears need replacing. If the bronze thrusts are gone check for wear in the diff carrier. I have seen it so bad 2 washers could be fitted. Best to check for spline wear on the hub using a magnifying glass. Check wheel spline wear by looking in from the inside of the hub. Wear is apparent by a ridge in the spline about 5/16" in.
I should also point out that the "Bs" fitted with a rear anti sway bar are also prone to getting a loud 'ping' when going on & off the throttle this is caused by movement in the pinion spline & is cured by removing the pinion & putting a few drops of 'Loctite' on the spline & refitting the pinion.

Garth
Garth Bagnall

The best way to check for play in the diff is to put on the handbrake & rotate the driveshaft by hand. Put a small mark on the diff pinion flange & the casing to check clearance. 1/6" to 1/8" play is good. 1/4" to 3/8" play means the diff gear thrusts & or gears need replacing. If the bronze thrusts are gone check for wear in the diff carrier. I have seen it so bad 2 washers could be fitted to each gear.
Best to check for spline wear on the hub using a magnifying glass. Check wheel spline wear by looking in from the inside of the hub. Wear is apparent by a ridge in the spline about 5/16" in.
I should also point out that the "Bs" fitted with a rear anti sway bar are also prone to getting a loud 'ping' when going on & off the throttle. This is caused by movement in the pinion spline & is cured by removing the pinion & putting a few drops of 'Loctite' on the spline & refitting the pinion.

Garth
Garth Bagnall

Data:
The splines on the wheel rim splines show little or no wear. Except for spare. I will replace this when money permits. Only use for emergency.

Hub Splines:
New condition = 2.450"
Danger = 2.420"

L Rear Hub Spline = 2.4125 ( bad - replace)
R rear Hub Spline = 2.4340 (poor - replace)
L Front Hub Spline = 2.4455 (good)
R Front Hub Spline = 2.4495 (good)

Re-phasing drive shaft yokes. While I have it apart, replacing U-Joints with grease fittings both ends.

Replacing thrust washers in differential. Greater than 3/16" of an inch play as determined in thread measure.

Leaf Spring height:
Measure from Centerline of Hub to bottom edge of chrime strip.

L Front = 13.75"
R Front = 13.5"
L Rear = 14.25"
R Rear = 13.5"

I am going to try to replace all bushings, rubber axle pads, shackle plates and hope to see some improvement. If not, will try replacing both leaf springs from ProperMG.

Sound like a good plan of attack? Trying not to replace leaf springs unless I see no improvement with new bushings et.

I appreciate everyones help and Steve great explanation on thrust washer replacement steps.

Best regards,
Doug
DT Toms

I have been reading these threads with interest.I see nobody has mentioned the splines on the inner axles. These can wear and cause knocking. AL.
Alan P

Alan,
Good point. I did check the inner splines of the axle and they shown n0o msigns of wear.

Appreciate yopur added input.

Best regards,
Doug
DT Toms

This thread was discussed between 27/06/2005 and 06/07/2005

MG MGB Technical index

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