ShopTalk Forums | Aircooled VW Tech & Restoration Help

I am setting up new R&P in new gusseted rhino case and need info.
specs;super diff w/ spool insert, crown side cover, hd pinion retainer, new 3.88 r&p.
Question? Ive made several shim changes from .2mm-.8mm keeping backlash between .002-.005 with preload on sidecover at .007ish. I am not satisfied with the patterns I am getting. they all show patterns on the heel of the ring gear and I can't get the pattern to move toward the toe and or nose of the pinion. The best I've seen is with a .5mm(.020)shim with a pattern on the heel of ring gear and middle of the tooth; however still heavy pattern on bearing end of pinion for about 1/3 of the tooth. I tried decreasing - increasing backlash with very little pattern change. Could someone tell me the effects of pattern change vs pinion shim size?
Also do you think this pattern above would hold up to 250+ turbo engine in heavy car.
I hate to do this for my friend and tell him he needs to put 60k+ miles on it to breakin the R&P hehe.

Thanks for any and all help on the topic.
Gary

A thinner shim should push the pinion deeper into the crown gear. Of coarse, backlash will be gone untill you move the crown gear towards its cover to compensate. On a side note, increasing/decreasing backlash doesn't have too much influence on gear contact patterns, unless you're talking rediculous backlash clearances.

Did you know you can incriment the position of the pinion by .05mm?

I have heard of guys moving the contact pattern slightly off the center of the tooth away from the bearing in an attempt to extend pinion life. The theory is that since the pinion gear's teeth always start to crack at the bearing end, moving the contact away would increase it's life.

I've always set the contact in the center. Maybe KCR will pop in here and tell you what shim he uses for that bearing/case/R&P. What R&P is it? Ratio, G, K, O?

Type1 3.88 k and I have gone .05 mm either way off the .5mm shim and the pattern seems slightly better at the .45mm setting but as you say they always crack at the bearing end. Ive always been able to get the pattern toward the nose of the pinion but not on this R&P. The old case (stock gusseted) pinion hole was worn out so bad you didnt even have to heat the hole just push it right in hehe. So told my friend to get new case and HD side cover for the right side. This is a new Brazilian R&P one of five that I have access to and I hope there isnt something wrong with the batch . I wont know that until I replace the one in my drag gearbox.

The new Brazilian 3.88s normally take between a .028&.032.That's thousandths,not fractions of a mm(just to clarify).Anything is possible,especially with new ,non German parts.I normally try for matching the factory pattern.I have friends that run the pinion in deeper or even shallower,for differant reasons.But,I see no benefit in their r/p life as opposed to my setups.I personally would not run the Brazilian 3.88 in anything hi perf.Let us know how it works out.

Kevin, have you heard yet of anyone that's rolled the dice on those Brazilian 3.88s in a full drag car with at least 250 hp?

kcr wrote:...I normally try for matching the factory pattern...

The second pic is a little hard to see, but do you consider this a good pattern?





Thanks!

I say it looks good...good heel/toe contact, but it may be a tiny little bit on the deep side if the picture is accurate on my puter.

Jeff
I would give anything to get that pattern on this R&P or at least in the middle of the tooth but there must be something wrong I havent found yet because I cant get the pattern off the heel ( or outside of the ring gear). This R&P acts as if the tooling was off when the gear was cut . I will post pic if I can figure out how to do it of what Im talking about for everyone.
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Frito, If you're doing your checking with the worn case you mention, that may be the reason you can't get a good pattern. The bore is always beaten in the direction that would yield a heel-heavy pattern.

You say your R&P set is a Brazilian-made 3.88K?? To my knowledge, the Brazilian 3.88s were 3.88G. Either way, the strongest 3.88 is the German 3.88G. The Brazilian R&P will likely shatter in a drag car.

Pablo
Thanks for reading this post. I will double check the K or G . This R&P is being installed in the new gusseted rhino case. Hate to hear they will crumple in drag race gearbox. My main question is relationship of the pattern with shim change(ex thinner more nose on pinion thus moving pattern toward toe of ring ect.). I surly dont want to wear the case out with a hundred shim changes already done 8 even though I knew the best was around .020-.030". Just thought someone could help me and anyone else outhere with a little tip to reduce the amount of shim changes to get the correct pattern. I wish I could post a picture (worth 1k of words).

Thanks again for your time in responing.

Gary Cooper

Frito Bandito wrote: This R&P is being installed in the new gusseted rhino case. Hate to hear they will crumple in drag race gearbox.

Well, --- now seems like a good time to make the change to a good, used German 388G.

Gary,

With a 250 HP turbo, I do not care what you do to a type 1 trans.... you will break it sooner or later. Sure, you can do what you can to make the R&P better, but there are too many weaknesses in a type 1. (1) the case itself-- a rhino is very little (if any) better than a late style type 1. Even if the R&P is set up perfectly, the case still flexes. (2) weak output splines... I have seen many of these break (3) 1st gear is somewhat weak unless you buy a good set from a reputable company. If you do not do any drag race type of starts then it may live for awhile. When you take a transmission designed for 60 HP and put over 4 times through that, well.... lol.

Gary,when all else fails,try something drastic.Try a couple .006 shims,or go drastic the other way,try a .036.Or try another r/p.Those Brazilan 3.88s are cheap.or just scrap that and go with a good used German 3.88.I saw your post about the #s on the r/p.I know the 8/31 is 3.88.Im confident the smaller # is the factory shim used(in mm).The larger # is the matching number.But that doesn't mean that using the factory shim depth is gonna be the same .They don't have a guy beating on side covers all day long checking these things.So,for us with a wide variety of possible variances in machine work,(cases,diffs,r/p's.side civers)we just have to figure it out per application.

kcr wrote:They don't have a guy beating on side covers all day long checking these things.

LOL Kevin I know what you mean. After doing some thinktankin I have come to this conclusion ; I first built this gearbox 6 or 7 years ago for this guy and it has broken 2 R&Ps one I did and then another guy did the last one for him and looking back on my notes ( shows I haven't built that many mainly my own lol) I saw that I noted the pattern was too close to the heel and this last one was the same way? Hum. What is common here well new case ,thats out , Super diff and crown steel side cover, well i can change side cover easy enough just to see if the pattern changes and I'll do that tonight and will post yea or nea.

BTW Henry I didn't give all the info because I wanted this post to show shim to pattern, However this is swingaxle with Erco bought HD mainshaft 3.78, 2.35 2nd with 1.47 & 1.04 (great job on the stacks (pat myself on the back)if there is one thing I can do setting up the gears is it besides building motors (my favorite past time besides racing)).

This is a great forum and thank all involved.

Gary