If you like our site, please consider joining our club!
By joining you will help ensure that we can continue to provide this service
JOIN HERE!

R90/6 slipping in low gear

User avatar
cbclemmens
Posts: 216
Joined: Sun Apr 25, 2021 2:21 pm
Location: Apollo, PA
Been thanked: 4 times

R90/6 slipping in low gear

Post by cbclemmens »

My R 90/6 (with sidecar 154K miles) has been slipping in low gear. Not a smooth slip but a clunk-clunk-clunk slip as if the dogs in the gearbox are jumping from tooth to tooth. So, I figured that I would need to replace the gear or the shifter dog or both. I took the box out and the rear cover off, exposing the gear. I learned that in the five speed that 4th gear doubles as the shifter dog for 1st gear. But after examining both closely it does not look as though that is the problem. There is a little bit of wear but it doesn’t look to me to be enough to be causing the problem.
Has anyone had a similar problem and, if so, what caused it? Does the wear on the dogs appear enough to be making them slip?
I would hate to spend $500+ replacing these gears only to have them continue to slip.
All ideas, opinions, suggestions, and/or recommendations are welcome.
10-Q all in advance.
Craig
IMG_4634.JPG
IMG_4635.JPG

User avatar
Randolph
Posts: 74
Joined: Tue Jan 13, 2015 11:31 pm

Re: R90/6 slipping in low gear

Post by Randolph »

How did the shifter unit check out? I've got my 5speed apart also and the large cam gear was looking pretty ratty. The cam gear slots (for the shift forks) were getting rough.
If the fist gear fork isn't getting pushed and held in place it could cause the gear dogs to not fully engage.
I replaced it with the BMW2valve "improved" version (Part # 2331611) and also the small roller bearing (Part # 2331572).
Not sure if this helps, but just another thing to look at.
-Randy
PS. always replace the pawl spring!

User avatar
cbclemmens
Posts: 216
Joined: Sun Apr 25, 2021 2:21 pm
Location: Apollo, PA
Been thanked: 4 times

Re: R90/6 slipping in low gear

Post by cbclemmens »

Randy; Thanks I checked the shifter cam this morning. When the shifter arm is in this position the dogs are up snug and I don't see how they could slip. I am going to check the end play with plastigauge. See if that tells me anything.
Craig
IMG_4636A.jpg

cwf
Posts: 155
Joined: Sat May 15, 2021 5:52 am
Location: London, UK
Been thanked: 2 times

Re: R90/6 slipping in low gear

Post by cwf »

Presumably you've checked the clutch plate thickness? What about the teeth in the rear wheel that engage with the final drive, are they worn out?
Charlie.
75/7+ offroad sidecar; 50/2; R 35; XR125V; XR200A; Solex; 1939 Hillman Minx DHC.

User avatar
cbclemmens
Posts: 216
Joined: Sun Apr 25, 2021 2:21 pm
Location: Apollo, PA
Been thanked: 4 times

Re: R90/6 slipping in low gear

Post by cbclemmens »

IMG_4643.JPG
Plastigage shows excess end play. I'll add a shim and try again.

Charlie; I will be putting in a new clutch while it is open, but the slippage is not smooth, it goes clunk-clunk-clunk, like slipping from dog to dog. I think the problem is either excess end play or the shifter is not getting the gear in all the way.

Craig

Carott
Posts: 64
Joined: Tue Apr 14, 2015 9:18 am

Re: R90/6 slipping in low gear

Post by Carott »

Craig,
Have you inspected the "cush drive" on the input shaft of the gearbox?
A weak or broken spring would allow it to slip over the cams with a pulsing clunk.
Brett

User avatar
cbclemmens
Posts: 216
Joined: Sun Apr 25, 2021 2:21 pm
Location: Apollo, PA
Been thanked: 4 times

Re: R90/6 slipping in low gear

Post by cbclemmens »

Brett;
Thanks for the suggestion. I pulled out the input shaft. The shock absorber spring and cam appear to be in good shape. I don't see evidence of slipping here.

Craig
IMG_4644.JPG

Carott
Posts: 64
Joined: Tue Apr 14, 2015 9:18 am

Re: R90/6 slipping in low gear

Post by Carott »

Craig,
It was just a thought.
I'm glad you checked it before putting the gearbox back together.
Hope you find the issue.
Brett

Jim D 5112
Posts: 200
Joined: Fri Oct 27, 2006 3:00 am
Has thanked: 1 time

Re: R90/6 slipping in low gear

Post by Jim D 5112 »

My experience with some other brands the drive dogs did not always show major wear. But they would no longer maintain engagement when under a load. Replacing both the mail and female gears always resolved the problem for me. I saw some broken cases when someone continued to ride the bike while this was happening.

User avatar
cbclemmens
Posts: 216
Joined: Sun Apr 25, 2021 2:21 pm
Location: Apollo, PA
Been thanked: 4 times

Re: R90/6 slipping in low gear

Post by cbclemmens »

With 2 shims on the output shaft the end play is measured by the plastigage at about 0.05 mm. That might be a little too tight. The Haynes manual says it should be 0.0-0.1. I'll look for a thinner shim.
Craig
IMG_4645.JPG

Post Reply