84SD. When slowing down especially with relatively firm braking from interstate speed there is a noticeable shimmy only when the brakes are applied. When going slow with light braking, the brakes seem to hold then loosen as if the rotors weren't straight.

All brake hardware was replaced within the last couple of years and don't have a huge number of miles - rotors, calipers, pads, hoses on all 4 wheels and including front wheel bearings with seals.

I automatically figured something was amiss most likely out of round rotors. I looked at the fronts last weekend and the wheels turn freely, rotors don't appear to be warped as the drag of the pads is nice and consistent. There is no significant lip so the rotors aren't worn significantly. There was no indication of anything out of round.

I pulled the rear wheels today and there appears to be no unusual wear on the rear rotors and they also turn smoothly and with consistent drag.

What might I be missing? Could it be the drive shaft? I think the flex disks were done but perhaps not the center bearing.

Tangent: I want to look at the parking brake shoes. Rear rotor is stuck to the hub. Is there an easy way to force it off without warping it? It's been a while but I don't remember any trouble removing rotors before. It's a slip fit and held on by the lug bolts. A BFH on the crown of the rotor didn't loosen it and I don't want to damage the rotor.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Oh man, I've been chasing the same thing for years. Since I got the car in 2011, in fact. I replaced every single replaceable component on the front, including all brake parts and steering/suspension stuff. I've also tested the brakes on each wheel by jacking it up and checking how it turns with brakes partially applied. I'm confident that it's not a braking problem, although prepare for many a "warped rotors" suggestion to follow. On my car I did all the driveshaft parts, so for me that did nothing. I keep thinking I have it fixed and then a day or two afterwards something settles and it goes back to the pulsing wobbly feeling while braking.

My best guess at this point is the rear control arm or subframe bushings. There is literally nothing else I can replace. I'll be doing that when I get all the parts to do everything (CV boots and the like). But I'll watch this thread with interest and will post back if that fixes it. It's certainly disconcerting.

Out of curiosity, does your car tramline (follow cracks in the road) or get affected abnormally by side wind? Also, have you replaced the master cylinder? That's the only original brake part I have left, it just wasn't giving any of the classic symptoms of being bad so I left it.

I should add that mine's a 123 wagon, but I suspect that we both have the same problem. Just need to figure out what.

-Rog

Does the SD have antilocks? My 84 would do that sometimes when turning hard and hitting the brakes firmly but it took a pretty good push on the pedal to get that reaction. It didn't feel like they were grabbing but more like releasing then doing their jobs. Only one wheel in the front would do this according to which direction I was turning.

__________________
84 300SD
85 380SE
83 528e
95 318ic

Rotor pulsation is caused more by thickness variation as the rotor spins than rotor wobble, however if wobble is bad enough it will pulse.

Another consideration for pulsing is rotor pickup, this is where brakes are repeatedly used hard , car is brought to a full stop and brake pressure is still applied. Pad material will stick to the rotor leaving a bump / altered friction surface.

If you live in a road salt area, check the back of the rotor, you may have rust spots there.

This car does not have ABS. I think that was a late 84 model change. Both the 85SD and the 85 parts car have ABS.

All front suspension components have been done - ball joints, guide rod mounts on and on. Only the sway bar bushings and tie rods weren't done in this refurb. Sway bar bushings looked brand new probably because they're out of the weather and tie rods were done out of necessity shortly before and had no slop.

The PO said he had "had the brakes fixed". He didn't wrench so half fixed things. I "think" the master cylinder is what he did because the rest of the brake system was trashed. I put all new parts on in except for the master cylinder. Calipers are A1-cardone which are a crap shoot but appear to be working as supposed to.

The car drives exceptionally well but does still follow the road crown a very little. It is a joy to drive and the little pull doesn't detract. It may even be because the monkeys at Firestone only adjust to specs without regard to how the car handles. I may add some caster as a test.

The motor mounts, trans mounts and diff mount have all been changed with as high quality parts as I could get but not OE. I want to check the engine shock mounts because I did the poly fill that was discussed and haven't taken the time to make sure they're still good.

I either did the drive shaft flex disk and the center bearing and carrier or only the flex disks when I bought the car. I can't remember which but may have it logged. I checked the flex disks today and they look new. I couldn't see the carrier because it is behind the cover plate and I was running out of time to get everything back together. There was no obvious extra play when I pulled on the drive shaft.

I will check the setting of the front wheel bearings with a dial gauge but they were set per FSM before. When **** is not working, you can't assume something is working just because you replaced parts unless you check.

The plan is to set the bearings with a gauge and use an old torq wrench to measure torq required to turn each wheel without the brakes creating any drag.

Does anyone have an easy way to remove the rear rotors gently without a possibility of warping them? I'll check parking shoes next time rear rotor is off.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

At this point, if it's a brake problem for either of us I'll eat my hat.

As for your rotor, I've done it this way before with good success:

https://www.youtube.com/watch?v=pMuHKDI00rw

-Rog

duh, should have opened my mind. I've got a bunch threaded rod of various sizes used for bushing install.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Perhaps it's fixed. I decided to look at the brake install again then went through a readjustment of the wheel bearings. Brake pads were removed, adjustment collar was loosened then bearing free play was adjusted with a gauge. Finally,a lug nut was installed on both hubs and required torq was measured with anold beam torq wrench. Almost no torq was required. Pads were reinstalled and brakes appear to be working correctly.

This issue has never showed up before in years of messing with wheel bearings on multiple cars. At least it's fixed. Now, on to the clock which works on the bench but not installed and the tach that just quit. Hopefully, a connection was missed.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Wheel bearings being loose will certainly cause wonky behavior, good idea checking and hopefully fixing.

If the clock works on the bench, it's good. Since it grounds through the instrument cluster, you likely have a bad ground or an oxidized connection. Can also be the issue with your tach that quit since it grounds the same way. Don't overlook any metal bars or solder pads on the back of the cluster, the bars are often the ground links between the various instrument pods.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Good job on fixing the problem?

All I figured was a slight warp that may be amplified in heating. Seems like grabbing at vapors though.

Cheers!

snapped_bolt

__________________
'81 240D For now, a good place to borrow new parts
'80 300TD Probably will be put back into service!
'79 240D BACK IN SERVICE SINCE 09/16; limited use, oil leak. Guide pin r/sealed/replaced. Still a leak. Front crank seal....