Clutch pedal over-center helper spring

[Kenneth1948]

My ’84, 633, 5-speed has a very stiff clutch. It requires a very strong left leg. You can modulate the clutch OK (when you get used to it) but it’s very tiring in traffic.


I drove an ’82, 733 5-speed for years and the clutch was nothing like the 633.


I am replacing some of the hydraulic parts: Clutch master cylinder and slave cylinder. In the process I discovered the “Clutch pedal over-center helper spring” mechanism but it doesn’t seem to be “helping.”


Perhaps someone, with experience with this clutch and this mechanism, can help me improve my clutch:


Referring to the photos and diagram (with grateful acknowledgement to Bentley)

Picture A Tabs shows the two tabs on the base of the “helper spring”
Picture C Groove shows the groove or ledge on the firewall where the two tabs connect. You can just see the two wear marks on the groove.
This groove can also be seen in profile on picture B Bentley where it’s marked “B”
Picture C Groove also shows the spring with threaded rod attached to the pivot at the top. The rod length is adjustable, presumably for pre-load? The lock nut was loose as shown in the picture,

So, it’s all there and was connected. Perhaps someone can point me in the right direction to adjust it properly so it will help with my very stiff clutch pedal.


All help is much appreciated, John aka Kenneth

A Tabs.jpgB Bentley.jpgC Groove.jpg

[Bert Poliakoff]

looks to me that you have a crack in the bracket. A not uncommon thing. I don't know if still available, but a fellow on Mye28 board has a repair kit. It is basically a piece of steel bent at an angle to fit the bracket and reinforce it. I don't know if it's the same person, but someone else on that board is also selling an upgraded spring assembly for that application

[Kenneth1948]

Hi Bert, thanks for your response. I don't think the bracket is cracked although it looks like it in the photo. I cleaned it up and put a piece of card behind it for contrast. Here is a close-up picture. Looks flimsy to me but not broken.
The threaded rod may be bent a little, it looks like it in one of the photos. I will straighten it very carefully however I don't think that would cause the severity of the problem.

I'm not sure where to go next.

I might try assembling the linkage without the master cylinder and try operating it and adjusting it that way and see what the "action" is like.
It should go "over-center" than push in the direction of the firewall somehow?
(being very careful with that compression spring, looks like it could mangle a finger or hand!)

I have not found anything new yet on other boards. Replacement spring NLA on 528 board. I will keep looking.

D Bracket.jpg

[DesktopDave]

I had the same problem on my '81. The over-center spring had fallen off the mount, it was just dangling there. I even think the threaded adjuster had been bent too, now that you mention it. It appeared to me that it's just held in by friction & spring tension. The mount is not a really well engineered solution IMHO. However, I do think the over-center spring is a clever way of modulating the clutch action.

I recall loosening up the spring keeper nut to lower the spring tension enough to mount the retainer tabs into the bracket mounting groove. I had to try several times, as the tangs would easily dismount and much is in the way. It's fiddly, and space is tight, no doubt about it. Once I had it secure (as possible), I kept tightening it up until the spring felt 'right'. Made a pretty big difference.

It doesn't really push in the direction of the firewall at all. When the clutch pedal is pushed in, the upper clutch pedal arm swings the eyelet end of the spring up, more of a parallel motion to the firewall instead of a linear motion. I wasn't sure if you were asking about the concept, so I hope this won't come off as condescending, but here's my explanation of how this clever little system works: The spring needs to pivot at both ends, so it's equipped with an eyelet and that tabbed base as a simple hinge. The spring is angled in the resting position, and when the pedal is pushed, the eyelet describes an arc. As the eyelet swings through the arc, it resists until the spring is perfectly centered at about the halfway point of the clutch pedal travel. Once the arc goes 'overcenter', the spring then assists in proportion to the pivot angle. That's why these springs can hold a clutch pedal down to the floor against a weak master cylinder. I'd guess that's why they switched to just using the clutch spring as a pedal return mechanism. I don't recall if the adjuster is just for preload, or if it also doubles up as the fine adjuster for the clutch pedal return height.

[Kenneth1948]

Not condescending at all Dave, I looked at the Bentley diagram as I read your description and now I understand how it's supposed to work so that's very helpful. Everything seemed to be in place when I took it apart but something definitely not functioning correctly. I will find some time to work on it this week and report on progress. Bert mentioned Mye28 board. I found this thread which is also helpful:
https://www.mye28.com/viewtopic.php?...enter#p1519051

[DesktopDave]

You know, I also seem to recall the clutch eyelet having an eccentric bolt on the clutch pedal arm, perhaps to adjust the final pedal height? I'm not 100% sure it was on the E24 though...I'm a little foggy on that one.